87 OMC 800 loud thunk

[subcrx]

I purchased my boat a couple months ago. Ive been doing extensive repairs throughout the stern. Since day one ive been having trouble with the shifter. Was very hard to get out of gear at all times. I narrowed that down to the idle. It was around 1100 to 1200 at all times for the 5.7 liter. Now I have the shifter working smoothly I have this strange thunk. Happens all the time, like every 30 seconds. Then I increase the throttle it sometimes goes away. or it acts up when im getting on plane. It doesnt happen all the time.Seems as if I play around with the throttle it stops. anyone heard of this or seen it? it worries me. Im afraid to take it far out of the harbor now.

 

[wire2]

Re: 87 OMC 800 loud thunk

You need to get the idle down to ~500-600 rpm. Above that, the torque on the shift dogs in the lower unit will tend to lock it in place. That's also what ESA is for.

The periodic clunk feels like you ran into a submerged piece of 2 x 4 with the outdrive? It's likely the same dogs slipping over 1 tooth b/c the corners are rounded.

I had that the 1st season after I bought the boat new in '84. I took it to dealer in 2nd season, just after 1 yr warranty, cost $600.
The new dogs were a different shape, obviously OMC had many complaints & changed the part. You *may* have the old style.

What year is yours?

 

[whywhyzed]

Re: 87 OMC 800 loud thunk

1987 should be a Cobra, in which case go here and read:

www.hastings.org/~stuart/cobra

 

[wire2]

Re: 87 OMC 800 loud thunk

I figured the 87 was a typo, since he said 800. That's why I asked year.

 

[KaGee]

Re: 87 OMC 800 loud thunk

Either way, if the dog gets rounded, he's looking at a rebuild.

 

[subcrx]

Re: 87 OMC 800 loud thunk

sorry guys for the confusion, its a cobra. Ive adjusted the cables to a point where it doesn't slip much anymore. It slips every now and then maybe once and a while a second after engaging. I'm sure i have a worn dog. Ill live it out for now. Would just replacing the dog alone help a bunch or will I need gears as well. I'm a cheap *** and like shortcuts.

 

[wcsparky05]

Re: 87 OMC 800 loud thunk

i've been told and read that a clunk is quite normal, and much better than a noise of gears grinding. the clunk is just that, the gears grabbing and the splines lining up. take that with a grain of salt, but i've learned a lot in the last 2 years since i've owned mine. i can say i pulled the entire outdrive and taken it apart, put it back together, and started it up last week with no issues.

 

[whywhyzed]

Re: 87 OMC 800 loud thunk

......

 

[wire2]

Re: 87 OMC 800 loud thunk

1 clunk going into gear is ok, repetitive ones afterwards are not, especially loud ones. Dogs with rounded corners have no appreciable effect on the gears, I'm confident yours will be fine.

 

[subcrx]

Re: 87 OMC 800 loud thunk

ohh its loud enough to get everyones attention on the boat hehe, Its very intermittent. hasn't happened in some time, its mostly when getting out of the hole.

 

[whywhyzed]

Re: 87 OMC 800 loud thunk

......

 

[subcrx]

Re: 87 OMC 800 loud thunk

yup thats the sound, I know its the dog, but how much time do i have left before teardown, think i will make it through summer?

 

[whywhyzed]

Re: 87 OMC 800 loud thunk

y......