Rebuild Struggles

[Mayor118]

What I meant was 36cc is 36cc..........won't matter on the brand, or even the squish band for that matter. If it's 36cc on a 701, it should only make around 175psi. So that's sort of wierd.

I had to have the cylinders machine for a one over. The rear piston started to mark the walls and get hot. The believed root cause was the rear crank seal.

It’s interesting this ski never had a rebuilt and the original owner owns a Yamaha dealer where I purchased it.

I guess the overall question is changing out the pistons x1 and having the engine machined for those could change my compression values to push me into race fuel?

 

[Myself]

I've seen the Pro-x pistons raise compression. I've also seen the Wiseco 'Pro-Lite' series pistons raise compression. I personally have NOT seen that with any other brand. Just going oversize on the bore doesn't affect compression too much to even matter........unless it's a 'big bore' setup.......then EVERYTHING changes!

 

[Mayor118]

Ran a tank of avgas through for break in. Boat seems solid with some small carb adjustments.

However I’m getting some vibrations when at low idle (no wake zone) that seem much different then before. You can also feel it slightly in the bars on plane. It’s been all winter since I have been on it but it doesn’t feel right.

The boat has new motor mounts which I used the original shim locations along with a new mid shaft which I also used the factory shim locations. When changing alignment as per the manual everything seems to be aligned. I pulled the plugs and checked different points throughout as I rotated. It’s hard to get anything in there but confident it’s good.

Then pulled the ride plate and went through the bolts on the pump. Again all seems correct. Just doesn’t feel right in my gut and I have seen skis misaligned shake themselves apart.

 

[Mayor118]

I've seen the Pro-x pistons raise compression. I've also seen the Wiseco 'Pro-Lite' series pistons raise compression. I personally have NOT seen that with any other brand. Just going oversize on the bore doesn't affect compression too much to even matter........unless it's a 'big bore' setup.......then EVERYTHING changes!

These are Pro-x pistons on the fresh build. Will check the compression again after the tank I ran. Avgas was not as much as I thought so if it’s still high I might just run it all season.

 

[Mayor118]

spent some time on the ski today. Still seems like I have a vibration on the low end side. Decided to run without the hood and see what’s going on. The entire engine seems to be shaking to the point the flame arresters are slightly blurry from the vibration.

Something is definitely not correct.

Where should I start because I believe the couplers are positioned correctly.

Try and move shims around at the motor mount and test ride?

 

[Myself]

Those hard vibrations are always in the driveshaft or pump.

 

[joeschuit]

If the motor is shaking like that, it sounds more like the idle and/or low speed mixture is off and is running rough till it gets past it. If you really want to narrow it down you can remove the midshaft housing temporarily and run it motor only to see if the shakes go away.

 

[Mayor118]

If the motor is shaking like that, it sounds more like the idle and/or low speed mixture is off and is running rough till it gets past it. If you really want to narrow it down you can remove the midshaft housing temporarily and run it motor only to see if the shakes go away.

Thank you for the details!

First ride was a definite rough running and worked to remove that. It seems now that the power is good throughout. Had two other stand up riders with motor building experience take a rip and we worked thought the tuning. They didn’t comment on anything I’m feeling. I also was focused more on the tuning if that makes sense. Pushed another tank of avgas through and I just have this feeling it’s not correct. That’s only two tanks on the build.

I hoping I can get a qualified opinion next time I ride with that group at the lake. In the meantime, maybe I’ll try your idea and see if that narrows down the issue. It’s a strong boat. I just concerned about pushing it.

I have the coupler cover off. And that seemed to get really hot.. it could all be in my head. I’m not sure.

 

[Myself]

The coupler was hot because something is binding, bent, etc.

 

[Mayor118]

The coupler was hot because something is binding, bent, etc.

I checked alignment again at 10 points on the coupler and it seems perfect (some pictures).
Then used the caliper to mark a square I had laying around. Can’t really measure that location well. Based on the findings it looks like I’m slightly over the 2-4mm.

Would this account for the vibration I’m feeling. With the plugs out everything is free and the mid shaft is new but aftermarket.

If so my solve would be to have the mid shaft repressed to fall into the factory tolerance? Do you think I’m tracking right in the thinking here?

 

[WFO Speedracer]

How did you handle the engine alignment when you put it back in ?

A lot of people think you align the couplers with the dampener in place , you most defiantly don't , you remove it , what happens if you leave it in, well the dampener tries to pull it into alignment , defeating the whole purpose of aligning it , align the coupler using the proper shims , mark where everything goes then install the dampener and the shims in their correct location .

On a Yamaha really you have to start with the pump and the midshaft alignment tool , get the driveshaft aligned properly and lock that down, then install the midshaft and get it locked down and sealed to the hull , then align the engine to the midshaft , I know , I know , I hate the way Yamaha designed this but if you want right that is your only option to get it there.

The only thing worse than aligning a Yamaha setup is aligning a 440 Kawasaki setup.

 

[Mayor118]

I marked everything as I pulled the engine out before the rebuild. All shims went back to the same location. Two things were changed going back in since I had to replace my motor mounts and also the mid shaft. I used the same shim location for the mid shaft.

I’m hearing you say this…

Buy alignment tool
Align shaft
Align coupler with correct shim locations
If correct remove and add in damper
Bolt up and recheck
Go rip.

Any insight into my coupler gap. Is that a mid shaft press issue or maybe the alignment is causing a consistent larger than spec gap?

Sorry for all the questions. It’s hard having a ski so close to being done and really not trusting it.

 

[WFO Speedracer]

I marked everything as I pulled the engine out before the rebuild. All shims went back to the same location. Two things were changed going back in since I had to replace my motor mounts and also the mid shaft. I used the same shim location for the mid shaft.

I’m hearing you say this…

Buy alignment tool
Align shaft
Align coupler with correct shim locations
If correct remove and add in damper
Bolt up and recheck
Go rip.

Any insight into my coupler gap. Is that a mid shaft press issue or maybe the alignment is causing a consistent larger than spec gap?

Sorry for all the questions. It’s hard having a ski so close to being done and really not trusting it.

Alignment and gap are two totally separate issues , yes you have the sequence correct , I would say if you replaced mounts and the midshaft most likely given the symptoms you described , the couplers being hot and weird vibrations in the driveline that is no longer in alignment.

 

[Mayor118]

For the alignment tool is there a specific brand?

 

[WFO Speedracer]

Cold fusion used to be the brand but I believe they are out of business , I got mine from here :

https://weeksbrothers.com/product/drive-shaft-alignment-tool-yamaha/

I think that's the one you need just check to be sure .

 

[Mayor118]

The alignment went well and the vibration went away after some further carb adjustment. Over all the ski is running well and put a few tanks through during the holiday.

This was a big test of my skill set and the information provided here really helped me throughout. Wanted to thank each of you for the support and keeping a 25 year old SJ on the water.

She lives again!

 

[WFO Speedracer]

Great news and congradulations !