1985 OMC 800 Stringer - Thump (?)

mkrall56

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1985 Bayliner 1950 Capri - OMC 5.0L Stringer Drive - Shift Issues(?)

The last three times I have taken my boat out, I have noticed intermittent "thump" in sterndrive when going from standstill to plane. It does not happen every time but when it does, it goes like the following:
  • Boat Idling at ~500 rpm in neutral
  • Push throttle into forward position, hear the sound of boat going into drive ( slight ratcheting sound of gears engaging I assume, plus a very slight thump when it goes into gear)
  • Boat starts to move forward
  • When RPMs get to about 1200 or a little higher, I hear/fell a brief single thump
  • Boat continues on plane and no other sounds or vibrations noticed
Last time I was on water, I tested a start from standstill to immediately near WOT... about one time out of three I would hear and feel a thump just after boat is underway.

Last month the boat was at shop and the stern drive fluid levels were all checked and good. The engine was tuned up and runs well. I checked the fluid in the lower unit today and it’s still full.

I know very little about stringer stern drives and not sure if this is a shift cable adjustment issue or something more nefarious, like issues with the internals of the stern drive. Stern drive had major work on it two years ago to tune of about $3000. My father owned the boat at the time so not sure exactly what was done, he mentioned the seals where done and I assume the water pump but not sure what else.

I have an appt in late January with boat shop and not sure if it’s still safe to take out for light duty fishing in bay until that time or if its best not to risk causing damage. I was also hoping to get some feedback on what the possible issues might be so that I am more aware going into the appt.

Thank you!
Mike
 

southkogs

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How is the ball gear? That is a place you could have some bumps.

How about the gear lube out of the upper and lower? Any metal pieces/shavings in there?

I would also look at the drive shaft between the upper and lower gear case (pretty simple to disassemble). Then maybe even see what's happening at the prop shaft; are the splines and pins all locked up properly?

Welcome aboard.
 

racerone

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Sounds like it is jumping in and out of gear.-----The beginning of total clutch dog and forward gear failure.-----Best to call a shop ( if you can find one ) who can and wants to replace the pinion , forward gear and clutch dog.
 

mkrall56

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Thanks for the replies, I have an appt with a local OMC shop in late January. Here is pictures of the ball gear.
 

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racerone

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Those ball gears are worn.----But not the cause of the THUMP !!
 

Scott Danforth

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ball gears are past their usable life

the thump is probably the dog gear and a mis-adjustment of the cables/shift interupt. What ever you do, dont damage that $900 lower shift cable.

a worn shift dog wont get better, it will simply get worse.

could also be worn vertical driveshaft splines. if thats the case, you have about 2-3 more thumps prior to the splines completely failing and leaving you stranded. if you havent had the 3-piece driveshaft replaced yet, you may want to look into it. its a when they fail thing. they all fail. check your fathers receipts.

when you check fluids, you have 3 gear boxes to check. the intermediate gear box, the upper and the lower. you have to check all three
 

Redrig

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at a minimum , you need to a factory manual and do the procedure called "nominal neutral adjustment" That basically makes sure you are getting enough travel from the dog clutch in and out of gear. I can give you the basics and the measurements if you would like before you take it into the boat shop . It could be as simple as that adjustment.

but in all reality as these guys mentioned , its probably doing that because the teeth of the dog clutch are rounding and slipping out of gear when under load , giving you that clunk.

Time to pull the drive and tear into it .
 
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mkrall56

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Thank you all for taking time to reply, the info provided is greatly appreciated. I plan to check my Fathers receipts on the out drive work this coming week when up there for the Holiday. I hopefully will have a better idea what was done a few years back. Given the unit is original beyond any work that was done then, it may be a multitude of issues and items that would need to be addressed.
I am mildly mechanically inclined, and interested in reading up on the "nominal neutral adjustment", I have both manuals and plan to look into it more.
Thanks again.
 

Scott Danforth

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, I have both manuals and plan to look into it more.
what do you mean you have both manuals? you have the original OMC shop manual published by Ken Cook company, right?

because if you have a Haynes, Clymer or Chilton manual, you have knee pads or something to prop a wobbly table up with.
 
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