Exhaust valve to piston interference.......

I'm trying to finish things up with this new motor and figured I'd better check valve clearance good. I'm having issues with the exhaust valve just barely tagging the piston. So little in fact I didn't notice it at first. Had to pull the head back off and confim it with the small mark on the piston. I've advanced the cam as far as I can and still hit. I'm trying to get at least .090 clearance on the exhaust side. My questions are:
What is the minimum exhaust valve to piston clearance?
Will a thicker head gasket resolve my issue?
There's no exhaust valve relief, Do I need to have the pistons fly cut?

This cam is .798 lift on the exhaust side and 284 @.050. I'm headed out now to check what the least amount of clearance I have is. Thanks!!! Brian

I set up for .080 -.090 vertical clearance with .025 - .030 radial clearance. I have run as close as .035 vertical ( customer didn't want to spend any more and took the risk) but... if the valves float bad things happen fast

are you checking with checker springs or "the"springs your gona run? did you figure valve lash in?

Cyl. head is?

Just checked mine to see what the minimum is, .060 is where I'm at. This is with a .041 compressed head gasket. So a .060 gasket would give me .079???

cool40 wrote:are you checking with checker springs or "the"springs your gona run? did you figure valve lash in?

I'm using the springs I'm gonna use and not figuring it accounting for lash.

Lem Evans wrote:Cyl. head is?

TFS streets that Charlie did with the raised intake runners

An exh. valve relief is needed i.m.o.

I had that same problem with my .060 460 in my Mustang..I took die grinder and cut a relief in the pistons while still in the engine...I don't recommend it ,and it ain't the prettiest thing I've ever seen,but it's been together since 2004 without being apart. I think if I ever pull it apart I'll have JetBoat Bob to cut the reliefs the same ...if I pull it before it comes apart??

Lem Evans wrote:An exh. valve relief is needed i.m.o.

X2. Don't take THAT chance.

Race Ready Fabrications wrote:

cool40 wrote:are you checking with checker springs or "the"springs your gona run? did you figure valve lash in?

I'm using the springs I'm gonna use and not figuring it accounting for lash.

so your not counting lash? if not then you have more room than you think. how are you checking it? most of the time i check ex 10*btdc,int 10*after tdc.set the rockers up with lash,as youd run it,set an indicator on the retainer and turn it to 10*btdc. now run your lock down with a short wrench,dont use your good arm thats how i do it anyway.works for me.lol

Please do not find a reason to do the wrong thing........put an exh. relief in the piston.

Brian,

PLEASE,,,X 10 on what Lem said. Aren't those pistons Sealed Power/TRW with a stock diameter pin? Those pistons need an exhaust valve relief with that much lift and duration. If not, you'll be bending exhaust valves and tearing the engine down again really soon. Get the pistons out of it and do the job the right way. That's why you mocked up and checked clearance anyway. If you go with a thicker head gasket, you'll be losing compression.

Pull an exhaust valve out of the head and then put the head back on without the valve. Use a center finding punch through the guide to punch mark the piston when it's at TDC,, or you can take an old junk valve, cut the head off of it and sharpen it to a point on a lathe. Then drop the old valve through the guide and punch the piston. Any good machine shop with a piston vise ought to be able to take it from there and flycut your valve reliefs.

Charlie

Race Ready Fabrications wrote:I'm trying to finish things up with this new motor and figured I'd better check valve clearance good. I'm having issues with the exhaust valve just barely tagging the piston. So little in fact I didn't notice it at first. Had to pull the head back off and confim it with the small mark on the piston. I've advanced the cam as far as I can and still hit. I'm trying to get at least .090 clearance on the exhaust side. My questions are:
What is the minimum exhaust valve to piston clearance?
Will a thicker head gasket resolve my issue?
There's no exhaust valve relief, Do I need to have the pistons fly cut?

This cam is .798 lift on the exhaust side and 284 @.050. I'm headed out now to check what the least amount of clearance I have is. Thanks!!! Brian

Other than notching the pistons ... Your best option is advancing the cam till you have .050" intake piston to valve clearance and getting exhaust rocker arms of less ratio than what you have.

Lem Evans wrote:An exh. valve relief is needed i.m.o.

bbf-falcon wrote:

Lem Evans wrote:An exh. valve relief is needed i.m.o.

X2. Don't take THAT chance.

c.evans wrote:Brian,

PLEASE,,,X 10 on what Lem said. Aren't those pistons Sealed Power/TRW with a stock diameter pin? Those pistons need an exhaust valve relief with that much lift and duration. If not, you'll be bending exhaust valves and tearing the engine down again really soon. Get the pistons out of it and do the job the right way. That's why you mocked up and checked clearance anyway. If you go with a thicker head gasket, you'll be losing compression.

Pull an exhaust valve out of the head and then put the head back on without the valve. Use a center finding punch through the guide to punch mark the piston when it's at TDC,, or you can take an old junk valve, cut the head off of it and sharpen it to a point on a lathe. Then drop the old valve through the guide and punch the piston. Any good machine shop with a piston vise ought to be able to take it from there and flycut your valve reliefs.

Charlie

I appreciate the concern and the advice from everybody. These are probe pistons, I'll get one marked tonight and get them over to Mat Wright and let him fly cut them for me. Just another set back that's all

Here is a piston cutter if anyone ever has a need ... go to http://www.lindytools.com/ click on the tools drop down...and you will see the in head piston notcher...

I'ved used that tool and the tool from Isky imo the Isky is much better .