25 replies to this topic

[Gdowle]

I have had the centre main cap machined down to accommodate a centre main cap strengthener. I dont remember the thrust washers being able to swivel side to side when i took it apart. Please can some one tell me if its ok for the thrust washers to move with the change of direction of the crank. Here is a picture. You can see that the tabs from the washers are not pointing the same way. End float is good.

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Edited by Gdowle, 19 July 2011 - 10:31 PM.

[Cooperman]

The thrusts MUST NOT rotate or they will friction weld themselves to the block! (seen that, it ain't pretty, except pretty expensive to fix). The tabs must sit in the retention slots in the cap. If they move radially there is a problem with either excessive, that's really excessive, end float, or some issue with the slots. Take the cap off and see what the problem is. Measure the end float with the cap removed and just the thrust bearings in the block in place. Float should be between 0.002" and 0.004" measured with a DTI.

[Gdowle]

they dont spin right round they just move say .5-1cm back and forth. So if the crank is spinning in one direction they wont move. I think the slot for the tab have been machined out to make room for the main cap strengthener. The shape stops then spinning right round on my main cap. End float is all good and they are new thrust washers

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[Cooperman]

You have to prevent this movement. it looks as though an error was made when the cap was machined.
There used to be a not-dissimilar problem with the 6 cyl Triumph engine and the solution was to drill & tap two small holes into each side of the cap, maybe M3 or M4 fine (or maybe 4BA in English would be good). Then drill and countersink each thrust bearing and use some silver-steel countersunk screws to locate the thrusts, Loctited into place.

[Gdowle]

Thanks, i will have to give it a go. Of course its all back together now but if its going to cause problems i want it sorted.

[Paul Wiginton]

Is that a 998?

[Joe555]

What about getting a wider strap with the grooves machined in the strap? Do get someones opinion first because its only an idea.

[Ethel]

As above, strapping 998's can wipe out the slots for the thrust tangs. I think someone now makes a strap specifically for 998's. I'd screw the thrusts on (plenty of countersink): no guarantee the strap will seat accurately enough to locate the thrusts.

[MRA]

We do.... we also machine them so that they actually work, who ever did this didn't think about the job we leave the ........ just take a look at the picture attached ...................

[Cooperman]

I just checked what was done on the Triumphs. The thrust bearings were drilled with two holes in each thrust of 1/8" clearance. Then the cap was drilled at 1/8" and aluminium dowels were inserted at a slight push fit into the caps. The dowels were cut off flush with the thrust bearing face and the aluminium wore slowly as the thrust bearing work, but the thrust was prevented from moving radially.
This may be a solution for you and I'm sure Martin (at MRA) would be pleased to do at a reasonable price it if you sent him the thrusts and the cap.

[MRA]

I think it may be a little expensive to ship from New Zealand though.....

[Gdowle]

thanks for your help. I think i will see how much a machine shop will charge to dowel or counter sink some screws in the face of the cap and thrust washer. How much would MRA minis charge for the work if i paid for the postage to and from Canada?

Yes its a 998 by the way

thanks

[MRA]

Canada ... where did I get New Zealand from then ???

£20 inlcuding the dowel 6082T6 alloy

I would recomend the dowel method as it allows for a little movement...

This doesn't happen on a 1275cc engine.

Edited by mra-minis.co.uk, 21 July 2011 - 05:34 PM.

[Gdowle]

ha ha i thought that too. 20 squid sounds lovely, I will take it down the post office this weekend and see how much. Just post it to the address on your website?

thanks

[MRA]

Yes the address on our website is correct

Don't forget to include both thrust halves for the cap....

Edited by mra-minis.co.uk, 22 July 2011 - 11:34 AM.