Crankshaft bush tolerance

[namloop]

Hi to all
I am just about to send the crankcases and shaft over to the machine shop to have the new phosphor bush line bored however I cannot locate a tolerance to bore bush out to over the diameter of the crank end.
Any assistance appreciated.
regards
Stephen

[Brian]

You need .001" - .0015".

[namloop]

Many thanks Brian I will advise engine shop.
Stephen

[Goldy]

Yes I did 1 to 1 1/2 thou and it turned over freely with no problems.

[A10Boy]

I dont wish to be pedantic, but what you require is the "clearance" between crank and bush, not the "tolerance" which is the deviation on a dimension. 

[Goldy]

I disagree, if you add a tolerance of 1 to 1.5 thou onto the shaft diameter you will get a clearance of between 1 and 1.5 thou.

[kommando]

A tolerance on a shaft of 1 to 1.5 thou means it will pass inspection with a variation of 1 to 1.5 thou which would vary the clearance by that amount, if you want a clearance of 1 to 1.5 thou then the tolerances on the mating parts (bush and shaft in this case) making the assembly must have much tighter tolerances than the required clearance to make it achievable without additional machining.

[muskrat]

Splitting hairs.
 

[duTch]

When i had my big ends ground last week, they called it 'oil clearance'......!...?

[A10Boy]

As Kommando alludes too, If you ask for a bar or anything to be machined to one inch with a tolerance of 1.5 thou, then you could get a bar with a permissible variance of 1.5 thou. That is the tolerance, its like an allowable inaccuracy.

If you ask for a clearance of 1.5 thou, as in this timing side bush situation, then the machinist will give you a jounal OD at say 1.350 and a  bush ID at 1.3515 which is the journal plus 1.5 thou. That is the clearance. This is a very precise measurement.

Clearance and Tolerance are two very different things.

BTW Sorry if anyone considers accuracy in these matters to be splitting hairs.

[muskrat]

 You are correct Andy "Clearance and Tolerance are two very different things"
The tolerance is 0.0005" if the clearance is 0.001" - 0.0015". Accuracy with this is paramount when we're talking 1/4 thickness of a short and curly.
 I think Stephen has got the size and terminology now.
Cheers

[A10Boy]

That's excellent news. No mistakes then.