Piston / bore clearance

[Axkiker]

Im in the process of specing out the motor im building. The engine specs I have show production piston clearance should be .0030 - .0042

So my question is how to determine my clearance. I have measured the pistons and bore. Once I calculate a total clearance do I then take that measurement and divide by 2 ? Or is that measurement what should be compared to the .0030 - .0042 spec.

Hopefully that makes sence.

 

[daydreamer1252]

Piston clearance is an "overall" spec and not .003 on both sides of the piston. Subtract piston size from bore size to determine clearance. Of course this is assuming NEW pistons and FRESH bores.

 

[alldodge]

Im in the process of specing out the motor im building. The engine specs I have show production piston clearance should be .0030 - .0042

So my question is how to determine my clearance. I have measured the pistons and bore. Once I calculate a total clearance do I then take that measurement and divide by 2 ? Or is that measurement what should be compared to the .0030 - .0042 spec.

Hopefully that makes sence.

Edit: scratch that was thinking ring gap

Look here https://www.youtube.com/watch?v=ZVSd8-b0Ntk

 

[Walt T]

The right way is to use a bore gauge and a micrometer.

Stick a feeler gauge strip between the piston and the cylinder wall. Use the largest you can slide in there tightly. Divide that value by 2 and that is the piston to wall clearance.

 

[daydreamer1252]

Sorry

 

[Axkiker]

So I think I have read 2 different answers in this thread. One which says its an overall measurement and the other to divide by 2.

Any hints on why to do either or what situation.

If it means anything I dont have to use feeler gauges. I have a full set of inside and outside mics.

 

[Bt Doctur]

Think of it this way, the plug measures 1 inch the hole measures 2 inches. That means you have 1 inch of clearance between the plug and the hole or 1/2 inch around the plug.

 

[alldodge]

So I think I have read 2 different answers in this thread. One which says its an overall measurement and the other to divide by 2.

Any hints on why to do either or what situation.

If it means anything I dont have to use feeler gauges. I have a full set of inside and outside mics.

One uses a bore gauge, this kind of gauge ensures it will be perpendicular to the bore when measured. An outside micrometer is good but you can be off center so to speak. So without a bore gauge your bore measurement will be off. The outside micrometer will be accurate for the piston. Bothe are divided by 2 to obtain clearance measurement.

Feeler gauges is divided by 2 as well

If you have the block bored, the machine shop will have a bore gauge and should provide you with measurements if requested. Feeler gauges are better then nothing but a bore gauge is the only accurate way to do it

 

[Axkiker]

One uses a bore gauge, this kind of gauge ensures it will be perpendicular to the bore when measured. An outside micrometer is good but you can be off center so to speak. So without a bore gauge your bore measurement will be off. The outside micrometer will be accurate for the piston. Bothe are divided by 2 to obtain clearance measurement.

Feeler gauges is divided by 2 as well

If you have the block bored, the machine shop will have a bore gauge and should provide you with measurements if requested. Feeler gauges are better then nothing but a bore gauge is the only accurate way to do it

Out of curiosty why do you feel an inside micrometer is not acceptable. Granted a true bore gauge is easier, but I have always been taught that an inside mic is also acceptable if properly utalized.

I do have a bore gauge that I use for mains etc. Its just not large enough for the bore.