Oil leak at tach drive

[Shovel Jockey]

My sons 75B has developed a oil leak that seems to be coming from the tach drive. I degreased the engine, took it for a short ride and it reappeared. I do not have a decent breakdown of that area so I was wondering what would or could fail that seals oil here and how do you fix it? Joe

 

[jchrisk1]

There is an o-ring in there. You will have to take the side cover off (or I would anyway) because there is a washer at the bottom of the gear on the shaft that could fall off inside. It's just the one 10mm bolt to remove the drive gear. It can sometimes be a pain to get it to slide out, but it will come out.

 

[DogBunny]

It can be caused by part # 3 in this drawing:
http://www.biker.net/74-76_650_parts/engine/650ABC_tach_gear.pdf
This seal can be replaced without draining the oil or removing the side cover, or causing shim # 8 to fall out as jchrisk1 noted.
In my opinion, this is more often the cause of the leak. You might even be able to simply tighten part # 4 to get the leak to stop. If you try that, first loosen # 4 to free it, then tighten. You will need to fab or improvise a tool to engage the two wide slots in part # 4.
If you do replace # 3, it is usually stuck in place, and hard to dig out.

 

[5twins]

Note just exactly where the oil is leaking from. If it's coming from the cable and threaded sleeve, it's the seal. If it's coming from where the sleeve housing (#1) fits into the case, it's the o-ring (#2) .....

I usually find the o-ring all flattened out and in need of replacement. Best bet is to replace both the seal and the o-ring. Even with new, good parts in there, you may still get some oil "sweat" in that area.

 

[C-Los SD]

Which way does the seal go? Lettering facing out or in towards the motor?

 

[5twins]

Open side faces in, lettered side faces out, or up in this case.

 

[xjwmx]

Lettering facing out or in towards the motor?

Flipping a part so that the lettering is visible is a general rule about correctly orienting such parts.

It's easy to work on that thing without taking the side cover off. Provided nothing is stuck too bad. The trick is to while you're manipulating things to push 7 down with something so that 8 doesn't fall loose into the motor. I have an emergency NAPA o-ring in mine, But I recently got a couple of original hi-temp red spares from a dealer. The hardest thing is probably just getting the cable off, because it eventually rotates enough to bind in the part that drives it. Note that 5 goes into a hole in 1, I think it is, so 1 has to be turned right.

 

[5twins]

I think there's just a groove around the sleeve (#1) for the tip of screw #5 to fit into. Don't forget washer #6, that's a copper sealing washer.

 

[xjwmx]

^Mine was a hole. I remember my helper (unnecessarily) admonishing me to turn it the right way

 

[C-Los SD]

Thanks! I'm doing a engine build and had it all apart. It was a pain un-screwing # 4 out, I had to heat it with the MAP tourch and it cooked the the seal so no way of knowing which side was out.

 

[MtnBoy]

Also posted on another thread. My leak is around the cable. Removed the cable and the threaded piece. Seal underneath was shot, ordered a replacement. Question is how to remove the defective seal? Will I have to remove #5, 6 and 1 to tap out the seal from the bottom? Can I keep pressure on the drive shaft while removing #1 and avoid the dreaded lost washer scene? When replacing the threaded piece, #4, is any kind of thread sealer required? Thanks.

 

[MtnBoy]

Parts here, any advice on the seal?

 

[5twins]

Yes, you can remove #1 if you hold the shaft (#7) down in place. No sealer required on the threaded sleeve (#4). Just screw it down in tight against the seal.

 

[xjwmx]

For holding 7 down, a phillips will center itself in there good and not slip. My helper did that while I slipped 1 up over the phillips and then to put it back in it slipped down the phillips. My helper was an oilfield mechanic on a bike that I met somewhere in the midwest while I was looking for an open parts store on a Sunday. I was headed for the oilfields of N. Dakota so I tried to get him to go along. Could not talk him into abandoning his current life

Getting the cable out has always been a bitch until the other day when I had to get it out to replace a broken cable. I pulled on it with a vice grip until I actually tore it in half. After scratching my head I grabbed what was left with a needle nose turned it (I think it was clockwise) opposite the direction it usually moves, which undid the bind, and what was left just lifted out easy as pie.

 

[jd750ace]

Timely post. My last "big" leak is the tach drive. Think I'll pull that tonight. Thanks.

 

[MtnBoy]

Easy to do. Just completed replacing the seal. Good advice earlier. Use a phillips to hold #7 while removing #1. Insure the groove in #1 where the seal fits is free of old seal/debris. Made a tool to R/R #4. On my machine #1 has a hole for the bolt. Take a marker and mark on the top of #4 where the hole is. Makes it easier to line things up. No leaks Thanks to all.

 

[GeorgeOC]

Hoping to ressurect the conversation here. I am looking for any good advice on pulling the #3 seal for the tachometer assembly. Any thoughts on getting that bugger out? Thanks folks!

 

[TwoManyXS1Bs]

George, your timing is impeccable. I just replaced my tach drive seal, at the same time as your post. Had I known, I would've taken a pic. Long ago, I ground down the tip of a mechanics pick specifically for digging out tiny seals.


I just get the pointed tip behind the seal and pry/lever it out...

 

[GeorgeOC]

George, your timing is impeccable. I just replaced my tach drive seal, at the same time as your post. Had I known, I would've taken a pic. Long ago, I ground down the tip of a mechanics pick specifically for digging out tiny seals.
View attachment 89365

I just get the pointed tip behind the seal and pry/lever it out...

I knew there was something I needed at HF... Off to market! Thank you TM! The paint can tool and coat hanger methods were just not getting it done...

 

[GeorgeOC]

Thank you again TwoMany. This did the trick...