Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties OK lets try these valve questions

OK lets try these valve questions

Post Thu Dec 14, 2006 8:55 am

Posts: 801
Location: Planet Earth
What would be any ill effects caused if any by running an exhaust valve for an intake valve in a UL? Wondering if the larger margin, (over .100) would help the valve last longer and run cooler? Or would it tend to run hotter than a thinner margin intake valve? Only modification to the valve would be to back cut the valve at a better angle to increase flow. Even with that mod, it would still be a bit heavier than an intake valve.

On an intake valve, would a margin of approx. .050 be OK or should it be replaced with a valve that has a wider margin?

Most of the new repop UL intake valves I have had in hand have a margin of .050 or less.


Post Thu Dec 14, 2006 2:57 pm

Posts: 614
Location: Roxboro, North Carolina, U.S.A.

There is at least one sidevalve 45 near here that has been running for years, with the 4 exhaust valves that I installed. During WWII, burnt exhaust valves were the most common failure, as few were adjusted on a regular interval. After the war, shops kept more exhaust on hand for sidevalve machines, as burned exhaust valves were the rule, for the same reason. But, they didn't stop there. They used exhaust in both holes, also. No ill effects.


Post Tue Jan 02, 2007 2:23 pm

Posts: 80
Location: Las Vegas, Nevada, USA
I'm running all exhaust valves in my BTSV and it is running great. :D

Post Tue Jan 16, 2007 11:29 am

Posts: 530
Location: Ogden, Utah, USA
When we got our 37ULH it had some problems with the intake, lots of leaks. When I went to fix it the nipple in the front cylinder was loose. So off came the cylinders to see what we had. We had a full set of Ex valves in all four places. The valves were a bit rough and pitted and the guides were way loose on the valve stems. So new valves and guides were put in place along with a new nipple. The guy who runs the only shop in Ut. with some flathead parts on the shelf was vey interested in the old valves so he could put a iron head UL back together. Worked a nice trade for the old valves. He was running just fine a couple of weeks later. With the intake fixed and a new set of rings we had a very nice and unusal daily driver. The wife loves it with a very broad tourqe and easy to use clutch I can't get much time on it. The point is the Ex valves worked fine. I was glad to get the bike back to stock configuration but those Ex valves should last forever in the intakes. Harder and cooler would equal a long life.
Steve H

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