86 OMC outdrive clunk

[plane_crazy]

the out drive clunks /shimmies at all throttle settings. Can feel it through the whole hull. Kinda like smooth run clunk, smooth, clunk etc. Upper and lower gear cases look like new. New ball gears. The lower drive has steering slop. Could this cause the problem?

 

[plane_crazy]

Re: 86 OMC outdrive clunk

Anyone have this problem or have any ideas?

 

[Bondo]

Re: 86 OMC outdrive clunk

Ayuh,... The shifting dogs in the drive are Worn Out,+ need replacing...

 

[plane_crazy]

Re: 86 OMC outdrive clunk

Had the shift dogs out. Look like new, no rounded corners. I even interchanged the forward and reverse dogs. they are the same. by doing this they engage on the opposite side of the dog. No change?
The bottom end looks like brand new.

 

[plane_crazy]

Re: 86 OMC outdrive clunk

Ran the whole season last year with this problem. After the season was over I tore down the bottom end, no wear, then I replaces the ball gears. The ball gears were the only part that shows wear. same clunk at idle speed or 30 mph.

 

[plane_crazy]

Re: 86 OMC outdrive clunk

Anyone have an idea. Can't find anything visual.

 

[bruceb58]

Re: 86 OMC outdrive clunk

Normal to have a clunk. What RPM is your engine idling at? Should be around 700 RPM.

 

[plane_crazy]

Re: 86 OMC outdrive clunk

It's not the clunk while engaging in gear. It happens while under power. Continuosly.

 

[Howard Sterndrive]

Re: 86 OMC outdrive clunk

how and when did this clunking begin? suddenly? radually or after rebuild of gearcase?

sounds like a couple of teeth in the drive don't like each other.

with the gearset ratios, you'll find it might take 200 revolutions for a particular pair of teeth to meet each other.

(I thought someone might have a "hunting tooth design" calculator app online somewhere but I can't find one. found a program called gearbox calculator which has it but it has to be d/l and installed in 3.1 or win 95 haha)

But if you get the frequency of the clunk and do some math with the ratios, you'll be able to see if it matches the hunting pattern and meeting of 2 particular teeth in the upper or the lower.
here's the formula:
http://www.vibrationschool.com/mans/SpecInter/SpecInter50.htm

or just give the teeth counts and I can work it out

Were your ball gears worn on a 45 deg angle at all?

 

[Howard Sterndrive]

Re: 86 OMC outdrive clunk

The lower drive has steering slop.

can you elaborate on that?

the lower drive is the only part that steers

shims under the upper exhaust housing cap are used to adjust the "float" or clearance for the lower to move on the upper.
too much clearance will contribute to milky oil in the upper.

 

[plane_crazy]

Re: 86 OMC outdrive clunk

Got the boat last year. Floor was rotted. Replaced floor. Previouse owner had outdrive serviced and rebuilt. His son then used it and he didn't know how bad it was abused. From the get go the shifter cable was out of adjustment. Took apart bottom end and re did shifter. Ran the boat and noticed drive clunk.
From reading I thought bottom end was destroyed from out of adjust shifter.
Tore all the gears and clutch dog out. All looked like brand new. Re-assembled. Problem stayed the same. Ran the whole season with the clunk. Took apart bottom end to look for ware. All still looks new. Upper end looks like new also. Only ware was ball gears, so I replaced them. Still no fix. I can move the bottom end left and right about 1 quarter inch. Could this be loading up then releasing causing the clunk?

 

[Howard Sterndrive]

Re: 86 OMC outdrive clunk

no, sounds like you have a couple of mis-mating teeth.

if it does it the same in reverse as forward, then it's in the upper gearbox