Topic: CB750K engine crank OIL SEAL. 3rd try most likely the charm...

[fasturd]

Hey guys.

I have a question regarding replacing the oil seal on the points side of the crank. This is the seal under the points plate. I seem to have a pretty decent boot wetting oil leak at this point. I removed the cover and the points plate and unfortunately cannot really see if it is the main crank seal or the oil o-ring at the bottom of the 6mm shaft. I will replace the o-ring regardless but I am wondering if the oil seal can be replaced without tearing down the motor? Is this one of the seals that can be removed from the outside?

Any suggestions would be greatly appreciated.

THanks in advance,
Bill

[Bob Wessner]

It's a lipped seal so to be replaced properly, the cases have to be split, kind of a bummer. Mine drips as well, but have decided to overlook yet another inadequacy of my bike given the effort to make it perfect.  However, in all fairness, I seem to recall past threads about folks fixing this without splitting the cases and using some adhesive. Try a search and see what you come up with. I never felt comfortable with that solution though.

[CB750F2]

Bill, yes you can change the crankshaft oil seal without splitting the crankcases. Search for topic number 5118 or "oil dripping from points cover". The thread was started by Bob who has already replied to your question. Pat

[fasturd]

OK, sounds like regardless I should replace the litle o-ring and then if it keeps leaking go for a seal-o-dectomy.
IF the Honda seal is flanged and hard to drive in I wonder if purchasing a standard oil seal in the proper dimensions with out the flange would work if glued into place with 3 bond or similar?
The factory exploded view does not show a flange on the seal...

Thanks for the help!

[fasturd]

I pulled the 6mm shaft and replaced the  6mm x2.3 o-ring. The leak has been lessened but not sure its gone. I wll watch and see. If not I will be ordering a factory seal from Honda as well as a standard seal by dimension without the supposed Honda flange. Regardless I will be installing from the outside with an appropriate sealer if there is one. I will document the process wether or not it works!

Thanks for the info.

[fasturd]

After reading up on all the opinions and doing a little asking around here is my conclusion.

The Honda Oil seal does have a very small flange, aprox. 1 mm. It sits in a groove cut into the case it is NOT on the inside of the crank case. I bought 2 factory oil seals (7.00 each) I did NOT cut the flange off the first one. I cleaned up the seal seat and coated the seal with Hondabond and tried to drive it home. The flange caught and tore the rubber coating. One seal down. Putting a little more thought into the next one as I only had one seal left for tonight. (I ordered 3 by dimension from a local seal jobber they do NOT have the Honda flange or the metal seal that the Honda item does.) I will eventually try them also if this last one fails.
We used a burnishing tool to cut a slight taper into the case, Then we cut off the lip of the seal. I lubed the area and the seal with WURTH HHS2000 a super slippery synthetic spray grease. I held the seal in place and drove it home with a large socket. It took a couple of good whacks but it is in place minus the factory flange. We reassembled the points plate and checked the timing and no leaks. We then saddled up and rode to the Quickie Mart to buy a lottery ticket as this may be our lucky night. When we got back I rolled it into the shop and so far NO oil. Before replacing the original seal, which by the way some BOOB had put in backwards there was a literal Triumph puddle everywhere I parked. I took off the points cover and it was still clean and dry.
Obviously the real test will be with a few hundred miles under its belt but so far so good and so dry.
I will have the other seals on hand if this one fails. They are more of a traditional seal but in the correct dimension to fit the crank and the case. They would save the trouble of cutting the flange off and they cost less than $2.00 each. I will post more on the subject if the Honda seal fails.

[fasturd]

Well, I was wrong. It WAS sealed... .

After a nice highway drive to a local bike night everything was dry and dandy. On the way home I subjected her to a little more high RPM flogging and was rewarded with a wet foot... So seal number 2 also failed.

When I took it out to see what was up it was apparent that it was leaking around its base. Now remember this is a seal being driven in from the OUT SIDE. Not placed in properly as per Honda assembly instructions.

