340 build

This post was made from internet searches discussing the matter of removing material from Piston top nothing more.


If you mean grind/cut the tops, of course you can. Depending on the piston, it'll determine how much you can cut. This is normally done on a lathe from what the machine shop told me. I had to do this on an engine and based on Wiseco's recommendation, we were able to cut down .030" off the top without sacrificing the strength. Well, I guess that might be debatable but they said that builders have done this many times before and we wouldn't be the last.

Turning down the top off pistons is part of blue printing. You should check deck height on all pistons, sometimes you’d have to move rods and pistons around to get the perfect deck height, and then the last resort would be turning down the top of the piston. This can be done in a conventional lathe. You’d need to balance the pistons after your done. There are other things you can do, but not going to get into it.


It is fairly common in the performance community to spot face pistons for increased valve/piston clearence.

As posted above it should be done on a milling machine not by hand with a grinder. You also need to consider the thickness of the piston crown. If you mill off too much you will break the piston due to the weak spot you created.

You need to do some homework to figure out some things before you decide what you need to do.

You need to measure the piston crown thickness where the valve pocket would need to be machined.

You would need to determine how much interference you currently have plus additional clearence you need to prevent valve/piston contact during over-rev or high engine rpm due to valve float.

Then you need to determine if there is enough "meat" on the piston to allow you to correct the problem. The proper way to do it is probably to order special pistons to your specs for this build and sell your current pistons.

You really need to get on the phone with the major engine builders like Axis Power, and Cobb they both have probably already determined what the likely clearences are and how successfull the "corrective machining" would be.

Custom machining the pistons after the fact is probably not cost effective. It is much cheaper to do this sort of work when the pistons are ordered unless the engine build shop routinly does this sort of work and already has fixtures set up that are suitable for these pistons.