Piston clearance on Mark IV 454
 

Going .060 on a rebuild for a 454. Does anyone have a recommendation for piston clearance?
The pistons are Sealed Power H693CP with the teflon coated skirts and my machine shop is not too familiar with clearances for boat motors (great huh?) box says minimum is .0015 but I don't want to run that close. .004 .005???

Thanks in advance

really??

I am certainly not the master engine builder that some on here are but I am pretty sure that the hyperutectic pistons do not like a lot of clearence. .004-5 is forged piston territory. the hypers are more brittle but also do not expand like the forged. with that big a clearence they will probably eat themselves.

so .0015 would be a good clearance?

really what?

Call Sealed Power and get it right.

H & D,
With the coated skirts you cannot measure the piston correctly so you have to go by the bore size on the box. I generally add .001" for marine and high performance car and truck engines. The H693's are a cast Hypereutectic piston and do not need a lot of initial clearance becasue they do not expand as much as a forged piston. If your machinist uses a torque plate and finishes the bores to 4.311" you should be good to go.

You can try calling Sealed Power but I have found thier tech line to be pretty weak as far as performance and marine info.

You might also want to open up the ring end gaps a couple of thousanths also. I am pretty sure that if you read the instruction sheet that comes in the piston box it will tell you this too. If you use a non file fit ring set they should be just about perfect.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Thanks Bill