During this trial and error process I also sourced a few "spec" oil seals. That are similar dimension to the Honda seal but with out the small flange and secondary metal inner seal.

I pulled the factory seal back out and replaced it with the spec seal and a little Honda bond.

So far the spec seal has been holding up. These normal seals are meant to be driven into place so there was no modification needed to get the seal to fit.

Now there were a few other problems that seemed to pop up (mainly due to my taking the previous owners word that the bike had had some professional service done).

The Valve cover breather tube was vented into the oil tank. The crank case vent was vented to air and the spigot from the tank that was supposed to go back into the crank was plugged... So after getting the seal to hold I was now PUKING oil everywhere. I did a little reading of the factory manual and of course Honda routes its breather lines CORRECTLY and plugs the crank case hose in to the back of the tank. Nice, no more oil soaked back wheel!!! And no more BP sized oil spills everytime I come to a stop.

With everything buttoned back up, all hoses routed properly, the spec seal in place and a new o-ring on the points shaft I have no oil on my shoes, ground or tire.

Now it only has about 10 miles on it and I plan on pushing it this weekend to see if I can make it leak but (again) so far so good. IF the seal stays in place and doesnt leak I will post the part number incase any of you want to give it a try.

By the way the spec seals are less than $2.00 each!

[fasturd]

I have aprox 50 miles on the new seal and so far everything is dry as a bone.

The new seal is working as it should and the PROPER routing of all the breathers has helped all the other oil puking problems... Jeez now all there is left to do is fun stuff!

[andy750]

Well done and great write up! Can you post details and source of the spec seals? Thanks very much and happy riding!

cheers
Andy

[fasturd]

Wow, sorry I thought I did, Hmmm. I will have to go dig up the parts bags and get the numbers. Sorry I thought I had this postd already!

[Spanner 1]

Hey Fast, could the engine vent plugged/routed wrong deal have caused a pressure build-up in the crankcase causing the crank seal to weep ? Normally no pressure in the crankcase = no pressure on the crankseals...... maybe ?

[fasturd]

I am not sure. I think there may be another issue at play here because I have solved the seal problem but I still get excessive oil vapor out of the oil tank vent hose especially at sustained high RPMs (like 70-90 mph).Enough to wet the rear wheel.
I am pretty sure everything is routed correctly and I think I have the proper amount of oil. I am wondering if the crank case is getting pressurized by blow by and causing the problems... Still scratching my head. The engine runs strong, starts easy and idles well and doesn't smoke on acceleration or deceleration. I may have to borrow a compression and a leak down tester and see if that gives a clue. I love the bike otherwise.

[fasturd]

Hey Fast, could the engine vent plugged/routed wrong deal have caused a pressure build-up in the crankcase causing the crank seal to weep ? Normally no pressure in the crankcase = no pressure on the crankseals...... maybe ?

Actually the main reason it leaked in the first place was because previous owners mechanic pushed a stock Honda seal in up side down from the out side... Now matter what it was destined to leak.

[fasturd]

Well done and great write up! Can you post details and source of the spec seals? Thanks very much and happy riding!

cheers
Andy

OK sorry about the delay. I thought I posted this weeks ago.

The factory crank seal part # for the RIGHT hand side is 91201-300-003 this is the "oil seal" 30x42x8 mm. It has a slight lip that makes driving it in nearly impossible. But it is a much better seal when installed PROPERLY by splitting the cases.

After seeing how well driving this in from the out side does NOT work I had a local bearing vendor find me the following seal based on dimensions. it is from;
ISP International Seal and Packing Company
their part number is 30X42X7AN which is just one mm thinner in depth than the stock Honda part. But it has NO lip to tear off while being driven in place. It is not a perfect solution but I had no intention of taking this bike apart just to fix this issue. I cleaned the area VERY well and used a little Honda bond as well. Again it is not a perfect solution but it is a way to solve the problem if you are not ready to rebuild your engine.

The Honda part was many times more expensive than the standard seals which were About $2.00.

