slow idle rattle

With the boat out of the water, grab the end of the shaft and see if there is any play up and down or side to side. If there's alot, the strut bushing is worn.

thanks for the replys. Strut bushing is ok. It does idle real slow in gear, so I will idle it up.

I believe the noise is probably coming from the damper plate. Basically the springs rust and break thus cuasing the rattle at low rpm's. This is what probably needs to be replaced. Worth a look.

Also Set your air screws in gear. A smoother idle will result, as well as off-idle performance.

You have a good running motor if it will idle in gear at 400 rpms.

You remove the engine or the transmission and visually inspect, not fun, that is why it is a good thing to replace even if not broken when you have the engine out for a major overhaul. Certainly it is a lot easier to try a higher idle speed first in this situation...-Joe.

Sorry David but i have to completely disagree with that. Even with a properly applied and perfectly working damper idle speed is a factor in proper fuction of the transmission. The lower the speed the more likely it is that slight misfires, firing order etc will cause the transmission to not feel a steady enough output from the engine to prevent this type of noise. Constant running at low speeds while this condition is occuring will cause failure of the transmission. Borg Warner has in fact recommended raising the idle speed up to 1000-1200 for situations where the springs in the damper maybe weakened or misapplied slightly. Flywheel size, shaft length and weight, propeller balance, etc all have an effect on the proper application of a damper. Either way believe me low rpm alone can cause this issue and it can destroy your trans.
-Joe.

Joe:

You will notice that I never recommended a lower than 600 rpm idle speed and, in fact, stated that I agree with the figure. What I did say is that if everything is in good order, the engine/tranny should not rattle when the rpm falls (I did say "set" and maybet should have said "falls") below 600 rpms. If it does, something is worn, broken or otherwise not in proper adjustment.

FWIW (not recommending), when I was having trouble with my '77 Martinique, the rpms were frequently under 600 rpms for extended periods of time while idling around. The worn distributor and corroded carburetor made it almost impossible to get a steady idle speed from one day to the next. So, close was good enough until I finally decided to replace the components. Never did the engine/tranny rattle or make unusual noise. So, what I am saying again is that I think that the problem with "Rootracing's" setup is that he has a weak or failed damper plate. Sure, raising the idle might mask the problem, but that does not make the underlying problem go away. If the rattle goes away at 600 rpms, then fine, he might want to just leave well enough alone and it may last a long time. If the rattle is present at 600 rpms, my suggestion is to inspect and/or replace the damper plate. That is my advice, because that is what I would do.

Well, could be. I base things on my experiences. Neither my '77 nor my '93 would rattle when the idle was below 600rpm (for whatever reason).

Why don't we just leave it at: Set idle to 600 rpm in gear. If it still rattles, inspect the damper plate for broken (or weak) spring(s).

A loose prop will cause a rattle as will other things as well.

That vintage, if the tranny is out I would just replace it. Summer is too short to fix things twice.

yep, me too.

Mental note **
Don't fly Boat Dr Airlines ...where we run it til it fails

gottaski..........boat repair shops,like mine, love that state of mind .my dad called it penny wise and dollar foolish.but who am i to say.......

Yes, dampner.