Rod Posted January 12 Report Share Posted January 12 Could someone remind me of the size and pitch of thread for Dnepr petcock (MT11) fitment into the fuel tank. Thanks Quote Link to post Share on other sites
Northernduck Posted January 13 Report Share Posted January 13 Should be M14 x 1.5. If nobody else confirms, I’ll check tomorrow when I’m home. ND Quote Link to post Share on other sites
Rod Posted January 13 Author Report Share Posted January 13 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). Quote Link to post Share on other sites
Northernduck Posted January 13 Report Share Posted January 13 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. Quote Link to post Share on other sites
Northernduck Posted January 13 Report Share Posted January 13 Petcock internals. The brand new standpipe was bent and needed to be straightened before drilling out! Quote Link to post Share on other sites
Rod Posted January 14 Author Report Share Posted January 14 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? Quote Link to post Share on other sites
Serious Black Posted January 14 Report Share Posted January 14 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. Quote Link to post Share on other sites
Northernduck Posted January 15 Report Share Posted January 15 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 Quote Link to post Share on other sites
Northernduck Posted January 15 Report Share Posted January 15 I haven’t tried that Rod but your approach seems good, let us know if it works. ND Quote Link to post Share on other sites
Rod Posted Tuesday at 10:18 AM Author Report Share Posted Tuesday at 10:18 AM 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. Quote Link to post Share on other sites
Northernduck Posted yesterday at 03:16 AM Report Share Posted yesterday at 03:16 AM Great to hear Rod. Lapping in a petcock valve body was a new approach to an old problem. ND. Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.