Crank Thrust Surface Trouble

[BCjohnny]

chimpvalet, most of the fixes here should be perfectly usable if carried out to a reasonable standard. Generally most things are possible, but they have to be 'economic', also. That means different things to different people.

A lot of this will boil down to if you can do it yourself, or how cost effectively you can get it done. It might be as economic to buy another crank, or they might be rare enough/have a common problem that configuring an alternative might be a better answer. Only you can gauge this.

FWIW welding would be my last choice at this stage. Good luck.

[ProPower engines]

I disagree with not considering the welding process.
When its a repair cost V replacement cost of very hard to find parts welding the thrust face is very viable option
It will restore the crank to like new or better then new size and done correctly will outlast the engine for the intended purpose of the resto project.


I have done many cranks in this manner and never had an issue to date with any of them and some are driven daily most were used with a manual trans some automatics but the result is its easy and cheaper then getting a suitable replacement hard to find expensive crank.

JMO

[wyrmrider]

polishing all the grinding marks off the thrust is essential

[chimpvalet]

To Dan T., the thrust flange is separate from the flywheel hub and is much, much less massive. Section depth at its root is less than .250" and the backside face tapers out to the peripheral edge. It also serves as an oil shield ( forgetting the correct term at this moment ) for the rear seal. That it is only just so ( barely? ) substantial leads to my search for advice on welding it back up. So more concern in that regard than for thrust clearance / end play, ahead of getting those dealt with. Looked into the recommended website for alternative thrust bearings and I like what is offered there, the product is a substitute for the OEM thrusters and looks to be adaptable.
To ProPower, the crank is of U.K. origin, made of a spheroidal graphite iron, comparable AFAIK with what is nodular iron over here. So not exactly "steel". One local shop of repute suggests they have success in welding such cranks, BTW.
Car from which engine was recovered was written off by way of a none too serious front-end collision, as is the way these days. I have wondered whether the failed thrust bearing, which I was later to find twisted into a pretzel in the sump, might have interfered with driver de-clutching for a sudden stop. Seems plausible enough.
To CLShore, thanks for the alternative thruster tip. I see the vendor creates full, rather than half-circle bearings. Gives me some comfort thinking thrust load will be more broadly distributed.

Steve

[ProPower engines]

Spray welding may be useful in this case and a good welder and reputable shop should have good success doing the job.
Now I have seem great spray welding on cast shafts and some not so good. I have only one welder I know here that I would trust a sensitive job to and I am sure in your neck of the woods it would be the same. While the UK is known world wide for producing castings/forgings that stand the test of time as well as repairability if it were me I would seek the shop that could restore the crank to a machinable condition before I went the thrust bearing repair route.

It's just a matter of finding the right shop to do the work.Like I mentioned they are few and far between and the talent that goes with that is a dying art and not being taught in any schools these days.
It will be an old school guy that is skilled in the repair of components because replacement parts were too costly to buy or just plain not available to them.

[machinedave]

I have had many crankshaft thrust surfaces welded and reground back to standard size with no problems at all. If I recall the last time my crank grinder charged us $69 extra to weld the thrust.

[clshore]

Typical TW failure goes like this:
The thin layer of bearing material gets worn through, either from poor lubrication or contamination.
Resulting steel-steel contact is a very poor bearing combination that exhibits accelerated wear.
The increased clearance is enough to allow the front TW to drop off of the retaining edge of the lower bearing cap.
This then allows the rear TW to drop off of the retaining edge.
Sometimes the TW will be trapped briefly between spinning crank and block before falling, explaining the pretzel found in the sump.
Now crank thrustface contacts the rear of the block, again a very poor bearing combination, leading to more damage to crank and block.

[Sir Yun]

on turbo a-series of high output (say more than 250 bhp instead of the 68 odd it was designed for) the thrust washers get eaten a lot due to the heavy pressure plates.
Some people have converted to oil fed thrusts not unlike the pics shown above but with a feed hole and that seems to work well.

[wyrmrider]

pics shown above?

[Kevin Johnson]

pics shown above?

imagesXR1X1056.jpg

[Sir Yun]

page 1 robert1

[allencr267]

I wouldn't call the robert1 pic a fix until its leading edge is radiused/beveled so it isn't scraping lube off the thrust surface and notching into those countersinks for lube to enter & radiusing/beveling their edges into non-scrapers, though It sure do look pretty.

The most difficult thing is getting the crank grinder to do what they hate doing, using the side of their wheel.

[robert1]

It did not need a radius to clear the crank as the I.d. Is larger than the radius on the crank. Didn't really need chamfer on either end as this is the front side of the cap and normally the force on the bearing is from the rear but I know you new that from your keen eye to detail. The fix lasted until the owner did something else to finally finish off the motor for ever. I first built that motor for a sprint car in 1990 it lasted until around 2008.

[DaveD]

I'm a late commer to this question but I build and raced an 1148cc triumph Spitfire since 1972. I've noted that the question of WHY has been glanced over ever so lightly. I ran into this in the middle '70's while I was doing an normal rebuilt on the motor for my next race. At the race I had a problem shifiting and noted the clutch was not releasing. When I drained the oil I saw metal, Not good. The the thrust washers on the rear of the crank were destroyed. This had never been a problem before. I decided that the clutch was the problem, but a visual inspection of the clutch did not show any problems. So I made a test stand. The results were interestng the "brand new" clutch had a small deformation which caused the clutch fingers to not release. Result: new clutch, no more problems.

As to the fix of the thrust washers. The photo of the"bronze alloy" washers with screws was close. My engine machine shop pinned them using the same material so any wear would not be a problem. We used the "bronze alloy" for the rear washer, both halves, the front washer does not see the clutch pressure so standart washers/spacers work just fine. If you need to repair the surface on the crank. Spray welding is OK. I've used these "bronze alloy" washers ever since.

[Dan Timberlake]

......... as this is the front side of the cap and normally the force on the bearing is from the rear but I know you new that from your keen eye to detail. The fix lasted until the owner did something else to finally finish off the motor for ever. I first built that motor for a sprint car in 1990 it lasted until around 2008.

Was the front thrust face worn? I'm thinking adding material to the front surface would move the nominal crank location forward, which at the limit would use up rod side clearance or annoy the timing chain.