Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
you have had something bouncing around in there. part of a bearing cage, something.
Running on 1.5 cylinders
- Thread starter SuperJet-Dave
- Start date
- Location
- Rochester, NY
The piston sleeve has no marks whatsoever. If something was bouncing around you would think the sleeve would have some marks?? Not really sure what is going on there with the “good” cylinder
My money is on the head already being damaged prior to the last top end replacement. Possibly even used off ebay or something. That would explain the dome damage while the pistons/bore are fine.
- Location
- Rochester, NY
Did swap in the carbs from my other SJ. Problem stayed the same. At least now I feel I can 100% eliminate the carbs as the issue.
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
- Location
- Los Gatos, CA
Look again, the piston head had matching marks. Something was or still is bouncing around in there.
Piece of spark plug porcelain, piece of big end rod bearing, ball bearing cage, etc.
It may have already passed out the exhaust but I would want to know where it came from.
I don't know that particular head but it seems like it should have some kind of gasket?
- Location
- Rochester, NY
I cannot see any loose piece that might be bouncing around. I blew air and vacuumed the piston area. Nothing?? As you said it could have already exited. Still weird that there are no marks on the piston sleeve wall. Not sure I will ever find out what is was :-(
And this is the cylinder that is performing well!
Still am no farther in determining what is wrong with the other cylinder.
I have new orings coming. Planning to use them and ultra black RTV to seal it back up and see if there is any difference. Seems like others are not using a gasket with this head. Anyone have thoughts on if this is ok?
They don't use a gasket, oring seals the combustion chamber and rtv seals the outer water jacket. Your compression numbers are way off on that engine, should be 185 ish. Dents in the dome out at the edge can compress the ring land and keep the ring from expanding/contracting. I guess the debri could of come from the other cylinder, and got pushed back in the other cylinder on the exhaust pulse ( long shot)...... The cylinder should be pulled and crank and Pistons inspected. split the cases to inspect both sides of the crank bearings...
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
Dave. Start at the top of the carbs. Are there any bolts missing from the flame arrestor adapters. Any chunks missing from the flame arrestors. Look at the butterflies, are both screws there? Remove intake, Are all the screws there for the reed pedals. If you do not find anything. Then you need to pull your cylinder and inspect the wrist pin bearings. If nothing there, split your cases and pull your crank and inspect every bearing for damage.
You have had some FOD (Foreign Object Damage). It came from somewhere, and I doubt it got sucked up by the air intakes.
What ever caused that damage bounced around for a few RPM's then got spit out. You most likely are not going to find what it is laying on the piston. You might find more like it in the bottom of the cases. I would advise not running your motor until you have gone through everything.
You have had some FOD (Foreign Object Damage). It came from somewhere, and I doubt it got sucked up by the air intakes.
What ever caused that damage bounced around for a few RPM's then got spit out. You most likely are not going to find what it is laying on the piston. You might find more like it in the bottom of the cases. I would advise not running your motor until you have gone through everything.
- Location
- Rochester, NY
I put in the new orings and sealed the head with RTV. Compression in both cylinders is now 170 psi. It still does not run on the rear cylinder only (it does run on the front cylinder only) I gave it a quick test ride, and it ran a little better, but basically the same really.
I pulled the head again to check.
See the pic.
(1) The front head has noticeable buildup (I assume carbon) where the rear does not. Any idea if this points to a problem with the rear cylinder?
(2) Also notice the small damage on the edge of the rear piston head. If the “F” is 12 o’clock, the small damage is at 3 o’clock. This was there before. Could this cause enough to weaken the performance of the rear cylinder?
If no other suggestions come up, I think my next step will need to be to tear down the motor as you guys have suggested. Just out of my expertise at this point :-($
After test ride:
Before test ride:
I pulled the head again to check.
See the pic.
(1) The front head has noticeable buildup (I assume carbon) where the rear does not. Any idea if this points to a problem with the rear cylinder?
(2) Also notice the small damage on the edge of the rear piston head. If the “F” is 12 o’clock, the small damage is at 3 o’clock. This was there before. Could this cause enough to weaken the performance of the rear cylinder?
If no other suggestions come up, I think my next step will need to be to tear down the motor as you guys have suggested. Just out of my expertise at this point :-($
After test ride:
Before test ride:
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
You have had stuff bouncing around in that one as well, not as much.
