Base gasket oil leak.

Hi all,

I have a 1981 KZ750 E2. About 10k kilometres ago I replaced the head gasket and o-rings for what seems to be a pretty common oil leak. Recently it started leaking again on the right side. So, last week, when I was doing the valve clearances, I thought I'd whip the head off and try to re-seal it. I had read on this site about how it is basically a 50/50 chance of disturbing the base gasket. First time it seems I was lucky. This time though the base gasket will not seal.
Just wondering what now? I know the engine has been re-ringed at some stage because a piece of cooling fin is broken on the block just below the head. If I pull the block, should I fit new rings? Should I move this thread over to the rebuild section? The engine is running really nicely apart from the base gasket oil leak.

I am doing an engine rebuild here and have a little bit of experience with these engines so my insight is limited but here are my thoughts:

Changing the base gasket should be done when you do a head gasket because pulling up on the head has a good chance of separating the cylinder base.

It is a seal for the engine case pressure as well as keeping oil from leaking. The case has some pressure in it though not a whole lot which is why your bike didn't leak right away.

Changing the gasket is pretty straight forward, the hard part is removing the old gasket. I ended up using a plastic scraper and finished it up with a plastic abbrasion wheel on a dremel. (They don't last long so buy many if you go this route and keep the dremel moving)

If you don't mess anything up you should be able to reuse your rings and everything. But since you are in the engine I would measure the gap of the piston rings, cylinder diameter and pistons just to have the numbers and see if your within spec.

My $2.00 worth...my phone doesn't have a 'cents' symbol haha.

Ironically, my 750 twin came from the factory with some kind of super adhesive on the base gasket. Never leaked through two head pulls, but was a bear to remove the cylinder when I finally had to change the pistons. The kawi mechanics told me they use yamabond or something similar on the base gasket to make sure it never moves or leaks.

As for new rings: I would do the old test of measuring compression cold/dry then shoot in oil and see how much it goes up. If not too much (less than 10 psi) rings are probably sealing OK.

Hi peavylotus,

Thanks for the info. I'm wondering if you can rebuild the top end with the engine in the frame or out. If done a bit of reading and am aware of the dirt issue, do you find it easier to do this with the engine in or out of the frame? I seem to have got the idea that you could do this in the frame with the oil pan removed so hopefully any dirt would fall right through.

Cam chain is within wear limits, but getting close. 128.3mm. I can see where all this is heading... I'd like to be able to pull the motor out, split the cases, repaint them, renew all the worn parts... What I'd like to do and what I can do are different though. Does anyone know if the cam chain is within wear limits, should you replace the gears on the cams? I would assume all the guides should be replaced. Is the length I measured worth worrying about. Thanks in advance everyone.

Hi bodyhunter,

Good idea on the compression test. Bike is running well as I've just done the valve clearances and balanced carbs. Compression test will at least give me a better idea on the rings.

You can rebuilt the top end with the engine in the frame, that's how I started. I pulled the head off and cylinders, had them bored and lapped the valves. But I ended up having to take the engine out because there were massive build ups of old gasket in the oil pan. I think someone scraped the valve cover gasket into the motor and then just said F*#@ it.

Removing the old gasket from the base of the cases with the engine in the frame can be done by wiping the engine case cylinder base with acetone or other solvent that evaporates fast and preferably not an aerosol can. Put some Duct tape around the openings and covering up everything with tape then you won't have anything fall into the case. I say duct tape because when you hit it with the scraper you can re-stick it without the adhesive wearing out as with masking tape.

If you replace all the sprockets and guide I would replace the chain so they wear-match and you won't have excessive wear on your new parts. They make the cam chains with master links from Z1 enterprises.

Not sure on the can chain wear specs since I'm not next to my manual.

I want to push you away from splitting the cases cause the bottom end is rock solid and can get really tricky dealing with the gear shift components. Also when your inside the engine there really isn't much you can do as far as replacing worn parts since the crank and connecting rods don't desperate.

peavylotus wrote: You can rebuilt the top end with the engine in the frame, that's how I started. I pulled the head off and cylinders, had them bored and lapped the valves. But I ended up having to take the engine out because there were massive build ups of old gasket in the oil pan. I think someone scraped the valve cover gasket into the motor and then just said F*#@ it.

Removing the old gasket from the base of the cases with the engine in the frame can be done by wiping the engine case cylinder base with acetone or other solvent that evaporates fast and preferably not an aerosol can. Put some Duct tape around the openings and covering up everything with tape then you won't have anything fall into the case. I say duct tape because when you hit it with the scraper you can re-stick it without the adhesive wearing out as with masking tape.

If you replace all the sprockets and guide I would replace the chain so they wear-match and you won't have excessive wear on your new parts. They make the cam chains with master links from Z1 enterprises.

Not sure on the can chain wear specs since I'm not next to my manual.

I want to push you away from splitting the cases cause the bottom end is rock solid and can get really tricky dealing with the gear shift components. Also when your inside the engine there really isn't much you can do as far as replacing worn parts since the crank and connecting rods don't desperate.

Actually There is plenty of stuff that can be done by splitting the cases. You can change your camchain. Inspect and or backcut the transmission. You could also have your crank inspected and welded. If you wanted to spend the extra cash you could have the crank indexed. If you plan on changing the base gasket and head gasket, i would inspect and replace all worn idlers. The transmission isnt tricky at all. just follow your manual. If you plan on boring it out i would replace the cam chain. You wouldnt want to go thru all that work and have a cam chain break. Also the dogs are known to wear on the trans allowing to pop out of gear. Its usally second gear that goes first. Also if running a big bore kit you could also twist the crank. I usally just stuff rags in all the holes so dirt cannot fall down thru. Usally you wont need to replace cam chain sprockets. Ive never had to replace the first one, besides to install slotted sprockets. Also allot of people wouldnt recommend installing a cam chain with a master link. I wouldnt install a cam chain with a master link, but thats just me.

Speaking in terms of beginners including myself, I don't feel comfortable advising someone whose original plan to change a base gasket and wanted to avoid pulling the engine from the frame to split the cases.

Though if you have the drive to fix her up sweet, I would take the advice from power stroke fan cause you would end up with a really sweet, good running bike in the end.

Its also true that following the manual you can pull every piece apart and put it back together and have a running bike in the end. Modifying info can be sourced through this forum as well.

Depending on your fluency with machines and what money can be saved by doing the work on your own you will be balancing skill, plans and money. Though In every which way the fun will be there cause its a blast to be the hand at which put life back into a motor. Choose you adventure

Apart from my lack of experience, the only apprehension I have with splitting the cases is sealing them again. There is no gasket, so cases would have to be very clean. I've decided to get the frame powder coated, so the motor is coming out anyway. Maybe it will be better to start a thread in the projects section after all.

Works/seals every time and gaskets come off clean when required....


Note gasket on a 1075 build coming off clean...

Old Man Rock wrote: Works/seals every time and gaskets come off clean when required....

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Been using the brush- on Coppercoat since the 70's. Sure beats scraping all those gaskets!!!

The old gaskets just peel right off!! No muss No fuss!!!

I sprayed the nos base gasket on the side going to the cylinder. Read on here it helps keep it outta the way when getting the cylinder over the rings and it did. I did only spray the gasket part and left the rubber center section alone though thinking it would seal better that way. Sounds like the next guy might have a time getting it off the case side .... and for sure it's not gonna be me. :lol: