Front cylinder O rink keeps going

[DaveRoeser]

I have taken of the head 4 times now. The front cylinder O ring was blown and a head bolt broken off. O have tried replacing the O ring and even tried liquid gasket. Compression all the way up to 150, runs great for 5 minutes than dies and won't run. Rechecking the compression, its down to 25.

Think it might a water cooling problem with the front cylinder? Oil injection problem. Could it be heat cooking the front seals?

I have drilled out the broken bolt and replaced. Looking for clues.

 

[kustomkarl]

It's possible that the front head might be warped and not sealing to good. I would have it checked for warpage.

Karl

 

[derek]

replace the cylinder. 650 jugs are pretty cheap. just be sure you get the right one. last 3 numbers on casting number are 380 for a 650-382 for a 650x. you probably have a flaw in the o-ring groove.

 

[DaveRoeser]

replaced the broken head bolts, but the seal blew on the front cylinder again but at a 90 degree angle from where it has blown times before.

I'm thinking this cylinder is getting hotter than the other and a melt down occurs. It appears that water is clear to flow in the manifold above the cylinders. Oil is injected before the carbs, so it's not an oil problem.

The dome has some dings in it. When I fixed the head O ring the last time I had compression up to 150. Would replacing the cylinder be the problem???

Thanks for your help.

 

[derek]

check the o-ring groove in cyl carefully. make sure all water passages are clean. pull the exhaust manifold off the ski. the water hole below the exhaust outlet is where the cyl gets water from. if somebody got a little overzealous with rtv silicone, the hole could be partly or fully sealed shut. now, with head and exhaust manifold off, take a 1/4 inch drill bit and put it into the water hole on cyl below exhaust outlet. spin it around and it will clean out the passages. one to the front and one to the back of the hole. turn engine so the piston is all-way up and pour water into cooling passage around the piston. use a funnel. pour slow. don't get it into the motor. it should run right out the water hole you just cleaned. in fact, try it before you clean passage to see if it changes. now take the exhaust pipe. the big water hose hole goes straight to the 2 water holes that cool the motor. blow in the hose hole and you should be able to seal off both holes on top with your fingers. seal one at a time and you should feel no resistance through each hole. at this point you have pretty well checked out the water system for your engine. let us know how it worked. good luck. but we make our own luck.

 

[DaveRoeser]

Piston maybe hitting head.

I just had a friend look at the domed head and he thought the piston was rising a hair to far and striking the head causing the problem and the dings.
We looked at the pistons and it sure looks like the one is a hair to high on the up stroke.

Could be a issue with the piston arm connection. He was advising to have the dome milled out so the piston fit inside again. Otherwise take the motor apart and see if piston arm is problem.

What does anyone think of those ideas?

 

[robin savell lloyd]

I believe that when working with any moving parts inside of the engine you should know for a fact what the probblem is and not try and compremise by milling the one head to fix the extra throw. I would think that this engine will soon fail if one piston is traveling higher or it will be out of ballance and premature falure may accure. fix the problem do not make it worse. good luck Robin :cheers:

 

[derek]

the piston can not go up too far. if something starts to fail it would not go up as far as a bearing is failing. put the pistons at the midpoint of travel and turn crank back and forth. does either piston stay still at all while the other moves? even the tiniest bit? if so you need a crank. means you need a motor. wait, this is a 650. read the part numbers on the cylinders. last 3 numbers are both 380 or 382? or do you have one of each? 382 is a 650x motor jug. 380 is 650. diff is 382 cyl is 1 mm taller to keep piston and top ring down inside cylinder to keep ring from burning away. if they are mixed you need to get a pair that match. i have 1 .5 mm over 380 jug i don't need. i know a guy with a decent set of standard cyls. pretty sure they are 650-non-x. wants $50 for the pair. the heads are also 1 mm different to compensate. there is a 1 mm ridge between combustion chamber edge and seal surface. on 650x head, chamber comes down flush with edge of o-ring surface. but if you have 2 different jugs, one is holding the head up higher than the other forcing the head to be at an angle.

 

[derek]

cyl part numbers are easy to read on the pto cyl. right on back above pto. the front one is hard, but if you look right above the rotary valve you should be able to read the last number whether it is a 2 or a 0. i bet your front one is a 380 and rear one is 382.

 

[robin savell lloyd]

cyl part numbers are easy to read on the pto cyl. right on back above pto. the front one is hard, but if you look right above the rotary valve you should be able to read the last number whether it is a 2 or a 0. i bet your front one is a 380 and rear one is 382.

Very good point Derek. With out knowing the history of this ski any thing is possable. Could of had shade tree mechanics like us working on it before. :rofl:

 

[DaveRoeser]

The ski is still on the lift, but I was able to check out the rear number, 382.

I bought it from a shadetree mechanic who worked out of his home in Northwest nowhere, Wisconsin. He told me the owner had run it out of oil, and he repaired the engine. It has been running fine for 3 years.

Once my boys return my boat, I'll tow the ski to the launch and bring her home for a cylinder swap. I'll keep you posted.

Thanks a ton!