Blaster 94 wave blaster one cylinder has 128 psi , the other zero compression, any ideas why?

[n8r]

Hi, I just picked up a 94 Yamaha wave blaster. I checked the compression with a compression gauge. The rear piston reads around 128 psi ( at 4800 ft altitude) but for some reason the front cylinder reads no compression at all, maybe 1-2 psi. The motor turns over ok and doesnt make any strange metal clunking noises or anything. Sounds ok. When I put my hand above the spark plug hole with the plug removed I can feel air pulsing out the holes pretty good, but when I plug the hole with my finger I can't feel any pressure under my finger. When I checked the compression with the gauge I did it several times and made sure it was screwed tight to make sure it wasnt a faulty reading. Same results every time. I looked at the top of the piston with a flashlight and could see no evidence of any hole in the piston. I could see some streak marks on the cylinder walls but not gouging or scraping. It just looked like surface streaks.

Does anyone have any ideas as to why it would be reading basically zero compression in the one cylinder? shouldn't it be reading at least 10 or more psi if there was no hole in the piston even if the rings are toast? The top of the piston was covered in carbon. I'm assuming the next step is to remove the head and inspect inside, but I wanted to at least see if it might be something simple I'm over looking like reeds or something before I go pulling the motor apart. I don't know much about these Yamaha 701 motors. What would be the recommended rebuild that I should do? If the piston looks ok can I just re-ring and hone the one cylinder, or is there more than that I need to do to fix the motor properly? Thanks for any help or ideas

 

[ChrisFiore15]

Just pull the head off..
And check out whats going on in there..
Could be a blown out head gasket..
could be a chunk of piston missing, could be a lot of things..
Take those bolts out and yank that head off, post photos up here.

 

[n8r]

Just pull the head off..
And check out whats going on in there..
Could be a blown out head gasket..
could be a chunk of piston missing, could be a lot of things..
Take those bolts out and yank that head off, post photos up here.

Ok pulled the head off. The front cylinder and piston are toast. That explains the zero compression. It's obvious to me that it overheated and seized. The rod and bottom end look clean and there are no signs of any crap falling down in there. Do I need to go into the bottom end, or is there a way I can flush it out without taking it apart just to make sure nothing got down there? I noticed there was some sand inside the cylinder walls where the water flows through that had accumulated in the bottom of the jug. Also There was some sand and some small bb or smaller sized pebbles inside the big rubber water hose that goes around the outside of the exhaust pipe. I'm wondering if maybe the cooling system might have got plugged and caused it to over heat. The only thing is that the rear cylinder and piston didn't look too bad to me. What would cause just the front cylinder to overheat and seize? One last thing: my water box has a crack in it and is all black inside full of carbon. Is this normal to look like this and is that extremely bad if the water box is cracked at the top? THanks

 

[n8r]

What do I need to do as far as rebuilding this top end? Can I reuse the cylinder, get it resleeved, or do I need a new jug? I figure it's best to get a complete top end rebuild for both cylinders. Any ideas how much I can expect to spend and the best place to get parts. Thanks

 

[charliebcd]

I am in the same boat as you are! I was wondering if you were running pre mix or do you have any of your water lines popped off? i think my was running on a wrong premix or wasn't jetted properly for the elevation i am running.

 

[n8r]

I am in the same boat as you are! I was wondering if you were running pre mix or do you have any of your water lines popped off? i think my was running on a wrong premix or wasn't jetted properly for the elevation i am running.

I have never had the ski running. I just bought it yesterday as a project to get running. I will definitly check the water lines. Im also going to shoot pressurize water through the whole cooling sytem to make sure nothing is clogged. It looks like some small pebbles were sucked in to the water that cools the exhaust

 

[550/440]

Lots of possibilities as to why that failed. Crank seals, lean front carb, crank bearing coming apart, water ingestion, etc. There are some good places to pick up replacement parts, but the best thing you can do is find a competent mechanic in your area that will work with you to get your engine back together. Definitely replace the crank seals and check all the crank bearings prior to setting a new top end on there.

 

[Jpass]

Mine did the same thing last year only I holed a piston due to rear crank seal leak and apparently a loose spark plug. I pulled the motor and had my mechanic replace the seals in the cases. The cylinder were bored and ported. New pistons, rings, gaskets and a bunch of other stuff. I think I paid $800 for the job. Compression was pushing 200psi right after the rebuild. I am now at 185-190 with about 10 hours on it. She runs like a champ, but needs high test with a splash of race fuel until the compression comes down a little more.

 

[PAVLOS]

Usually its the back piston that gets baked the reson why ???? (I have never found out 18 years now) the sand in your cylinders is ok its normal for all skis that ride in the surf,the crack in the water box is also ok it happens often to all b1s (why the b1 61x and not the sj 61x an other query) any way from what I can see from your pics is overheating !!!!! check the little tube thats located on the cylinder head in the front that goes to the exhaust chaber,if its packed with sand then maybe hot water is trapped there causing the front cylinder overheating.

Good luck