Will the same year merc 120 s/d replace an 888 s/d?

[turbosetch]

On sunday my 888 pre-alpha drive locked up completly in the top end. Looks like a piece of gear broke off and seized.

I found some one with a 120 pre-alpha drive. It all looks the same and I am checking the gear ratio with him..Will this work for me?

Is it just a different sticker on the 120?

 

[Don S]

Re: Will the same year merc 120 s/d replace an 888 s/d?

The gear ratio is different, and the input shaft is shorter.

 

[turbosetch]

Re: Will the same year merc 120 s/d replace an 888 s/d?

So what if I change the input shaft out with the old one and deal with the gear ratio if it is a problem perhaps with a prop change.

He mentioned the ratio might be 1.6 and I think mine was 1.5..pretty close. My RPM's were a little low on the old engine anyway.

 

[Haut Medoc]

Re: Will the same year merc 120 s/d replace an 888 s/d?

Nope the 120 would /should have 2:1......
You need a 1.5 :1....
'Course if you put on the 120 upper you'll get the rpm's you're looking for & then some!.....
Just kidding, you are wishfully thinking.....
It won't work right......​

 

[Don S]

Re: Will the same year merc 120 s/d replace an 888 s/d?

Props have to be within a certain range of pitch to be usable. That is why there are different gear ratio's.
Besides, the 120 gears aren't even strong enough to put up with a V8.
If you do try it, and finally get a prop made to get your WOT rpm in the right range, you will need a fort night just to get it up on step.

 

[turbosetch]

Re: Will the same year merc 120 s/d replace an 888 s/d?

Got it. Well I took the 888 apart just now and it blew a tooth right off the lower gear below the input shaft gear. It wedged some gear tooth parts between the upper gear and the housing. I took the crown nut off and can't get it apart its completly seized up from the wedged in part.

My thoughts are a rebuild gear kit won't even work here since the case is scored pretty bad now and of course its all jammed up.

I can't understand why it blew apart like this. It had plenty of fresh oil and no water in it. When I replace the seals in the drive I took all of this apart and was careful to assemble the way it came apart with the shims but perhaps I missed. Maybe just its time.

I'm going to look for a newer non-pre-alpha style to replace it with if I can find one.

Will my lower half bolt onto an alpha I or should I get a complete unit?

 

[Don S]

Re: Will the same year merc 120 s/d replace an 888 s/d?

I can't understand why it blew apart like this

Impact is what breaks gears. Logs, rocks, whatever. It may not happen immediatly, may take another 25 to 100 hours, but they will usually break a gear after a solid impact.

Of course on old drives, plain old age will do it.

 

[turbosetch]

Re: Will the same year merc 120 s/d replace an 888 s/d?

1973..older than I am. Oh well thanks for the help. I identified my drive as a 1.5:1 like you said. Time to search. I have been working on this boat for 2 months now so I could go to Homer this weekend....doesn't look good.

 

[TBarCYa]

Re: Will the same year merc 120 s/d replace an 888 s/d?

I have the exact same drive with the exact same problem although mine is a couple years newer. I've been told that the upper and lower share oil thru a small passage and that replacing the upper without disassembling and cleaning the lower will eventually lead to failure of the lower. I found a site that has replacement units (complete upper and lower) for around $1200 but it doesn't state that they are Mercruiser drives, just Mercruiser Replacements. The stickers don't say Mercruiser either.

PM or email me if you're interested and I"ll give you the link.

 

[Bondo]

Re: Will the same year merc 120 s/d replace an 888 s/d?

Ayuh,....... Those SEIs are a 'ell of a Deal,....... iboats has them Here I believe....