Crank journal sizes
Turbo Mini Forums

Hi lads

Looking at buying the shells and gaskets ready to build my engine,
When I picked up my crank from the supplier he advised out of the cranks he has one was ground to a smaller journal size then the rest but couldn't remember which one it was

My question is-
What sort of sizes should I be getting for mains and big ends?

The reading I got on my vernier for the big ends was 44.08mm and 50.71 for Mains

All help is appreciated or If I could be pointed in the right direction

Many thanks
Jack

Jack Jones

Big ends came in two sizes, s and non s.

S= 1.625" 41.275mm
Non-S=1.75" 44.45

There is an exception to this rule. There were i think. 2 Non-S cranks that were 1.625". But i cant remember what casting numbers they were.

Thanks sam, just to confirm that'll be the standard sizes right?

Jack Jones

Does any body know the mains sizes?

Jack Jones

Im sure the sizes are in the haynes manual, also id use a calibrated mic to check things like that. My vernier I use at work cost over 100 quid and its only ever used as a quick guestimate/ compariter.

Edited by wez on 16th Jun, 2011.

one day boost will be mine!

If Haynes is to believed, mains are 2.001" (which is strange, I allways thought they were exactly 2") which is 50.84mm

So, if your vernier is accurate you have standard size mains but quite badly worn and you have -0.010" big ends but quite badly worn.

For reference, 0.25mm is virtually identical to 0.010" and because these are imperial cranks the regrinds (and hence undersize bearings) will be in steps of 0.010"

Your mains are 0.13mm down (not enough for it to be a 0.010" grind) and your big ends are 0.37mm down (enough for it to be a -0.010" grind plus further wear but not enough to be a -0.020" grind).

So the obvious question is how accurate is your vernier ???

They can be very accurate but usually aren't due to wear/abuse. Personally I would use a micrometer.

Also, how many places around the circumference did you measure at - because of the cyclic loading, the journals nearly allways wear into an oval shape.

So even if your vernier isn't absolutely accurate, measuring at two or three different places around the circumference will give a reasonable indication of wear.

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

Bearings come in either +10, +20 and maybe +30 thou.

From your measurements, your crank does not fit any of these common re-grinds.

As you don't know, and don't have the tools to check, I'd take the crank to a local machine shop and ask them to measure it and supply the correct bearings.

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

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hi rod,
thanks for the info,
i picked the crank up from carl when he did a bit of machining for me (i forgot to ask for my crank to be hardened with the rest of the work, so i swapped it with one of his he had laying about),
as everybody knows on here carl is a top guy and his work is second to none so im sure its my vernier as its a cheapo peice of shite

wil, that is a very good idea, i hadnt even thought of that, thanks

Jack Jones