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Paul Coleman

How can I tell if the shell bearings are worn?

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I'm trying to decide (again!) what to do with my engine. How can I tell if the shell bearings are worn?

Thanks, Paul.

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cant really tell without dropping sump and inspecting them. if you got good oil pressure chances are there be ok

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Yes stupid of me, I should have mentioned that I have the engine in pieces d'oh!

Paul.

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Then you can either have them measured (doubt you have the bore gauge equipment), or use some plastigauge and clamp them around the crank using the block.

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If they look a smooth matt grey colour with no copper colour showing they will be fine. You should also check the crank journals for 'roundness' with a micrometer.

Having said that, if you have mixed them all up, I would be reluctant to re-use them.

Steve

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Thanks for the replies. I will check the plastiguage as I don't really know what that is...

They look grey with no copper colour showing. I have kept them labelled so I know which pair came out of which area but I didn't label them top and bottom as I assumed that shouldn't matter?

I'm told by the previous owner that the engine had a full rebuild less than 10,000 miles ago so I'm reluctant to spend a lot of money if I don't need to. However, the head had been skimmed beyond all hope so I've got another one. I took the engine apart just to visually check and clean everything (it was painted in red paint!) but I'm going to get the liners re-seated and re-sealed whilst I've got it apart.

I also had the crank professionally checked so I'm happy with that.

Thanks, Paul.

Edited by Paul Coleman

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If you have it in bits anyway, I'd be inclined to change the shells as a matter of course...you say the crank is within spec. so new shells gives you effectively a new bottom end. Top and bottom shells can make a difference, as the forces on the top half of the shells differ from those on the lower half...the pistons produce higher loading on the bottom half of the main bearings and the top half of the big ends.

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I'm reluctant to spend any money at the moment. I'm planning on having the whole engine rebuilt professionally at some point but not now due to lack of funds. I'm not very mechanically minded so I'm finding it difficult to determine what I can and cannot get away with. I might find the shells and take some pictures....

Paul.

Okay, I've taken some pictures. Here's the worst big end bearing...

dscf0005aj.jpg

It has a line scored along it on both halves. What could cause something like this? Does this even matter?

And here are the other three...

dscf0008yl.jpg

dscf0009s.jpg

dscf0010ih.jpg

Here's the worst main bearing which has some copper showing...

dscf0006qp.jpg

Again, why would this wear only at that point? As I said before I've had the crank professionally checked and they said it was okay (it's been ground to +0.020"). I'm wondering if I bought a complete new set and put them in whether after 10 miles it would be exactly the same?

And here are the other 4 sets which don't seem too bad - no copper showing on the rest...

dscf0007m.jpg

dscf0011c.jpg

dscf0012u.jpg

dscf0013v.jpg

I'm now not sure what I should do!! Can anybody advise please as I don't really know what I'm looking for?

Thanks, Paul.

Edited by Paul Coleman

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dont want to sound rude but you are fumbling around in the dark.i am a fully time served hgv fitter and ok not worked on petrol engines much, but rebuilt loads of large diesel engines anything from 10/14litres and to be honest i think the tollerences are to critical on the lotus engine to be messing about with it yourself. you might end up making the engine worse than when you started. now you got the engine out and stpipped down can't you find a local engine builders and let them look at it. they might not have worked on the lotus engine before but at least they will have a good idea what there doing. you could always find out what all the torque settings and tollerences are and pass on to them. sorry for being so negative but after reading all the different posts you have wrote think you will struggle by yourself.ps the shells dont look to bad to me .

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Yes I'm beginning to think this is not such a good idea!

Paul.

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Paul, I'd agree with Robin generally.

if you want to re-build the engine fully in a couple of years (or less) then yo can probably get away with those shells (there does look to be one line in the worst ones), but I would ask the question, why not simply have it re-built now. If I had the time free, I'd say I'd help you do it, but I'm a bit rushed at the moment. I'm sure some others could help, even try Sparky/ Wookie to see if they'd do the re-build for you using minimal parts.

Andy

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Since you mixed up the upper and lower halves (if I'm reading correctly), I'd say don't put them back in. The lower shells on the main take more stress, and the rod shells (as opposed to rod cap) on the connecting rods take more stress/wear.

But if the crank is in spec both in diameter and roundness, I'd just go ahead and buy new shells and bolt it back together. Your shells look evenly enough worn (except for that one main) that I wouldn't be concerned about too much... If they had moon-shaped wear or something similar, I'd be concerned.

As far as I know, .020" is as far down as the shells go (I've heard of .030 but have never found a source), so if you do any work to the crank you'll have to have metal added to it, or start with another one. So I'd just go ahead and bite the bullet and buy new shells now, get back to enjoying the car, and don't fret it.

The worn corner on the one is from either a (very very tiny) piece of grit behind that corner of the shell when installed, or a piece of flash on the top/back side of the corner, or maybe the shell is too thick at that point. Or maybe there is a bump on the block/cradle at that corner. Maybe it moved (rotated/spun) ever-so-slightly.

I've had what you are seeing on that shell happen a couple of times, but it has always been on the corner with the locating tang. What I do now is seat the shell in the rod/cap/block/cradle and very very closely inspect its fit; occasionally there is a "gap" -- "gap" is not the best word, as we're talking too small to fit all but maybe the thinnest feeler gauge blade in there -- between the back of the shell and the part it is fitting into. I then look for what could be causing it (i.e., is there something pushing it away). It has happened with the .020 shells, non-oversized on the outside, that the actual locating tang on the outside of the shell protruded farther than the gap was deep on the block or rod -- and also protruded out farther than on the .010 shells. So what I did was very carefully and minimally sand (with 1000-1500 grit) the back of the tang on the shell (don't mess with the block or rods) and keep test-fitting it until that ever-so-slight gap goes away and the shell seats like the others do. Since that is not the "tanged" corner of the shell, I'd suggest measuring its thickness with a micrometer and comparing it with the thickness of other of the same corners. Also look/feel to see if there is a ridge or something at that edge on the back side -- it should be perfectly smooth. Again, with all of this, I'm talking very very small degrees here -- too small to see for some, perhaps use a magnifying glass.

