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Petcock Rebuild Hate?

  • Thread starter Thread starter cal_look_zero
  • Start date Start date
C

cal_look_zero

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I see a lot of hate on rebuilding petcocks... what's the reasoning behind it? Is it just a lost cause? Quality of rebuild kits? Quality of mechanic rebuilding it?

I only ask because I rebuilt mine today in the course of about 10 minutes (After carb dipping the metal bits for 24 hours and giving them a good "how's your father") and it seems to be working fantastically well.

Just curious what I should be looking out for... ya know aside from the obvious; leaks/too much fuel/too little?
 
If you rebuilt it and it does not leak and functions normally then all is well.
Apparently a lot of petcocks suffer ireparable wear in the machined area where the conical "cock" turns. If there are striations due to particulates int eh fuel the thing is toast.

Is your tank rustfree? If so your petcock may have been spared exposure to crap entering it.
 
That makes sense. I was trying to figure out why people were having bad luck on rebuilds; makes sense if the metal is damaged and not allowing a good seal. Thanks!
 
Put the bike on the center stand and take a piece of tape and mark the oil level in the sight glass..putting the top edge of the tape at the top level of the oil. Let it sit with the petcock in the on position overnight or for a day or two. In the mean time look around the bike often for signs of leakage or anything seeping from the airbox. If the level in the crankcase rises above the initial level the tape documents, then probably fuel is getting to the crankcase via a bad petcock. if theres anything slightly damp on the bike its also a sign of leakage. Also be aware that if signs of leakage are present you dont want to crank the engine over right away. I suggest that if you see leakage from around the carb boots or whatever, you pull the plugs and spin the engine over to be sure you do not hydrolock the engine. I have heard of bent rods from this situation. if you even suspect fuel has gotten to the crankcase, drain it and start over..4 quarts of oil is way cheaper than a blown engine or spun crank.
 
Petcocks can be really frustrating to rebuild. In the course of rebuilding several of them for some reason I couldn't get them to function without
a leak.
Sometimes the leaks are external, and those are easy to fix, it's the internal ones that drive me crazy. By leaking internally I mean when your fuel is in the on position but there's no vacuum when the engine isn't running
it should shut off your fuel completely. I'd often get a occaisional drip and when left overnight some accumulation (not good). The little O ring on the diaphram has to positively seal for it not to leak, everytime. Sometimes those surfaces it mates with get worn, pitted, or slightly out of round which contributes to internal leaking.
I've recently had some success, I think it is in part by the warmer weather, as the O ring tends to expand and make a better seal.
 
What rebuild kit did you use and for what petcock.

I'm all in favor but most rebuild kits I've seen are **** poor quality.
 
Nessism said:
What rebuild kit did you use and for what petcock.

I'm all in favor but most rebuild kits I've seen are **** poor quality.
Click to expand...

I got it from Z1... came in a blue package; looks pretty generic. I'm at work right now, but I'll update later when I'm reassembling my carb ;)

chuck hahn said:
Put the bike on the center stand and take a piece of tape and mark the oil level in the sight glass..putting the top edge of the tape at the top level of the oil. Let it sit with the petcock in the on position overnight or for a day or two. In the mean time look around the bike often for signs of leakage or anything seeping from the airbox. If the level in the crankcase rises above the initial level the tape documents, then probably fuel is getting to the crankcase via a bad petcock. if theres anything slightly damp on the bike its also a sign of leakage. Also be aware that if signs of leakage are present you dont want to crank the engine over right away. I suggest that if you see leakage from around the carb boots or whatever, you pull the plugs and spin the engine over to be sure you do not hydrolock the engine. I have heard of bent rods from this situation. if you even suspect fuel has gotten to the crankcase, drain it and start over..4 quarts of oil is way cheaper than a blown engine or spun crank.
Click to expand...

WOW, thanks for all the intel. Didn't know there was so much to look out for.

This is probably covered in another thread, but if I get some residual leakage, could I put a basic inline fuel valve into place in the interim? Just a basic on or off deal?
 
i dont know about another thread, but it has been covered on the floor of my garage..ones experience that can prevent anothers misery is priceless.
 
yes..its called a pingle valve..but be sure to turn it off everytime you shut off the engine..its a basic on/off replacement for the vacuum petcocks.
 
Last edited:
cal_look_zero said:
I see a lot of hate on rebuilding petcocks... what's the reasoning behind it?
Click to expand...
Not really any "hate", just that the success rate tends to be about 10-15%.

That's rather dismal for a device that is actually rather simple.

I have never had to use a kit to rebuild any of mine, but I have had to clean out the selector 'drum' and the passages. Using a wire cup wheel in a Dremel tool will clean the scum off the inside of the cylinder. Some 400-grit paper will smoothe the outside of the drum. A touch of synthetic grease will keep them turning nicely.

.
 
For what it's worth I've used rebuild kits loads of times and they've always been fine. Bear in mind I'm in the UK - I'd guess our kits are made by the same guys who supply the rest of the world but they might be different.

Note. I know NRP make replacement slide diaphragms in the UK so maybe they are also making tap kits.

And also for what it's worth, I would never use a Pingel. For some reason Pingel think they are made out of platinum or other precious metal (must do to justify the price) and that o ring just loves to perish quickly and spill petrol everywhere :mad:. Best non-OEM tap I bought in recent years was the one Z1 stopped selling because of complaints - maybe I'm just lucky :)
 
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