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Thrust Bearing Issue

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Brosky

Brosky

Great Pumpkin
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It's been a while since this topic came up and I was looking over some bookmarks that referred to this subject. Tom had written one about the quality of the parts themselves, comparing one against the other and that thread is here:

https://www.britishcarforum.com/bcforum/ubbthreads.php/ubb/showflat/Number/308070/page/1#Post308070

I had mine measured at the time that I was having my first clutch replaced with the long saga of the Gunst installation (which I don't ever want to re-live) and my end play was .008", which is within spec.

Since I had the oil pan off for powder coating, I asked Erik to check the end play again, since there were three clutches in and out of the car a year or so ago. Low and behold in less that 2,500 miles, the reading is now at .012".

I don't beat the car and I really took care of it when I had all of that clutch squealing with the Gunst, so it just goes to show how fast these things can go.

I'm wondering if that constant pressure had anything to do with the accelerated wear? I went 53,000 miles and had .008", including what ever it was when it rolled off the line and to go to .012" in such a short mileage seems a bit quick to me.

I did have a spare set of each size, so I'm OK with that, but I wonder if the clutches had anything to do with this.

Any thoughts?
 
I think non stock (strong) clutch springs are the main factor in thrust bearing wear. I realize the crank may tend to "walk" even though I don't understand the physics that causes it. On the other hand, spring strength of the pressure plate springs is easy to identify as causing forward force on the crank. The stronger the spring the more forward force on the crank.
 
I agree and I think that with the added pressure of a spring loaded bearing designed to "push" against the pressure plate constantly, it would only add to the wear factor.
 
Paul, what surprised me was how thin the bronze coating was on the clad bearings. The photos actually make it look much thicker than they are because they are slightly rolled over the edge of the steel backing. In reality I doubt there is .010" thickness when new.

I was not sure the solid bearings would wear better, but I felt they would at least wear consistently because they would not get into a different material after a thin coating of bronze.
 
Yes, I agree with you on that Tom. Mine will get the clad for now, but the new block assembly that I'm planning to build in the spring will get the others, I assure you.

I think that getting that other setup out of there will only help.

Come spring, I'll be asking for info from your build.
 
FWIW, the 'fix' that makes the most sense to me is having the bearing cap modified to take another pair of thrust washers. Herman van den Akker does this, and I've not heard of a single failure in quite a few years now. Neil Revington does it too.

Most engines (including the TR2-4A) have "full circle" thrust bearings.

The plated bearing inserts are a very standard construction, also used in rod & main bearings with great success. The theory is that brass by itself is not strong enough, so the steel backing gives better strength while the brass (and usually lead alloy on top of the brass) provides a better bearing surface.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]so the steel backing gives better strength [/QUOTE]

As usual, what you say makes sense, Randall.

I'm going to rebuild a spare engine over the spring and summer and I'll be looking to correct this potential issue with that engine when I do that job. It will probably have a few more horsepower than this one.
 
vettedog72 said:
On the other hand, spring strength of the pressure plate springs is easy to identify as causing forward force on the crank. The stronger the spring the more forward force on the crank.
Click to expand...

Only when you're disengaging it though, right? The clamping force of the pressure plate/clutch plate/flywheel is internal to that system, until you push on the clutch pedal to compress/release the pressure plate- the reaction force for that comes from the crank thrust surfaces. So it does make sense that elevating the force with a higher spring pressure would accelerate wear, making it all the more beneficial (IMO) to leave the car in neutral with clutch engaged while sitting at a traffic light. Thought this bore clarification and hope it isn't too much of a statement of the obvious!... Pete
 
Very true, Pete.

Which is why I think that my problem was accelerated by the additional required stiff spring installation that kept a constant force against the pressure plate by keeping the throw out bearing fully engaged all of the time.

It never went into a "free state" where it wasn't turning with the engine at whatever RPM, but kept a constant drag or force against the pressure plate.

We all agree, from what I can see.
 
Brosky said:
I'm going to rebuild a spare engine over the spring and summer and I'll be looking to correct this potential issue with that engine when I do that job. It will probably have a few more horsepower than this one.
Click to expand...

Oh no Paul, now I'm going to have to vicariously spend your money... hmmm... Carrillo rods, high rpm billet crank, nice cam, lightweight steel flywheel, ........
 
What??? No Fidenza aluminum flywheel???

I've located a 75 engine with about 60,000 miles on it. I want to have it line bored and decked, crank machined & balanced, new pistons, rods, something like a GP-2 cam and then I'll install my recently cc'd head on it.

I don't want a high rpm screamer, just a nicely done street engine that will be reliable, idles nicely and has a few more ponies to push my old butt around a bit quicker.
 
After reading what Kas Kastner wrote about the TR6 motor, and all the stories I've heard of not being able to keep alloy flywheels on the crank ... I vote for steel as well.

I've got an alloy on my TR3A, so I'll see what it looks like when I take it apart. Supposedly they aren't as hard to keep mounted to a TRactor motor, so hopefully I'm OK ...
 
Brosky said:
We all agree, from what I can see.
Click to expand...
Oh, well, I guess I have to be the contrary one (as usual). TR6 thrust washers are a very common failure; by no means limited to cars with the Gunst throw-out bearing. And there are many other cars that have springs to load the TOB into the PP all the time. Plus the force exerted by that spring is only a tiny fraction of the force to compress the PP. So IMHO that isn't the problem, or at least only a small part of it.

'Plain' bearings like the thrust washers rely on a thin film of oil at all times, to prevent metal-to-metal contact. If the film goes away, the resulting wear is very rapid. So, although I can't prove it, I believe the overly stiff pressure plates commonly supplied for the TR6 are a much larger part of the problem than the relatively puny preload spring supplied in the Gunst bearing kit.

Can't find it at the moment, but somewhere I've read that someone contacted AP and was told that the commonly sold pressure plate is the wrong application altogether ! They (AP B&B) make a TR6 plate, but the one being sold is from a Volvo or something. That is supposedly the explanation for the 'cranked' fingers in the PP; the original PP had flat fingers.
 
Brosky said:
What??? No Fidenza aluminum flywheel???

I've located a 75 engine with about 60,000 miles on it. I want to have it line bored and decked, crank machined & balanced, new pistons, rods, something like a GP-2 cam and then I'll install my recently cc'd head on it.

I don't want a high rpm screamer, just a nicely done street engine that will be reliable, idles nicely and has a few more ponies to push my old butt around a bit quicker.
Click to expand...

Oh, I wouldn't be saving you any money here. /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif I'm not talking about a lightened stock flywheel here... I mean a really nice steel flywheel made to be only a hair heavier than the alloy versions. I'm a huge advocate of lightened flywheels for these cars as you know. If I had to do it over again, I'd opt for the 12 lb. steel version. All joking aside, I think you'd be doing this engine a dis-service if you don't add that mod to your list of things to consider.

Get the GP2 and a good flywheel and we'll have nearly identical engine setups. You'll really like the extra power the cam gives. BTW, I rarely take mine over 5000rpms, any more than that and I'm wasting revs.
 
Point me to the flywheel that you so reverently speak of, oh wise one.....
 
Just keep adding to it. I'm going to just bookmark this thread for future reference.

Thanks again,
 
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