35 GTR
Stage 3... Bps parts
250 hrs

I've got some vibration issues... Cracked case cover, top of mikuni cover broke off, broke oil cooler mount, cracked fuel pump bracket, cracked exhaust bracket where it mounts to the case, hand gets numb after 10 minutes of running

The vibration isnt very noticeable... It's not like the thing is bouncing all over the place. Matter of fact I didn't think I had a vibration problem at all until I cracked the sump and found all the other cracks. So it's gotta be some high frequency vibration. Checked the motor and everything looks fine, clutch assembly, drive shaft, planetary all appear to be running true. No noticeable change when in neutral, in gear, or throughout the rpm range. At idle in neutral the tiller bounces slightly and when I grab it you can feel and see the high frequency vibration in my arm... arm Looks like jiggling jello... But this could be normal, I just don't have anything to compare to.

Prop is in great condition, hardly worn, but I'll have this checked for balance anyway just to rule it out.

Here's the question. Has anyone tried balancing the internals...crank, c-rods, piston, cam, flywheel? and what's the chances my vibration is coming from this? I got the motor on the bench right now with the case cover off but was thinking i might want to do a full disassembly while I'm here and balance the guts.... before I order a new cover and crack it again

Anyone got some insight?

Just because a prop is in great condition doesn't mean it's balanced. I'd get it checked for sure

Agreed... It'll be checked ASAP. I hope it is the prop, pretty easy fix

What's the chances this could cause it? Custom skeg but it's deeper and the torque tab is bigger than stock. Could be causing cavitation? Didn't seem to run any different when I put it on. Been on there for 200 hours.

It's the out drive all the weight is on the crank clutch reverse and drive belt that's a lot of the problem until you get all that balanced you are spinning your wheels my 2 cents.

So you're saying it's not likely to be coming from the guts... Gotcha. How do I check for balance in the clutch, planetary, belt, and drive shaft when it all checks out visually? Any other method?

I understand this is pointless convo if it's the prop

I'm sure a machine shop could do it

Clutch parts (rotor or disc), belt, and prop are the main causes of vibration with a GTR. Reverse unit, maybe, but more than likely it is one of those three.

Prop checks out... balance was perfect

If worried about Internals then remove the clutch and planetary gears and belt and just let it run on frame and see if it still shakes.

Ya i did that. No change. Crank spins perfectly true. Motor bounces around a little but nothing that looks out of the ordinary, to my untrained eye at least. Been talking to Hoyt, he's sending some shims to tighten the belt. Also sending me a softer belt to try that he says can help with these issues. He's basically saying if everything checks out like it has that it may just be the nature of the beast... slap a new cover on there and let her buck. Apparently the new cover is warrantied for a year. Said if i have another problem within the year to call him and he'll figure out what to do next.

Gotta give it to Hoyt by the way... been a pleasure to work with.

Never hear nothing bad about Hoyt that's for sure!! Hopefully you will get it figured out!
Who done your mods?

Thanks for the good wishes. I installed the mods, parts are all bps. Had to have the heads reworked after about 100 hours... intake valves were warped and leaking pretty bad but bps covered it free of charge. BPS has been pretty good too, a little tough to get on the phone sometimes but they've always done me right when i needed something

It's definitely not the nature of the beast if its still doing it with all that bs reverse stuff hanging off the back of the crank
Stock motors run perfectly smooth with all that bullshit off of them

Sent from my iPhone using

Good luck I played this game for almost 2 years

sent from the marsh

So you're saying there's a chance? What happened after 2 years?

^^^he said unit.

New cast lower unit!

..

Check the compression in each cylinder, one might be weaker than the other.

Or one might be stronger than the other!

Compression was up in the 220's on both cylinders last i checked. I've been getting some dieseling since i had the heads re-worked, which was only about 12 hours ago. Starting to think the crack may have developed as a result of that and maybe not so much the vibration. Anything above 91 octane is tough to get around here... someone know of an additive to increase Octane? Not a big fan of running a hotter motor either though... not sure if that will be an issue.

That's some high compression...

Does this motor have an advanced timing key?

No, never messed with timing

Dieseling can be cause by a couple of things. Your motor could be running too rich and leaving carbon deposit in the combustion chamber that will continue to burn once the engine is turned off and ignite unburnt fuel. You can try running SeaFoam or some sort of cleaner through the engine to clean the deposit and then correct your A/F mixture. Another thing that can cause Dieseling is you can have tiny sharp edges and inside the combustion chamber that stays at a combustable tempature and continues to ignite unburnt fuel. In correct timing can also be the cause of Dieseling in a engine (reason I asked about advance timing key). Also if your fuel does not meet the octane rating needed for your compression ratio it will cause detonatiion and dieseling.

Now on to your question about balancing the rotating assembly. You can not get a true balance due to the design of the journals on the crank shaft on these engines. You can make it better but will never get a true balance.

Timing keys also offset the balance on the rotating assembly. They do help with giving the motor beter throttle responce, but will make you loose on the top end.

Thanks Jamie B. I run SeaFoam through every other tank of gas. I'm open to trying to advance the timing. I'd trade top end for better performance on the bottom anyday... but it sounds like this may make the motor more unbalanced. What's the best way to get a timing key? and I assume the install is a simple process. I probably won't try it until i get everything buttoned up and running "normal" again.

Running a 175 main, and a 25 pilot by the way.

I should also let the motor idle for a minute or two before shutting it down... which i haven't been doing.

Another thought you reminded me of... I havn't adjusted the A/F mixture since the recent headwork... I'll definately do this.

I wouldnt run the timing key if you cant purchas 93 octane.

I'm some what thinking with his compression, he might can actually retard the timing a tad to get the peak pressure far enough past TDC to correct it.