Refitting the crank

I got the crankshaft polished at Southern Rebores near Crawley- great job fellas, really like the satin effect on all the journals.

Polished Crank- clearing all oil ways in the crank... 

I cleared the internal oil ways with a compressed air line.

...and in the block, blasting through from the Gallery along the drilling and also from the bearing holes out

I changed the main bearing shells for the new +10s I got from SJSportscars. One thing I noted was that the bearings as fitted weren't quite right. The lower centre should be a plain bearing and the upper centre a plain-with-hole. All the others are groove-with-hole. This motor had a plain-with-hole fitted in the lower position and a groove-with-hole in the centre upper location. This is probably not a serious problem, at least there was a hole to coincide with the bearing oil inlet, but it wasn't right so I got the right bearings for the 907 motor.

Note incorrect plain-with-hole in centre position of MPB

... and incorrect groove with hole in top centre position
in block

I replaced all the shells with those indicated as correct for this motor in the manual:

Note plain bearing in centre lower position (i.e. in MBP)

Note groove with hole in centre upper position (block)

The rear lower shell required a notch to be filed in its upper edge to allow oil to seep through from the bearing to the newly made groove filed in the MBP. This delivers oil to exiting the bearing to lubricate the rear thrust washer. The manual assumes that it will be possible to obtain a specially modified bearing from Lotus for this purpose. - Perhaps once you could, but these are not available at present, so I had no choice but to file the notch myself. There isn't much to go on when it comes to filing this groove as sadly the illustrations in the manual are of limited use. This shell is a groove-with-hole, yet the manual shows it as a plain; furthermore the location boss is on the left, yet the manual shows it on the right - which none of the various combinations actually have in this position. However the dimension given (0.5cm from the location boss) places the notch within the shell groove which makes sense. However there is no indication of how large the notch should be. The size may actually be critical since too large a hole might allow too much oil to exit the bearing, running it too dry and flooding the rear of the motor leading to rear oil seal troubles. Too small a notch would fail to lubricate the thrust washer. The illustration shows the groove as I filed and fitted it in my first attempt. I formed a shallow notch virtually across the centre groove, but thinking about it later, this may well be too large. I decided to fit the bearing whilst I waited for further information. - OK- foolhardy perhaps but at least it gives me a chance to practice assembly and using the sealant in a dry run. 

Note notch filed in bearing groove below alignment guide allowing oil through to newly
made chamfer. I am not absolutely sure that this is the right size so I may end up redoing this.

I applied red engine assembly lube to all the top shells in the block (block inverted) and including the two thrust washers (copper faces outwards)...

Assembly lube on upper shells (block inverted)

...and then laid the crank in the recess- this was a little awkward as you must ensure that both thrust washers remain firmly back in their grooves or they prevent the crank from dropping in squarely.

Thrust washers pressed back into their recess- journal drops in squarely.

Crank in place in block

The next step was to add Red lube to the shells in the MBP before applying PG307 "Gemlok gasket maker" to the mating flanges of the MBP.  The sealant can be applied as a continuous bead or a continuous film. There are no suggestions as to how this should be done but I chose to do the latter ensuring that the sealant passes inboard of all bolt holes. I also applied it around the bearing shells, I don't think its needed as a sealant here, but assuming that the sealant will have some thickness, I didn't want these to mate at a different distance apart from the periphery of the panel, possibly distorting it or pinching the bearings. 

I don't seem to have a picture of this but it wasn't as easy as it sounds since the PG307 is sticky and tends to form lumps. I do suspect I will be redoing this step of the assembly with a modified rear bearing shell- so if that happens at least I will be better prepared to spread the sealant next time.

The manual states that the nuts securing the MBP are 12mm or 8mm- this is not true they are actually 17mm and 10mm. I sorted out the appropriate sockets plus extensions and pre-set two torque wrenches to the correct torque so that all was ready for quick attachment of the MBP. The MBP then fitted smoothly over the block studs.

