Topic: Piston to valve interference after decking? (650 cam, 60mm Pistons)

[Trad]

Hey guys,

I want to know if anyone with a similar setup on their 550's have run into any issues. The shop said that they decked roughly 3 thou off the head and didn't deck the cylinder at all. I am a bit worried about piston to valve clearance on with the 650 cam. Should I foresee issues?

My setup is as follows.

JE-60mm pistons (DMP 572 Kit)
650 cam
KPMI HD Valve Springs

Any insight would be much appreciated.

Cheers,

-JJ

[bwaller]

I expect those Dynoman piston/valve reliefs were designed to allow clearance with higher lift cams than the 650 piece. However there is no logic assembling without checking clearances firsthand yourself.

[lucky]

.003 thousandths is almost nothing. BUT... sometimes the valve only clears by .010 thousandths,
Better check it.

[PeWe]

Check the clearance when timing the cam. When the cam lobe is on its highest point and press the valve maximum.... tighten the valve adjuster screw until it stops which is hitting the piston. You'll know if its enough then. How far could you press the valve?
If you need to check the piston to combustion chamber clearance, clay must be used.

Over sized valves might hit each other...? That's another question


EDIT: I have over sized inlet valves in my CB750 K6-76. I did radial check twice. Assembled pistons, cylinder, head, (I used old gaskets). Use a drill or punch that fits the valve guide exact and punch marks on each piston at TDC, IN and EX. You'll see if the pocket for valve need to be grinded. I measured the radius of my valves and verified on piston min. + 1mm clearance around. Not tightened head bolts (nuts), only the 2 guides that make sure that the head is correctly positioned relative cylinder. Same with the guides cylinder-case, must be on. (short metal pipes)

My new piston pockets had to be grinded on one side for my over sized IN valves. Used the Dremel.
After that I did a final test with modelling clay to verify the valve prints in pockets and also piston to head clearance. Timed the cam here for first time. Disassembled everything to base, new base gasket pistons finally assembled with rings, cylinder, new head gasket, head on with final tightened bolts.
Timed the cam again, double checked the valve clearance by tighten the adj screws max down. I had thoughts about min. 1,5-2mm clearance to not worry. EX is the worst according to the threads I have read here, the EX valve is chased by the piston....

Wiseco's homepage...
- What is minimum piston to head clearance? -
Rod material, the mass of the piston, and piston-speed are the factors that determine this. Steel rods in a big block usually require .045. Steel rods in small blocks require at least .036. Most imports can get by with as little as .030. Aluminum Rods generally require .010 more clearance than steel rods. *Remember, the compressed gasket thickness can vary from .025 in steel shim applications to .040 for composite and up to .100 for some copper gaskets.

-What is minimum piston to valve clearance? -
It is different for every different valve-train configuration, but depends more on cam timing and valve-train mass more than anything. Cam duration is the key; actual lift doesn't really come into effect, as the piston is half-way down the cylinder by the time the valve is at max-lift. The usual rule of thumb for an engine using rockers is .080 on the intake and .100 on the exhaust. The most common problem with broken valves comes not from lack of vertical clearance, but in fact a lack of radial clearance. Because of manufacturing variance in the cylinder heads, a piston must to be built with a valve pocket that is larger than is needed. Always clay or use other steps to measure clearance around the edge of the valve. Most of the time measuring one cylinder is not enough as a problem can start at one end of the engine and get progressively worse down the length of the engine.

[Trad]

I am using OEM sized valves. When I talked with Buzz at Dynoman he said a few thou off the cylinder head was nothing and I'm good to go with the setup I'm using and claying is most likely a waste of time in this application. If I had oversized valves, or anything taken off the cylinders as well I may run into some issues.  The reliefs on the JE 60mm pistons are larger than stock so I should be golden.

Thanks for the input as usual guys!

-JJ

[754]

 Some good advice was given , you chose not to take it.

Assembling various non OEM parts without claying has bit many people.

[Trad]

Some good advice was given , you chose not to take it.

Assembling various non OEM parts without claying has bit many people.

I may still clay but the only non OEM parts are the pistons (with larger relief cuts than stock) and the KPMI valve springs. Everything else are "NEW" oem pieces from the new valves, guides, new oem rockers (that were hard as hell to find), and everything else. Even the cam is OEM (650)

I will most likely still clay to be safe but I'm honestly not too worried after evaluating the situation.

No need to be a grouch

[bwaller]

We're not trying to be grouchy, but people have taken the easy route before...

You're trusting someone removed 0.003", not 0.030". I agree, you're probably ok, but spend a few hours and be sure.

[754]

I am not being grouchy, but there are no, I mean few..shortcuts in engine building.
Knowing for sure is best, besides if you change to hotter cam later, you will then already know if it fits.
 If someone helping you is wrong, you buy parts twice, then do it rright the second time.
Now to your head,
 .003 thou is the thickness of a hair, now I have taken only that off some heads.. But they were single chamber, and i take the time to clock in with a dial indicator.
 My experience has been most engine shops, use a level rather than dial, then take 10 thou if it looks pretty flat, and charge the rate for every pass of the cutter' taking only 3 thou and it actually cleaning up means it probably did not need it
 If you took a skim cut till all corners cleaned up, then 3 thou.. That makes more sense.

 But hey do it without checking if you want, I wont be grouchy if some parts start kissing each other...but you will..