Tach drive Oil Leak (2010)

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Dec 26, 2007
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Looking for ideas how to stop the oil leak from my Mk lll tach drive. I just replaced the "O" ring and it leaks. When I took it apart the previous owner had 2 "O" rings.

It's as snug as I dare.

Ideas welcome
 
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Aug 6, 2005
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Thinking back on my 850 and it's terrible tach drive leak, the o ring didn't fix the problem. I know I used an older 750 drive, but couldn't tell you what year it was, but it did have an oil groove machined into the shaft and my 850 drive didn't. The 750 drive stopped the leak 100% and I got the drive off ebay. I am assuming the MKIII drive is the same as a 73-74?
 
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Not to be a breather apostle, some people have reported a proper breather will eliminate the tach oil leak, amongst others.
 
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Dave, I thought to say that, but since I haven't done it myself didn't feel right, but I know the 750 drive does work, either way a cheap fix.
 
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Oct 19, 2005
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Install breaker, stuff 2 750 oil pump nipples up tack drive and put stiff grease in the cap, or spend for vendor miling to place two Honda seals in.
 
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Put 2 O-rings in tach drive the first month I had the bike. Has lasted 38 yrs. Was going to have it machined (someday) but no leaks. Using Mity-Mite valve for past 6 years though. Windy, they are only $3.98 here at Pep Boys. You paid too much! I have a spare just in case.
 
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Feb 28, 2009
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Honda seal for tach drive Part # 91207-222-000 $8.00 Australian ea
 

Fullauto

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Even with seals fitted, mine still leaked. One way valve in the breather cured it. No more leaks anywhere.
 
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Fullauto said:
Even with seals fitted, mine still leaked. One way valve in the breather cured it. No more leaks anywhere.
That's been my experience, as well. Only makes sense. With a pressurized crankcase, oil stands a good chance of passing the seals. I don't know how many times I changed the crankshaft seal, only to have it still leak. Finally wised up and installed the XS 650 PCV valve. No more leaks, anywhere.
 
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The graphic and advice only mention a single seal in a row, while all the vendors and folks like me who have dry tacho drive stack Two seals of what ever kind in there. Obviously if less internal pressure less motivation for oil to seek its way back home in the earth.
 
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Feb 7, 2010
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Or this one
This drawing is a little deceptive. There is a relief on the top of the spiral gear that slides into the housing slightly. Also there's a 7mm shaft on the gear that ends where the o-ringed shaft's tang slides in and the upper tanged shaft is 6.25mm. The bore for the seal has to be taken out the seal's thickness past where the relief slips in. And the Honda seal, if that's what we're using, has a bigger o.d. than the relief, so boring starts at the bottom of the housing. The Honda seal is 14.5mm o.d. x 7mm i.d. x 5.5mm thick..
 
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