A word about studs and nuts; I think a perfectionist would use new studs and bolts throughout the block reassembly. This would be very expensive and I suspect unnecessary because, because the existing ones are in very good condition. I cleaned all studs with a brush and chased their threads with an old tap. All nuts and washers were cleaned ultrasonically before being brushed through with pipe-cleaners or tissue. I oiled the threads and torqued it down. The crank still rotated smoothly once the MBP was fitted so that at least is good news.

Cylinder liners - honing and replacement

Well dear reader, having decided that the liners in this motor were serviceable but not perfect I set about commencing the rebuild. First was to hone the liners prior to fitting new rings. This gives the new rings something to break in against and the (ideal) 45 deg cross-hatching that honing produces, allows oil to cling to the bore.

For honing I used 3-in-one-oil or ATF- whichever I have to hand to lube the bore. I used a Draper engine hone 56246 covering the range 51-177mm. This comes fitted with 180 grit stones and I bought a set of 240 for a second pass.

Honing unit fitted in cordless handheld drill

Honing in progress, avoid the clamps at the top and avoid pulling the
hone out of the cylinder while running!

To get a 45 degree hone the tool needs to be moved up and down in the bore at the same speed as it rotates. I found this was achieved by using the slow speed setting on the drill and depressing the trigger about halfway. Plunging could then keep up with the spin and 45 degrees hatching resulted. although to be truthful this wasn't as good as I had hoped.
A couple of the cylinders came out I thought rather well.

But others wouldn't clean up properly, some marks remained on the walls and no 4 had some evidence of very slight pitting where I assume that some water had rested on to of the piston during storage. I decided it would undoubtedly be best to fit at least two new liners and if I'm doing 2....

... yes, you guessed it and the inevitable mission creep set in- I ordered 4 new iron liners from QED motorsport and a whole load of bits (shells, rings, gaskets etc.) from SJS.

Christmas comes early in Surrey! Two packets from SJS and another from QED- partly unpacked!

I bought a puller to remove the old liners from eBay- £50. It looked rather puny when it came but in fact it worked very well.

Liner puller- threaded studding looked puny to me but it worked well. I'm sure with a little ingenuity this could easily be replaced cheaply with a couple of bars and some studding.

puller in use...

once the seal of the liners was broken they slid out easily by hand.

The sockets into which the liners had been fitted were a bit mucky but looked OK. However once the liners were out it was possible to see that the lower side of the motor had silted around their bases with sediment from the water jacket. Lots of it! This was highly satisfying to remove and clean out.

Note crud surrounding the base of the liner sockets

It was easily scraped out and rinsed away

Clean block sockets

Hopefully removal of this muck will help cooling.

The new Liners arrived but- as you might guess they just wouldn't fit! The old sockets once cleaned and lubed slipped back in easily, but the new ones - no way!... and I was unwilling to force them.

I cleaned the sockets with a drill-mounted wire brush.
This did the trick and liners 4-2 slid in with silky smoothness with
hand pressure alone

Sockets cleaned and ready

I would also say that it helps if you rotate the block to ensure that the cylinders are vertical so that gravity helps them slide in square, they can jam if they don't get dropped in vertically. The only fly in the ointment was the last liner- in cylinder 1. This just wouldn't fit. The other 3 liners would go into any socket and were completely interchangeable, but this liner would go into none of them. It seems to be an oversize- perhaps a quality control issue for QEDmotorsport to think about? I therefore resorted to the hone and after a several burst with frequent checking I did manage to get this liner into the no-1 cylinder position. It was still tighter than the others though.
At this point I checked nip- you will remember that the old liners were on the low side of acceptable at around 1-1.5 thou in nip. Nip is actually only adjustable one-way. You can remove material from the liner step which will lower the cylinder and decrease nip but there seems to be no way of increasing it. Lotus could presumably sell ring shims to go round the liners but they don't. Thus the nip is simply what it turns out to be... and in this case I was lucky in that the new liners sat slightly higher at 2-2.5 thou. All were the same so all was in order to go ahead and use the sealant to fix them in place.

