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MG Midget and Sprite Technical - Crankshaft Thrust Washers

Apologies in advance for more fairly basic questions.

The endfloat I have at present is 0.008". The workshop manual specifies three to five thou float. The current thrust washers are standard and showing no signs of wear, measuring 0.088".

A single pair of + 5 thou washers should bring the endfloat back to 0.003" Can I mix them and use standard one side and + 5 thou the other? If so, which should be to the front and which to the rear of the bearing?

The engine is apart partly to address rear-end oil leakage. I'm sure the plastic seals I fitted 2500 miles ago are responsible. I'm thinking of using cork this time round? What is your preference? Also, would soaking in oil ahead of installation help to swell the cork?

Any comments gratefully received.

Colin
C Mee

I personally prefer cork to plastic as it seems to seal better. I use them dry but coated with Hylomar. I also put hylomar or wellseal between the rear main bearing cap and the block.The original 948 engines mentioned this but its omitted from the later ones. I seems to reduce oil leakage
Bob Beaumont

Yes you can mix the thrust washers as you say. My inclination would be the oversize ones towards the front (crank pulley) side of the centre main. Not sure why. I guess if you were being careful you might see where the con rods naturally positioned relative to the crank big ends. But with only 2 thou difference between the thrust C washers I doubt it makes much difference.
GuyW

Colin, are you sure the leakage comes from the sump to main bearing cap joint? Or is it the perennial problem of the ineffective scroll seal?
Les Rose

Les, thanks for your comment.

After I re-built the engine in 2020 it didn't lose any oil for quite a while. What eventually started out as drips has since increased fairly steadily. If it was the scroll I think it would have been relatively consistent.

The back of the crankshaft flange was dry and I would have expected to find it wet with oil if the scroll was leaking badly.

There was a good covering of oil down the rear of the sump and when I removed the sump there was oil in the groove between the two ridges on the semi-circular seal.

I don't fully trust the scroll but it was quite clean and clear of blockages or debris. I'm pretty sure it's the semi-circular seal that has produced the ever-increasing flow - famous last words.

Colin


C Mee

Never heard of soaking the corks in oil before use. Like Bob, dry, and hylomar, with a dab under the eyebrow, and rear main cap.

Same answer as Guy for the thrusts.

anamnesis

Bob
The Mk1 WSM says to put Wellseal between the block and rear crankshaft main bearing cap. The Mk2 says to use Hylomar. I don't have a WSM for a later model but I have used Wellseal on 1275 engines.
Alan Anstead

Yep, I think it's in Haynes too Alan, and for 1275's.

Edit my earlier post.

Almost the same answer as Guy for the thrusts. But o/s towards the flywheel side, which is where most thrust is experienced from clutch pedal pressure. The fronts wear least, as do the thrust surfaces.
anamnesis

Anam, I think you are right in putting the thicker ones at the flywheel side of the centre main.
Not because of greater wear as I think the copper(if that's what it is) surface will be the same. The thickness difference will be in thicker steel backing. But given there is some wear to be corrected, the crank needs to be pulled back to a pre wear alignment, rather than pushed further forwards
GuyW

True Guy. I'd forgotten that bit about how the o/s thrusts are made.

anamnesis

With your .005" os thrusts is that an overall (pair) measurement or .005" each.
If it's overall I'd poke them in even if it's down to one or two thou. As long as there is 'some' clearance, it will be fine.
IF it .005" each then there's nothing wrong with mix and matching but yeah as the wear will possibly be from having the clutch loaded at startup with zero oil pressure then the thicker washer would be best in the rear
USA spec Mazda mx5's have a real issue with theirs as the engine won't start/crank without having the clutch depressed, they wear their thrusts enough to let the washers drop out, then it gets nasty from there on-----

willy
William Revit

Thanks Alan/Anam

Apologies I have checked again and my 1275 WSM does DOES mention using Hylomar between the cap and the block.
Bob Beaumont

This thread was discussed between 28/10/2025 and 29/10/2025

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