Engine Failure ... double check my analysis

[the MfM]

Symptoms

Port Engine stalled at high speed
Checked safety switches and found rear hatch wasn’t locked

Ran it again and it was fine at idled but stalled at high speed.
This time it wouldn’t turn over.

Let it cool down and it turned over and started.


Figured it was may be lean seizing and or blocked cooling.
Checked Plugs and found the #3 plug had no gap.
Also could see the top of the piston was dented.
Zero compression on #3

So I pulled the engine yesterday.


...to be continued

 

[the MfM]

Here’s what I found

Piston top edge is broken on exhaust side. Otherwise looks OK besides the obvious missing ring and the scratches. And some wear from seizing... oil was working but with zero compression it wasn’t getting any fuel.

Connecting rod looks rusty?

 

[the MfM]

So I just rigged up a block off plate and started by pressure/vac testing the cylinder head cooling. I couldn’t get any pressure/vac readings.

I made a plate for the intake and put a pressure gauge on the #3 cylinder.

Hooked up air pressure to the COOLANT port and immediately got pressure on the gauge in the #3 cylinder hole.

 

[the MfM]

So to me it looks like I have an internal head gasket leak that led to a shattered piston crown when cold water hit the hot piston.

Anyone disagree or see anything else?

Any other tests worth doing before I pull the head?

 

[UnorthodoxCreations]

Seems like pulling the head is inevitable so I'd do that next. Good luck.

 

[Jgorm]

Either bad hg, cracked block, or your block off plate is not sealing. I'd run a leak down test on each cylinder while you turn the engine over (user low psi). You'll know where the leak comes out. Then pull the heads.

 

[the MfM]

Had some time to do a pressure test... good news/bad news...

Ran a constant 5psi into the crank. Was getting air out the coolant line. I sprayed the engine with windex to look for a hairline crack in the block... couldn’t see anything.

BUT I am made the block off plates out of PVC trim boards. Which apparently are very porous. Lots of bubbles coming out of the edge grain.

So I need to get some gasket material and try the tests again.

 

[Jgorm]

I wouldn't stress the leaking board. Hook up 10 psi to each plug hole one by one while you carefully turn the engine over. Realize it might doing for to the pressure. You'll hear it from there intake, then exhaust, and you'll feel the resistance when your in the compression region. That's where you want to see if air is going out sooner place it shouldn't, and if there is a major difference between cylinders.

 

[the MfM]

I wouldn't stress the leaking board. Hook up 10 psi to each plug hole one by one while you carefully turn the engine over. Realize it might doing for to the pressure. You'll hear it from there intake, then exhaust, and you'll feel the resistance when your in the compression region. That's where you want to see if air is going out sooner place it shouldn't, and if there is a major difference between cylinders.

Ok, I get what you’re saying now, I’ll try that tomorrow.

But I’m not sure with the #3 cylinder having 0psi compression what if anything would happen? Though i suppose if air is getting into the coolant line again that would confirm the head gasket?

Thanks

 

[Dan_NC]

I agree with your assessment, likely a head gasket. Start with the cheapest and, if necessary, work your way up (in terms of $$) from there.

 

[the MfM]

I agree with your assessment, likely a head gasket. Start with the cheapest and, if necessary, work your way up (in terms of $$) from there.

It’s tempting to just pull the head and look to see what I see on the gasket. But I’ve got all winter so I’m trying to be methodical and determine the cause. It’s also possible it just caught a ring or the ring locating pin fell out.


Couple other things that I noticed...
Someone has been in this engine before. They used yamabond instead of a gasket on the lower crankcase halves. It’s possible they reused the head gasket.

The pissers have some black/oil staining underneath that I hadn’t noticed before. Though I know you can get some exhaust out of them when running on the hose. Not sure that should be happening when on the water.

 

[Jgorm]

#3 with 0 psi won't help. The other cylinders might help confirm if the block is cracked or it's the hg. It's going to have to come apart for sure.

 

[the MfM]

 

[Weeb]

Ouch. Good luck.

 

[the MfM]

Ouch. Good luck.

Pretty straight forward at this point. Ended up finding a fair bit of sand in the cylinder head around the #3 piston. Probably could have just cleaned the aluminum transfer off and thrown a new piston kit in and been done with it.

But someone else had rebuilt the engine before and reused the old gaskets where they could and yamabond where they couldn’t. So I figured it’s best to split it and put in new seals which were probably 20 years old. Getting the flywheel was a PIA.

I found a good deal on a used cylinder head with pistons that came off a running ski so I’m going to order some new rings and throw it back together.

