Top end shot - need advice

[jharvey1984]

Hi all. Long time lurker, first time poster.
I finally bought my first stand up ski earlier this year (2009 superjet). The guy I bought it from had only had it for one summer and only ridden a handful of times (it was his first stand up and it was "too much for him" which is why he was selling). According to him he was the second owner (bought from the original owner). It has a factory b pipe, protec half girdle, blowsion arrestors, msd ignition, etc. but he also mentioned to me that the original owner had some group k work done (he didn't have any documentation or anything but there was a group k sleeper sticker on it so I assumed that might have been the kit that was used). The guy said he had always run pump gas (92 octane). Ski had great compression (185 psi in both holes) when I bought it and ran like a scalded dog. I used it probably a dozen times this summer with no problems until recently. It started running really rough (like it was on one cylinder) so I did all the normal stuff (new plugs, etc.) but that didn't fix it. Did another compression test and this time the rear cylinder wouldn't build compression (barely moved the needed on the compression gauge - still 185 psi on the front cylinder). Pulled the head and found this mess.



Broken ring, partially melted piston (all right at the exhaust port side of the piston). The head is shot too as the broken piece of the ring got smashed around inside the combustion chamber.

I did some measuring with calipers and it turns out this thing was a 760. The internal cylinder bore was about 84.5 mm. The top of the piston also had a 50 stamped on it which I'm assuming is .5 mm over 84 mm? So now I'm thinking the group k mod was really a big bore "hammer" kit, which according to their website includes the following and requires running 96 octane:

HAMMER" 96 OCTANE kit components
Cylinder porting & decking
Cylinder boring, hone, & chamfering (one oversize)
Cylinder head modification
Carb boring & circuit upgrade
Hammer cooling system upgrade and by-pass
Ignition flywheel lightening (-.4 lb.)
Rev limiter modification
Case porting and matching
ENGINE PARTS
"Factory pipe" exhaust pipe with exhaust manifold (all models)
Boyesen reed stuffers
R&D flame arrestor
753cc - 781cc Sleeve & Big Bore Kit (All)
Cylinder boring, Porting, Modify cylinder head dome, Piston Assemblies, Gaskets, Bore cylinder & install sleeves (send cylinder, cylinder head, and top case)

I've got a couple of questions and also looking for what to do going forward:
- Could running pump gas (92 octane) with this mod be what caused my failure or is there something else going on that I need to remedy prior to repair?
- How can I get this thing back together? As you can see from the pics above the head is shot. I have purchased a stock head but according to the above group k documentation the head would have been modified during the kit install. I'm assuming I would need to send the new head to group k to have similar work done? I'm also unsure about which gaskets to use on the head and cylinders...
- The cylinder walls look great - I haven't measured them out yet but assuming they are all in round/in spec/etc. could i just drop a new set of same size pistons in after a good cylinder hone (not do an overbore?)
- anything else I haven't considered?

Thanks in advance for any advice. By the way - i am strictly a recreational rider if that matters

 

[fastgtfairlane]

looks like a crank or rod bearing is starting to let go and went through your top end. probably sat with moisture in it for a bit. 84mm is the stock bore for a 760 so the .5 would me .5mm oversize. theres no way that piston came apart like that and didnt do any cylinder wall damage. if it were me id probably send it back to group k since they did the work on it originally and should have documentation on it. i would be prepared for a full rebuild including a crank. if the head has removable domes, you could just replace the bad dome and run the head. otherwise just upgrade to a ada girdled head. with the 61x cylinder youll definitely want to run a head girdle with a high compression head as the 61x cylinder is a very thin casting and are known to crack below the transfer ports on the front corner of the intake side of the cylinder.

 

[Big Kahuna]

looking at the shape, I would bet that was part of the piston ring that broke off and started bouncing around. Either way, time for full rebuild and crank inspection at the least. Any reputable builder could fix this. You are in Soddy Daisy, there are plenty of guys that ride up there that could help you out Kevin Rowe, Dustin Higden. Paul Lehr @Jr. is just 2 hours south of you (LPW). He could do all the machine work and supply you with the parts.

 

[Sparkplug]

I've seen multiple engines grenade pistons and the cylinder be fine. Literally at least 50 in my years.

High octane is only needed when high compression combines with long bursts of wot. You can run a engine that has 230 psi on 91 octane if you never hold the throttle wide open for more than a few seconds. I run my dasa 1100 10mm stroke 185 psi on 91. With ethanol no less. And it's totally fine.

