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Crankcase leak problem

Posted by njdpo (My Page) on
Mon, Jun 16, 08 at 14:42

Hi all,

I am working on a motorcycle engine - but I suspect this problem has been seen by members of this forum. I hope you can help.

This is a 4 stroke Yamaha motor 1980 xt250. This motor’s crankcase is split vertically during its manufacturing (nicely done / assembly) … My problem is that this motor is leaking oil, the crankcase oil weeps from the case (due to an accident many years ago). The weeping oil is coming from the split case (and broken gasket?), thank god the case isn’t cracked… Re-torque-ing the case has not helped with the weeping issue (perhaps a little).

I know deep down in my heart a new gasket should be installed. My friend sized it up very well “Awww Mann … your gonna be one day in - and one day out” He’s right... its gonna take a while for it to happen… and I really don’t want to (or have that time). Where not talking about an old (and simple) Briggs, these cases have a lot of stuff in them (tranny, oil pump, clutch, O.H.Cam, etc).

If I can fix it externally without pulling that motor and cracking those cases open. I might try it. Please forgive me …

I am thinking :
- Silicone sealant: quick/easy to work with, easy to remove from engine - maybe , don’t have any experience trying to seal a motor. I don’t think its going to work ... How about you guys ?
- JB Weld: I think this would make the problem go away. Very difficult to remove, don’t need to use a lot of surface 2in x ¾ in. Don’t want to glue the cases shut in that 2 inch long strip.
- Gasket set: No brainer - this is the way to do it right… I Don’t want to open that motor …

I think my next move is to try a silicon sealer externally … but want to hear your thoughts before I go out and buy anything.

Thanks all

Follow-Up Postings:

RE: Crankcase leak problem

njdpo: Tufftorq sent me a seal kit for my 71G tufftorq tranny a year or so ago. It had some kind of sealant to be placed between the tranny halves. Since a motorcycle engine and a tranny of my type are of similar metal composition, I'd be willing to bet it just might work. It is manufactured by the Permatex company. It comes in a tube, and is grey in color. I'd try to find some of this compound, clean up your case very well - even use disc brake cleaning spray cleaner, and put this compound along the seam of your case. It is worth a shot.

RE: Crankcase leak problem

Hmmmm - Permatex ... Now that you mention their name It seems to me ive worked with some really heavy duty stuff of theirs a number of years ago...

I found their website on sealants and gaskets


ill have to do a bit of reading on my options.


RE: Crankcase leak problem

I don't know about your specific engine, but a lot of MC case halves use a sealer instead of a conventional gasket.
I overhauled a 74 Subaru engine about 30 years ago and ISTR that I used Yamaha sealer for the case halves.

RE: Crankcase leak problem

njdpo: I found my tube of sealant. Sorry, but it isn't Permatex after all. Though Permatex makes some very good products. This is called Big Shot Mega Grey. Has a label similar to Permatex - that's why I got it mixed up. Part number 99949. Made by VersaChem. Says it is for water pumps & thermostat housings import vehicles. Sensor safe, High Temp, Low Volatile, Low odor, Non-corrosive, OEM Approved. It is a small tube with about .75 oz. Permatex may make a gasket maker compound similar to this. OR, call Tufftorq ( and they'll probably sell you some and ship it. Just something to think about.

RE: Crankcase leak problem

Go to the Yamaha dealer and get the sealer for the job. I use to use on a lot of automatic transmissions back in my rebuilding days. Enjoying retirement now. It is a sealant made just for sealing aluminum case halves.

RE: Crankcase leak problem

In response to: " It is a sealant made just for sealing aluminum case halves. abh"

I am really interested in knowing more about this magic stuff.

Can you tell me was it something you dumped in the oil?
Did it get applied externally ?
Would it foul up a oil pump for a 4-stroke?

Do you remember any names for it ? Im getting on the phone with a service department now.

Seems like the permatex group has some spray on products that look like they might do the trick - very interesting.

Thanks all ... any more ideas - please keep them coming.

and thanks for not flaming me with splitting the cases and doing it right.

RE: Crankcase leak problem

njdpo, you might as well face reality. There is no magic potion to pour into any oil compartment of any machine that will stop an oil leak caused by missing gaskets or cracked cases (without also clotting beneficial passages as well). If such a product existed, you wouldn't have to search for would be well known to everybody. The only products aimed at reducing/stopping oil leaks in machine assemblies are those that claim to swell seals (and thereby slow or stop the leak). The actual efficacy of any of these products is dubious and largely because of the placebo effect imparted by their purchase and use. Your best bet for affecting an external cure for this leak is to first drain out all the oil in the sump. Lay the bike over at an extreme angle (or just lay it on it's side if you feel like taking the battery out and removing the gas tank first). Clean off all traces of leaked oil and dirt using spray carb cleaner and a scotch brite scuff pad. Clean a path about 1.25" on each side of the crankcase seam. Allow this to dry completely (use a hair dryer if needed). Make certain that no residual oil runs out of the seam (if it does, clean off again like before). Mix up a batch of JB Weld (or similar high strength epoxy). Begin appying the epoxy at the outer edges of the cleaned area and work toward the seam. Coat the entire area you cleaned and scuffed and try to keep the layer thickest over the seam. you can speed up the curing/setting of the epoxy by using a heat lamp or other non-flame source of low heat. You will probably have to keep wiping the epoxy back toward the seam until it begins to set up to the point it does not sag or run. Allow the epoxy at least 24 hours to cure and hope for the best.

RE: Crankcase leak problem

Thx Mownie I was thinking of a JB Weld procedure very similar to yours...

I going to use this process as my last resort, as I hate the thought of gluing the front half of the case shut.

I see that Permatex advertises a product that might fix this problem. Im gonna grab me a can sometime this week and see how it goes.

If all else fail im gonna break out the JB Weld ... Ill you guys know how I make out .

I got one more call into a yamaha dealer to ask about that sealer mentioned earlier.

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