How to check valve to piston clerance?

[Guest]

... on a 850?

I am putting the engine together after a re-bore and since the head and the cylinders mating surfaces were planed I'd like to make sure there is enough valve to piston clearance.

Thanks

[Nessism]

... on a 850?

I am putting the engine together after a re-bore and since the head and the cylinders mating surfaces were planed I'd like to make sure there is enough valve to piston clearance.

Thanks

Clay

[blowerbike]

Clay

Aiken?
i should have known

[Nessism]

Aiken?
i should have known

Got me.

Okay, so now tell him how much clearance he should have... .050"? .150"?

[blowerbike]

well now he is in a mess...
with the machine work done he has to re degree the cams or they will be off really baddddddddd.
get back with me once he has some slotted sprockets and is degreeing the cams.
lol@Clay Aiken...i kill myself sometimes

[GregT]

The Kiwi way is plasticene rather than clay...
How much have you had off the gasket faces ?
if it was just a cleanup cut - say less than .010in I wouldn't worry, you'll still have more than .060in valve to piston which is heaps for a road motor.
Again if it was this little off I wouldn't bother degreeing the cams unless you want a tad more performance - and that's all it'll be worth.
If on the other hand you've taken over .020in off then yeah, you've got to do it right.
I'll do a Ray here & say if you want to talk it over ring me on 03 318 0013

Greg

[Guest]

thanks guys, yes it was just a "clean up" and if my metric/imperial calculations are right that comes under 0.010 in inches

[BadBillyB]

I'm Aiken to know the answer too....Ha!!....All jokes aside, I always use really thick solder. I am thinking what I used (long ago) was .090" solder. Assemble the motor, set the cams and with the spark plug out, bend the solder where it will reach the back of the valve cut out. Roll the motor over and if it "grabs" the solder, it is soft and will squish. Take the solder out and measure the flattened area. Add .010" for good measure (no pun intended) to account for piston rock etc....If the measurement is good, no need to take it back apart to measure/remove clay....I seem to always do things different than most others, but my method is sound.....Shoot for .050" on the intake (minimum) and .100" on the exhaust. Exhaust valves can "float" on an overrev.......I feel like such a forum troll since I just got out of the hospital and cant go/do anything.....But I like it here......Billy

[rapidray]

The EASY way to do it is to set up a dial indicator on top of one intake bucket & with the cam at full lift, push down on the bucket EASY till you feel resistance. Look at the indicator & see how much it has traveled. Repeat the procedure on the exhaust side. You want a MINIMUM of agout .050-.070 on the intake & .100 on the exhaust. This is INCH!!! NOT mm! Ray.

[TeamDar]

Ray, correct me if I am wrong, but shouldn't this test be made with the piston at TDC of the exhaust stroke or maybe from 30 degrees before to 30 degrees after TDC? The least amount of clearance can occur without the valve being at the maximum lift but usually during the overlap period near TDC of the exhaust stroke. Dar

[KC1908]

Always done it Bad Billy's way with solder. Been using that method for nearly thirty years now and never had a problem.

[blowerbike]

all this trouble and your not going to degree the cams?
you can make the clearance anything you want then.

[rapidray]

Ray, correct me if I am wrong, but shouldn't this test be made with the piston at TDC of the exhaust stroke or maybe from 30 degrees before to 30 degrees after TDC? The least amount of clearance can occur without the valve being at the maximum lift but usually during the overlap period near TDC of the exhaust stroke. Dar

Actually, Dar, I think it's closer to 20 degrees before & after. For what these guys are talking about here, though, with stock parts I think they will be ok checking at max lift if they have the cam timing correct. Anything with big cams that I build I check in 5 degree increments, 20 before & 20 after, & don't have problems. The amount of material removed was so little that I wouldn't even be concerned about cam timing with all stock parts. Ray.