Thick Thrust Bearings
Turbo Mini Forums

I'm making slow progress on my K100 build but the block is off to MED next week to be bored etc.

Next big job is sorting out some thrust washers.

The engine consists of a 998 block bored +0.120" and an 850 crank giving a nearly square bore-stroke. Should be good for 9000 rpm, but will probably be limited to 8k.

The problem is that the crank centre main journal is 1/8" wider than the 998 so special thrust washers are needed.

I'm discussing having some made with Oselli but expect this to cost megabucks.

I've got a chunk of phosphor bronze that I could use to make some myself, but I'm not too confident that I can get them accurate enough.

The option I'm considering is making some spacers out of an old set of thrust washers by thinning them on a surface grinder. i should be able to get this done locally. The standard washers are about 0.090" thick so just need around 0.030" taking off.

The lip that holds the washers in place in the block and cap is only 0.060" deep, so this will not hold both the spacer and bearing in place, so I need to locate them somehow.

I could just TIG the spacer to the washer but I expect some distortion, so not happy about that one.

So I could either just locate the spacers and washers with dowels or fix them with screws.

Which way would be best.

Photos courtesy of FastCarl and Wil_h

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Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

how different are small bore thrusts to large bore ones?

there was somon on the vintage mini racing forum who was looking at doing thicker thrusts for putting S cranks into A blocks.

I'd deffo go with the screws if using 2 thrusts. This is because I'd rather any iol stays between the crank and thrust rather than between 2 thrusts.

I can't see that using 2 thrusts screwed on would be a problem.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Edited by Paul S on 18th Nov, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Paul , claqmp the two parts together in a vice with soft jaws, the just run the tig along the outer edge using no filler rod, you would get no noticable distorsion if you leave it in the vice to cool

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

ahhh,

found the post i was thnking of,

dosent actually mention whether they are small or big bore.

http://www.atfreeforum.com/mk1mark/viewtop...&mforum=mk1mark

I agree with Carl that an autogenous weld, performed clamped in a vice, is unlikely to create distortion enough to worry about, BUT, I would be concerned about the affect the heat of welding would have on the bond between the bearing material and the steel backing plate.

Not the bearing material itself, but the bond......

Also, your local machine shop may refuse to surface grind the spare washers to make your spacers unless you have removed all the bearing material first - it could wreck their wheel otherwise.

Schrödinger's cat - so which one am I ???

Thanks guys.

Right, I have a plan. I'll try it out on some old thrusts.

I'll TIG them together, back to back. Maybe a couple of short tacks rather than a continuous weld.

Then linnish the bearing material off one side. If there is any damage to the bond, then it will be apparent when trying to remove it.

Then I can get the machine shop to gring it to the finished thickness.

I'm hoping that a magnetic grinding table will pull through the bearing material.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Schrödinger's cat - so which one am I ???

Interesting, let me know how you get on as I'm also interested in a set of "fat" thrusts for the same reason.

This is the wrong way. Fitting S-cranks in A blocks would need THIN thrusts. I would know, as I'm fitting an A crank in an S block
I'm having .030 ones ground down.

Edited by Vegard on 18th Nov, 2008.

If all goes well paul i may ask you to make me some or at least steal the idea that works so i can fit the 850 crank to my build.

Oselli have come back with a price of £90 which was less than I thought it would be. They would still need finishing to size on a surface grinder.

I'm still going to TIG a couple together first though. It's good to have a fall back position if necessary.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Why surface grinder, what about fly cut?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

would it be possable to tack them to a piece of round bar and finish them in the lathe

http://www.astonmartinparts.co.uk/

Well, I think this might just work.



I did the lower one first, tacked it in about 7 places and managed to damage the bearing surface slighly.

After a bit of cleaning up, rubbed it against a bit of 1200 on some glass and oil to lubricate and it very quickly came up clean. Hence no distortion.

I linished the bronze off the other side and there was no evidence that the bond was affected.

The upper one, I just tacked at each end and at the two points where the bearing surface is relieved. Came up much better. OK as long as the four tacks are enough.

Not sure whether to do the lower tanged one again. I've probably only lost about 1% of the bearing surface.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

just put the worst ones on the radiator end where thy won't take the clutch force.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

yes, i agree, better remove it now than have it flake later.

How did you get on with this Paul? Have you had them finished to size yet?