1999 7.4 MPI Vibration

JohnGordon

Member
Jul 19, 2010
161
Traverse City, MI
Boat Info
1999 330 Sundancer, 7.4MPI, V-Drive, 4.5 Westerbeke, Raymarine A98, Full Camper Canvas, Vitracore-So
Engines
7.4MPI, V-Drive
Bought the boat in 2014 and only ran it during sea trial and winterizing. When we bought the boat I knew there was a problem with the port motor and ended up rebuilding it. During the sea trial and winterizing I seem to remember the starboard motor running very smooth with no issues (of course now I am doubting myself). After rebuilding the port motor and doing everything else the boat needed (a year and a half worth of fixing) ;when I started up the starboard motor I noticed a vibration. The vibration happens at all RPMs regardless if it is in gear or not. I can't figure it out and have had several mechanics look at it and suggest that there is an internal problem with the motor. The motor has no problem hitting WOT with adequate power and we have put at least 50 hours on it with the vibration. The motor is a Jasper from 2010 and I have no idea how many hours are on it; computer says 495.

Here is a list of what I have checked/replaced/fixed:
  • Full tune up while boat was being worked on(now on the 2nd set of plugs and third cap and rotor
  • Tested/cleaned injectors (all passed)
  • Replaced all sensors
  • Compression check (185 on all cylinders except 7&8 which were 175)
  • Swapped harmonic balancer, ECM, complete distributor between motors
  • Replaced fuel pump and pressure regulator
  • Removed, cleaned, and resurfaced exhaust manifolds and risers
To me it seems like a rhythmic vibration and everything is pointing to a mechanical problem. I am willing to try anything so that I don't have to pull the motor this winter. Can something happen to the damper plate that would cause the vibration? A marine mechanic friend has heard of Jasper only boring out 1 cylinder when rebuilding a motor.

I am at a complete loss here. I would have no problem pulling the motor if I knew for sure that there was an internal problem, but I am not sure.

Thanks in advance for any suggestions.
 
You can't see it vibrate much. But, if I or someone else stands on it or puts a hand on it while the RPMs increase you can definitely feel it. It's most noticeable under load, but the vibration is there in neutral as well. Huge difference when in gear and you throttle up port and starboard separately. It has the distinctive transmission "rattle" when in neutral at idle.
 
did you change out the plug wires and the coil wire?.....were they part of the 'full tune up"?......

cliff
 
My first thought was an old distributer cap allowing some cross arcing. Since you replaced it, follow Cliff's advice and triple check the firing order. Not sure what else to suggest other than stop running the motor until you figure out the problem. It would really suck to watch the motor grenade itself.
 
My first thought was an old distributer cap allowing some cross arcing. Since you replaced it, follow Cliff's advice and triple check the firing order. Not sure what else to suggest other than stop running the motor until you figure out the problem. It would really suck to watch the motor grenade itself.

actually 'techmitch' suggested to triple check the plug wires to be sure you have the correct firing order.....regardless it is a good suggestion....it can be easy to get them crossed...

cliff
 
could the distributor be installed a tooth off or 180* backwards?.....if you removed the distributor and re-installed it you may have installed it incorrectly.....been there done that....

be sure the rotor is pointing directly at plug wire #1 in the distributor cap when the #1 piston is at TDC on the compression stroke....then double check wires to be sure they are installed correctly on the distributor cap....

cliff
 
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I have had the plug wires off and back on no less than 4 times. I am back to an old set of wires; this started on the old set then I switched to a new set and now back to an old set. On the 3rd or 4th cap and rotor. Plugs have been changed 2 or 3 times. I have checked the firing order numerous times. Tried the complete distributor, coil, and ECM from the other motor. I just had the distributor out to rebuild it with a new pickup coil.

If wires were crossed I doubt it would have the power it has or be able to easily hit 4100-4200 RPMs.

All plugs have a good color to them when I have changed them.

All of the above with absolutely no change in the vibration.

Has anyone ever had a damper plate/coupler do this in a V drive?

How about a bent push rod? I thought this might be a possibility as this would not show up on a compression test, but it would affect running.

I was really hoping it was going to be something simple, it is starting too look like something internal.

I appreciate all of the responses so far and keep them coming if you don't mind.
 
A bent push rod would not cause the vibration. A bent connecting rod could do it.

How about a compression test.

One other thing, are there timing marks on the crankshaft harmonic balancer?
Check to make sure that cylinder #1 really is at TDC when the timing mark indicates so.

IF this is an externally balanced motor, AND the harmonic balancer outer ring has slipped, you could throw off the "balance" of the rotating assembly, causing a vibration.
 
