OMC 400/800 Changablity

[djensen.id]

I have an 84 OMC Stern Drive with a bad upper. The prop will not turn when put into gear. I can turn the prop by hand with it in gear and there is some resistance like gears or splines slipping. I had a mechanic tell me that it was most likely the upper and that it would be expensive to fix. I have access to an complete 800 with 21:17 ratio and I am wondering if I can replace the 400 with it? I am not sure what the ratio is on it. It does not have a shift cable but mine is good, are they interchangeable as well? I will need a new prop as well so some guidance on that would be great as well if the drives are interchangeable. I have the 3.0 liter GM engine.

Thanks for the help.

djensen

 

[Scott Danforth]

welcome aboard

look for a 1981-1985 stringer 400 to make your life easy.

 

[kenny nunez]

The 400 has a ratio somewhere around 2.0 to 1. The 800s with v-6/V8 are in the 1.5 range. Plus the 800 you are has no shift cable, do not even consider it. Remove the oil drain plug on your upper and check what comes out. Oil with the appearance of liquid graphite is really bad. But if the oil looks good you may just need the water pump and upper pinion shafts. This is a part that is notorious for wearing out and the parts are still available as after market. Sierra has them listed.
If you decide on looking for another drive try to find out if it came from a running boat that was being repowered.

 

[Scott Danforth]

to add, the common problem with all stringer is the 3-piece vertical drive shaft... the splines fail. not a question of if, however when they will. as Kenny stated, it may be all it needs is the two upper pieces of drive shaft.

 

[southkogs]

... and ...

If the engine will start and idle with the outdrive attached, then your upper is mostly fine. Check your lube and stay on top of it, but the upper is spinnin' anytime the motor is running. So it sounds like your upper is likely fine.

 

[djensen.id]

Thanks for the information guys. It was very helpful.