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Petcock rebuilding issue

chuck hahn

chuck hahn

Forum LongTimer
Past Site Supporter
78 1000C...I got a rebuild kit from Z1 and very carefully made sure the seating surface for the oring on the diaphram that seals against the front half was clean. Assembled it all and the darned thing still leaks.That oring on the plunger is the only thing thats supposed to stop the fuel from coming down..right? Unless of course its on prime. If i fiddle withn this and cant get it to stop, then are there any sources for aftermarket new ones??
 
You can stretch the spring a little to put a bit more pressure on the O ring but if the sealing surface is buggered it will leak no matter what.
 
Had already stretched the spring when I originally put the kit in..I think I have found the problem though. I took the back off of an old 750 petcock off to see if things looked the same and noticed the Oring on the rebuild kit was a bit thicker than the one on the 750 diaphram. So for the heck of it I slapped the diaphram and back from the 750 onto the 1000 petcock and put a few gallons of fuel in the tank. Whalla...has been sitting on a fresh clean piece of cardboard for about 1/2 HR now and narry a drop. Other than the thickness and overall diameter of the orings, I cant think of any other factor that was causing it. What do you think???
 
Chuck, I tapered a wooden dowel to match the taper of the seat the o-ring seals up against, then coated the dowel with valve lapping compound.

mine didn't leak after that.

rustybronco said:
finished my $1.98 petcock overhaul a few days ago. I think it came out well considering it was completely plugged up and corroded so badly I had to drill and scrape out all the passages, polish the sealing surfaces with 1K paper and reconditioned the tapered seat which was pitted (where the o-ring seals fuel flow), using a wooden dowel and valve lapping compound.

3~4 hours of work and it looks like new again.

PICT3079.jpg
Click to expand...
 
I had taken some brake cleaner and a Qtip to the seat Dale. It didnt have a nick or anything and was quite shiney. Like i said..threw on the 750 back and diaphram and nothing else and now it seems to be sealing properly. I cycled it a few moments ago with a suck on the vacuum port and it let fuel out and sealed right back up. Goona do it again right now and recheck it. I also have some different left over orings from some carb oring kits and I am gonna see if one is a bit smaller and do a bit of experimenting with the rebuild kit but with a smaller thickness oring and see what happens then. If it works it will probably confirm my theory.
 
Dale...that part number is for both those seals?? Will ned the same for the Cooley at some point.
 
Chuck, that p/n is for just the gasket below the package. the o-ring is from my 'stock'.
 
I had so much fun learning how to rebuild petcocks. Out of 4 I got 3 to work, I didn't try with the 4th one because it was for a G model, fuel hose in the wrong place.
What I found is there's a little breather hole in the 2 o'clock position when you look at the petcock from the front, it has to be UNCLOGGED and align with all those other holes, the one in the diaphram and the one on the block between the two halves of the diaphram. Also, that round 5 hole piece that goes under the switching lever works better if new. They flatten out and get hard as rocks, they need to flexible enough to be able to seal.
Also, lubricate the hell out of it, I used WD-40. When putting on the back piece along with the diaphram and block, I very carefully put in each screw and allowed all those pieces to find it's own center, I tightened each screw to the point where it just started to have all those surfaces touch, then the next screw, turnig each just a little at a time until it was tight.
This piece, and not the diaphram, or the spring tension, or diaphram O ring was the culprit causing the leaks in my petcocks. I didn't have to replace a diaphram or O ring on the diaphram. I did clean out the deposits on the O ring seat though.
http://www.ebay.com/itm/NEW-OEM-SUZ...4125&pt=Motorcycles_Parts_Accessories&vxp=mtr
 
Cycled the petcock yet again and its still dropless..Dale, I looked up that number and see its for that 5 hole gasket. You wouldnt happen to be able to measuer the OD of that oring and the thickness of it would you? Nothing in the spares box I have will work.
 
chuck hahn said:
Cycled the petcock yet again and its still dropless..Dale, I looked up that number and see its for that 5 hole gasket. You wouldnt happen to be able to measuer the OD of that oring and the thickness of it would you? Nothing in the spares box I have will work.
Click to expand...
Chuck, I might have a few spares that I can send you.
 
No leaks from the lever seal..just that oring on the diaphram seems to be too thick in the rebuild kits. One thats just a bit thinner around and still fits the plunger will solve the problem when i go to redo the Cooley petcock.
 
rustybronco said:
Steve, I think not paying enough attention to the o-ring sealing surface is what causes most petcock re-building to fail.
Click to expand...

There was indeed quite a build up of garbage there. They also get pitted, I did polish my seat up trying hard not to get it out of round. Very critical for it to seal.
 
Dale..PS. I wasted an entire afternoon tinkering with this. I will get that emblem adhesive off very soon.
 
Chuck Hahn,
I have a brand new aftermarket petcock (not a rebuild) that started to let fuel through after about 3-4 weeks. From all the tinkering we have done it seems that the O-ring is too small and doesnt seal enough, but i havent tried anything with stretching the spring.
Thanks for the thread, gives me another idea to try.
 
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