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11 hours ago, Northernduck said:

Should be M14 x 1.5.  If nobody else confirms, I’ll check tomorrow when I’m home.  ND

Thanks ND - really helpful. It's the usually problem of finding alternatives to the stock petcocks which invariably weep, seize or snap due to crap metal (happened to me twice over the years).

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Confirmed, it's M14 x 1.5.  I replaced the original (seized) with another original and haven't had any problems but I modified it a little bit first.  They have (or should have) ample fuel tolerant grease in them or they are not going to last.  Too much grease and it can impede fuel flow, mine suffered this.  I also struggled to find an off the shelf crush washer to seal it in a manner that the petcock was orientated in the right direction when tightened correctly so I eventually made one out of aluminum on the lathe to the correct thickness.  

Further mods include drilling out the orifices to a larger diameter, again for better fuel flow, including the standpipe that is supposed to prevent debris from entering.  On that note, there was originally a smaller annular shield around the standpipe at the base that is designed to stop debris coming in when running on reserve, I had some problem with this (I think it was in poor shape or loose or something) and removed it.  So I avoid using reserve as much as possible.

If you google Ernie Frank and Dnepr/Ural etc you should come across a  downloadable PDF where he reviews all models of Ural/Dnepr petcocks which may be of assistance.

ND.

 

IMG_1307xx.jpg

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Thanks ND, I will see if I can overhaul rather than replace. Thanks for pointing me to the Franke archive, great resource. The main problem I'm having with this petcock is fuel weeping through to the carbs when in the off position, no matter how tight I adjust the brass valve stem. Will follow your mods, re-assemble using some red rubber grease (I've not done that before), but was also considering lapping the brass valve stem into the valve body with some fine valve grinding paste, is that something you've done or heard of before?

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You should deburr the ends of the brass stackpipe. Often they are crimped over by the cutting tool. I also chase through the body with a drill when the tap is in the open and reserve position as the tap often isn't aligned.

 

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12 hours ago, Serious Black said:

You should deburr the ends of the brass stackpipe. Often they are crimped over by the cutting tool. I also chase through the body with a drill when the tap is in the open and reserve position as the tap often isn't aligned.

 

Definitely.  I found the same, whatever they used to chop the standpipe to length left the fuel entrance burred, partially blocked.  ND

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Yep, the stack pipe was partially crimped over at the tip, and the weeping was being caused by scoring of the valve stem and body, bits of crap have obviously got trapped between the two at some time. I drilled the stack pipe then spun up the valve stem and lightly took some fine wet and dry cross it. I couldn't get in to dress up the valve body surface, so once the valve stem had been cleaned up, I gently lapped it in to the valve body with some fine cutting paste -  2 x 10mm nuts on the threaded end and then 10mm socket on a speed wrench. The result was a nice snug fit that really benefitted from the red rubber grease on the rebuild, the valve action is now smooth and no weeping in the off position. Thanks guys. 

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