Gear lash, odd sound in Sea King 15

[auldscott]

OK, confession time: I’ve never had an OMC 15-18 hp so don’t know what is normal.

My 1962 Sea King 15 just started making a sound, something between a buzz and a whir, that is RPM dependent. It only happens in neutral; shifting to forward or reverse stops it.

Perhaps unrelated, when the LU is in gear, the propeller has about 1/4 turn of lash. In addition, there is a pronounced sound of gear teeth engaging when the driveshaft is turned by hand. The motor seems to run fine, with no odd noises when shifting or when running.

Are these things normal?

Thanks.

[fisherman6]

I will start by saying I have a number of 15-18hp OMCSs of 50’s and 60’s vintage. One of them is, in fact, a 1962 Sea King 15. I’m still trying to sort out an issue with mine that keeps it from pumping fuel, but that’s a different topic.

Some gear noise is normal for these motors and some make more noise than others. I do have a couple of questions about your case though.

1. Is the RPM dependent buzz / whir yours is making coming from the gearcase or possibly somewhere else? You mentioned it only does this in neutral, but the vibrations to motor makes changes a bit when in gear and under load.

2. A 1/4 turn of lash in the prop shaft when is gear sounds like normal clutch dog engagement. Meaning, if it is in gear whether forward or reverse and not running, the prop can be turned approximately 1/4 turn freely between the drive lugs of the gears.

3. Are you turning the drive shaft by hand with the lower unit removed from the midsection when you get the pronounced sound of gears engaging? These gearcases have fairly coarse gears and feeling and hearing them meshing is normal, but if it seems excessively rough or loud, there could be an issue.

4. It sounds as if the only timagine you are experiencing any gear whine is while running in neutral and it goes away once the lower unit is shifter into gear. Is this true? In my experience, the whine is usually heard while running in gear more so than the gearset being run in neutral. That almost sounds like there may some bearing wear in the gearcase which is allowing the gears to slop a bit when the clutch dog isn’t fully engaged one way or the other. The whole gearset runs all the time minus the clutch dog and the prop shaft. The clutch dog being engaged in tongue lugs of either of the spinning drive gears spins the prop. That may be taking out some of the free movement of the gears and reducing the whine when in gear? Forgive me if I ran you thru something you already know. I don’t know how familiar you are with these gearcases.

5. How.long have you had / been running this motor? It sounds like this sound is only a recent occurrence.

-Ben

OldJohnnyRude on YouTube

[auldscott]

Good thoughts!

1. I can’t tell where the sound is coming from, although it is clearly audible with the motor at normal depth and idling in neutral. It does not sound like gear whine, but I can’t rule that out.

2. OK on the 1/4 turn of lash being normal.

3. Yes, turning the drive shaft by hand with the LU removed. It sounds like what I am hearing from the gears is normal for these motors.

4. I’m not at all familiar with the 15/18 hp gearcases so all is new to me.

5. I’ve had the motor for about 9 months and have run it for a good many hours without problems. The overheating (other thread) first appeared recently after several hours of operation on a boat with three people aboard, but it is now evident when I am running solo.

[fisherman6]

Lots of places rattles develop on these motors. The cover latch roller on the hood gets worn and the gasket in the lower pan relaxes it’s seal. These things can make the cover rattle or buzz. The grab handle in the back of the cover can get loose. The rewind can make all sorts of strange noises. Those are a few things to check if you aren’t sure where the sound is coming from.

I’m working on a 1958 Johnson FD 18hp now. When I service that water pump I’ll make a short video and demonstrate the gear meshing sound and feel so at least you have something to go by. I’ll PM you the video link.

As for the overheat condition, I read that thread also. Certainly try Ben Dittmar’s method since it can’t hurt and often works. Replacing a grooved wear plate is a big help also. Sealant between the plate and the gearcase helps, but I have not always used it and still had good cooling. Sometimes exhaust pressure does have ill effects on water flow at higher speeds tough.

Here is a link to Ben Dittmar’s video.

https://youtu.be/beykqxzwfxM

The biggest difference between the Chrysler water pump and the OMC is the wear plate. The OMC wear plate is slightly crowned or raised in the center so it’s best to replace the worn plate instead of honing it flat as Ben did the Chrysler plate in his video. Hope his helps. I should have a video on the 18hp OMC gearcase this weekend sometime and I’ll send you the link.
-Ben

OldJohnnyRude on YouTube

[Mumbles]

quote auldscott:

My 1962 Sea King 15 just started making a sound, something between a buzz and a whir, that is RPM dependent. It only happens in neutral; shifting to forward or reverse stops it.

In addition, there is a pronounced sound of gear teeth engaging when the driveshaft is turned by hand. The motor seems to run fine, with no odd noises when shifting or when running.

To give you peace of mind, the 18 gearcases do have an inherent whining noise in them, but it only seems noticeable when they are in gear and above idle speeds. If you can hear or feel the gear teeth engaging, it might be time to get inside the gearcase to check things out. Are there any small metal filings in the gear oil?

These motors have roller bearings on the rods and if the crank journals or throws have chatter marks on them from the rollers, the motor will make a whirring noise. Pinpointing the noises source can be tricky sometimes as the noise can travel up the drive shaft making it seem like the powerhead is the culprit.

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[auldscott]

Thanks, everyone! as well as those who responded privately. I’ll be looking for a chance to pay y’all back.

auldscott

[fisherman6]

Auldscott,
I just sent you a PM.
-Ben

OldJohnnyRude on YouTube

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