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. 

Removing the Sump- fixing oil pickup pipe filter

I hadn't meant to drop the sump because I believed that the lower end of this motor is fine. Sadly that belief was seriously challenged ads I started to clean and decarbonise the head and piston crowns. Diesel EGR spray cleaner is an excellent way of loosening carbon and if you can arrange for the component to sit in it for a while so much the better. The first problem came as I cleaned the head, There was a mark in cylinder no 3- its in a non-critical area and shouldn't affect gasket seating but I wondered how this had been caused.I cleaned the pistons in all cylinders and got a shock. Piston 3 shows markings of exhaust valve contact and piston 4 has inlet valve marks as well.

Piston No 4 Exhaust side down-most

Piston No 3 Exhaust side down-most

Pistons 1 and 2 were unmarked. I was told that this motor was in good condition, yet these marks could indicate a timing belt failure at some point in the past. However I also know that the motor was rebuilt so maybe this was why. If so then any damage should have been fixed and perhaps the pistons were simply reused. Although marked, they are obviously quite serviceable. However this obviously raises the spectre of potential damage to the bottom end, bent conrods or damaged big and little end bearings not to mention possible main bearing damage. I was clearly going to have to investigate this and one tip I had got from the forum was to check the oil pick up pipe filter for debris. Since this is in the sump there was now no choice, I would need to drop it, check the filter (and possibly bearings) and clean out the sump.

Removing the sump was very simple and I forgot to take any pictures. However, as I had already removed the front and rear seal carriers it was simply necessary to undo all the bolts around the sump and tap it with a mallet to loosen it. The trick (if it be a trick) to removing it is to tilt it towards the exhaust side to make sure the baffle clears the oil pick up pipe filter rose.

Sump detached with baffle in place-pretty mucky

I detached the baffle and degreased it as well as the  sump, cleaning them with paraffin and then POR15 degreaser before spraying it clean. Much of the old Wellseal came off at this stage.


A word of warning though as the baffle gets very slippery in POR15 and it has very sharp edges- as I now know to my cost!

A quick look at the oil pickup filter showed me what I was fearing- there was a lot of debris trapped there. In order to remove the pick up pipe you need to first remove the hex retaining plug in the Auxillary housing. There is a special tool for this but in my case the plug was very loose and a suitably sized bolt also works well. (Pictured after removal). I can also say that  a motorcycle wheel spindle key will also fit and is easier to turn with a spanner- I will use that when refitting and I need to compress a new olive!

Bolt head fits the hex profile on the pipe retaining plug and unscrewed easily

 The pipe is then held on by a bearing cap bolt midway along and  the olive compressed below the hex plug. I removed the bearing bolt using a breaker bar and slipped the pipe bracket off the stud before  immediately retightening the cap bolt. The pipe was then drifted down through the nylon olive and detached. The old olive was fished out with a wire probe. Now I could look at the filter properly...

Crud in the oil pickup filter

 The filter was gummed with quite a lot of debris- (its looking less and less like this motor has been rebuilt). I tried to flush this out with paraffin and a brush but its quite tangled into the mesh and the only thing that happened was that the oil filter disintegrated. Shockingly its only glued together and after 40 years or so the glue is clearly no long doing its job.

Filter cap has detached from rose.

I cleaned the filter thoroughly using paraffin and carb cleaner spray, clearing each of the gauze recesses with a toothpick and flushing with lots of paraffin.

At least filter rose is clean

Mag probe passed though cleaning liquid.

The filter did eventually come clean. I tested the debris with a magnet and found that its a mixture of magnetic and non magnetic metal material including some very fine wire fibres almost like hair.  There was clearly some bearing metal in there and possibly also copper from the thrust washers- but how much is too much?...  and given how hard it was to clean, has this stuff simply been carried over from a previous problem? There was also quite a bit of wellseal so there's a lesson there for reassembly.

I am clearly going to need a new filter rose, but as new ones are quite expensive (£30) and need to be brazed onto the pick up pipe I thought I'd try a repair first. In order to do this I used joining screws of the type used to connect kitchen cabinets.

Joining screws as supplied (above) and as cut (below). Splines at top of female screw will help to anchor it in the plate.

 These are too long as obtained for kitchen use, so its necessary to cut the shaft of the female screw to 1.7 cm and the screw itself to app 0.8 cm. This has been done in the pic above. The next step is to make some clear room between the folds of gauze app 180 degrees apart round the rose by gently folding two adjacent pleats apart. I then drilled a 5.5 mm hole in the lower plate of the filter (the one that had detached) and a 4 mm hole through the top opposite the first- supporting  them on a wooden block. The joining screws then simply pushed though these holes the splines retaining the female screw and tightening then allowed the filter to be set at the right distance apart to give a good seal around the mesh. Once sorted I removed the screws and applied thread lock to the female screws before joining the two sections together.  I used only two screws which gave a good solid seal but 3 or 4 might be better.

Oil pick up filter repair

Oil pickup filter screen repair