Honda CX 500 Forum banner

Petcock Repair

8K views 34 replies 11 participants last post by  Thumper 
#1 ·
A few weeks ago my petcock sprouted a leak. I already had one needing repair in my junk box, so I decided to tackle the repair of both at once. Here’s how I tackled the job.
Auto part Engine Automotive engine part Vehicle Family car

Notice that the cover plate is swaged on? Some would say “riveted” though they’re not technically rivets. It’s tempting to drill off the “rivet heads”, but wait. You’ll need a well centered screw hole to put it back together. Use those “rivet” dimples to center your drill. I drilled a .070” pilot hole, followed by .089” to take a 4-40 thread. Both holes on the basic petcock are through holes. On the vacuum petcock, one through hole and one ¼” deep blind hole.

Next I used a flat file to remove the “rivet heads”. They’re aluminum and much softer than the steel cover plate, so it’s an easy task. I went ahead and tapped my 4-40 holes at this point.
Auto part Automotive engine part Carburetor Cylinder

Then carefully pry the cover plate off. It’s still swaged on tight, so go slowly and work your way around the perimeter several times. Once the cover plate is off, I enlarged the holes by just .002” to ease reassembly, and brushed it clean.

The first problem I encounter is a broken outer seal o-ring (left). This is a “double seal” 3/32 inch wide x ⅞ inch inner diameter, AS568A-118. I bought the actual double-seal (McMaster p/n 90025K246), but the round o-ring is much more widely available and will work just fine.
Coil spring Product Auto part Knockout punch Bumper



The next problem is with the inner seal.
Auto part Carburetor


A chunk is missing from the front side.
Yellow Auto part Automotive wheel system Wheel


But the back side still looks servicable.
Yellow Circle Auto part Wheel Metal


For one of my repairs, I’ll just turn the seal around and use the better side. For the other petcock, I’ll try something else.

It looks like a new seal is available from Honda
Auto part Vehicle Wheel


but I wasn’t completely sure the fit was right, and I felt like experimenting anyway.

I used standard o-rings. Size AS568A-107,(3/32” wide x 7/32” inner diameter) fit the ports snugly, but bump into one another a bit. I sanded flats onto them to fix the problem.
Auto part Suspension Coil spring Washer Screw


And then they fit fine.
Auto part Automotive engine part Wheel Bearing


Lube with a non soluble grease like Molykote and reassemble with 4-40 x ¼” screws.

Auto part Cylinder


It's a new repair and it remains to be seen how long it will last, but I'm hopeful. At least it's working again for an investment of 40c in o-rings.
 
See less See more
10
#5 ·
blue fox and all

i am sorry but i disagree with putting this in the wiki till the durability of the repair is tested and proven

wekadog i mean you in no way any disrespect to your ingenuity and skillset

and i am all for "emergency" work around repairs

but to take a unproven repair that involves gasoline and a bunch of liability as the quality/safety of the repair depends on the person doing it not the parts

to prevent leaking is wrong and therefore it should not be in the wiki as a forum "endorsed" repair

we will watch some SQUID go "i can do that"

and turn into a fireball cuz they are to unobservant to watch for fuel leaks

honda engineered that part as a single part to prevent roll up

a new petcock can be had for 18 dollars delivered i for one will go that way and stay safe

lets not help anyone to hurt them selves
 
#6 ·
Murray, I share the spirit of your concern, but maybe not the extent. With a proper outside O ring installed, there should not be any external fuel leakage even if the inner cluster is compromised. That being said, I'll hold off on adding it to the Wiki until enough time has passed to assure that this is a safe and proper fix.
 
#7 ·
i thank you for that

i do understand however my concern is that you or i or wekadog and others have experience doing repairs

as well as the judgement and fitting ability to solve problems deburr and successfully pull it off

putting something in the wiki "sanctions" a repair and will make it so it will be attempted by someone with no experience

i urge everyone to remember this

playing with gas and an ignition source is a recipe for disaster
 
#9 ·
IMHO:

Then we have to be very consequent !, ....always !.

No answers to questions such as:
I want to cut my frame and weld on other pipes.

I want to repair my front brake.

How can I align my bent frame; can I use a torch?


To ask for their skills and their knowledge...... this is worthless.
There is no one who will admit not knowing something.

A wrong repair of a brake, a bad welded frame, a too much annealed frame part, ... can hurt many people and can damage other things.