This is the liner sealant I got from SJSsportscars- its Permabond A1044. Seems to be a thread and pipe sealant and  general engineering adhesive I suspect there are satisfactory cheaper alternatives out there- some of which were probably already in my stock!
Anyway it didn't come with any instructions but a search on the web found them. Degrease thoroughly, abrade surfaces with emery paper, clean and degrease again before applying sealant. Obviously the sockets were already roughened from my brushing, so that left only the liners themselves. The use of methylated spirits wasn't recommended as it might leave a residue (presumably the dye?). Anyway I used meths for an initial degrease, scuffed with 240 grit paper and degreased both liner and sockets again with meths followed by cellulose thinners. Then I applied the sealant.

... before fitting the liners. Now degreased and roughened, all liners proved stubborn to fit. No more silky slide in, all of them needed persuasion with a rubber mallet!  I supported the block from underneath whilst I did this as the block is only mounted at one end on the engine stand. I'm not at all happy with this procedure as the silky fit was more satisfying. I suspect there is something I could have done to ensure that this assembly process went more smoothly and if anybody knows what that is please let me know. Maybe sealant around the base of the liner could have acted as a lubricant? I also think that some appropriate 2-4 thou shim washers would have been a great idea. If positioned under the liner clamps then I could have used the clamps to push all liners down to a specified, matched and accurate nip.

All 4 liners in place

Liner clamps refitted- I tightened then to finger tight and then one flat
more on the nut as I didn't want to risk driving the nip lower.

Finally I left all liners to sit undisturbed for 24 hours before I recommenced the rebuild.  I see on the forum that Loctite 567 is recommended for this sealing job and used as a ring around the shoulder...  Ooops! I - hadn't seen that in time. Well I guess my sealant will have pushed up around the shoulder anyway as the liner went in, but to be at least a little more confident  I think I will test the block by filling it with water to ensure that the liners are actually sealed- even at normal atmospheric pressure as I do NOT want my fluids mixing! Actually at this point I decided that I had scratched the crank with the micrometer in my passion to measure it, so I've now decided to get it checked and polished before refitting- I don't want to endanger my lovely new shells! That will be my next task and hopefully I'll get the crank back before I go on holiday.

Overcoming Dysmetria!

Well here I must express my apologies to true engineers- stop reading here, this bit isnt for you. This is where grapple with my inability to measure things accurately and the very tight limits of tolerance given by Lotus in the workshop manual. Since my problem is practically clinical I have coined the term dysmetria!  I am also concerned that the figures in the Lotus tech data section might  not be serviceable wear limits but tolerances in original manufacture so how worn is too worn?
Anyway this blog will be of no interest to the serious and experienced mechanic but it will at least document my struggles with measuring devices and the reasoning behind my decisions (be they right or wrong!)... how hard can it be?

Cylinder nip:
This is the height to which the cylinder liners project above the crankcase surface. You can measure it using a straight edge across the cylinder and a feeler gauge between that and the block. Or you can use a depth

Using a depth micrometer through a hole in the straight edge,
its tilted for photographic purposes- obviously use it vertically.

micrometer measuring through a block also positioned across the liner. I did this both ways, feeler gauges gave a higher value of 1 thou for cylinder 1 and 1.5 for the rest. The Micrometer gave 0.5 thou for no 1 and 1 thou for the rest.
Liner nips (if not the same) should show a smooth gradation from back to front, ups and downs will prevent the head gasket from seating, this appears to be fine. The cylinder liners are magnetic so these are presumably the original iron liners and for these the manual cites values of  1-5 thou for engines after 12478. If the feelers are right then I am in spec, if not then its tight on the low limit. I must check that I haven't depressed the liners with over tightening of the liner clamps. 

