Valve to piston clearance

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dartlove

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So I need some valuable advice, not asinine comments. I have a 383 that I stroked to a 496. My problem is that the block was decked so bad that the pistons are .023" out of the hole. I put on .060 cosmetic mls head gaskets to bump up compression slightly. Problem now is exhaust valve is hitting the piston. I am not sure what to do. Do I get a thicker gasket? Do I start over with another 383 and new machine shop. Or do I eat the almost $1900 in machine work & pistons and start over with a 400 block. Any viable help is appreciated.
 
If there is enough meat on the piston, the valve relief can be made deeper. I'm not to familiar with big blocks but if you have 1.6 rockers go with a 1.5 ratio. Another option is to change the cam for something with less lift. Sink the valve seats in the head, but I don't think that helps flow any. I don't think a thicker head gasket is going to get you safe clearance without doing something else.
 
I currently have harland sharp 1.5 rockers. Cam is custom grind
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This probably isn't the answer you want to hear, pull the engine down and cut a deeper eye brow for exhaust valve clearance. While you are at it, double check the intake.
 
No engine expert here, but what about milling piston tops down? By another shop.
Sorry to read.
Milling pistons will just reduce compression. It won't effect valve to piston clearance unless you machine the pockets completely out. Machining the pockets deeper is the answer (if there's enough material) A simple piston swap would be a good plan if you don't want to switch cams.
 
Your best option is to have valve reliefs/eyebrows cut into the pistons for valve clearance... But that cam has huge lift at .643"/.660" and will require deep cuts... You should check the thickness of the piston before machining to make sure that you will not break through the tops when making the valve reliefs deep enough for that much lift...

Or see if there are any other pistons available with shorter dome and deeper valve relief pockets...
 
Did you degree in the cam ? If so what did you set it at.


Good point, but with that much lift and duration in that cam, I don't think that it's possible to 'degree' enough clearance for the valves...

He needs pistons with deep valve relief pockets...
 
383's and 426's are the same bore of 4.25", there should be some options out there with that common size of bore...
 
Brian6pak is correct!
If your exhaust valve is hitting before the intakes, your cam has not been properly phased in with the crank. and is most likely in a retarded position. (not the owner, the cam!)
The Int valve is a larger diameter valve and will always hit the piston before the exhaust does. (when the cam in installed correctly, or even straight up, or 0)
The cam card shows the cam in 2° ahead. (advanced) This makes the Intakes even closer to the piston at TDC.
The short of it.... slow down, double check your cam position, and decide accordingly.
If you find you need deeper valve releifs, Isky sells 'notch cutters', so that you can perform notches with the engine mocked up.
BTW, a .060 gasket will reduce your CR by more than a point..
also too. gross valve lift has absolutely NOTHING to do with how much valve clearance you will have, that is a function of duration at .050. (the valves are full open when the piston has swept waaaay down the cyl in crank degrees equal to the lobe centers.
 
This is my first build of this magnitude. First time using milodon gear drive. (Still don't quite understand) . Thought I had it. When I did the clay neither valve touched. Also wasn't quite getting valve lift on intake according to cam card. It wasn't until I put all together prime and rotate that I run into problems.
 
You need a clearance of .080 intake and .100 on the exhaust. No way your going to do it with head gaskets. You need to fly cut the pistons. If you have enough material.
 
Thought I had knowledgeable help when I started this. Quickly found out I didn't . I do have another 383 block. Would it be worth a shot to find a different shop and try again? I only used the shop I did on recommendation. They used to build my father-inlaws Chevy comp eliminator motors. I do know of a good reputable shop an hour away.
 
I think it would be worth looking into the possibility of cutting deeper valve reliefs than starting over.
 
Naw, just fix what you have. Degree the cam properly, cut the valve pockets if the pistons can handle it or change the cam if you have to. Your combo should be a screamer.
 
My friend has a 498 and he had the same problem, the cam was off and when I set it up right it had .080 clearance, his cam was a .600 lift, Ross flat top pistons that came out of the hole also not much but enough, I used .080 Cometic gaskets. It started out with 12.5 CR and I think we ended up with about 11.0:1 and It runs great. I would definitely double check the cam. The exhaust should not hit and the intake clears.
 
Naw, just fix what you have. Degree the cam properly, cut the valve pockets if the pistons can handle it or change the cam if you have to. Your combo should be a screamer.
I have the trick flow 270's max wedge, indy 400B intake the cam specified, topped with an AED 1100. Car weighs 2660 with me in it
 
As mentioned, your cam timing's outta whack.

The Toyota engines I race now have 20 thou shims to stack on the block when the factory turbo'd them.
Bigger turbo, more shims.

Back in the day, we tagged 4 - 5 welds on a sacrificial valve, sharpen, then use a piece of fuel line and clamp to limit the valve depth, and use an e!ectric drill to machine deeper valve reliefs.

Good luck.
 
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