Coolant in crankcase after rebuild

J

Jacob 'Berg

Member
After my bottom end rebuild and replacing the top end I could not get the bike to fire. Pulled the crankcase drain and about 3-4 oz of coolant spilled out. Any ideas on where this may have come from? Bike ran maybe 10 seconds before dying, but I kicked the living day lights out of it trying to get it to fire afterwards. Head O-rings, base gasket, center gasket? Any other possible areas where the coolant could get into the crank case?
 
I pulled the head off and the O-rings are seated correctly. I will pull the jug next and look at the base gasket and the mating surfaces on the cylinder and case halves. If I have to split the cases again, where should I look?
 
The only place that coolant can get into the crankcase is at the coolant passage that crosses through the case halves at the front.
 
gasgasman said:
The only place that coolant can get into the crankcase is at the coolant passage that crosses through the case halves at the front.
Click to expand...

Thanks Girard. I guess the cases are coming apart again, unless it is the base gasket:( I thought the mating surfaces were clean before putting the halves back together. Should I use any RTV or sealant in this area to ensure I do not have another issue?
 
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Was the coolant in the crank case or the transmission?

What made you drop the crank case? noticeable loss of coolant with no external visible signs?

You'd be quite unfortunate to damage a gasket in the area where the coolant runs across the front of the engine. Very unfortunate. Not impossible though.

How do you know the head o-ring or base gasket didn't leak? Kids been playing in the shed?
 
Jakobi said:
Was the coolant in the crank case or the transmission?

What made you drop the crank case? noticeable loss of coolant with no external visible signs?

You'd be quite unfortunate to damage a gasket in the area where the coolant runs across the front of the engine. Very unfortunate. Not impossible though.

How do you know the head o-ring or base gasket didn't leak? Kids been playing in the shed?
Click to expand...

Coolant in the crankcase and cylinder. Not in the transmission.

I dropped the drain bolt because I could not get the bike to fire after my rebuild. This was part of my least invasive troubleshooting process.

New O-rings were seated properly. It could be the base gasket, I will pull the jug next.

If it is not the base gasket it appears the leak will be between the case halves.
 
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Jacob 'Berg said:
Should I use any RTV or sealant in this area to ensure I do not have another issue?
Click to expand...

Absolutely no RTV. The fuel will dissolve the silicone.
If you do wish to use some sealant, use Yamabond.

If you use the wrong bolts on the case halves, that can cause a coolant leak. Too long of a bolt will bottom out before it tightens.
 
If its coolant in cylinder its most likely orings.id bet 1 has jumped out slightly when head has seated.took me a couple attempts and some careful stretching to get mine to sit still long enough to clamp down.check the oring grooves carefully for any grit.if you do take cylinder back off for base gasket, check the studs are tight before reassemble.did you torque correctly the head nuts or go by 'feel'?
 
gasgasman said:
Absolutely no RTV. The fuel will dissolve the silicone.
If you do wish to use some sealant, use Yamabond.

If you use the wrong bolts on the case halves, that can cause a coolant leak. Too long of a bolt will bottom out before it tightens.
Click to expand...

I had the bolts stuck through a sheet of cardboard so that it matched the profile of the bolt pattern in the cases.
 
barossi73 said:
If its coolant in cylinder its most likely orings.id bet 1 has jumped out slightly when head has seated.took me a couple attempts and some careful stretching to get mine to sit still long enough to clamp down.check the oring grooves carefully for any grit.if you do take cylinder back off for base gasket, check the studs are tight before reassemble.did you torque correctly the head nuts or go by 'feel'?
Click to expand...

O-rings are new and well seated when I pulled the head. It seems the coolant would get pulled into the cylinder just like the fuel charge, even if the leak was below the combustion chamber. I will double check for debris.

I torque the head nuts to spec.
 
Was your original reason for rebuilding because engine needed a freshen or was there a 'blowup'? just wondering if it had been overheated or melted itself if the head/cyl could have a crack etc
 
barossi73 said:
Was your original reason for rebuilding because engine needed a freshen or was there a 'blowup'? just wondering if it had been overheated or melted itself if the head/cyl could have a crack etc
Click to expand...

I needed to replace transmission parts. There is another thread on the transmission.
 
Replaced the base gasket and put the top end back together. I saw no evidence of a leak at the base gasket. I left the crank case drain out, filled the coolant system and coolant is dripping out of the drain. So, the cases are coming apart again. Just lucky, I guess.
 
Bummer. Try re-tightening the case bolts.

I have a new center gasket you can have.
Lemme know.
 
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