Mains and Big ends.
No pictures for these but here is my experience.
Direct micrometer reading on the journals was difficult, it tended to jam, it wasn't easy to see whether you were at right angles and truly across the diameter. This seemed just an easy way to scratch the nice polished surface! Its probably much easier if you have a way of mounting the heavy and cumbersome crank on the bench so it can be easily rotated and examined.
The solution I found was to use engineers' calipers/dividers which were light and easily set to the journal diameter, they were great for testing roundness. The calipers are then measured with a digital caliper gauge. This worked really well. All my journals came out at the expected diameters allowing for the regrinds inferred from the shell markings and there was no detectable out of round at all. Good news here then!

Bores- using the bore gauge.
Setting the gauge: 
Chose an extension anvil of a length close to that you wish to measure- I used 95mm. Insert the gauge at the top and depress it to give one full revolution and clamp it in place. Check that the combined anvil and gauge base is longer than the dimension you wish to measure. 
In order to compare cylinders it doesn't really matter what you set the gauge on, but for actual measurement the gauge must be set up. This is difficult without a setting ring (which is prohibitively expensive) so I have to use a micrometer. In this case set to 95 mm and clamped lightly in a vice for support (I have too few hands for this job). Set the gauge between the micrometer pins using the sprung pip between the wheels and the anvil tip. Even though the surface area of the pins is small, its still essential to rock the gauge to make sure you know where the needle hits its minimum. This is 95 mm so you can set the gauge ring to zero at that point and lock it off with the clamping screw. This is fiddly!

Use
You can then insert the gauge to the required depth in the bore, orient it in the required direction and rock it gently along the plane of the anvil whilst watching the gauge for the minimum reading. 0 represents  95 mm, so reading from zero to the needle maximum deflection gives the difference between the actual bore and 95 mm. Readings counted from zero to the left are oversize, those to the right undersize, provided the needle has passed through the zero (95 mm) point. If it hasn't then they are still oversize so read them from zero anticlockwise. Watch out for the full rev counter although if the gauge is set close to the measurement to be taken  this may not be needed. 

The bore gauge is very accurate and thus tends to generates different readings every time! For reproducibility of  readings its essential to put it in the same position for each measurement. This is tricky. The manual states manufacturer's values measured in the thrust plane (i.e. 90 deg to the crank and in the plane of conrod movement) at 50 mm depth. I drew markers on the gauge 50 and 100 mm up from the measuring tip and aligned these with the cylinder top to take the measurement. My gauge is marked to 0.01 mm per division, I estimated 0.005 by eye when the needle was between divisions.

Bore gauge measuring 90 deg to thrust direction, note depth marks on stem

I would be lying if I said that this was an unqualified success. However I did get a consistent picture. I measured at parallel to the crank, 90 deg to crank and 45 deg to crank in each orientation, i.e. 4 measurements at each point. In all cases the thrust dimension was the smallest at each level and the measurement at 50 mm down was smaller than that at 100 mm in all cases except cylinder 4 when there was virtually no difference at the two levels. Taking the largest recorded value for the bore in each cylinder thus means using the 50 mm, thrust plane measurements which were:
Cylinder 4, 95.355; Cylinder 3,  95.345; Cylinder 2, 95.34 and Cylinder 1, 95.34 mm. The manufacturers spec gives max values of  95.288 and 95.308 for a 912 LC motor depending on whether the liners are type "A" or "B". Pistons and liners come as a matched pair and I have "B" pistons (marked on crown), therefore "B" liners. This means my bores are worn by my "best guesstimate" by 0.047, 0.037, 0.032 and 0.032 mm or 1.9, 1.4, 1.3 and 1.3 thou. Lotus took the view that something was "in spec" or not, they didn't specify wear limits or  give regrind suggestions for the crank; it was right or it wasn't. However most UK motors of the time were more tolerant and a rough guide of 2 thou per inch of bore diameter was tolerable. In fact a typical first bore of say  an Austin A series motor would be 20 thou and by these criteria these cylinders are still serviceable. Remember, the aim here is to produce a serviceable road car not a racer or track car so I'm hoping this will be sufficient. 

Thrust washers.
Rear Thrust washer was clearly worn more than the forward washer.

