DIY valve lapping for the LO206

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Deleted member 21174

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Just curious where valve lapping fits into the LO206 program? For example on a heat cycled head that as already been professionally touched up is it helpful to do some light valve lapping during the season?

Or as a practical matter is it just simpler/easier to send the head out to a pro?
 
i only ever touch my LO206 valves when absolutely necessary. only after a good leak down test. if i don't have a significant loss in pressure, i don't mess with them.
 
If the seats have been cut and the valves lapped in at rebuild, and then they begin leaking again, I tend to think there is a reason why that is more significant than a quick lapping in.
 
Depends on how it was "professionally" touched up and how long ago it was done.
I very seldom lap valves.
Quite often the scenario goes like this.
1. Leak test, then lap the valves.
2. re-leak test, re-lap the valves
Repeat step 2 multiple times until the valve has a gouge in it and it still leaks.
Put in a new valve and it still leaks.
Repeat step 2 etc
 
why do we lap valves so often?.....because there is leakage between the valve and the seat. So, some racers will also cut the valve seat and then lap the valve. Why do we have to cut the valve seat....what is causing it to need to be cut? The culprit is the exhaust valve guide being worn. These guides are made of sintered steel which is nothing but pressed powder, and don't take heat very well. When the valve guide wears, the valve will not seal on the valve seat. Lapping the valve will not cure the problem.....cutting the seat will not cure the problem. Briggs realized they had a heat problem and their band aid was to raise the exhaust guide out of the exhaust port to help cool it. Then, they came up with the "Heat Disperser" to help with the heat problem. The Intake is no problem because the Intake guide is down in the Intake port and the fuel/air mixture cools the intake guide. The exhaust guide needs replaced. When you remove the valve spring...push the valve up a little and check the wear by moving the valve back and forth. If it moves sideways more than a couple thousands....it's worn and needs replaced. Now.....when you remove the guise, don't hammer the guide out, use a press. These heads are cast aluminum....Chinese cast aluminum at that, so beware. Before you press the new guide in, it will have to be reamed, and the best way is to use a lathe. Using a .2485 chucking reamer, ream it with cutting oil. Clean with brake kleen and press into the head. DO NOT PRESS IN TOO FAR, just to the groove on the guide. Using WD40, and a .250 flex hone, run the hone thru a few times...don't over do it. Now that you have a new exhaust guide in place, you will have to cut the seat to match the new guide. Take light cuts and keep checking by putting in the valve and holding up to light to make sure you see no light coming in around the valve and seat. After you cut the seat..THEN lap the valve to seal . See....wasn't that easy? Unless you have the proper tools to do this, I suggest having an qualified engine builder or machinist do this for you. Hope this helps everyone. If I can be of any help to anyone, I do these heads all the time. You can PM me. Some will say, "I'll just buy a new head!" The head you have is already heat cycled so hang on to it.
 
I shared an article I wrote for Tech Talk Tuesday about a year ago in the 206 groups.

https://www.facebook.com/groups/Briggs206Racers/permalink/2715686961843028

I'm not sure everyone can access this since it's a private group.
It's also posted on our Facebook page, if you scroll down through enough posts far enough to find it.

https://www.facebook.com/Carlson-Motorsports-384076905358773/

It's a lengthy article with lots of photos, so go check it out if you want to spend the time.
Hopefully this link takes you right to the article. Sorry I'm not a bit more tech-savvy.


Using fine lapping compound is ok, but anything course/medium/etc. should be avoided - you'll likely do more damage than good.
Good valve guide and seat work is worth the investment.



-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
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