Forum » Engine Building Fundamentals » Thrust Washer Question

Thrust Washer Question

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


Page 1
Author
216 Views

On my MG Midget (1.5L, same as Triumph Spitfire), there is a known issue with the thrust washers. They are coated steel 180* washers, and once the coating wears off the steel causes friction and wear, resulting in the washers wearing thin and falling out into the sump. There are better washers now available that are solid brass so no coating to wear off, which is supposed to help the problem. I have seen some people take it a step further and machine a lip into the end cap along with tapping a few holes, allowing them to mount a second thrust washer, essentially making it a 360*. Do you think this is worth the extra effort or overkill?

The car is just for fun spirited driving with the occasional autocross, nothing serious, but it does have some mild modifications and I want to keep it as healthy as possible. The engine is coming out anyway to replace the clutch and fix a leak on the gearbox so it is a perfect time to do any preventative work.

Ok the first point is that if the thrust bearing is wearing then you have issues as this would suggest that the thrust face of the crank is breaking through the oil layer. A key point to remember for any of the bearings in the engine is that they rely on an oil film supporting the crankshaft. There should not be metal-to-metal contact. If there is, no bearing in the world is going to last. On this basis I'd hypothesise that the root cause is oil flow to the bearings and the quality of oil being used.

I've been involved with a LOT of Mitsubishi 4G63 engine builds and the early versions from the EVO 1-4 had lots of trouble with thrust washer failure despite the fact that these are a 360 deg design. I improved the situation dramatically by having slots machined into the surface of the thrust bearing to promote improved oil flow to the surface of the bearing. I had two small slots machined vertically down from the crankshaft journal and then these opened out into radial grooves that distributed the oil to the thrust surface. With that modification and a high quality synthetic oil I never had further issues.

Following from the video, most people forget that fitting a clutch with a heavier pressure plate will increase the force on the thrust washer in proportion, sometimes that can be too much for them, especially if held down for periods at high rpm - drag start line, for instance...

I hadn't come across your method of supplying oil to the thrust face, but there are a couple of old school methods that may help some folks - or may not?

a/ with engines that have the thust washer at the rear, some will drill through the washer and block into the bearing oil feed drilling in the web/rear of the block - I suppose that could also be done for other webs with an angled mill end?

b/ use a fine file to form SMALL chamfers at the ends of the grooved, block shell from the oil groove to the loaded thrust washer side - I use this method but don't know how effective it is as I don't use heavy pressure plates, but never had issues and have frequently re-used shells when there are NO wear or marks evident*.

*naughtly, but sometimes budget, availability or timeconstraints require it and ensuring the engine is CLEAN during assembly, regular servicing and good oil can go a long way.