major vibration

[wilkin250r]

I bought a Duncan Racing motor on eBay, a PC2000 340cc powervalve, complete with carb and pipe. This thing pulls strong, but it's got a major vibration issue.

I contacted Duncan Racing, and they said it normal to vibrate a little more than stock. Well, this vibration ain't normal...

So what could be the issue? Do you think the guy that built this motor put the counter-balance on wrong?

Perhaps the crank isn't true?

What else can you suggest that would cause this?


And, MOST important, how do I fix it? Am I going to have to throw another $1000 at this engine to get it to run right?

[Pvt. Maggot]

prob the counter balancer berring...or he put it together wrong.

[AtvMxRider]

Originally posted by Pvt. Maggot
prob the counter balancer berring...or he put it together wrong.

[310Rduner]

I would check all the motor mounts if you haven't already.. but i assume you probably already have.

you might just end up having to take split the cases and take a look at the counter-balancer bearings.

Listen for a kind of whistling or whining kind of sound.. exactly what it sounds like when you blow the bearings.. when i blew mine there was NO WAY i didnt notice the sound.. i could hear it almost over the engine reving. If it starts to get like that.. just shut it off immediately.. dont even mess with running it you could get some bad things happening.

When we split my cases.. the bearings litterally rolled out of the housing for the counter-balancer..:eek2:

I Flipping freaked out.. just sitting there counting dollar signs at all the things we found... lol(first time into cases)

[AFTERMARKET]

I was ridding in Glamis and my counter balancer bearings Failed, then the C.B. decided it would like to eat a hole through the entire main case. No vibrations or noise just a loss in power as the seconds went on! This was on my 370 R
The only time I have had vibrations like that is when I broke or snapped a motor mount. Is it a stock frame?

[CBW]

you shouldnt need to "split the cases"--referring to the main center cases---- to check out the counterbalancer.........just take off the clutch side case. Then there is a plate with two bolts in it to the front of the crank...,remove them and rotate the CB until it aligns itself up with the bore -----and it will come out----and you can inspect the bearing directly on the CB,,,,the other bearing is in a holder and is on the stator side and the stator case, and flywheel will need removed to check that bearing in the holder.

But,,,,since you express a severe vibration.......It sounds to me like that whoever put the motor together---(most likely not the motor builder but the previous owner) may have not aligned the "dots" that is stamped in the gears----and it is possible that the CB is out of time with the crank, IE: as the piston goes up......the cb weight goes up also--or anywhere in-between....... and it will vibrate very badly.

Thats just my opnion,,,,,,But who knows,,,,,,,:confused2

[Guy400]

Is it possible to get the counter-balancer installed 180 deg. out? I know when I had my LT I was over at MacDizzy's site and someone was complaining about a vibration problem with a motor they had purchased unseen and come to find out the guy assembled the c-b incorrectly.

[CBW]

Originally posted by Guy400
Is it possible to get the counter-balancer installed 180 deg. out? I know when I had my LT I was over at MacDizzy's site and someone was complaining about a vibration problem with a motor they had purchased unseen and come to find out the guy assembled the c-b incorrectly.


Yes.....and quite easily as a matter of fact....

..............the primary drive gear on the crank has index marks to align correctly with the crank and also the CB drive gear.....if it is out of time the motor will experiance excessive vibration,,,the outer gear on the crank is to drive the gear on the rear of the clutch basket and consequently the tranny and is not as critical

[wilkin250r]

Is it possible to install it just 1 tooth out of phase?

[CBW]

Originally posted by wilkin250r
Is it possible to install it just 1 tooth out of phase?


yes...and the more teeth out of time the more vibration you will get. It can actually feel like a jack hammer when revved up if it gets too far out ot time..

,,,,,,,,.i forget how many teeth the gear has.......but its over 30 and only one is the correct tooth......the one with the ----> . ;)

[wilkin250r]

That's gotta be it, then. Or the crank isn't true.

How much does it cost to true the crank?

[CBW]

Originally posted by wilkin250r
That's gotta be it, then. Or the crank isn't true.

How much does it cost to true the crank?

I have no idea.......but truing the crank may not be all that much,,,,,,,,but the labor to split the center case halves, and reassemble after truing the crank may cost ya.....:confused2

[wilkin250r]

Yeah, I figured it's going to be $500 for pulling it apart and putting it back together, but is it going to cost another $250 on top of that just to fix the problem?

[CBW]

Originally posted by wilkin250r
Yeah, I figured it's going to be $500 for pulling it apart and putting it back together, but is it going to cost another $250 on top of that just to fix the problem?


Maybe,,,,,,,,but rather than true a stock crank,,,,,,,just purchase an aftermarket crank,,,,,,,it may be around the 250 mark---i forget how much they are. Then you'll know its all good :)