Rear Thrust (copper side)

Front Thrust washer (Copper side)

Both were measured with a micrometer, front 2.33 mm and rear 2.29 mm. I don't currently know if they both had the same diameter when fitted but it seems likely as the extreme tip of the rear washer was thicker at 2.32 mm. If so then wear would account for an extra 0.04 mm (0.0015") end float. End float I have found  to be right on the max with these washers fitted, so it may be sufficient to simply replace them with new standard sized rather than oversized. Rapid wear of the  thrust washers was a problem with early motors and required a modification (see post: modifying main bearing panel). I will add a pair to my shopping list.

Piston to bore clearance.
This motor has type B pistons corresponding to the design used in 912 Std compression engines, compression ration 9.44:1. Since the pistons have to work in the bore the clearance between them is an important determinant of wear. I am taking this as the difference in bore as measured perpendicular to the crank at 50 mm depth and the piston diameter measured at the widest point which is the skirt. Pistons may vary in diameter at different points to allow for expansion and its not stated at what point the diameter is measured. I measured them both directly using a digital caliper and indirectly with engineers' calipers.  These were very useful to check the diameter around the circumference. I could then measure the calipers using a digital measuring caliper. The measurement was cross-checked with a 100mm micrometer measuring directly on the piston skirt app 10mm up from the lower edge.

Pistons measured at the skirt (mm); 
Piston No: 4, 95.14  ; Piston No 3, 95.14; Piston No 2, 95.18  ; Piston No 1, 95.19
Calculated clearance: Cylinder No 4, 0.215 ; Cylinder No 3, 0.205; Cylinder No 2, 0.16; Cylinder No 1, 0.15
The manual gives the values for piston-to-liner clearance of 0.11-0.15 mm. From these figures Cylinders 1 and 2 are almost within tolerance of 0.11-0.15 mm but 3 and 4 are over. However as with other places in the manual its not clear whether Lotus are providing figures for the tolerance in manufacturing or permitted wear before service is required, and again I'm up against the "as new or replace" doctrine which I just cant afford to do. Taking my cue from Brit cars of the same period, then wear of up to 3x the original spec was permissible and again mine are well within this. Piston measurements are hardly down from stated diameters and I think the existing liner/piston setup is reusable.

Piston Skirt 
Since the piston gets hotter at the top than the bottom, the crown expands more than the cooler bottom of the skirt. For this reason and to ensure that the piston is almost straight when at temperature, the piston is made to be tapered, being wider at the bottom because this will expand less than the top. This skirt flare is detected by an increase in piston diameter from pin level to skirt base. However, if a piston has suffered overheating then the skirt may expand and contact the cylinder wall. When this happens the  piston is forced into  a straighter configuration and does not contract back to its original shape when it cools: the larger diameter at the skirt is lost. Termed "skirt collapse" it can be eliminated by checking that the skirt diameter is greater than the diameter at the pin. In my case this was true in all 4 cylinders. It is possible to check the angle of this flare (grade) but  I was happy to find that skirt collapse wasn't a problem in this motor.

Piston Ring-to-Groove Gap
This is cited for a Std compression 912 as 1.5 - 3.5 thou measured by slipping a feeler gauge in between the ring and the groove land. All cylinders were similar and all gave a higher value of  6-7 thou for ring one and a more likely value of 4 thou for ring two which is within the specified range (just!). A larger than expected gap could be generated by a thinner ring or wear in the piston groove. I was expecting rings one and two to be the same thickness because only one gap is quoted in the manual for both compression rings and piston groves are the same width. However this difference in observed gap size was practically all accounted for by a reduced thickness in ring 1 since when each ring  was removed and measured with a micrometer it was clear that ring 1 (1.52 mm or 0.059 ") is  thinner than ring 2 (1.57 mm or 0.062") by 3 thou. When the actual thickness of each ring is added to its clearance measured by the feeler gauge it generates the groove width, which is practically the same in both cases, supporting the conclusions above that the pistons are probably not significantly worn and still usable if not perfect. Its not clear whether this difference in ring-to-groove gaps is due to similar wear in all 4 top rings, or simply the fitting of a replacement ring set that had thinner top rings to start with! I think these are unserviceable whether through wear or incorrect installation and so it seems likely that new rings would be a good idea.