Is your engine raw water cooled or possibly has a crank driven raw water pump? Could try running with the belt removed to eliminate accessories mounted on the front.
Not familiar with your drive coupler, but if there is a way to disconnect it, it would help to isolate your problem at the back end.
You have posted that your engine has adequate power and is hitting WOT. Assuming "WOT" is what it is rated at and the same as your second engine, you can pretty much rule out any fuel/ignition problems in my opinion.
If something mechanical internally is coming apart, it should more than likely make a tick, knock or show signs of contamination in the lube filter. Has any of your mechanics cut a filter open before suggesting a tear down?
I have no experience with Jasper but did run into one long block that was sent out from another builder that had different cylinder heads installed. Compression test was good but had the same vibration symptoms you have described but from the get go. They should be of the castings.
 
Could this be in the transmission? You say there is a rattle (that's somewhat normal), but the fact that you have checked / eliminated the obvious causes. Not sure how to troubleshoot that.

My experience is vibrations are fuel / ignition related (ie a cylinder not firing) or an accessory / pulley and possibly the harmonic balancer - especially if these components were removed and installed on the Jasper block. Internal issues tend to be a tick or knock. The fact that it is a re-build opens up a lot of possibilities, and having eliminated all of the obvious causes, your only option might be a teardown. But even then you might not find it - and is it worth the time and money. If it were me I would have to decide how bad the vibration is, is it getting worse. If the engine otherwise runs well, I might just run it until something happens.
 
I was thinking if there was a bent push rod it would change how far a valve is opening and therefore change how well the engine runs.

The engine is raw water cooled. I have removed the belt and run the engine with no change.

There are no noises coming from the engine or the transmission except for the damper plate rattle at idle. I have tried to get my bore scope down the inspection hole at the top of the bell housing, but really couldn't get far enough to see the springs or hub.

The engine hits 4200 easily. Suggested WOT is 4000-4400. Top speed is 35, which from what I have read this is about average for this boat.

I have swapped the harmonic balancers between engines with no change.

The vibration is bad enough that is has backed out the exhaust manifold bolts.

The vibration is not getting worse. Most people that ride in the boat can't really tell until I rev the port and starboard motors separately. I checked the hours and we are getting close to 100 hours with the vibration. Honestly, I am getting so frustrated with this that I keep running the motor at 3400 while cruising and hope that it blows so then I actually know what happened. We have about another month of boating and if nothing changes I will plan on pulling the motor and transmission before putting the boat away for the winter. I am fortunate that I have the facility to store the boat and do all of my own work except for machine work on the block and heads. I might get lucky and it may just be the damper plate and I don't have to get into the engine.

Thanks for all the suggestions and replies.
 
did you verify that the rotor is pointing directly to the #1 distributor post when the #1 piston is at TDC on the compression stroke?....if not the ignition timing will obviously be off to the point the ECM cannot completely compensate but the engine may still be able to run however it will be rough....

good luck...
cliff
 
UPDATE:

After last season I decided to pull the engine and rebuild it hoping to find the cause of the vibration. Due to a busy work schedule I didn't get started until June, and pulled the engine beginning of July. Engine went back in beginning of August and the boat was in the water for the first time this year August 09. This was a Jasper re-manufactured engine from 2010(according to Jasper) a previous owner had installed.

What I did:

Separated transmission from engine- Found rubber chunks in bell-housing from the damper plate. Found that parts of the damper plate were hitting the flywheel. The damper plate looked like it was a little warped or bent. I replaced the damper plate.
20190705_182813.jpg 20190705_182757.jpg 20190705_131809.jpg 20190705_182742.jpg

Tore the engine down- The crankshaft was from Scat and was the stock replacement model. Found the crankshaft a little beat up, possibly had been in an engine that failed. The crankshaft also looked like it had been re-balanced at some point; he holes drilled in it and the welding just didn't seem like it came from the factory. The rest of the engine looked great. Very little wear on the bearings even though we ran it with the vibration for a few seasons. I replaced the rings, crank, bearings, and gaskets. I replaced the crank with the exact same model that I took out.
20190705_183046.jpg 20190705_182834.jpg 20190705_182831.jpg 20190705_183058.jpg

In conclusion:

The vibration is completely gone. I don't know if it was the crank or the damper plate. I don't think the rubber pieces that disintegrated in the damper plate would have caused the vibration. The crank to me is suspect, but I don't know if I want to pay to have it checked.

Of course while the engine was out I: Pulled the generator to replace the timing belt, rebuild the governor, adjust valve lash, replace the anti-siphon valve and hoses, touch up the paint. Re-bedded the strut, underwater exhaust tube, and the rudder tube. Painted the bilge. Replaced bilge pump float switches. Replaced the shaft seal. Isolated the generator muffler. Installed an accumulator for fresh water.

Thanks to everyone for the suggestions as I worked through this. Let me know if you have any questions.
 

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