Am I making any sense? Or am I getting too wordy?

Also, I'm comfortable re-using the rod bolts 2-3 times. I had an engineer friend (who builds Lotus race cars) do the math for me, and given the grade of the bolt, the diameter of the waist, and the torque required in the 907 (around 85 ft-lbs on the rods, IIRC), that amount of torque is actually nowhere near enough to stretch the bolt. So don't waste ("waist", ha ha, pun intended) your money on new rod bolts right now.

Long story short: If I were in your shoes, limited funds, interested in doing a full-out build later, crank down to .020" under but still in spec, I'd buy new shells and thrust washers and bolt that bottom end back up. Plastigauge it with the new shells to be sure, but if it was fine when you took it apart, it should be fine when you put it together. Also, when you fit the new shells, closely and carefully visually inspect the fit of each one; they should be identical under close magnified inspection. Between this and the Plastigauge, you should have enough information to feel confident putting the bottom end back together, provided that it was running good when you took it apart. Some people get very fussy about these engines, but they're really not that precise; at the end of the day, they are a [very cool, awesome, sweet] 1970s engine with wide enough tolerances to need 20W50...

Just my .02. . . .

- T

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Standard shells are quite cheap..but those for reground cranks are a lot more expensive. I personally wouldn't reuse shells where the copper was showing through.The line around the big end has probably been caused by a very small piece of grit which either got in there during assembly, or was lurking in the oilways and found it's way into the bearing that way. I can't stress enough just how squeaky clean all the parts have to be when reassembling! Muck gets in everywhere, and cleaning all the oilways and parts before assembly is probably the largest part of th rebuilding task. I take out all the threaded sealing plugs and squirt through the oilways with paraffin or similar under pressure...my old aeromodelling squeezy bottle has always proved useful here! Use a good assembly lubricant on the shells and journals, fill the oilways with oil as you go, then replace the oilway plugs. You can pause during reassembly, before you fit the cambelt, fit an oil filter and use a hex bit in an electric drill to drive the auxiliary pulley, and thus the oil pump. With oil in the sump, you are then pressurising the bearings and you will hear and feel the effect as the pressure builds up..make sure you have blocked the oil pressure takeoff first or you'll get a faceful!!

Since shells tend to wear before cranks, changing the shells with the crank within limits should prevent any wear taking place on the crank. Mine's done in excess of 100,000 miles and was still perfect the last time I measured it about 3,000 miles ago. Remember this isn't rocket science...a methodical approach should see you through; buy a book on engine building (there are lot's, look online) and give it a go. There's a first time for everyone!!

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Yes I'm very tempted to have a go at this myself. I can't afford to pay a fortune to have it rebuilt professionally and I know that the professionals will always air on the side of caution and just replace everything. But I spent a bit of time this morning pricing everything up and it comes to serious money if I just replace everything.

What to do...

Paul.

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Paul,

If you have more time than money in the end this experience will most likely make you a top notch Lotus service tech. IMHO doing what you can do is what it is going to take. I went through all the most thorough of preparations on my rebuild and still had to remove the head gasket due to an oil leak around oil pressure feed to the head (Cometic vs Lotus Original) so there are no guarantees no matter how meticulous you are.

What I see on the bearings are at very least some possible lower oil pressure. Engine isn't going to self-destruct unless there was something horribly wrong to begin with. If by chance you didn't mark the bearings as to which rod or main cap they came from then you might have problems with accelerated wear.

By all means get the service manual and read, read, read..

Best,

Jeff

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Hi Jeff

I haven't taken the big end bearing shells out (they're the ones on the con rods right?) but I have removed the main bearings. I know which piston goes with which liner and I know which shells go with which position on the block. However, what I don't know is which shell came from the top and which came from the bottom. I can measure them with a micrometer (when I get a new battery for it!) and then see how much variation there is in each shell. At that point somebody may be able to tell me if they are usable or not.

Cheers, Paul.

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Be difficult to make a sensible measurement of shell thickness with a micrometer as the shells are curved and standard micrometer anvils are flat. Having read through all your postings, and seeing that you intend to have the motor professionally rebuilt at some stage, I think the best thing would be to simply reassemble what you have. There doesn't seem to be anything there that ought to cause short term failure...if reassembled with care I would anticipate that you'd get several years more use out of this engine. Also, now you've got this far, you'd probably be able to do a pretty professional job yourself, when the time comes!!

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Paul,

As long as you have the right pairing of the shells you should be in good shape. Clean everything well so not to have a oil leaker. If you pull the liners make sure they are sealed well on return. You can run a ball hone through the liners to get them ready for new rings. Just make sure when it comes time to purchase the head gasket only go with the factory one.

Take your time, clean, clean ,clean and read the manual thoroughly.

Best,

Jeff

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I hate to say it Paul but Tony's right. I wouldn't be putting those shells back in, and I wouldn't be putting new ones in without having the crank checked.

I couldn't bring myself to go to the drama of rebuilding it and putting it back in, with the slightest suspission I'm going to have to take it all out again.

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Hi Roger

I had the crank professionally checked and it's okay. I've now figured out which are the top and bottom shells by the slight staining marks on them so I'm pretty confident they're going back where they came from. I'm going to have the bores honed whilst I'm at it and the head is being pressure tested and checked for flatness.

Regards, Paul.

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