oil pump driven tach drive broken

[nagrod]

Any ideas on what might cause the damage shown in the two pics attached? The two tabs on the end of the oil pump worm drive gear are broken off. The bike has been a project, with lots of down time so I can't say when it happened or give any specifics. After the latest burst of enthusiasm, and I'm close to on the road now, I found this. The break doesn't look too fresh as the broken ends of the tabs are a little worn. I discovered this when the tach stopped working completely, before it had been very jerky. The tach cable spins freely and the drive connection the cable fits into on the tach is also free. My biggest concern obviously is that it not happen again but I don't know what to look for. In the meantime a new worm drive gear is on order from SRM.

Thanks

Rick

[tombeau]

Mine had one tang on it broken when I got it.
Don't know why. Possibly the rev counter cable had got nipped between the bottom yoke and the steering locks.
Would the rev counter breaking cause the cable to seize?
Cheers,
Iain

[RichardL]

Must admit, I'm no expert in this (but can't quite stay out of it). First thought is as Iain says, seized cable. Then I thought that maybe the drive spindle got seized in the tach adaptor, or the tach adaptor became loose or is just missing. So, do you have one of these?

Richard L.

[tombeau]

I'd like to think that in the case of the cable seizing, the tang would break rather than cause the oil pump worm drive to stop turning..
Cheers,
Iain

[RichardL]

Tangs for mentioning this. Makes sense.

[nagrod]

Second time trying this, my first reply is lost in space, apologies if it shows up! Richard's comments make sense. I have the adapter and it was on tight but a look shows some gouges spiraling around the spindle so I'm thinking some piece of something got in there and maybe jammed long enough to break the tangs. I'm assuming this is lubed by leakage past the worm drive? I wish the weak point was the spindle, it would be a lot easier to repair!

Rick D

[chaterlea25]

Hi All,
I would think that the most likely cause is misalignment??
The oil pump is not a good fit on its studs and can be moved about to some degree
When fitting the pump lift it towards the crank worm, BUT make sure theres a little play in the engagement of the pump gear and crank
Trial fit the rev drive with its housing, the screw holes in this are somewhat oversize, check that it seats flat against the casing and then turn over the engine several times to check theres no tight spot

The only other thought I have is ,
Was the gear that broke original or aftermarket?? Maybe overhardened ????

HTH
John O R

[trevinoz]

I think that the most common cause of the tangs breaking is the owner trying to remove the oil pump with the tacho drive still in place.

  Trev.

[trevinoz]

Rick,
              The "gouges" spiralling around the shaft is in fact a scroll for driving any oil back.
There should also be an "o" ring on the shaft.
I don't bother with the miniscule "o" ring but I counter bore the base of the housing and fit a suitable "o" ring there.

  Trev.

[RichardL]

Trev,

I was wondering if those were grooves for driving back the oil (a la the speedo drive gear shaft), but it didn't seem to me that the piece with the grooves showing actually rotated. Or does it?

Richard L.

[nagrod]

Hi guys - Well that is an interesting fact about the grooves! The parts in question are all original. I've owned this bike since 1966 and had the engine apart twice, the last time about 10 years ago. I have worked on it way way too slowly but it is so close to back on the road now. In the 10 year ago work I did have the oil pump out so I must be the culprit. In those 10 years the bike has not run all that much, too much of the other things in life happening but I did get it out every once in a while and I felt the tach was working but not smoothly. The idea of a misalignment sounds very possible and I'll pay close attention when it goes back on. A closer look at those "gouges" does show that they are not accidental but that there are two sets almost identical. That piece which I am calling a spindle does rotate, driven by the oil pump. I don't understand where the O ring would have gone originally, parts book doesn't show this assembly at all! As the steel spindle rotates in the aluminum threaded adapter the tach cable threads on to so I would think some oil should seep through. Does counter boring the base of the housing and fitting an o-ring then take the place of the gasket allowing oil into the spindle bore but not leaking outside the housing?

Rick

[trevinoz]

Rick,
            Have a close look at the spindle and there should be a very fine "O" ring fitted.
The "O"ring in the base of the housing will help prevent oil passing the shaft and ending up in the cable and on the ground.
The original fitment did this but not very well or maybe all of them that I have seen are worn out.
You still need the gasket between the housing and inner cover.
Alignment shouldn't be an issue as there is no way it could be out unless the crankcase and inner cover were machined incorrectly.

  Trev.

[nagrod]

I think you guys have found the answer to my question of how this happened in the first place(broken tach drive). When I removed the pump there was the paper gasket but no fiber gasket on the forward stud. I had the pump out some years ago and must have put it back without that forward gasket. I think this may have cocked the center line of the pump off from the centerline of the tach drive spindle allowing it to stress the tangs on the worm gear and eventually break them. I am sometimes my own worst enemy!

Rick D

[chaterlea25]

Hi All,
I, never had much success with the spiral/ o ring setup 
I eventually made my own housing containing two sealed miniature ball races
I sleeved the spindle up to 8mm to fit the bearings, the housing needs longer screws to hold it in place
Its been on there 6 or 7 years now with no leaks
I should take some photos of it for the guys here on the forum
I need to make another for the RGS Project!!

Regards
John O R

[RichardL]

Careful, John. You'll soon be manufacturing them.