Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles stock gas shut off valve

stock gas shut off valve

Post Tue Jul 13, 2010 9:45 pm

Posts: 31
Location: los Angeles., ca
I've looked thruogh the old posts, didn't find what I needed. I'm looking for a petcock (shut-off vave). my original thru tank valve is leaking slightly, enough to cause problems. I ride it several times a month, then it sits for a few months. I know the after market alignment tools need work. Can I take the valve apart and hand lap it? (eye ball alignment,mostly). and make it work or should I just put a valve in line. I am using an inline gas filter now. A little history.I'm riding a 1944 EL, I have owned it since 1979. rode for about two years. have a trophy from the dirt diggers motorcycle club, circa 1981 for a race at Ascot park in Gardena Ca. someone here was probably there. I then took it apart, found frame cracks etc. it sat in baskets for many years. My wife said "Just! put it back together" before the kids get out of highschool .Oh well I had to do what the wife wanted. I rode it again the day after my 50th birthday May 2005. now 5 years later I get to address some more issues. oil questions another post

Post Wed Jul 14, 2010 7:25 am

Posts: 641
Location: Wisconsin, USA
I removed the steel stem tip and replaced it with PEEK. Pressed the new material in at .004 and then just to be sure it would stay put, I cross drilled and pinned the insert with 16th" brass rod. So far so good. The peek is a little softer and more forgiving than the steel tip.

Post Wed Jul 14, 2010 7:59 pm

Posts: 31
Location: los Angeles., ca
thanks, amklyde, I'm not a machinist. That might be a little ouy of my league. Is PEEK similar to JB Weld? I've heard of it before, but not sure what it is or does. Is it moldable at a certian setup point?

Post Fri Jul 16, 2010 8:15 am

Posts: 1676
Location: Interlaken, NY USA

The old tried and true fix is to press off the threaded portion on the rod, it's splined. Then use cigar ash as a lapping compound to do the final lap in of the tip in the valve seat. Cigarette ash is too coarse, as I understand it. ( I don't think it needs to be a Havana, by the way). I've used it on the earlier brass petcocks on Knuck/flathead tanks to some sucess.

Post Thu Sep 09, 2010 9:46 pm

Posts: 31
Location: los Angeles., ca
I bought a replacement thru a local shop. I put it in blindly. It leaked like a stuck pig!! Upon inspection the seat looked like it was grooved vertically every 90 degrees. perhaps waiting for someone to machine it its mating part. oops, I'm not a machinest. I tried my original seat, the part at the bottom of the tank, and the new shaft, that almost worked. still a little bit of seeping gas. I think I will now try lapping the 2 best parts as suggested by earlier posts. thanks everyone for your help. any other ideas are welcome.

Post Sat Sep 18, 2010 10:10 pm

Posts: 7
My stock gas tanks didnt have the valve assembly and the guy who helped me build my knuc had the factory aligment tool he checked the tank and it didnt need any thing. however my after market valve assembly did require my lapping
it in some before a good seal was there. i used automotive valve grinding paste. low presure full turns then back , wash out and look for clean shinnie mateing ring on seat and rod.

Post Sun Sep 19, 2010 8:32 am

Posts: 3158
Location: Central Illinois, USA
I was under the impression that the threaded portion of the shut-off rod must be removed for proper lapping.

After several unsatisfactory attempts, I found that the most leakage was indeed a problem of alignment.
But the factory alignment tool has a serious flaw: metal must be bent passed true so that it can relax back to true, and smacking the tool with a hammer just doesn't cut it!

So I machined a tapered tap for the threaded bung, and drilled and honed the center for a ground 1/4" pilot rod:

Just looking through the hole gives a great indication of mis-alignment.

The pipe to the left in the picture has a top cap brazed into it. This can be used to massage the top of the tank when necessary, and the long tap at the bottom can be used to force the bottom straight as well, until the pilot rod slips through smoothly.

But even with a lapped and aligned petcock, I have alwasy relied upon a pair of pliers ground to safely clear the paint to snug things up if the machine was to sit for an extended period of time.

PS: Thanks Kyle!
Now I have one more item to use to whittle down my hoard of PEEK scrap!
PhenylEthylEthylKetone is the greatest stuff invented since flaked flint.
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Post Wed Oct 20, 2010 2:29 am

Posts: 5
Location: Sacramento, Ca...USA
....Knuckle fuel tank valve. I have the original thru tank deal...lapped the valve/seat with fine grade Clover goes 1/2 block if I forget to open the valve...doesn't seep at all...
The question about PEEK...that's type of hard plastic that must be machined....but has abit of 'forgiveness ....might be good for valve...
Tapered seat with 4 vertical lines at 90 degrees?...sounds like someone tried to cut seat with 4 flute tool and didn't allow tool to float a little at end of cutting...I've seen this type of stuff before...

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