 

[dabomb6608]

Not sure if I misread, but that is completely normal to see yamabond on crank case halves. The crank case halves don't have any sort of gasket/oring. The only way to seal is with a liquid gasket. I use Threebond 1211 on all of my engine rebuilds to assemble the crankcase. Light coat on mating surfaces and on crank seal lips. Grease on inside (crankshaft side) of crank seals. For the other gaskets, generally speaking the metal gaskets are reusable at least a time or two unless there is obvious damage. Little film of grease on assembly for those.

Sounds like you've got a handle on things though. I've found a little bit of heat and a impact gun help on the flywheel removals. The hammering helps pop them off. Going to cost a pretty dime with 6 carbs but I highly recommend rebuilding all carbs with Genuine Mikuni kits and also doing your Needles/Seats (they aren't included in kits).

 

[the MfM]

Not sure if I misread, but that is completely normal to see yamabond on crank case halves. The crank case halves don't have any sort of gasket/oring. The only way to seal is with a liquid gasket. I use Threebond 1211 on all of my engine rebuilds to assemble the crankcase. Light coat on mating surfaces and on crank seal lips. Grease on inside (crankshaft side) of crank seals. For the other gaskets, generally speaking the metal gaskets are reusable at least a time or two unless there is obvious damage. Little film of grease on assembly for those.

Sounds like you've got a handle on things though. I've found a little bit of heat and a impact gun help on the flywheel removals. The hammering helps pop them off. Going to cost a pretty dime with 6 carbs but I highly recommend rebuilding all carbs with Genuine Mikuni kits and also doing your Needles/Seats (they aren't included in kits).

Thanks, I didn’t realize that there was no gasket for the crankcase halves. The other engine didn’t have any squeeze out so I assumed it was a gasket... Maybe the factory/last person did a neater job applying it. I’ve always used threebond 1184 on two strokes. Not sure what the difference is versus 1211? I know I don’t want anerobic goo.

I did completely rebuild all the carbs before last season with mikuni kits...amazing how much better it started and ran. Probably going to pull the rear carb apart and put a new kit in it just in case. But I now think the sand in the cylinder head caused it to overheat.

 

[WREKS]

@the MfM I quote "But I now think the sand in the cylinder head caused it to overheat." That will do it. When I bought my 2007 SX the sales video showed beaching as the way to enhance the fun. I was having overheats from the beginning. Now I avoid the shallows. Jetboats are bottom feeders. I am not convinced once it is in it can be flushed out. Best in your endeavors!

 

[dabomb6608]

Thanks, I didn’t realize that there was no gasket for the crankcase halves. The other engine didn’t have any squeeze out so I assumed it was a gasket... Maybe the factory/last person did a neater job applying it. I’ve always used threebond 1184 on two strokes. Not sure what the difference is versus 1211? I know I don’t want anerobic goo.

I did completely rebuild all the carbs before last season with mikuni kits...amazing how much better it started and ran. Probably going to pull the rear carb apart and put a new kit in it just in case. But I now think the sand in the cylinder head caused it to overheat.

I agree, the sand is probably a heavy culprit here. Knowing carbs were just rebuilt then if anything at least do a pop off test and open up that rear carb to check fuel pump check valves, inner fuel filter and the needle valve. Just to make sure there isn't a issue there. I don't see any reason to replace parts in them if you don't find a obvious issue.

It's true the difference a fresh/thorough carb rebuild can make. Most issues get covered up because these boats don't get ran like a jetski. Plus they just behave differently due to the added weight/handling natures. Add to that the fact that as performance deteriorates over several years it can go completely unnoticed because it is a gradual change versus a instant change from one day on the lake to the next.

I don't know the difference between 1184 and 1211 either. Years back when I was new to working on skis I was recommended 1211 over on greenhulk.net by some of the "veterans" of the sport at the time. Have rebuilt many engines since then (I run a small jetski repair shop now) and never had any issues. That doesn't mean it is any better or worse then 1184. Probably one of those situations where either one isn't wrong with minor chemical property differences between the two.

 

[the MfM]

Read some old pwc forum threads. Seems half recommend 1211 or the loctite equivalent and half say 1184 (yamabond 4 or Hondabond 4). The Yamaha service manual specs “gasket maker” with no other product specs.

I’m sure any of the above would work but I’m going with threebond 1184 mostly because they call it a crankcase sealant on their product info page and I’m familiar working with it.

1211 is an RTV sealant which doesn’t necessarily have as good fuel resistance. Though it seems plenty of people have had no problems.