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1988 90 Hp Yamaha Compression

J

jodee95

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Hello Thanks in advance for your help.. 1988 90 Hp Yamaha Motors runs very well Shift shaft is the original Non Stainless Steel metal is getting thin but it still shifts. Over the last year new Tilit trim motor and new water Pump..
Just did a recent compression test number are ALL even at 87 87 87 (Tried a different gauge with same results)

My question is I understand to change the shift shaft the power head needs to be removed.. Do I keep the P/head going or change out. I have seen most 90 HP Yamaha compression number above 120?

Any thoughts here? I know the P/Head bolts are going to be a bear I was going to have someone do the work....I love this motor It is light weight and has plenty of power to move my 17ft Bos Whaler along But those low number have me concerned...Thank you
 
I'll start by saying if the shift shaft you are talking about is the one that goes from the powerhead to the lower unit, you don't need top pull the powerhead to replace that.

Looks like factory spec on the 90 is about 130 pounds so at 87 she is getting a little tired. You can generally pick up a rebuilt/reman 3 cylinder powerhead for about 3500 bucks (you supply the ignition, carbs etc etc simply swap the block (intact).

For somewhat under 1K you can usually rebuild, so depending on your mechanical abilities it could be a good winder project for ya...
 
Graham Thanks for the info If I decide to do the shaft for now is it more complicated than changing the water pump? When I take down the lower unit does the shaft just drop down Thank you again for your help Joe





galamb said:
I'll start by saying if the shift shaft you are talking about is the one that goes from the powerhead to the lower unit, you don't need top pull the powerhead to replace that.

Looks like factory spec on the 90 is about 130 pounds so at 87 she is getting a little tired. You can generally pick up a rebuilt/reman 3 cylinder powerhead for about 3500 bucks (you supply the ignition, carbs etc etc simply swap the block (intact).

For somewhat under 1K you can usually rebuild, so depending on your mechanical abilities it could be a good winder project for ya...
Click to expand...
 
Yes, the shaft should come down with the unit. It is (splined) into a little stub shaft which forms part of the linkage up "under the hood". I believe on this particular model there may have been a circlip (one of those round horseshoe looking things) up near the top of the shift shaft. They were mostly removed the first time the water pump was serviced and never replaced - in fact Yami considers it an obsolete part.

If by chance it is still there the shaft may appear to "bind up" when it drops the first 2 to 3 inches. A "good heave" usually convinces it to let go :)

Usually the most frustrating part about changing out any part of the shift shaft is getting it lined back up properly. There is a cam at the bottom of the shaft (in the gear housing) that ultimately shifts gears for you. If you don't get it back correctly you may have forward and no reverse (or numerous combinations of either) - can be a pain (especially after you have put it back together for the third or fourth time and it's still not right - not that I would personally know :))

Don't want to scare you, it is definately a "do it yourself" type job in you are even semi-mechanically-inclined.

I would however, get ahold of a decent manual (in this case I actually like Seloc's better than Yamaha factory service manuals. The Yami manuals "assume" a fairly high degree of awareness/proceedures for these motors, while Seloc's "walks you through" the process).
 
Graham Thank you so much for taking the time to provide so much knowledge and detail... Like I said earlier I want to keep this motor going since they no longer make the 2 stroke 90 hp. I am going to check my cash situation and see if I can go with the power head if not change the shaft and go another year. I will obtain a Seloc manual for at least a point of reference. Have a great day! Joe
 
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