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Message started by sandmanred on 04/24/24 at 13:43:29

Title: Valve seat contact patch
Post by sandmanred on 04/24/24 at 13:43:29

I have my engine head apart and decided to lap the valves as long as I've gone this far already. The engine has about 15,000 miles and was running okay except for a few oil leaks on the head when I took it apart. After lapping the contact patch between the valve and valve seat for both intake and exhaust is now larger than the service manual recommends (1-1.2mm) and I'm more like 1.5mm on intake and 1.2 on exhaust. I reassembled and checked one intake valve for leakage using gasoline and it seems to make a good seal. Does anyone have experience to tell me if I can proceed with assembly or should I take the time to re cut the valve seats?

Title: Re: Valve seat contact patch
Post by DragBikeMike on 04/25/24 at 10:36:54

I wouldn't worry about it as long as the valves don't leak. The contact footprint will always peen out a bit as the engine runs. Lapping will exacerbate the condition. How long did you lap for and what grade of compound did you use? I generally only use lapping to do a quick check of the contact to see if it's too high or too low. I only lap with extra fine and limit the lapping to 15 seconds or so.

"I reassembled and checked one intake valve for leakage using gasoline and it seems to make a good seal. "

I'm curious, how do you fill a port or the combustion chamber with gasoline if you only have one valve installed?

Title: Re: Valve seat contact patch
Post by sandmanred on 04/25/24 at 18:20:38

I used Permatex lapping compound, not sure of the grading. They said it contains a variety of grades. And of course now I can't find the tube to tell you more. I could tell from the feel it breaks down very quickly, 4-5 twists and the gritty feeling went smooth. I lapped enough to get the majority of the pitting or about 5 or 6 cycles with fresh compound but to be honest I didn't count I was looking to remove most of the pitting. I couldn't completely cover the valve with gasoline but I could cover a solid 1/2 and wet it all the way around the valve. Pic is after lapping. I estimate the exhaust side to be close to spec and the intake side to be 1.5mm or so.

http://https://i.postimg.cc/pL4wz1SQ/IMG-9608.jpg (https://postimg.cc/NK8CwbBL)