For a ski to run, you have to have fuel, fire, and oxygen. If you have a cylinder that is not firing, you have a bad coil wire or plug. or you have a fuel issue. You have good compression. But this only amounts to the bore being good from top of the exhaust port to when the piston is at TDC. But you could have something cracked below that effecting the flow of your air fuel mixture. Pull the cylinder.
Also, that chunk missing on the intake side is not good. Usually it would be on the exhaust side if you had a major heat issue. right at the bottom left of last pic, by the threads. it looks like something has happened right at the edge.
For a ski to run, you have to have fuel, fire, and oxygen. If you have a cylinder that is not firing, you have a bad coil wire or plug. or you have a fuel issue. You have good compression. But this only amounts to the bore being good from top of the exhaust port to when the piston is at TDC. But you could have something cracked below that effecting the flow of your air fuel mixture. Pull the cylinder.
Also, that chunk missing on the intake side is not good. Usually it would be on the exhaust side if you had a major heat issue. right at the bottom left of last pic, by the threads. it looks like something has happened right at the edge.
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
Also, on your front piston, where you have those dings in the dome and pistons. Those will become hot spots......... at least try and sand them down some.
- Location
- Rochester, NY
Holy crap. There is a piston eating monster in my motor. The crumbs must be somewhere? In the crank? How could it function if all that piston metal is in it?
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
Damn.... your lucky that mess did not cause any more damage!
- Location
- Rochester, NY
I guess I should have called this thread “running on 1.5 pistons”.
Guessing I need to pull the motor and make sure the crank shaft is not damaged and is clean of metal particles, then replace the piston(s). I am new to getting inside a motor. Any helpful steps I should know about?
What piston brand? How do I determine the size? Should I a get a kit, or can the rings, etc be reused? Should I replace both pistons, or just the damaged one?
Sorry for all the questions, never done this before...
Also, any idea what caused this?.. and is the new piston going to have the same destiny?
Guessing I need to pull the motor and make sure the crank shaft is not damaged and is clean of metal particles, then replace the piston(s). I am new to getting inside a motor. Any helpful steps I should know about?
What piston brand? How do I determine the size? Should I a get a kit, or can the rings, etc be reused? Should I replace both pistons, or just the damaged one?
Sorry for all the questions, never done this before...
Also, any idea what caused this?.. and is the new piston going to have the same destiny?
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
Please go to Tech Faq section. There are several threads on this.
- Location
- Los Gatos, CA
Holy crap!! I have no idea how the piston skirt left the motor and did not cause more damage.
I recommend OEM or Pro-X pistons. Pro-X is a bit less expensive but the parts (piston casting and rings) are from the same factory as OEM.
You should replace both pistons, rings, wrist pins, circlips and wrist pins bearings. The piston kit will come with those parts.
Here is one example minus the bearings, around $110 per piston kit which is really good for OE Japanese hardware. Jetmaniac on this forum can get you all the parts including gaskets.
https://www.blowsion.com/pro-x-pistons-yamaha
You need to confirm the bores are good and were not damaged. And have them measured to confirm in spec so you can use stock size pistons, or if damaged or out of spec have them bored and matched to larger pistons.
Given how much foreign material moved through there it's probably worth a full teardown to confirm the crank is OK.
Should check the reeds while you are in there since that could also cause the poor running condition.
I recommend OEM or Pro-X pistons. Pro-X is a bit less expensive but the parts (piston casting and rings) are from the same factory as OEM.
You should replace both pistons, rings, wrist pins, circlips and wrist pins bearings. The piston kit will come with those parts.
Here is one example minus the bearings, around $110 per piston kit which is really good for OE Japanese hardware. Jetmaniac on this forum can get you all the parts including gaskets.
https://www.blowsion.com/pro-x-pistons-yamaha
You need to confirm the bores are good and were not damaged. And have them measured to confirm in spec so you can use stock size pistons, or if damaged or out of spec have them bored and matched to larger pistons.
Given how much foreign material moved through there it's probably worth a full teardown to confirm the crank is OK.
Should check the reeds while you are in there since that could also cause the poor running condition.
- Location
- Rochester, NY
Put in new Pro X pistons. Looks great compared to the mess I had. 180 psi in each cylinder. Motor starts and runs on one cylinder. Same for each cylinder! Yeah!
Thanks everyone for all the help on this one.
Thanks everyone for all the help on this one.
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
Still running on 1 cylinder? Did you pull the cases and inspect?
He meant it could run on either cylinder now. before it could only run on one, the other was doing nothing. Now when he pulls either plug it runs, albeit like poop. Both cylinder are firing normally now.