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Crank Thrust Washers


sadlotus
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Hi,

Just had a new main bearing and rod pressed onto/into the old crank.

Question is: I didn't notice before but now the rod touches the webs...

There doesn't appear to be any thrust washers.

Is the rod held centrally by the piston?

Are the thrust washers missing? Should there be any?

It's a Sherpa 92 1973

thanks

Paul

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Per the original layout, Mod. 92 big-end assembly does NOT have thrust washers. (There are of course, thrust washers/alloy distance pieces on the small end for con-rod location.)

Also, the hollow crankpin was plugged each end with a taper pin. I understand this was later replaced with a solid pin, but have never had this confirmed.

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Hi all, thanks for the quick replies.

I cant get hold of the person who pressed the crank at the moment, but he did give me back all the bits from before (unless he realised the two spare washers left over should have been fitted and threw them away - doh).

The old little end did have spacers which would have centralised the conrod on the crank, so it may have been like this from new, (nearly 40 years? possibly?) but the new rod has a wider bearing with no spacers and will allow it to slide within the piston, and the crank. Anyway, the old rod had signs of rubbing along its length where it had been touching.

Can someone tell me the width between the two bearing faces on the crank? I imagine these are critical and determine whether the crankcases go together without a gap. It will also determine the width of any thrust washers - although the parts book doesn't list various sizes, only 'thrust washer'.

Am I missing something here? (apart from thrust washers... possibly)

links to pics:

https://skydrive.liv...M5mqj1YC-f_gDg"

https://skydrive.liv...ACYU-Tdpw-Ac6e4

Ps how do you post proper easy to view pictures?

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Hi all, thanks for the quick replies.

I cant get hold of the person who pressed the crank at the moment, but he did give me back all the bits from before (unless he realised the two spare washers left over should have been fitted and threw them away - doh).

The old little end did have spacers which would have centralised the conrod on the crank, so it may have been like this from new, (nearly 40 years? possibly?) but the new rod has a wider bearing with no spacers and will allow it to slide within the piston, and the crank. Anyway, the old rod had signs of rubbing along its length where it had been touching.

Can someone tell me the width between the two bearing faces on the crank? I imagine these are critical and determine whether the crankcases go together without a gap. It will also determine the width of any thrust washers - although the parts book doesn't list various sizes, only 'thrust washer'.

Am I missing something here? (apart from thrust washers... possibly)

links to pics:

https://skydrive.liv...M5mqj1YC-f_gDg"

https://skydrive.liv...ACYU-Tdpw-Ac6e4

Ps how do you post proper easy to view pictures?

To your PS question:Y

ou need the www adress of the picture, copy it then click on the picture/photo button while writing the post, then paste the adress in and then it will show up.

Your pic's:

crank3.jpg?psid=1

crank1.jpg?psid=1

BTW. I have not a model 92 so I believe I cant get you the information you need and the crank is inside the engine too.

Edited by pschrauber
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Sadlotus -

That's clearly the wrong little end bearing........those needle rollers are doing nothing protruding outside the con.rod eye, are they ?

Your "old" set-up of narrow bearing and distance pieces looks far more like the original, as I remember it.

Edited by lorenzo
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Hi Lorenzo

There seems to be several perputations of big end and little end thrust washers. That wider 30mm little end bearing in the picture is the correct one if there are big end thrust washers, but not if there aren't, because as you say, the rod becomes fully floating.

I have two options; have the mains repressed with thrust washers or just replace the little end with a smaller 20mm bearing and new spacers. I need to have another word with my engine builder...

Note to Mr pschauber... I have an ex Finnish engine builder who is an aeronautical engineer, ex Finnair and very particular, unlike his Polish tractor mechanic helper. I try to keep a nice balace between the club hammer and the sliderule.

As to the distance between the mains bearing faces, I think this must be the length of the crank pin. By the way Lorenzo, mine is hollow with no pin, taper or otherwise, again, that's how it was when it came apart, as to whether it was like that when built...who knows.

Just want to know what's best for longivety and robustness, I'm sure the two little end spacers will work just fine, but will the mains thrust washers give a more positive location?

Think I've answered my own question there.

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Can't add to the above but having read it i thought i'd check out the price and availability of the big-end etc for my 191 while i'm preparing the crankcases.Con-rod kits listed by Bultaco UK and Sammy Miller for £110 and £156 respectively but i also found the France Trial Classic website which listed just the Big end bearing for 30 Euros! The question is why do they sell these on their own? presumably you'd need to replace the crank pin and thrust washers as well if they were available seperately .Are there service limits for the con-rods?

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a. Side-play / side clearance limit of the lower con-rod and the thrust washers is 0,25 mm.

b. Radial clearance for the bearing is 2,5mm in cross direction at the top of the con-rod!

c. If a and b is below the limits but the lower bearing feels rough while rotating the con-rod replace too!

Repalce always lower con-rod pin, thrust washers and con-rod together, if you detect one of a, b or c.

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The 325 conrod kits are supplied with full width little ends. You are expected to bore out the old little end spacers

to fit over the new little end and by doing this centralise the crank shaft. However these spacers woked fine when sitting along

side the old little end but when fitted over the needle rollers of the new little end the internal bore will wear.

The bore wears to the point were they collapse and fall into the lower part of the engine which results in piston damage

and seizure. This has happend to two of my engines and caused me to pull out of the 2004 SSDT on the friday.

The crank must be centralized at the big end and leave the con rod to float on the little end.

I believe that this only applies to the 325 and 340 engines. The 250 con rod kits do not require spacers at the little end.

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