A not a noted/ not remarked leaking fuel tap can be very unlucky only hurt a single person, maybe.......


Now: How to continue ?



Gruesse
W:)lFgang
 
#10 ·
Wolfgang, and all,
I've reviewed this, and Blue is taking the right course by holding off until we can see if Wekadog's plan works out. It does carry risk, just as all mods or fixes to old bikes. Even the most experienced wrenches hit pitfalls.

I point out that the WIKI is not really a "sanctioned" instrument/document. It is an open source depository for knowledge, albeit some of it is questionable and inaccurate. Vetting it all is a very daunting task, and there really is no one completely in charge of said vetting or review, so we are well advised to cross check with those here who have great depth in what ever area is being considered for inclusion within the WIKI, prior to it being added.
That said, being open source, any one is free to add to it, regardless, so we must use our own honor and wisdom before doing so.

Seems to me we are at status quo for now, so I hope this is satisfactory. I don't want to dissuade anyone from exploring new ideas and ways to improve on tasks, but I do agree that safety is paramount in any of these endeavors.

Joel in the Couve
 
#12 ·
Fondly remembering the days when a good idea could be presented to the masses without concern for the next Darwin Award winner using it incorrectly... We would rather folks just keep their leaking petcocks in service vice attempting repairs on them... A simple "Do at your own risk" should suffice for the legal eagles...
 
#13 ·
We tried this repair with Viton O-rings in the early days of Gasahol (mid 70s). The problem was dealing with the farms, running cattle with small Hondas and buying bulk fuel Gasahol. We couldnt keep the Honda petcocks alive when they refueled from their rusty old gravity feed tanks.

The problem is the outer ring raised edge is missing, which meant that fuel leaked between the O-ring "flats" and around the petcock handle if the lever was not perfectly centered on each position. When it was just right, it did not leak in the OFF position, but had a slow drip in every other position.

Was not a good solution, then. May not be any better, these days.
 
#18 · (Edited)
So, does anyone know if this [PN 16957-ZE1-812] fits the GL500 and other CX/GL vacuum petcocks?
It appears not. I emailed two eBay sellers to ask the size. One assured me it would fit. The other reported it was 15mm diameter. My GL500 seal is .840", or about 21mm diameter.

There's another seal advertised as fitting the CB500 that I have hope for. It's PN 16955-268-020. I've emailed the seller to ask the diameter of this one. He responds that it's "about 20mm".
 
#17 ·
It's only $1.50, next time I order something I'll tack it onto the order and see if it's the same or not.
 
#19 ·
I used one of the GL1000/1100 petcock seals that Randakk sells in a CX650E petcock (same as in the GL500/650) with good results. The outside diameter seemed too small when I installed it but when I inspected it a few months later it had expanded to the correct diameter. It did not expand to fill the space and all of the ridges were still clearly defined and still sealing well and the rubber had not appreciably softened or anything like that.

Randall decided that, even though it seemed to be successful, he couldn't endorse the application because 1) It did not fit correctly as supplied and 2) we were not sure why it had expanded and what would happen over a longer period.

It always sealed well but I ended up replacing it with a new non-vacuum one from eBay a couple of years later while trying to trace down a problem that I am now sure was caused by something else (water dripping off of the bottom edge of the fairing onto a spark plug cap that was not sealed to the wire well enough).
 
#20 ·
I used one of the GL1000/1100 petcock seals . . . outside diameter seemed too small when I installed it but when I inspected it a few months later it had expanded to the correct diameter.
I wonder whether that was this one:

Auto part


I emailed a seller of this part to ask the diameter; He responded that it's 20mm. That's pretty close to the 21.4mm (.840") I measure for my old seal. Even closer if seals actually do expand once put into service.
 
#21 ·
The GL1000/1100 petcock is not made to be rebuildable but Randakk had the seals made to his spec (same dimensions as original, better rubber). I can't remember the exact dimension but it was smaller.

But I have to wonder why anyone would mess around rebuilding the original petcock when they can just order a replacement on eBay and know that will work.
 
#23 · (Edited)
But I have to wonder why anyone would mess around rebuilding the original petcock when they can just order a replacement on eBay and know that will work.
My ex wife often wondered why I would mess around restoring an old Ford truck when I could just buy a new one. If minimizing investment of time and money were the goal, I doubt many of us would be riding 30 year old bikes. Noneconomic motivations reign in the hobby world.

