I have a problem that may end up in court. If any one has any experiance with the following please do offer suggestions.


My shop installed a reman 4.3 long block in a late eighties runabout. (Mercruiser). I test drove the boat: seemed fine to me. But the customer complained of a vibration present in the boat that was not there prior to the engine install. So I test drove it again. Still seemed fine to me. I called the customer to come to the boat so he could show me what his problem is. When he ran the tach up to about 1700 to 1800 and held it with the bow pointed high enough that you can't see ahead there is a "minor vibration" (my opinion not his).

It's my opinion that the vibration is normal under these conditions. Extreme prop shaft angle and and prop slip.

But the customer is always right. Right? So I took him at his word and assumed that there is a problem.

What we have done so far:

checked and rechecked alignment

Installed and ran a different drive and prop combo, made no difference
Pulled engine sent it back to the builder, he re balanced it again. He says it is balanced within a gram.

Still no difference.

I have taken a friend for a ride, he thinks it acts about the same as his boat that has the same engine. I took our service manager for a ride(A certified Merc Tech) He doesn't see a problem. They all admit that there is a vibration but it is common with the older 4.3 engines. Once the boat is throttled up and on plane it is very smooth all the way to full RPM's.

I'm out of ideas. The customer insists there is a problem. I'm not so sure. Now he is insisting on another engine. I don't think that it will help. I would throw an engine at it if I new it was the problem. My fear is going thru all that and end up with the same results. I am upside down in this job already. The only thing left to salvage is my reputation. But I'm not afraid to cut the guy loose if I have to. Any ideas or similar experiances would be appreciated.

Thanks,

Steve

It sounds as if nothing is going to please him, cut your ties refund the money and walk away.

Steve,

If the engine it self were mechanically out of balance, it should vibrate at the same rpm when it is out of gear. If it runs smooth at 1700 -1800 rpm out of gear, then it is not a balance problem.

I have seen instances where a carburetor tuning or ignition timing issue will cause a lean condition at certain rpm and load conditions, usually in the low to mid rpm ranges, and it feels like a "vibration" where it really is a missfire.

You might try varying the timing just a bit and see what happens. Was the carburetor rebuilt at the same time ? Maybe check the float levels etc.

Also, dont overlook the fact that the new engine is probably making a fair amount more horsepower than the old worn out one, so everything behind it including u-joints and the drive are under more stress and could be causing a problem that did not show up with the old engine.

A good way to approach it is to pretend the vibration just started without the engine ever having been touched, then troubleshoot from there.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md