Well, after some measuring, I’m a little confused. My piston to valve clearance does not look so good. Sine this is a blower motor, I had custom wiseco pistons order with a HUGE dish of –30cc. They also came with the normal cut valve reliefs. The cam is a decent sized cam with specs of 286/293 and 255/259@.050” with an overall lift of .598/.626 using 1.6RR. the cam is a mechanical roller.

My reason for confusion is that the machine shop told me that this is so rare to need more relief cut on the exhaust side. They said its been years since they had to cut an exhaust pocket as long as the pistons were made with decent reliefs cut for the application purpose. i know blower cams have much more exhaust duration but i would have thought my custom parts would have made for plenty of clearance. my intake is about .100" clearance.

My question is, has anyone else had any problems with exhaust piston to valve clearance? I suppose I could step down to 1.5RR on the exhaust and combined with the lash required, I would be around .090” clearance (in theory) and that would probably be good enough.

Any suggestions or advice? I tried advancing the cam and retarding the cam with little than about a .005-.007” differences in clearance.

Thanks,

Mike

 

You didn't mention what the clearance actually was for the exhaust valve. I still don't see how you could have a problem.

I have a 3.75 throw with 6" rods and have slugs with a -26cc dish and have a 563 lift and aint even close.

If we calculate backwards from your 1.5R that gives us about .044 clearance now with the 1.6's is that right?

We need your dimensions for the bottom end. If you are using a .039 head gasket going to a .050 won't add enough. You could step down to 1.5's that would be the cheapest way to go. The expensive way is to have the heads rechambered and put new valve seats in (ouch expensive)

You could also give the guys a call at TPIS they can tell you what's what.

 

measured wrong guys. at max lift, it was only .035" clearance from the retainer to the guide oil seal. i misinterpreted this for piston contact. not paying attention. have PLENTY of room when i did it right.

sorry.

thanks,

mike