So Conclusions to this measurement section:
Replace all rings
Fit new thrust washers (Std thickness)
Hone all cylinders.
Fit new big end and main shells- probably not strictly necessary but seems a shame not to do so whilst I am here!
Not perfect but hopefully all serviceable.

Modification to Main Bearing Panel

As I have discussed earlier, the MBP in this motor pre-dates a Lotus modification introduced to stop rapid wear of the rear crank thrust washers. The modification consists of using a notched main bearing in position 5 allowing oil to exit the bearing. A chamfer is then formed alongside the bearing allowing the oil to flow on and supply the rear thrust washer.  Early motors such as mine were recommended for upgrade the next time they were stripped. My motor has certainly been substantially rebuilt on at least one occasion yet this modification had not been performed. In later motors the need for this adaptation was removed by using a redesigned MBP. My first concern was that someone might have swapped the MBP for the later type, however enquiry proved this is most unlikely as block and MBP have to be machined closely together. Its not impossible to swap them but the cost would likely be prohibitively high. I was able to confirm that my MBP was original since both block and panel are numbered when machined together. This is the explanation for the number stamped on MBP web observed earlier. The block is in fact stamped with the same number but its hidden away behind the crankcase breather.

Block/MBP number here stamped on the MBP 

And here on the block behind the crankcase breather tube...

who would have known?

This meant that the modification was required so, using a small needle file, I created a chamfer on the right hand side of Main bearing no 5 (rear).

Main Bearing 5- rear of MBP, rear thrust washer slot visible before ...

... and after modification.

The next part is to file a round notch in top right hand edge of the lower shell 0.5 cms from the groove locating peg to allow oil to exit towards the thrust washer via the channel I have just made. It may be possible to buy a pre-notched washer, however I think filing the notch with a round file should be sufficient. Hopefully this will prevent in future, the wear at the rear thrust washer which increases end-float and I suspect is responsible for the greater longitudinal wear to cylinder 4.

Big ends and Crankshaft- remove and check

I am rapidly building up a list of items to measure on this motor- been putting that off because my measuring skills aren't that great, but hey will have to come to terms with it soon. However before I can measure the crank journals I have to remove the con rods and bearing panel or ladder retaining the crank itself.
Disconnecting the big ends was fairly simple, I started at no 4 because this is the area where the pistons were marked so presumably any damage would be in nos 4 and 3.

No 4 Big end cap

Hard to photograph but conrods and caps already
identified with number- in this case "4". 

I scratched numbers onto the conrod bolt heads as I  would like to reuse. in the case 4A and 4B, "A" referring to the bolt on the left hand side when motor inverted- ie inlet side.

The caps are undone a few turns breaking the torque with a breaker bar- no too hard, then give the bolt heads a tap with a soft mallet to pop the shells off the journals, unscrew the rest of the way and remove the pistons (CAREFULLY) by sliding piston and attached rod up the cylinder- take care not to scratch the bore with the con rod end. I found that the liner clamps I had made allowed the rings to pop out and I could remove the pistons fully without removing the clamps- they will have to come off for installation though.

No 4 big end journal

... and no 4 big end shells in place

Stamping to rear of shell

Quite frankly this all looked very good to me. The Journals were smooth and unmarked and looked in great condition. The main shells did show some wear but they have to wear as they bed in and nothing here looked excessive, simply well seated. There was no scoring to either the journals or the shells and this was not the cause of the muck in the oil filter. The markings to the rear of this shell suggested that the crank has been reground to -20 and this certainly suggests that some sort of repair may have been carried out in the past.
I removed the other 3 pistons and rods in the same way...

