Engine Rebuild - Oversize Main Bearing Bore

[rbgosling]

JAE have, or can source, all but the non-groove/hole shell (bearing 3 upper). My plan is to re-use the old shell for that one, as an upper shell it shouldn't be too worn.

[Esprit2]

I should have caught up on messages first, before posting my last message. Joe at JAE mentioned that someone had called to ask about +0.015 bearings... that must have been you, Richard. He said he was short one bearing, but thought another could be modified. Pretty much the same story you posted above. I hope it all works out for you.

Joe also mentioned that their source for +0.015" bearings has dried up, and they have very little inventory left.

Good luck,
Tim Engel

[DavidOliver]

There seems to be different ideas on the need for groove/Holed(yes) bearings on No.3 top.
Mike Taylor at Lotusbits knows it all. IIRC he has supplied me with non grooved, something to do with Australian supplies?? He will have the technical reasons for grooves or no grooves.
Personally I would try and get as tight a fit as possible with new shells.
If you need to drill the oil hole start on the inside to out and not located in the block unless you temporarily block the oil feed in the block to avoid swarf contamination.

Dave the cog

[rbgosling]

The need or otherwise for grooves depends on whether the crank is cross-drilled.

The purpose of the groove is to provide a little reservoir of oil under pressure. There is a hole in the crankshaft from the main journal to the big end journal, and oil can flow from the supply in the groove, through the hole, to the big end journal, to provide oil to lubricate the big end bearings.

If the crank is cross-drilled, there are two holes in the main journal, thus one will always be in the upper half of the bearing. Therefore only the upper bearing shell needs a groove. This is good because that means the lower shell can be plain, which will provide better bearing support, since the lower bearing shell has to take a greater load (crank pushed down by combustion loads). I think some earlier engines at some point had a crankshaft with only one hole in the main journals, so they required a groove all the way around to ensure a continuous oil supply.

All upper bearing shells have a hole in, to let oil in from the supply running through the cylinder block.

The middle main journal doesn't have a drilling to feed a big end, 'cos there are five main bearings but only four big ends to feed. Therefore the bearing shells there can be plain upper and lower, no groove needed, just a hole in the upper one to let the oil into the bearing.

(I spend my weekdays designing engines for Jaguar Land Rover, and started my career doing the same at Lotus, so I'm pretty competent on the theory. It's the practicalities of tracking down the parts I need that is more challenging!).

[Esprit2]

Richard,

There are some pretty complex dynamics at work in a crankshaft. Is there a funky harmonic that creates an unusual upward load in the #3 bearing web? If not, then why not use one more new upper shell, grooved with hole, just like on 1, 2, 4 & 5. They need the groove to facilitate conrod oiling. Number 3 doesn't need the groove, but does it cause any harm by being there? Why would it be a problem in #3 when it's not in the others. That's not meant to be argumentative as much as questioning. There might be a reason, in which case I'd like to understand what it is. Without such an upward load, wouldn't one more 'new' grooved upper shell be better than re-using an old, plain lower shell?

Regards,
Tim Engel

[rbgosling]

Fair point Tim, and I was thinking the same. But there were only 4 groove/hole shells available!

[rbgosling]

The bearing shells have arrived! Held up for a few days while they sent me a VAT demand, but here they are, with Lotus stickers showing the correct part numbers (although oddly the description for the grooved shells says +.01, which is a little concerning). I'll compare the material thickness with the old shells before installing, and then check the bearing clearances with Plastigauge. I'll let you all know how that goes, but it won't be this weekend, got other plans.

[rbgosling]

Just had a reply from Bell & Colvill, saying they can get the plain bearings A907E1171F (+0.15" OD, standard ID), and they are only £2.21!!! After I paid $30 each, plus transport, plus import tax, plus currency fees, for mine...

Oh well, if it ever proves useful for someone else, the link is here. Although there are no grooved ones available in this size, so this is of limited use, unless anyone can find the grooved ones elsewhere (and I didn't get the last set in the world!).

[rbgosling]

A row of "lipstick kisses" from the Plastigauge confirms the bearing clearance for all bearings is 0.0020", just within the 0.0022" allowable clearance. Happy with that!!



Looking at the original upper main bearings (not necessarily in the right order!), I'm feeling happy enough about re-using the central non-grooved one, it seems in better condition than the others:



And the crankshaft, conrods, and pistons are now all installed!! And I've made my first joint that has the potential to leak oil...



(Yes, I know the oil pick-up is missing in that picture, I didn't forget it, I just couldn't find it right away and wanted to get it all bolted up right away so the Wellseal would do its thing. The oil pick-up is installed now.)