Tacho Drive Oil Seal

[Martin6]

My cylinder head cover is back on and I've tried to fit the new tacho drive seal. I just can get it to work.

I'm putting it in the hole / shaft that the drive gear spindle exits the cover into. I'm putting the seal in, flat face outward. It goes over the gear spindle and flat against the cover, but I can't then get the end of tacho cable in far enough for the lock screw to engage. It seems to need to go 2 to 3mm further in. It engages fine without the seal in there. I tried putting the seal in the other way round, with the cup end outwards, still no joy. The old seal is definitely not in there and the hole in the cover is clean.

Any idea what i'm doing wrong? I'm reluctant to apply too much force to pushing the tacho cable onto the seal, but I have pushed it reasonably hard and the seal seems pretty solid.

[Bryanj]

It goes flat side outwards and are you sure the old one is out?

[Oddjob]

I seem to recall I tap them down with a long 8mm socket, just wide enough to go into the drive housing but the internal bit is wide enough to accommodate the drive gear shaft. Works on the 500/550 can't see why it wouldn't work on the 750. Seal markings outwards

[Skoti]

Is the oil seal the correct dimensions? Make sure it's the correct depth.

4.8x14.5x4mm
Genuine part number 91256-096-651

It's not normally a tight fit, mines pushed in by hand with a 1/4" drive 8mm deep socket.


Good luck

Skoti

[McCabe-Thiele (Ted)]

Check the new  seal is the same size as the old one if you still have it. Just in case a different drive unit has been used in the past.
Last thought is the cable an original part or is it corroded where it slides in?

[Martin6]

Thanks everyone. The old seal is definitely out and the area clean. The tacho cable and seal are new parts from David Silver. The cylinder head cover is from ebay. My old one was missing a chunk of gasket surface! I will compare/measure everything with what I took off the bike. Maybe something's incompatible.

[Spitfire]

Had the same problem on my 750F1, this is what I wrote at the time on the US SOHC site.

Well still having a few teething problems with the 76 CB750F1, but everytime I have a problem I either do a search on this forum or post my problem, don't think I could have got this far without the advice and encouragement I have recieved.
The latest problem was the tacho drive oil leak, it got worse, so I did a search and found the answer on the famous JohnK6 "How to rescue a CB750 from the garbage dump" thread, boy that should be saved somewhere.
Used a wood screw as advised and out popped the oil seal, 10mm 1/4 drive socket and in went the new one, as stated 5 minute job.

Cheers

Dennis

[clinto]

Had the same prob yesterday.New 750 seal and tacho cable.
Remedy was to really force cable  in.   .Perhaps seating/settling seal?

[Skoti]

Was it a pattern tacho cable?
If so does does the alloy cable end that fits into the cam cover measure the same as the genuine Honda cable end?

[Martin6]

Yep, not Honda on the bag. But it goes into the old cover fine. I can see some machining rings in the hole the seal goes into. They may be stopping the seal seating fully. I've been reluctant to force it in. I'll either do a light bit of sanding or use a little force with a suitable socket on the seal. I think a bit of force first.

[McCabe-Thiele (Ted)]

Red rubber grease usually works by hand.

[Martin6]

Ted's grease, a long Whitworth socket and heavy mallet did the trick. 👍

Am I the first to use Whitworths on a CB750? 

Motor now ready to go back in the frame, when it returns from the powder coaters.

[Oddjob]

If in doubt, hit it.

[Bryanj]

No the first Whitworth was used as a hammer on to the 12 mm headed oil filter bolt 3/16 i believe from memory

[johnm37]

Motor now ready to go back in the frame, when it returns from the powder coaters.

Will powder coating take the engine temperature?