Journal No 4, Note stamping to bearing ladder

Journals 2,3 and 4 Rear of motor to right

Journals 1 and 2

... and all were very similar. I am beginning to think that this motor was reconditioned and is actually in good enough condition to simply reassemble, however I may fit new shells at least. I will check on the meaning of the figures on the shell back before ordering a new set. I still need to get a micrometer on the journals to check for wear and out of round; but as it seems to have been ground to the maximum already I am hoping that there will be no such problems as that would mean a new crank 

Pistons and rods. 

The pistons similarly looked in fair to good condition. All rings free in their grooves, there was no sign of combustion blowing down the skirts below the rings in any cylinder. All pistons did have striations or marks to their lower skirts but these were marks rather than scratches and I couldn't detect any scoring with a fingernail. Similarly there were a few vertical streaks in the cylinders and also a few marks (stains?) but nothing that would catch a nail. I suspect that this is all in good condition with some marks from storage but all might benefit from a hone to clean up the bores a little, perhaps new rings would help too? I still need to measure the bores and check for ovality, check that the rings are standard like the pistons and check the ring gaps- I probably wont do all of them unless there is a problem as rings are fragile and expensive and so far my attentions to this motor have largely been unnecessary- serving only to provide a chance to make things worse! Ah well at least I am learning!

All 4 pistons in plastic tray

Pistons have absolutely no vertical play at the small end/gudgeon pin junction. They do however slide smoothly and easily sidewise. I am satisfied that these are OK and I wont be dismantling the set further- unless I decide to fit new rings.

view up bore, no 4 cylinder, all look really similar.

Main Bearings

So far I have not been able to identify any significant wear in the motor- there is some as there must always be, but not enough to account for the swarf in the oil rose. I will need therefore to look at the mains and thrust washers. The mains are a potential problem as this motor is number 20363. Lotus fitted a modified main bearing ladder from engine number 20875  to prevent premature wear of the thrust washers. Engines earlier than this received a makeshift modification to their bearing ladder performed either by Lotus themselves during assembly (engines 20793-20874); or to be performed by a service engineer whenever the motor was next stripped (engines Prior to 20793). This modification consisted of filing a chamfer to the bearing ladder at no 5 position and installation of a notched main bearing shell not used by motors after 20875. My motor clearly falls into this last category and so I cant tell whether that main bearing was modified or not. Of course this does mean that if the bearing panel has either not been modified at all, or modified but fitted with the more common and incorrect (plain) bearing, that the thrust washers might wear too  rapidly and this would be a very satisfying explanation for the coppery swarf in the oil pick up filter.

 I suspect one way of checking whether the thrusts are damaged may be to check crank end float, although I doubt that this is always definitive and I'm not sure that the state of disassembly that my motor is in currently will allow this test, so overall (and despite my trepidation) I probably do need to remove the crank to see what has been done.


On a practical note it is getting hard to see how I could support the motor whilst I remove the bearing panel or ladder. The engine stand was originally secured in 4 threaded holes. One was in the sump and had to be detached when this was removed. This left three, but now holding a lightened motor lacking head and sump so it has so far been OK. Removing the bearing panel would mean detaching another clamping bolt leaving just 2 which is clearly not going to be enough! I will need to rearrange the clamping bolts if there are suitable threaded holes, or detach the motor and break this joint on the bench- This will be awkward as I really want the crank uppermost which means supporting the motor inverted- but the cylinders are inclined and have head bolts protruding. Further I will need some considerable force to undo the bolts, and off the stand it will be hard to steady the motor. Ah well...  life would be boring without challenges.

Removing the Bearing Panel or Ladder

It took a while to reposition the tear-down stand. In the end I had to re-sling the motor from the crane and reattach the support rods from the stand end plate. It took a couple of attempts but eventually I got 4 good supports. One of the these was routed though a starter motor attachment bolt hole and secured with a nut. I had avoided using these mounts before because I didnt want to bend the motor end plate. However now the motor is so much lighter- and will be lighter still when I remove the bearing panel and crankshaft I think I should get away with it.

