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bore measurement

Engine Building Fundamentals

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Good morning all

I have a question regarding the bore measurements taken on a block that I received not long ago. the cylinders have been enlarged by 0.5mm. When I used my dual bore gauge at different places in the cylinders, the measurements varied between (0.008in) 0.203mm and (0.009in) 0.228mm.

Is this Correct?

Was this engine run for any distance, or is it a fresh rebore?

They should be exactly the same, wherever you measure, but if its a used block there may be some wear.

Before panicing, I would have the two measuring points check for accuracy in a test ring.

Hey Jean,

Measurements will change of when the bores where machined if they where machined with a deck plate on (a dummy cylinder head) as the bores will be round when a clamp load is applied and oval when no torque is present.

If you mean down the bore from top to bottom this could still be due to the above mentioned but... I would double triple check how you are measuring and setting the bore mic. They can be fussy to get an accurate repeatable measurement. Even when using a setting ring the correct method can have micron variances. As Gord says a test/setting ring is the best way of setting your dial gauge but these can be expensive, and setting off a mic is fiddly, if possible but a setting ring or find one to borrow, and keep checking the dial gauge through out measuring.

Where are you taking your measurements? I would take a minimal 3 (I would generally take about 5-7) depths at x and y directions, this will give you an idea of the shape of the cylinders. If it's possible to have a dummy head made this will help you get an idea of what the cylinders do when the head bolts are torqued down. This can be expensive when you are only building one engine of that one type, some machine shops will have these deck plates in if they are machining several of that type of engine so it could be possible to find one and borrow or ask for them to measure up your block.

Hope this helps

Dave's comment reminds me of an old technique - with the bare block, bolt down the head(s) with new gaskets to the correct torques. Then you can measure the bores from the inside of the engine, the crank' side.

Thanks Gord it's a great idea that I will apply ;)

Thank you D.C I understand better now.

It is the CA18 block which has been enlarged by 0.5min. the seller made it clear that the work was done with a torque plate bolted to the block with a cylinder head gasket.

the method i used to measure the bore is the same as the one you use in your lessons with the piston and micrometer.

the unit of measure for my bore gauge is 0.0005 in which is very small. at a certain level of precision nothing is perfect, or am I wrong?