I'd lean towards a bearing on the bottom end failing also. Complete tear down and inspection according to a fsm is in order.

Sent from my SM-G970U using Tapatalk

 

[jharvey1984]

Thanks guys - looks like ill be pulling and splitting the cases. Was hoping to not do that but if thats what needs to happen then thats what I'll do. Just curious what makes yall think it is a bottom end problem? Once i pulled the jugs and pistons i rotated the crank by hand - it feels/sounds good and there is no excessive play anywhere in the rods...

 

[kevbo]

Look at the bearings carefully. Its the thin retainer material that fails and that metal goes through the top of the engine. A little rust grinds through the retainers very quickly. High rpm also overloads these thin retainers and cause premature failure. You got the retail end of a bad tune with probably bad maintenance from previous owners.

 

[jharvey1984]

Look at the bearings carefully. Its the thin retainer material that fails and that metal goes through the top of the engine. A little rust grinds through the retainers very quickly. High rpm also overloads these thin retainers and cause premature failure. You got the retail end of a bad tune with probably bad maintenance from previous owners.

Ok thanks. What do you mean about bad tune? Like rev limiter too high?

 

[kevbo]

A high or even no rev limit will lower the life of nearly everything by a lot. It is possible that you got poorly made parts that failed sooner than expected. Manufactures sell everything be it good or bad. Rust is another thing that can happen with a little carelessness from an owner that greatly lowers the life of bearings. This is why I consider used ski engines as mostly garbage.

 

[Sparkplug]

Spinning by hand isn't 7k rpm. Kinda pointless to test bearings by feel like that. I've replaced many people thought were good.

Alot of times when the crank goes, it does that to the head and piston. Very possible it didn't. But why would you even take the chance. It's some Yamabond and time to check it out.

Sent from my SM-G970U using Tapatalk

 

[jharvey1984]

Ok guys I pulled the engine this morning and found a chewed up cold fusion coupling. I haven't disassembled the engine yet (that's next on the list) but curious if this could be a symptom or a consequence of the top end failure. Maybe engine misalignment caused crank bearing failure which is what a couple of yall pointed to as potentially what started all this.

These are pics of the engine side coupling:


And here are some pics of the pump side coupling:


And one of the plastic/rubber damper:


Adding a new coupling to the list of things to do - what is the advantage of this cold fusion coupler over a stock one. With this being a big bore, etc. does it need a stronger aftermarket coupling such as this one.

Sorry for all the newb questions. I am new to stand ups and Yamahas but a fairly competent mechanic otherwise. I bagged/tagged each of the four engine mount shim packs to reinstall but thinking alignment may need to be checked after seeing this. Is checking alignment with the cold fusion coupler the same as the OEM coupler which is covered in the manual?

Thanks again in advance for all yalls help. Looking forward to getting this thing put back together (correctly) and enjoying it for several years to come.

 

[jharvey1984]

Well just realized third pic is above post is pump side. Not sure how to edit posts...

 

[jharvey1984]

Ok so just to close the loop on this. I met with Paul Lehr this morning and he inspected everything. Found that the rear seal carrier “collar” on the crank was spun which caused an air leak and leaned out the rear cylinder. Got a new crank from him and he’s doing all the machine work to get me back on the water. Thanks everyone for the input.

 

[E350]

Your photos, observations, questions and narratives are top notch. Is it rude of me to ask you to continue this thread by documenting your rebuild as well?

You should see "Report Edit Delete" on the bottom left of each of your posts.

 

[jharvey1984]

Your photos, observations, questions and narratives are top notch. Is it rude of me to ask you to continue this thread by documenting your rebuild as well?

You should see "Report Edit Delete" on the bottom left of each of your posts.

Thanks 350. I see the edit button now lol. I will keep updating as it goes on. Going to be end of September to get parts back from Paul at the earliest and I’m a nuke worker going into outage season so will take some time but I’ll get it done eventually.

 

[fastgtfairlane]

Paul will do you solid and does excellent work

 

[Sparkplug]

Another thing people will probably Hate on me for. I run the oem yahama couplers with the oem dampener. As far as I'm concerned the am ones are total garbage. My 1100 has a waverunner green coupler on it with a oem used dampener. Extremely low vibration.

The only time people break couplers is when the mounts break and you slam your engine into your midshaft.

Sent from my SM-G970U using Tapatalk

 

[kevbo]

OEM Superjet couplers will occasionally break an ear off, it can make a mess of your mid shaft. I wouldn't use them. We haven't broken a three cylinder coupler yet.