Re-slung motor fastenings reallocated so all attach to cylinder 

block leaving the bearing panel free for removal.

 Now attached the motor could be inverted and the crankshaft end float measured. This was surprisingly easy, connecting a dial gauge as shown, although the reading face is positioned down and away from the camera. End float was determined as 0.21mm which is just over the recommended range of 0.08 - 0.2 mm, but still below the maximum permissible wear of 0.3. mm.

End float determination, gauge reading face downmost

 I was then able to remove the nuts from beneath the bearing housing taking the smaller nuts off first, loosening from the edges diagonally towards the centre. These were surprisingly dirty/corroded but none-the-less unscrewed easily with the breaker bar. One stud came out with its nut and will need to be detached.

Loosening bearing panel nuts

Before removing the panel I took note of how the oil splash shield had been fitted, although this was difficult to photograph, these pictures show engine inverted and from the rear

Note bent locating tab

End of flange cutout

The bearing panel needed a tap to release the seal but could be removed easily revealing the main bearings below. The upper shells remained attached to the panel and the crank remained in the block.

Bearing ladder inverted after removal, note main bearings in order with plain bearing in centre- mains 5-2

Mains 4-1, plain bearing in position 3.

There was no appreciable wear to the mains although they did seem to be in worse condition than the big ends. Number 5 main had the rear grooves plugged with sealing compound which might have impaired lubrication, I'm not really sure whether this channel is intended to allow oil movement.

Note sealant blocking the oil drain channel (?)

and partially blocking the opening on the other side.

The bearing panel had not been modified as per Lotus instructions, both sides of No 5 bearing cap were unchamfered and the expected notched shell was not fitted. Close ups of both edges to the no 5 position are shown below. Photo taken from underneath the panel from the rear

No 5 position in Main bearing panel (shell removed). 

Note that there is no chamfer to the edge of the bearing recess. 

No 5 position in  Main bearing panel (shell removed), 

panel inverted, note lack of chamfer to edge.

It was possible then to lift the crankshaft out of the remaining bearing shells in the block, leaving the shells behind.  The oil deflector fell out at this stage so just as well I had noted its location. The main bearings in the block were in similar condition apart form bearing shell 4 lower, this did show some evidence of scoring. However the crank was undamaged in this position o I assume that the bearing material has performed one of its tasks and accepted the wear caused by some contaminant protecting the crankshaft itself. 

Lower Shells 5 and 4

Lower shells 3 and 2

Lower shell no 1 main bearing

Scoring visible on lower shell no 4, this could catch the 

edge of a nail!

However the corresponding journal was undamaged

In fact all the main bearing journals on the crank looked to be in good condition but will need to be measured to be sure they have not worn.

Crank lifted out, all journals look good to me

The rear of all mains shows a value of 010 so the mains have presumably been reground to 10 thou undersize

Thrust washers were present and showed some wear, however this was confined to very specific areas at the corners.

Inner thrust washer in situ

... and removed, note wear to upper edges

Rear of thrust washer marked STD

The rear thrust washer was more worn, measuring it showed some 3-4 thou of material had been worn awayand this might account for some if not all of the coppery material noted in the pick up filter.

Copper face of rear (outer)  thrust washer, note wear pattern to surface.

In conclusion there was still nothing to account for all the fragments in the oil pick-up filter. I think it is possible that these are old materials but in any event I am currently hopeful that the motor can be reassembled fairly simply. I need to determine whether to fit new shells and I probably will, however the mains do present a problem as the expected modification to the panel and shell wasn't present. It is always possible that  the panel itself has been changed for the modified later version in which case no modification is necessary so I will check before I can be certain which bearings I actually require in the no 5 position. The crankshaft looks very nice but still requires checking for size and roundness. The most significant crank wear is actually in the region of front and rear oil seals so I will try to reposition the seals on reassembly such that their lips avoid these wear marks. This I am hoping is the lowest point of the rebuild. The engine is just about as far apart as it can get- and certainly as far as I want to strip it, so hopefully from here on things will be going back together.