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Checking bores for ovality
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john-saab



Joined: 06 Dec 2007
Posts: 341
Location: West Dorset

PostPosted: Sun Mar 11, 2012 8:02 pm    Post subject: Checking bores for ovality Reply with quote

I'm working on 3 different classic car engines at the moment, 2 are basic re-builds and one may need a re-bore. while the pistons are out I want to check for ovality and get an good idea of what size piston rings are needed.
What's the best "DIY" bore gauge to use? I want a gauge that will last..i'm not buying for one job, I want a tool I can use for many years...digital or mechanical?
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Inglewood



Joined: 28 Dec 2010
Posts: 183
Location: Stone, Staffordshire

PostPosted: Sun Mar 11, 2012 9:06 pm    Post subject: Reply with quote

A Mercer guage is mechanical and reliable.
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Churchill Johnson



Joined: 11 Jan 2011
Posts: 359
Location: Rayleigh Essex

PostPosted: Sun Mar 11, 2012 9:17 pm    Post subject: Reply with quote

As far as i am concerned there is only one make Moore and Wright, i would have thought that you should be able to get one of these non digital, secondhand, maybe look in one of the model engineering mags.
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Thu Mar 15, 2012 1:52 pm    Post subject: Reply with quote

I've never come across a DIY cylinder gauge.
Mercer dial test indicators are what the name implies. Only indicators - not measuring devices. They may be used to check ovality, but not normally to measure bore wear.
The tool you need is an internal micrometer. They are usually in a set wth different extensions for widely varying diameter. Moore & Wright being most common.
Bore wear is not the same all the way down and measurements for maximum wear should be taken at the top just below the wear ridge and ring gaps normally will be smallest at about mid-way down the bore.
Ring size should match the piston fitted i.e. Std, +.020, +.040 etc. Don't be tempted to fit rings marked for a larger size piston. The ring pressure on the cylinder will be wrong.
Jim.
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