Rage

Has anyone ever actually checked the piston to valve clearance of a totally stock 496HO? No assumptions, actually checked it with the playdough, low force checking springs and everything.

I have heard a claim on this that I can not believe and would like an independant source if there is one. Hard to imagine anyone feeling the need to check a stock 496HO but anyway the question is asked.

paradigm shift

I would call Ralar I bet they have checked. They have done lot sof testing and modifying on the 496.

I have read that you have to change pistons if you want much more lift than stock because clearance is tight.

http://www.raylarengine.com/

You could also check yourself with piston ATDC and use a dial indicator and spring compressor I would think without pulling completly apart. Just a thought.

Rage

The only way I have heard of that works for sure is to put a spot of play dough on the piston where the valves come closest, bolt the heads on with low force 'checking springs' installed in the place of the normal valve springs so as not to compress the hydraulic lifters, assemble / adjust the valve train and then turn the engine over by hand. Disassemble the heads and measure to what thickness the play dough has been compressed by the valves.

Yes, everyone including Ray@Raylar advise installing high relief forged pistons before putting a higher lift cam in the 496. No argument there. I am in search of the hard number as to the stock 496HO engine's valve to piston clearance when the above procedure is used to check it.

Rage

Anyone?

Raylar

Rage:

You seem as though you are really into the concise stuff here. Got an idea, put a cam in of known lift, degree the cam, clay the top of the valve relief and measure exactly to get your answer! Whola, game over!

Ray @ Raylar

Rage

I already measured valve clearance with clay on the new cam but not on the stock Merc 496HO cam. I wish I had when I had it all appart but I did not. My mistake. All I am now looking for is what is the minimum clearance of the 496HO valves (intake) with the stock Merc 496HO cam in a stock 486HO engine if anyone already knows. Consensus clearly is that if anyone would know you would but whether you are willing to share that information is the question. I prefer a rock solid direct reading if it is available.

Thanks as always for your input.

Raylar

If the stock cam is installed straight up the intake valve to piston clearance is about .070". This needs to be measured with the lifter converted to a solid plunger if you are using the regular valve springs for measurement or the lifter can be regular stock if you are using light checking springs. You need just a little bit of clay on the flat and radius of the valve pocket, then you need to use a razor blade, cut the clay section in half and make sure from the side of the cut you are reading the thickness correctly. The other real important thing to remember here is the valve springs that will be used with the new cam and the dial in location of the new cam, as these will affect how much clearance is adequate. The stock cast hypereuctectic pistons have ZERO tolerance for valve to piston contact! Good Luck

Ray @ Raylar

Rage

Thanks very much!

Bill