But I did just have a look at eBay. While basic petcocks certainly are cheap, the vacuum ones were more in the $80 range. It seems to me if the old one can be rebuilt for under $10 in parts and a half hour labor, it's justifiable on an economic basis as well.

True, that "if" is not an established fact, but there are a number of OEM seals out there. If it's just a matter of finding which part number will fit, why wouldn't you?
 
#28 ·
To produce a plug as shown in the picture is "none economic", but it makes fun :D
That looks like a nice alternative to the rotted rubber in my carbs. Would you mind sharing the dimension drawing for those plugs?

As for rebuilding petcocks, I don't want to take a stand for rebuilding over replacing. I chose to do mine because I thought it would be fun. And it was fun! It also got me on the road the same day, rather than sitting and waiting for my part to arrive.

But now I'm sitting and waiting for an eBay thermostat.

Mine was MIA. Otherwise, I might have tried to repair it ;-)
 
#25 ·
There is NO comparison when it comes to cost/mile. For the price of sales tax, excise tax, etc. on a new bike you can buy a nice CX/GL. State excise tax for my bike is $5.00 a year, on a new $15,000 shiny whatchamacallit it would have been over $900. If you buy new, you have to go the full boat on insurance, my premium would go from about $75 a year to over $1000 depending on the value of the new bike.

Once out of warranty be prepared, with specialized production, you can have 3 bikes with consecutive serial numbers which call for different parts on each one. Hell, you can't even look many parts up anymore, the manufacturer/reseler needs a serial number before he can even enter the online fiche. Friend recently needed a carb for his Suzuki, besides having to wait 4 months for it to come in, he was told how lucky he was to get one when he was shelling over the $900 for it. Hmmm, that's exactly what I paid for GL500I three or so years ago.

Plus, you can't park it just anywhere, you will give a *#%^k if it falls on it's side, if it gets hit by bats etc. After mine took a tumble off my lift (thanks to a "helpful" friend) I changed the broken brake lever and she was good to go. If it had been something else it would have Broken My Wallet.

I am with you guys though, what's the fun in just turning a key an going, any idiot can do that. It's incredible how many times an old cosmetically challenged bike will garner more attention and conversation than the latest and greatest ubber machine parked next to it.
 
#27 ·
I had a few grins reading this thread since I have also been considering the cheap Chinese non-vacuum petcock for a CB700SC I am rebuilding. This petcock has a fancy plastic knob that I want to keep so that is why I am rebuilding the petcock. It has melted plastic gunk clogging every interior pore from 15 years of old gas sitting in the tank. I have also had to make my own brass standpipe from brass tubing I got from the hobby store. Yesterday I ground off the rivets to open up behind the knob (and will have to drill and tap for new screws later)and will have to make my own rebuilt 4-hole thingy that has partly deteriorated. Am I crazy? For sure. But it is actually fun to me to force it back to life kicking and screaming while it is trying to jump out of my hands into the trash can. I can see the end to this little side job soon. If I fail, I can always get one of those cheap ones and try to overlook the loss of the original one's fancy plastic knob.
 
#29 ·
Um... I tend to buy consumables that fit both of my bikes (thermostats, rad caps, brake pads &c) online so I have it on hand for the next time I need it, but you do know that you can get the thermostat at any auto parts place. don't you?

Re the brass plug to replace the rubber one: If you are capable of making one you should be capable of measuring what you need, right Guelli?

That said, the rubber parts are likely to become NLA (if they already aren't) and even if they don't they must surely cost more than the O-rings so making them is starting to look pretty economical to me. One more reason I really need to get a lathe before I retire :D

As for replacing the seal with O-rings, that's one I didn't try but I would be very surprised if it lasts. Be very careful while trying it. It doesn't take much leaking fuel to start a fire.
 
#30 · (Edited)
you do know that you can get the thermostat at any auto parts place. don't you?
My local bike store had the thermostat, but I thought $30 was a bit on the high side. None of the four local auto parts stores recognized the part numbers I found in the forum archives. They only know how to ask make, model and year. I imagine I could have picked out one from behind the counter that probably would have fit, but the "no return" policy persuaded me not to gamble on a visual memory.

Really, I'm coming to dislike giving my business to these chain stores staffed by computer operators. It's a sad state of affairs but the last "real" auto parts store in my county - one run by a career auto parts man - closed five years ago.


