Board index Flathead Power-Technical Questions, Answers, and Suggestions K-Models No more "Wet up top"!

No more "Wet up top"!

Post Mon Aug 19, 2013 8:51 pm

Posts: 242
Location: Kirkland, WA, USA

Ok, we have gone over this a lot on the last 10 years or so..... but this is it. I cured the muther and it is dry up top, and runs like a raped ape! For a flat head....

The main cure is still using a restrictive device on the pinion shaft, unless you are using an original shaft for a K or KH. The sportster ones, generally have a restricter put in with the aftermarket set up, but they don't tell you what to do with them and they get left out. This causes way too much oil to collect in the bottom end, and the pump can not keep up.

The other problem is using advice to put a better flowing oil pump on it. Use the old KH pump with the pressure release valve in it. The newer '72 series has great ball checks and prevents sumping, but it feeds way too much oil and way too much pressure for the KH to handle. I found the parts and went back to the original pump, but put in balls instead of the rod things that they had when new.

I did not re-cut or lap in the seats, and mine still sumps up. This is a problem, so I got one of those one way anti sump valves from England and put that in the line between the tank and the intake on the cases, and it works like a champ! Just make sure that you fit it and then take it apart and fill it will oil and the line in too, or it will not draw the oil past the check valve! ... nt_count=1

The valve works great! No more sumping, and the plugs are clean as if they came out of my BMW car with electronic ignition! It is getting like 500 miles or better to the quart, and just runs hard. Well, I did put KHK Cams in with a Lienwebber grind on them.. it is peppy to say the least!

Finally, not wet up top!

Barry ... nt_count=1

Post Tue Aug 20, 2013 9:29 am

Posts: 825
Location: Pa. , USA
Thanks Barry, I'd like to check out one of those anti sump valves, where can I get one ? Tim
Vintage roadracing, Class C, AHRMA # 335

Post Wed Oct 23, 2013 4:48 pm

Posts: 242
Location: Kirkland, WA, USA

I looked it up on Ebay, and ended up buying three. One was too big, but I will used that on my '65 XLCH, the small one was way too small May work on a british 350 or something? The one I used was about 8 ml. outside die of the fitting, or inside die of the hose. You can google them by searching Anti Sump Valve motorcycle.

Post Wed Mar 12, 2014 2:49 pm

Posts: 1
Hello Barry,

I found a one way oil valve you can screwed in to the oil tank outlet, the other end I turned to 8mm to get a rubber hose on.
Is is recommendable to left out the original pump relief valve spring and ball, when using a one way anti sump valve?


Post Sun Aug 07, 2016 7:32 am

Posts: 242
Location: Kirkland, WA, USA

Follow up note:

After I cured the oiling problem, there was so little oil up top, that there was nothing to protect the exhaust valves from eating through the seats.... so I burned through the cast iron seats pretty darn fast, and it dropped about an eighth inch in about 2000 miles. I showed it to a friend, and he came up with the cure. He machined out the old seat are, and added a thin automotive hard exhaust seat. This work great, and makes the bike a one kick almost all the time. I can start it cold in two kicks. One to prime, and one to light her up! Most of the starting problems with these old KH models, are do to lack of compression in the front cylinder, as there is the one that gets less oil, and burns out the exhaust seat first.

If you want to ride your bike a few hundred miles a week like me, get some hard seats in for the Exhaust valves! The intakes will not matter, as they are cooled and lubricated by the gas.....

see on facebook: ... =3&theater

Oh, and leave the old ball checks in the pump, as they can't hurt!

Best regards,

Barry Mercer
Kirkland WA

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