Since you are in the vicinity you might as well change out the o-ring on the shaft for the points it is part# 91301-300-000 o-ring 6x2.3mm super cheap and worth changing as they can cause leaks that look like the crank seal is leaking.

Hope that helps keep your right boot dry!

[fasturd]

Well just to make sure I went back and checked. I used the factory manual when I straightened out what the previous owner had done, probably to hide the fact that the vent from the valve cover and the vent from the oil tank both spew very wet vapor... Hondaman suggested that most likely the valve seals are on their way out allowing pressure to build up in the crank. The routing is correct but I have not checked since wether or not any of the hoses are plugged but the evidence from the wet tire says all the hoses are flowing freely.
Also don't forget the previous owners mechanic installed the stock oil seal in up side down from the outside. No matter what the pressure that fix was going to fail and it did as soon as I started riding the bike. The aftermarket seal has not seeped at all BUT now I have this oil vapor issue to deal with that will most likely involve going through the head, which as you know will most likely lead to "other" stuff...
I did not yet check to see if the oil tank cap is vented and not clogged? Kind of a bummer as the bike runs well and pulls hard.

[Derrickwoods]

Any way you could post a pic of that aftermarket seal having same problem dont wanna split cases either thank you

[Derrickwoods]

Also how did you remove old seal reason i ask ive done a complete resto on a 78 cb and for some dumb reason i didnot replace that seal done all others forgot that one.   This bike has taken me 9 months to complete and im not gonna take motor out if i dont have to

[Davez134]

This is an old thread, so you may not get a response from the OP. I will help you out. I had the same problem about a year or 2 ago. oil leaking from this seal. As you can see in the pictures in this post, the seal was installed backwards (metal ring you can see should face inward, thats what's causing it to leak because the lip is not in its grove) I replaced mine with the aftermarket seals with no lip. Tried 3 times, very careful and used sealer around the seals. Each time they listed for a few hundred miles before a leak developed then worsened. The ONLY way to do it right is to split the cases. I know it sucks but if you want a leak free motor then it has to be done. It should only take a days worth of work to make it right for a long time.

Here is my post about the problem, I believe there is a picture of the aftermarket seal package in there for you if you still want to go that route
http://forums.sohc4.net/index.php/topic,139768.msg1691774.html#msg1691774

[Derrickwoods]

Do you think i should go ahead and replace all the other exsisting seals while its open also.   I am very mechanicly inclined so on a scale of 1 to 10 how difficult. Also will ihave to remove altornator and is there anything i should look out for..the  engine was overhauled about 4 years ago but it sit for over 3 years on my desk after i wrecked bike i took it out to powdercoat frame and all other parts and just this year got it back together thanks for help derrick

[BPellerine]

awhile back I had an orginal honda seal kit,still in the package,the seal in question had no lip on it,supposed to be for ko,but I dont know for sure,the seals are now in my buddies ko,maybe they updated the seal as time went on.bill

[Davez134]

Do you think i should go ahead and replace all the other exsisting seals while its open also.   I am very mechanicly inclined so on a scale of 1 to 10 how difficult. Also will ihave to remove altornator and is there anything i should look out for..the  engine was overhauled about 4 years ago but it sit for over 3 years on my desk after i wrecked bike i took it out to powdercoat frame and all other parts and just this year got it back together thanks for help derrick

Yes, I would replace all the seals and gaskets you remove/disturb while splitting the cases. It is not that difficult, you can do it with the top end still together just turning the engine upside down and removing bottom case half. I had never split cases before I built this motor, I was nervous about it but afterwards I thought "well that was pretty easy." You do not have to remove the alternator rotor, just cover and stator coil that is bolted to it.

[Derrickwoods]

Is there somewhere that o could find torque pattern and torque specs?

[Derrickwoods]

Also what bonding agent do you recommend

[Davez134]

Here ya go.
http://manuals.sohc4.net/cb750k/

Use hondabond between cases.

[Derrickwoods]

Thank you so much for all your help