Topic: 15 ohv head work?????

[nor66]

  Can anyone tell me how much  I can mill the head from a 15hp ohv without having vavle clearance issues?

[DarkNyte]

Well on mine it is about 45ths George vcan prolly tell you exact..

[George Herrin]

All depends on the lift cam you are using. Assemble the motor with head and old gasket with some modeling clay on the piston turn motor over by hand the valves will press the clay down disassemble and measure the thickness of compressed clay. This will tell you how much clearance you now have. You want a minimum of .030 clearance.

[birdman_express]

When we mock up a motor and clay it, we take off the head gasket and lash the valves to zero, would this be an acceptable practice in the mower motors as well?

[George Herrin]

Yes if thats what you are used to doing. I use the gasket and old one already compressed and zero lash. Its just how I do it. Again many diffrent paths to the same end result. Some are easier than others.

[birdman_express]

Here is another thing also.... we knew the clearance on the motor and knew we had enough for a certain cam, and changed the cam with just a tad more lift, but the duration was so dramatic that the valves hit. So mock it up again if you change cams.... been there, done that.... ack

[nor66]

thanks for the info I just didn't want to cut to much off and mess things up!, but from what I gather there is alot of room there for trail and error.Along with the port and polish work! thanks again George!

[George Herrin]

VERY WELCOME

[64Vair]

Snip:
...You want a minimum of .030 clearance.

George,
You seem like a guy who is pretty sharp.  I am sort of surprised by the above clearance.  Seems small to me.  On motors I have built, (V8's), I have notched pistons to have at least .125 clearance to account for all the dynamics that can take place in the chamber, not the least of which is valve float.  Even my con rods I want to have a minimum of .060 clearance and they don't float!  (Or if they did, a foot of clearance would not be enough!).
I believe you, it is just sort of surprising to me.  What sort of valve spring pressure do you run?  I was able to take my springs off without the use of a compressor.  Have not measured spring pressure yet, but would be it is only 15# or so on the seat, not sure what it would be open. 
If I could, I would like to ask you, on a Briggs V twin, (446777), how much clearance would you run on the rods?  I have not measured my clearance yet, but would like to know what you think for a mostly stock, lower RPM motor.  (plan on keeping it below 5000 or 5500 max.  It is used on a snow plow mower!).  I was thinking .0013 to .0018 with shooting for .0015
I am interested in what you think.
Thanks
Tom

[George Herrin]

.030 clearacne is what I have always shot for when doing anything with valve or spring bind clearance. It has worked for me regardless where I use it. Seat pressure is app. 40 rod clearance i run right at 2 thousands clearance using the plasti gauge  to check it. While you may want bigger clearances with automotive parts they are much heavier thus harder to control the movement.

[64Vair]

Much appreciate the reply George.  Will check to see what my rod clearance is, and if I change cams will check valve clearance too, but don't think I will have any trouble there.  I am keeping the motor very mild, not interested in RPM over 5000.  I don't have plastigauge, but I do have dial bore gauges that run from .750 to 6.000 in .0005 increments, so I am all set in the measuring department.
Thanks again, I am sure I will call upon your experience in the future for advise.
Tom

[George Herrin]

Anytime buddy.