Lucky Phil 2,007 Posted May 28, 2020 Author Report Share Posted May 28, 2020 Well I've finally put this one to bed. Due to available sizes for Viton/FKM seals I eventually had to machine down the oring grooves on the piston to 10.2mm od from the std 10.5 and widen the grooves as well to take a slightly wider 2.4 mm seal from the std 10x2.0mm. Someone at home with a pedestal drill may be able to do this with a small file and some care. So as shown in the previous image I have slotted the piston and drilled the housing to accept a 4mm grub screw that is now the open stop. I've modified the piston oring grooves as previously outlined and used Viton/FKM seals of 9.8 x 10.4 mm which dont swell in fuel. Put it all together with blue loctite on the grub screw to lock and seal it and you have a tap that doesn't leak and works smoothly and very nicely. The whole issue is the original Nitrile seals swell in fuel and cause jamming of the piston/plunger. Nitrile seal swelling in fuel isnt an issue between 2 fixed immovable surfaces where it can actually assist sealing but in this situation it's horrible. My main concern is wrenching on the tap when trying to shut it off which is being transmitted through plastic mounted tank integral threaded inserts. Wreck one of these and the tank is scrap. So as usual the OEM has literally skimped pennies on the seals and made the tap in some cases useless.Nice design but looks like the accountants got involved. Ciao 2 Quote Link to post Share on other sites
docc 3,762 Posted May 28, 2020 Report Share Posted May 28, 2020 Thank you, LuckyPhil, for the excellent insight and sharing! I wish I had this all done to my Manual Fuel Tap already as I am upon a Tank-off Maintenance interval and dread twisting on that thing like a knuckle-dragger. At least I know to isolate the tank with a spanner. I hope that works until I can preform this excellent modification. Lucky Phil rocks! Quote Link to post Share on other sites
Lucky Phil 2,007 Posted May 28, 2020 Author Report Share Posted May 28, 2020 6 minutes ago, docc said: Thank you, LuckyPhil, for the excellent insight and sharing! I wish I had this all done to my Manual Fuel Tap already as I am upon a Tank-off Maintenance interval and dread twisting on that thing like a knuckle-dragger. At least I know to isolate the tank with a spanner. I hope that works until I can preform this excellent modification. Lucky Phil rocks! If you need to remove the tap docc I suggest removing the tank fitting and then separating the tap from the fitting in the vise. Maybe Chuck could mod a few for people at a reasonable cost. He's got the equipment to do a superior job to me and he'd do one in under an hour easy. Ciao 3 Quote Link to post Share on other sites
Weegie 105 Posted May 28, 2020 Report Share Posted May 28, 2020 7 hours ago, Lucky Phil said: Well I've finally put this one to bed. Due to available sizes for Viton/FKM seals I eventually had to machine down the oring grooves on the piston to 10.2mm od from the std 10.5 and widen the grooves as well to take a slightly wider 2.4 mm seal from the std 10x2.0mm. Someone at home with a pedestal drill may be able to do this with a small file and some care. So as shown in the previous image I have slotted the piston and drilled the housing to accept a 4mm grub screw that is now the open stop. I've modified the piston oring grooves as previously outlined and used Viton/FKM seals of 9.8 x 10.4 mm which dont swell in fuel. Put it all together with blue loctite on the grub screw to lock and seal it and you have a tap that doesn't leak and works smoothly and very nicely. The whole issue is the original Nitrile seals swell in fuel and cause jamming of the piston/plunger. Nitrile seal swelling in fuel isnt an issue between 2 fixed immovable surfaces where it can actually assist sealing but in this situation it's horrible. My main concern is wrenching on the tap when trying to shut it off which is being transmitted through plastic mounted tank integral threaded inserts. Wreck one of these and the tank is scrap. So as usual the OEM has literally skimped pennies on the seals and made the tap in some cases useless.Nice design but looks like the accountants got involved. Ciao Rolls Royce Piston Aero Engines - a designer remembers by AA Rubbra, liking your taste in reading Phil..........a lot. A great read, as are many in that series if you love engines 1 Quote Link to post Share on other sites
Lucky Phil 2,007 Posted May 28, 2020 Author Report Share Posted May 28, 2020 1 hour ago, Weegie said: Rolls Royce Piston Aero Engines - a designer remembers by AA Rubbra, liking your taste in reading Phil..........a lot. A great read, as are many in that series if you love engines Yes John, great book. Another good RR one is "Not Much of an engineer" by Stanley Hooker. Ciao Quote Link to post Share on other sites
docc 3,762 Posted June 7, 2020 Report Share Posted June 7, 2020 Pretty sure this topic belongs in "How to . . ." I'll be moving it after I make this post. Having taken my tank off this morning for filter changes, I thought how nice it would be to have a functional manual fuel tap /petcock. Pretty inelegant to apply slip-joint pliers, even through a leather pad, to accomplish fuel shut off. I did note that my tap needs almost an extra half of a flat to close fully. So, only about 1/12 of a turn. Right annoying. Thanks, again, Lucky Phil! 1 Quote Link to post Share on other sites
cash1000 67 Posted November 4, 2020 Report Share Posted November 4, 2020 So for a non technical person could someone summarise what the solution is. Quote Link to post Share on other sites
Lucky Phil 2,007 Posted November 4, 2020 Author Report Share Posted November 4, 2020 26 minutes ago, cash1000 said: So for a non technical person could someone summarise what the solution is. Use the correct sized Viton or FKM seals and modify the tap body and spool to suit. If you send me one I'll do it for you. Might mean a month in postage though. Ciao 1 Quote Link to post Share on other sites
cash1000 67 Posted November 4, 2020 Report Share Posted November 4, 2020 Hi Phil. Many thanks for the offer. I've got a brother who is fitter & turner. Will see if he can follow your solution Quote Link to post Share on other sites
Lucky Phil 2,007 Posted November 4, 2020 Author Report Share Posted November 4, 2020 1 minute ago, cash1000 said: Hi Phil. Many thanks for the offer. I've got a brother who is fitter & turner. Will see if he can follow your solution For him it will be an easy task, maybe an hour or so. The key is the Viton/FKM material orings in the correct size as outlined in the post. Ciao 1 Quote Link to post Share on other sites
cash1000 67 Posted February 9 Report Share Posted February 9 Fitted new fuel tap. Still need vice grips to open & close it About that offer Phil 1 Quote Link to post Share on other sites
Lucky Phil 2,007 Posted February 9 Author Report Share Posted February 9 20 minutes ago, cash1000 said: Fitted new fuel tap. Still need vice grips to open & close it About that offer Phil You can send it to me if you like but your brother might be quicker. Ciao Quote Link to post Share on other sites
gstallons 791 Posted February 9 Report Share Posted February 9 What did you do with the old one ? You should be able to massage it back to normal . Quote Link to post Share on other sites
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