760 superjet terrible vibration

[superhondaz50]

Have a 760 engine that shakes so bad at idle to 1/4 throttle you can't even see the engine at idle, its just a shakey blur. Any ideas where to start, coupler is aligned the best I can get (engine sits) higher than aligned driveshaft. I'm thinking its a bad crank, any ideas? Its causing the venturies to dribble fuel and the ski runs like cr@p.

 

[Ducky]

Check the motor mounts next. If youre motor isnt aligned close to perfect, you need to fix that first so you can rule that out as well.

 

[superhondaz50]

Everything is lined up as good as I can get it...

 

[jo5hi3]

Everything is lined up as good as I can get it...

If the engine coupler is sitting higher than the midshaft coupler, that is your problem.

 

[superhondaz50]

Its only maybe 1-2mm higher. Maybe I'll have the motor mounts machined down.

 

[Ducky]

Its only maybe 1-2mm higher. Maybe I'll have the motor mounts machined down.

Are you using couch mounts? You can machine down the bottom, or egg out the two mounting holes a little bit and push the motor mounts closer to the outside of the hull. This will let your motor sit lower.

 

[superhondaz50]

SJ mounts, holes are so egged out the two rear mounts broke, bought two more and egged them out less, still intact but the engine sits high

 

[Quinc]

I find if my idle is overly rich it will shake like that.

 

[jo5hi3]

SJ mounts, holes are so egged out the two rear mounts broke, bought two more and egged them out less, still intact but the engine sits high

Removed your engine bedplates and open up the holes where they bolt to the cases. Move the bedplates in, this will help lower the motor also.

I find if my idle is overly rich it will shake like that.

His issue is not from being overly rich, its from the motor sitting higher than his midshaft.

 

[superhondaz50]

Alright, I'll see if I can get it lowered over the next few weeks. Gonna order some cold fusion motor mounts too. Maybe they will be a tighter tolerance than the OEM ones.

 

[Ducky]

Alright, I'll see if I can get it lowered over the next few weeks. Gonna order some cold fusion motor mounts too. Maybe they will be a tighter tolerance than the OEM ones.

You might want to consider RHAAS mounts. I know he can make them at different heights.

 

[orangefinger]

was this ski in the water already or just test run on shore ??

 

[superhondaz50]

I'll look into those

 

[superhondaz50]

was this ski in the water already or just test run on shore ??

Both, I think the ski has Parkinsons....

 

[orangefinger]

did u check the impeller, rope around etc.. ??

 

[superhondaz50]

Ya, it's all good down south

 

[augustaf]

Its only maybe 1-2mm higher. Maybe I'll have the motor mounts machined down.

That certainly is sufficient reason for vibration. They need to be of the same heights (exactly), not tilted or twisted in relation to one another.
Should one be a billet aftermarket and the other one oem cast, you may have a hard time aligning them due to difference in diameter.

 

[superhondaz50]

OK, I ordered the rhaas 1/8" lower mounts, those should get me going

 

[Harbor]

Might pull your engine and mid shaft and check your pump alignment. The pump could be out of align in such a way that it prevents nronal engine/coupler alignment

 

[superhondaz50]

Might pull your engine and mid shaft and check your pump alignment. The pump could be out of align in such a way that it prevents nronal engine/coupler alignment

No, the pump and midshaftis perfect, I used the cold fusion alignment tool...