Valve to Piston Clearance
Thread Starter
|
Club Member
Joined: Sep 2010
Posts: 1,692
Likes: 458
Valve to Piston Clearance
What is the minimum valve to piston clearance when building a twin cam engine? I had oiling problems with my previous 107 big bore engine and Im currently rebuilding it. I dont anticipate a valve to piston clearance problem but Im checking everything as I go to make sure its right so I plan on using clay to check the valve to piston clearance. I havent found much about this on line. What I have found is older and Im not sure if it applies to a 103 to 107 big bore. Thanks in advance for anyone who builds engines and knows what this spec should be for minimum safe clearance.
Seasoned HDF Member
Joined: Jun 2015
Posts: 8,055
Likes: 8,080
From: Canada
Rule of thumb on any engine is .100" on the exhaust valve, yes some run .080" but more is better. Intake can be less as its not trying to outrun the approaching piston like an exhaust valve is. You also need to check radial clearance and the best way is the playdough method. Put a little bit of oil on the valve faces so it doesn't stick to the valve and pull it off the piston ruining the test.
Last edited by hellonewman; Apr 29, 2020 at 07:42 AM.
Thread Starter
|
Club Member
Joined: Sep 2010
Posts: 1,692
Likes: 458
What I found so far on line was .09” on the exhaust and .06” on the intake. I think this particular article was referring to an evo engine so I wasn’t sure if these measurements apply to a twin cam.
Seasoned HDF Member
Joined: Jun 2015
Posts: 8,055
Likes: 8,080
From: Canada
The reason for the .100 is to account for some valve float. Ive run as much as .160 on some applications knowing the guy might miss a shift. Doesnt matter evo, Honda, Indian or Lamborghini. .100 is safe, so is .090 but I wouldnt go less.
Thread Starter
|
Club Member
Joined: Sep 2010
Posts: 1,692
Likes: 458
Hellonewman, I found a couple more sources that were talking about non Harley specific motorcycle engines. They both suggested .1” for the exhaust and .08” for the intake also. Sounds like good safe clearances. I guess if I were pushing those numbers by .01” I would go with it but not anymore. I’ll find out where I’m at this weekend. They also said to stick with a minimum of .05” side clearance in the valve cut out. Thanks for your reply’s.
Thread Starter
|
Club Member
Joined: Sep 2010
Posts: 1,692
Likes: 458
Ok. I used clay to check my front cylinder and thought I’d post my results as this will be available on line for others to see. I guess I didn’t need to worry about clearances. I didn’t figure I did but I wasn’t expecting what I found. There were no marks at all in the clay meaning the valves didn’t even reach the valve cut out in the piston. I put clay around the half moon valve relief and used a razor blade to cut it level with the piston top. Here’s what the build is.
-107” cylinders with a deck height of .027”
-pistons with a 3cc dome
-.030” head gasket
-ported heads decked to 84cc
-1.9” I take valves
-1.610” exhaust valves
- Red Shift 575 cams .575” lift
-107” cylinders with a deck height of .027”
-pistons with a 3cc dome
-.030” head gasket
-ported heads decked to 84cc
-1.9” I take valves
-1.610” exhaust valves
- Red Shift 575 cams .575” lift
Thread
Thread Starter
Forum
Replies
Last Post
