8 replies to this topic

[racingbob]

what should bigend show ground 10 1275 crank

 

and mains the same

[Cooperman]

The part number on the shells should have '010' after the main part number.

[racingbob]

i mean the size of the journal on bigend and main

[nicklouse]

i mean the size of the journal on bigend and main

I have no idea what you are asking even now.

 

are you wanting to know the journal diameters? then what crank there are more that one size for the "1275" crank.

[racingbob]

yes its the crank journal size when been ground 10 thou

 

have a 1275 gt crank been ground 10 thou

 

will this also be ok for my A plus rods

[mini13]

mains are 2" standard bigends are 1.75" standard, (or as close as you will probably be able to measure anyway with a vernier), they can vary a few tenths of a thou,

 

so you would be looking at 1.990" and 1.740"

[ACDodd]

For 0.010" undersized journals Mains should be 1.991" and big ends 1.741". These are my prefered sizes for a road engine. There is of course tolerances that need to be applied. Consider +-0.00025 as acceptable.

Beware a lot of crank grinding operators will struggle to hit this.

Ac

Edited by ACDodd, 01 November 2016 - 01:02 PM.

[Spider]

mains are 2" standard bigends are 1.75" standard, (or as close as you will probably be able to measure anyway with a vernier), they can vary a few tenths of a thou,

 

so you would be looking at 1.990" and 1.740"

 

Although that's how we all generally refer to them, when checking if on size etc, they are in fact not those numbers at all.

 

On the 12G1505, 12G1817, 12G1683 Cranks, the Nominal Size of the Mains is 2.0005 to 2.001" and for the Bigends 1.7504 to 1.7509".

 

The rolled fillet A+ Cranks are different, so beware. A number of builders in our parts haven't checked and have never appreciated there is a difference and then blame the 'crappy A+ Cranks for their bearing Failures. Nothing wrong with the Cranks or the Bearings, it's the nut on the other end of the wrench that's been the problem.

 

So on a 10/10 Grind that would be 1.9905 to 1.991" and 1.74904 to 1.7409".

 

While these may only appear small differences, remember the running clearance is only 0.001 to 0.0027" so it's not long before your outside of those numbers.

[mini13]

Amen to that,

 

measure, measure.... and then measure again!