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post #1 of 4 (permalink) Old 09-01-10, 08:00 AM Thread Starter
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Question Engine bore tolerances

Hi

New here. Comeing from Slovenia-Europe. I just rebuilding a 73 400M engine from country squire which we bought 2 years ago from the first owner in US and bring it here to Europe.
Main and rod bearings are bad and also camshaft and bearing.
Now I'm looking at bores and I just can't find anywhere in which tolerances the cylinder bores are still ok.
I have some data, but it's kind a confusing.
bore 4.000-4.002
taper limit 0.01
out of round limit 0.005

Confusing for me is that if I could have taper limit of 0.01, that means that bore with the taper in upper tolerance is 4.01 which is more than tolerance for the bore.

Is here any one that could give some data about this tolerances for the bore, or if there is any web page for this data?

Thank you

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post #2 of 4 (permalink) Old 09-18-10, 09:08 AM
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Re: Engine bore tolerances

Quote:
Originally Posted by feelsick View Post
Hi

New here. Comeing from Slovenia-Europe. I just rebuilding a 73 400M engine from country squire which we bought 2 years ago from the first owner in US and bring it here to Europe.
Main and rod bearings are bad and also camshaft and bearing.
Now I'm looking at bores and I just can't find anywhere in which tolerances the cylinder bores are still ok.
I have some data, but it's kind a confusing.
bore 4.000-4.002
taper limit 0.01
out of round limit 0.005

Confusing for me is that if I could have taper limit of 0.01, that means that bore with the taper in upper tolerance is 4.01 which is more than tolerance for the bore.

Is here any one that could give some data about this tolerances for the bore, or if there is any web page for this data?

Thank you
The 4.000-4.002 would be the factory bore tolerances. The taper & out of round are both wear/use tolerances. Taper causes the rings to expand/contract excessively each stroke. Some people will use oversize rings filed down to fit up around .005 rather than boreing. Probably better off doing it right if excess wear.
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post #3 of 4 (permalink) Old 09-20-10, 10:50 PM Thread Starter
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Re: Engine bore tolerances

I measured the bore and this are the dimensions

linear to piston pin
top - 4,00315
middle - 4,00276
bottom - 4,00315

90 degrees to piston pin
top - 4,00394
middle - 4,00433
bottom - 4,00394

So, what do you think is this still ok or should I rebore?

Thanks
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post #4 of 4 (permalink) Old 09-21-10, 08:13 AM
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Re: Engine bore tolerances

Seems to be in the tolerances listed. See if you can borrow a standard size ring & measure the gap. If in tolerance use them, if not get oversize rings & file them to get proper gap.
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