Re the brass plug to replace the rubber one: If you are capable of making one you should be capable of measuring what you need, right Guelli?
Well, yes. The only part that's any trick at all is the height. There's a retainer nub on the bowl casting that presses the rubber pieces in place. With noncompressible brass, I imagine you would want the clearance within .020" or so. Yes, I think I could measure it accurately enough. That would either entail an extra remove-reinstall cycle, or leaving them off while fabricating the pieces.

As for replacing the seal with O-rings, that's one I didn't try but I would be very surprised if it lasts. Be very careful while trying it. It doesn't take much leaking fuel to start a fire.
The o-ring repair is working fine so far. Of course this is only week two. In view of the problems reported by other members, I won't assume the repair is permanent. I'm keeping an eye out for the on-state drip reported by JimL.

I'm surprised you're not concerned enough about a sticking inlet valve to turn your petcock off when parked. I can understand a high degree of confidence in your carbs. I'm sure you've maintained them to the highest standards. Still, I would have thought that's a safety measure with zero negatives.
 
#31 ·
Here is the petcock repaired with the 'fancy' knob. The procedure should also work for CX petcocks. The aluminum rivet stubs were gently ground off flush with the steel backing plate on the bench grinder. The knob assembly was removed, holes were cleaned out, and the 4-hole thingy was flipped over to show its good side with MotoSeal gas-resistant gasket goop under it to fill in the old imperfections. The holes were drilled with a 3/32" bit. The holes were then tapped with a M3 tap and M3 allen head screws were put in. The brass standpipe was replaced with 7/32" x 0.014" brass tube from the hobby store, which is an exact match for the original, and I got a 3 foot length for like 4 bucks. I had to buy an O-ring for where it attaches to the tank. Also, the stock screen tube is too much money for me to spend so I am relying on the catch basin on the bottom of the petcock and an added inline filter.

 
#32 · (Edited)
Here is the petcock repaired with the 'fancy' knob.
That's looking good!

I have the service manual for the CB700SC sitting right here on my desk. I just looked at chapter 4 and, sure enough, there's the picture of your petcock. I never noticed before how distinctive it is. Your one looks a lot better than the one in the manual.

In your photo I think I can see hints of the "On" "OFF" markings engraved in the cover plate, normally obscured from view by the knob. I suppose they reasoned that if you can't see them, it doesn't hurt to leave them there.

I had to buy an O-ring for where it attaches to the tank. Also, the stock screen tube is too much money for me to spend
I always found it easier to get a good o-ring seal between the tank and petcock with a filter installed. It keeps the o-ring from slipping out of place. Here's an in-tank filter I made some years ago out of brass tubing and screen. You can use finer mesh screen than I did for better filtering. I just used what was on hand.

 
#33 ·
I just could not figure out a good standpipe screen design so gave up on that little refinement, yours is not bad.
It looks like you stick the screened portion on top of the standpipe?
Another thing I did to improve the seal at the joint with the tank in addition to the new O-ring was a half inch long drilled out piece of rubber fuel line pushed half in half out at the top of the petcock.
Drilled out some so the reserve gas could get thru.
 
#34 · (Edited)
It looks like you stick the screened portion on top of the standpipe?
My filter is dimensioned just like the OEM one. I drilled the tubing to match the i.d. Then I turned it against a file until the o.d. was right. Two turns of screen are pressed into the brass base, and crimped at top. The narrow section of brass is pressed into the fuel tank outlet until it bottoms out. The wider section protrudes into the petcock to host the o-ring. The standpipe carefully threaded down the center of the screen when installing the petcock.

Another thing I did to improve the seal at the joint with the tank in addition to the new O-ring was a half inch long drilled out piece of rubber fuel line pushed half in half out at the top of the petcock. Drilled out some so the reserve gas could get thru.
Sort of a rubber version of my brass bits. That should hold the o-ring in place. I guess you could also roll up some screen and push it into your rubber piece to strain the gas. It would be attached to the petcock instead of to the tank, but I don't see a problem with that.
 
#35 ·
I cut a notch out of the bottom end of the standpipe so the flow would not be pinched at the bottom of the standpipe hole and oriented the notch to the outboard side. You can see it when that knob assembly is pulled off. The danger was that if the standpipe bottomed out in the hole it could pinch off the flow.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top