View Full Version : 86 prostar vibration .......need ideas!

08-01-2004, 12:18 PM
bought a 86 prostar last week. the malibu boat dealer we bought it from told us that is has a vibration in the driveline and they didnt want to mess with it. we got a steal on it, but now need to fine tune it and get rid of the vibration. we replaced the prop, didnt help. the dealers mechanic told us it was the drive plate. here are the symptoms:

under a load such as taking off it vibrates pretty hard until you get on plane and back off.

it vibrates any time you accelerate, such as crusing at 25 and then upping the speed to 30 it will vibrate until you reach the speed. then i "seems" to get better. we are going to time the motor today to eliminate that. so, if the motor is timed ok and the prop and drive shaft are true, the only thing we have left is to rip the motor out and have the drive plate and tranny looked at. i want to nurse it along for the next 4 weekends so we can make this a winter project. please advise if you have any ideas on what or where we should be looking to find our problem. thanks- Jim

08-01-2004, 12:27 PM
If it's out of the water, rotate the prop by hand and check the prop shaft for any visible bend. if you have a dial indicator, that's even better. Look for .005" max. If there's a problem with the tranny, you don't need to remove the motor, just the tranny. If you have a chain hoist, it's not too bad, just make sure to support the back of the motor so it doesn't try to hang there.

If you're going to time the motor, do a compression test, check the point gap/dwell, plugs/wires/cap/rotor and filters, too.

east tx skier
08-01-2004, 12:39 PM
Jim, my brother-in-law's Supra had a vibration issue that sounds somewhat similar to what you're describing. It turned out that the stuffing box was improperly packed. Once the repacked it, the vibration disappeared and has not returned.

08-01-2004, 12:55 PM
where is the stuffing box? is that the piece that goes thru the hull? we took the prop off and ran the motor at idle like the dealer told us. there is no movement at all on the shaft. its a brand new shaft the way it looks. put a new prop on and still have it. once we get the motor out of the question, then i know its between the prop and the drive plate at least. the tranny shift so smooth that it makes me think its not the tranny. it shifts perfectly into forward and reverse with no slip, just the bad vibration when you load the motor. my main thing is that i want to make it another 4 weeks with this bad boy just like it is unless it a simple fix:) keep me informed if you have anymore ideas- thanks a lot guys- Jim

08-02-2004, 11:05 PM
ok, tonight i took the coupler / tranny apart to check. we find we have play in the strut which we dont know if its excessive and also when we took the shaft loose from tranny it moves around when the rubber boot is slid up. should this be tight and slide right into the tranny without moving the shaft? ours is off by about a little less than a 1/8 down and to the right. we dont know if the stuffing box is intact or good shape and how to tell . the dealer said 500 to line the motor. please advise as to what kind of play is normal in the stufing box and strut bushings. thanks-jim

08-03-2004, 12:28 AM
$500 to align the motor, assuming the shaft and strut are OK? What is their shop labor rate? That sounds really high to me. If you look at the shaft going through the strut in bright light, you shouldn't see any gaps around the shaft, except for the grooves that are molded into the cutlass bearing. If the bearing is too loose, the shaft can "whip" or gyrate as it turns and this can be the cause of the vibration. Check the rudder and strut to see if they have any movement when you try to move them by grabbing them and wiggling each.

08-03-2004, 09:06 AM
New (or relatively new struts/cutlass bearings really shouldn't have much play and as JimN says, you shouldn't be able to see light except where the grooves are (they're desinged to allow water to move thru) - we used to replace them fairly readily on cruising sailboats (that's my experience ( I'm still learning about "high powered" motor boats)) and it really wasn't a big deal - if I recall there are a couple of allen set screws that need to be loosened and then drive the old one out with another old one or a piece of old shaft - we also used to cut a slot in them length wise that would almost instantly releave the "tightness" - don't cut into the side-wall of your strut please....a newly packed stuffing box won't have much play either (an old one shouldn't have much play or it will leak too much) this is definetly something you should learn to do 'cause they need to be adjusted as the packing is "used up"

Hey, you may get extremely lucky and end up with a great boat for a song!

Oh yeah, $500 sounds high to me, sometimes aligning can take a half hour....

Hope this helps


east tx skier
08-03-2004, 10:38 AM
$500 is way high for alignment. It's running me about $350 labor to have the shaft I bent, pulled, replaced, aligned, repacked, and lake tested.

As for the stuffing, I hear that that isn't rocket science to repack or replace. Sounds like if you've got play in your shaft though, that it might not be the problem afterall.

08-03-2004, 12:31 PM
oakhill marine in "okoboji" is the only dealer in the area. the wounlnt even give me an hourly rate, jobs are done on flat rate. my thought is this, if they fix my vibration .........i will give them the 500. if the charge me and the vibration is still there, gonna be some fightin words! thanks guys, i will let you know the diagnosis they give me. Jim

east tx skier
08-03-2004, 02:51 PM
JimN, isn't there some book that most of the inboard dealers use to calculate flat rate prices?

08-03-2004, 05:54 PM
in Okoboji, the customers usually dont ask prices. It is a very HIGH end lake that most people just say "fix it" and the dealers can charge a premium for the service. Its bad guys like me that arent millonares........

08-04-2004, 09:05 PM
so get this! called the dealer today, who says hes has been working on inboards since they were all wood boats(30years) and that there is nothing wrong with the boat. the vibration is "normal" for that year mastercraft with the powerslot. he claims not to feel what we feel!!! the damn steering wheel would shake in your hands it was that bad. before i took it in to him i took the coupler apart and looked things over......do you suppose that something could have been bound up somewhere? he changed the tranny fluid as he said it was a little dark and recommended that we do plug and wires and maybe a carb kit or change to a edelbrock carb, but that the motor/prop/driveline are spot on...in fact he said our motor check out at .002 on all 4 sides of the coupler which he said is better than good. his thought were that maybe it had water in the gas or somthing flukie going on and that it came thru it???? I guess he is being fair as he only charged us $60.00 total to look it over and change the tranny fluid.

08-05-2004, 10:35 PM
i cant believe it, the dealer was right...........there is no vibration!!! whatever it is/was is gone. the only thing i can attribute it to is that something was bound up and when we uncoupled it, the problem was gone!! makes one sweet puller now

08-06-2004, 01:05 AM
That is great news. Sixty dollars well spent for peace of mind!