Piston To Valve Clearance

[Yammer-Hammer]

What is a safe PTV clearance at TDC for a yz426f? 2000 model stock cams? I'm asking because the work I plan to do to it I need to first make sure I can maintain a safe PTV clearance. Does anyone know what would be a safe clearance?

[grayracer513]

Generally, on the intake side you need at least the total amount of deck clearance plus .010”-.015” for piston rock (pivoting in the bore). On the exhaust side, you need 2 to 2 ½ times the clearance you have on the intake.

[Yammer-Hammer]

Generally, on the intake side you need at least the total amount of deck clearance plus .010”-.015” for piston rock (pivoting in the bore). On the exhaust side, you need 2 to 2 ½ times the clearance you have on the intake.

Okay thank you gray, what is the deck clearance supposed to be? My piston, the crown comes up and stops .018" before the surface of the deck. And I cannot find a measurement for it in the manual.

[Yammer-Hammer]

Also, the higher you go with compression the more retarded you want the ignition correct? Like say idk, 15:1?

[grayracer513]

Since the engine only has a 2.5" stroke, .016-.018" should be fine. 

 

The timing is not what you would necessarily use to compensate for high compression, octane number is.  It could turn out that the timing would need to be fudged one way or other, but mostly it's a fuel issue, and the timing will only need changing if the burn rate in the combustion chamber rises considerably.  BTW, 15:1 is probably out of the question unless you're planning to use exotic fuels, but then that would definitely require fiddling with timing.

[Yammer-Hammer]

I plan on using e85

[grayracer513]

I plan on using e85

Better stay with stock compression then.  E85 is junk fuel. 

[Yammer-Hammer]

We run e85 in a 327SBC running 13.2:1 with camel hump heads I'm sure e85 will work with 15:1 in a 426

[dirtbeater]

Isn't e85 the craps fuel with extra ethanol? I would think premium with some vp44 would be needed?

[dirtbeater]

Not vp44. Vp10.

[dirtbeater]

Vp110. Sorry vp44 is a diesel injector pump and I am not sure what a Vp10 is. Higher compression needs higher octane. 85 is about the lowest octane I have seen. Stick with stock.

[grayracer513]

E85 isn't 85 octane, it's 85% ethanol, and while it does have good octane numbers, it's a very low energy fuel compared with any decent blend of gasoline, even pump premium.  Junk, basically, IMO.

[dirtbeater]

I see, thanks. I am not sure if they sell it around here. I don't know that I have ever seen it.