Crankcase seal leaking

[Trigger]

Not all lip-seals are locked in place, most just press in.... so long as its the correct size and material...

Not all seals have 50 psi of oil pushing on the back of it. The lip is there for a reason.
And the seal in the picture is not a crank seal, I feel a bodge coming on and some damaged crank cases  looks like Fred Flintstone has already been in there.

[ka-ja]

I agree with Trigger, Honda did not use that type of seal just to be awkward, they were used because they keep crankcase pressure/oil in as opposed to keeping oil splashes in, would hate one to "pop" out at high revs.

[Bryanj]

 That picture shows the wrong seal, there should be a definite "Lip" on the side with the metal washer. The one in there has been bodged in and is probably why its leaking BUT why was it done in the first place as these don't often leak, is there a bigger problem inside? I have a NOS one in my hand as its the same as a 500

[Trigger]

Just for Paul Gledhill >>>>https://www.youtube.com/watch?v=tRsm2G7bulI

[Laverda Dave]

If you go to the effort of prising out the old seal and replacing it with new seal only to find it still leaks you'll have to remove the engine anyway. There's an old but true saying 'it takes longer to bodge a job than to do it properly in the first place'. If Honda could have saved a few yen by fitting non lipped seals they would have done. Save yourself serious frustration and a potentially wrecked engine and fit genuine Honda seals, you can renew the cam and primary chains whilst you are in there and have a fresh engine.
Good luck with whatever option you go for and keep us posted.

[Rob62]

Just out of interest blasta, you may want to look at the link below. The seal you have bought has no lip but has the correct part number?, i’m no expert on honda parts but it may be that the replacement seals are lip free to enable fitting without stripping the motor, if this works then you will have saved a ton of work or money.... so imo worth a try. However it does look to be pretty crappy around that seal so if it looks bad in there once you remove the old one it may be better to strip the motor anyway. Have a dig and see what you think. Good luck!

http://forums.sohc4.net/index.php?topic=74771.0

[K2-K6]

That one on the net site's interesting,  as pointed out above by Bryan they don't usually leak there. It's possible that both this example and Rob's posted one area suffering initially from crankcase pressure build up as someone has mucked about with the breathers on the USA one.

We had on here about 4 or so years ago a (can't remember who's it was)  blue 750 K2 in Kent that had the breathers connected wrongly and kept pushing oil out of different places, corrected those and went away.

It looks like previous owners go straight for the seal and make a dog's dinner of it.

If you want to put an original lipped seal into it,  put one of those smooth stainless jubilee clips around it, after first greasing with silicone, then place this against the cases and push the seal through with a drift. The rubber flange is just that and not supported by a steel lip inside (you'd have to check this).

The purpose of the lip in car crank applications is to make it, to an extent,  self sealing against crankcase pressure buildup and stop oil pushing past the outer edges. They are normal at the flywheel end to make sure the clutch doesn't get contaminated.

I'd still split this one to get a better longterm fix though, it's not that hard...... Is it?

[Trigger]

I think if you wrap some draft excluder round the end of the crank it may work, well it keeps drafts out 

[K2-K6]

 If the engine's that windy,  may need that on the piston rings 

[Blasta]

Thanks for all the advice, and thanks Rob62 for that link. All very interesting.

I've had the bike for about 6 months and the guy I bought it from had rebuilt the motor. He's in his 60s and has been riding/racing/rebuilding 754s since they came out in the 70s.

He did the motor many years before I bought it off him and sorted all the rest of the bike, I've done 1600km since.

I spoke to him after I posted this thread and he's offered to help me take the motor out and replace the seal. He also thought that the alternative option would probably work, and after reading the thread that Rob62 posted I think I agree. I think it's worth trying, if it leaks I'm really no worse off and I'll take him up on his offer.

So now I just have to get the old seal out, and as you can see from the pic I had a go yesterday and was unsuccessful. I'll have another go and let you guys know how it turns out.

[paul G]

Just for Paul Gledhill >>>>https://www.youtube.com/watch?v=tRsm2G7bulI

Not my favoriye episode 

[MrDavo]

If you really can’t be arsed to do a full strip down you could take the motor out, turn it upside down and undo the bottom case. You’d have to remove anything that attaches to both, I can only think of the ignition, clutch / alternator covers and gear change mechanism.

You could then lift the end of the crank to slip the old seal off and the new one on. Assembly is the reverse of disassembly, as Mr Haynes would say. The cases use sealant so getting a gasket in there isn’t an issue.

The are other seals you could / should change while you are there such as the final drive seal, but this looks like the minimum work route, the sort of thing I used to see going on in race paddocks when working to a deadline. There are potentially disastrous pitfalls such as the cam chain moving a tooth so you’d have to be careful there.

Others may be along soon in a state of shock to tell you why this wouldn’t work, it certainly isn’t the best way, but I am good at spotting a short cut.

[Tomb]

I know lads who've used that method but not even gone as far removing the engine from the frame, albeit not on CB750's, but on other Jap fours.

I'd still have a go at doing it with the engine in one piece first, as said, what's there to lose, just be careful to not damage the crank. After all you have documented evidence of it working (posted by Rob 62)

[Spitfire]

I always used to use the upside down engine route when working on CB750 gearboxes, why strip the top end when there is no need, just remove the side covers, gear change mechanism etc off and take the bottom crankcase off. Saves a load of work and hassle.

Cheers

Dennis

[Blasta]

Yes, I'd spoken to a few people and was going to do the upside down thing if required.......but I don't think it is.

I had another go at the seal and it actually came out fairly easily and I managed not to damage anything.

The new seal was a nice snug fit and I put a little sealant around the edge. [ Guests cannot view attachments ]

Looks pretty good to me and I'm pretty confident it's not going to leak (famous last words  ).

I've got a few other things to do to it before it's back on the road, but I let you know if it's worked when I get a few kms on it.