1977 Johnson 70 compatible lower units

[Cherokee-Runabout]

Hey there everyone, I am currently looking for a lower unit to repair a damaged one. I have seen one from a 1974 70hp and one from a 1986 88hp. Would either of these be compatible?

 

[racerone]

????--------The 74 will not work because shift is opposite.-----And the V-4 unit off the 88 hp will not work either !!!!

 

[BillP]

There are a lot of old 70 parts out there and many will fit but I don't know the break off yrs for 77. One word of cautions when you find one. Count the splines on the drive shaft to make sure they match yours. Commercial unit have more splines (to enable rapid high speed throttle shifts without stripping the splines).

 

[racerone]

???----The lower units required here are from a 3 cylinder motors 60 / 65 / 70 / 75 hp models.---From 77 to 1988 models.--Commercial units included.---Not sure where this idea of fine splines comes from for commercial motors.

 

[Cherokee-Runabout]

Racerone, thank you for the info. I'm attempting not to spend a thousand dollars for a new lower for a boat/ motor I paid $700 for!

 

[racerone]

A new one for those was about $4000 when they were available new.----What is wrong with your unit ?------ what is your location ?----So you would rather find an " as is unit " for cheap and risk having to pay for a seal kit installation ?

 

[Cherokee-Runabout]

The last time I took it out about a month ago the forward gear wouldn't engage right away. It took me shifting back into neutral a few times for forward to finally get forward to take, (All of this accompanied by irregular grinding noises) Secondly I am in Southern-Ohio. I am attending college full time and do not have an excess of money. Arguably I could save for another month and purchase the new l/u... I'm open to suggestions and any help. Once again thank you.

 

[flyingscott]

check your shift cable adjustment

 

[BillP]

???----The lower units required here are from a 3 cylinder motors 60 / 65 / 70 / 75 hp models.---From 77 to 1988 models.--Commercial units included.---Not sure where this idea of fine splines comes from for commercial motors.

The spline information came from M.G. Sanz (BSME & MBA), past OMC International commercial warranty manager responsible for USA, South America, Bahamas and Bermuda. He is in Orlando now. MGS has been a personal friend of mine for 35+ yrs and has my highest respect for credibility. It probably has something to do with year of mfg. I bought my 65hp commercial motor in 91 and this is what he told me when explaining the differences between it and the domestic (70) model...and there are a few.

bp

 

[racerone]

You need to be very carefull when you listen to a " corporate manager " and someone who sits at a desk !----There really is no difference in splines between a commercial motor and a pleasure motor.----Ok so you trust your friend in this case ?-----Then look it up in any parts manual the 91 model 65 hp commercial uses the same driveshaft as the 91 model 70 hp pleasure outboard !!!!!

 

[oldboat1]

Hey runabout -- tell Kasich he needs to do something about tuition assistance programs.... Might need the clutch dog replaced, but check gearcase for oil, and change it out if it's not fresh. If you've got a place to tinker, you can probably fix it but a new part would probably run $130 or so.

 

[BillP]

You need to be very carefull when you listen to a " corporate manager " and someone who sits at a desk !----There really is no difference in splines between a commercial motor and a pleasure motor.----Ok so you trust your friend in this case ?-----Then look it up in any parts manual the 91 model 65 hp commercial uses the same driveshaft as the 91 model 70 hp pleasure outboard !!!!!

I agree and you also have to be very careful listening to anyone. MGS was far from an ignorant desk jocky and could take down or assemble anything OMC made with his eyes closed. One of the things he did was travel overseas and physically check parts that were warranteed...a dealer would request a new lower unit under warranty. MG would often deliver it in person (surprise) and disassemble the old unit on the spot or bring it back to Ft. Lauderdate to check it. He said it was necessary to do this because of all the bogus warranty claims.This was also part of their R&D program.

I doubt your parts check tells the whole story and what motors were changed. Evidently OMC realized it was a problem at some point and made changes so I doubt early engines are the same. Same as when they changed from 100:1 back to 50:1 ratios. I will shoot him an email and see if he can shed some info.

 

[BillP]

So I wrote to MGS after writing the previous message about splines on my 65 hp commercial (domestic 70). He replied back and here it is:


I really dont remember much on the spline history. I do recall that they used a four spline on the upper side of the driveshaft and then they went to a fine 21-22 spline for that side. They also started using a neck down on the driveshaft to absorb some of the shock loads on the drive shaft.
Let me know when you are coming to the big city since I am on the road sometimes.
Looking forward to seeing you.
regards

Marcelo

 

[racerone]

???---All the 3 cylinder models ( commercial and pleasure ) went to a " fine spline " in 1989 model year.---That is after they had used the coarse spline for 20 years on these motors !!!

 

[BillP]

No pixxing match happening here with me racerone. I recalled back to conversations in 1991 and cannot speak for what actually happened at OMC 25+ yrs ago. It really doesn't matter. My whole and only intent of mentioning splines in the first place was to make the op aware of the differences so he didn't buy a used shaft that didn't fit. Bottom line is OMC 70s have different drive shafts and if I was pulling one off the shelf of a boneyard or auction site I would count the splines.

bp

 

[racerone]

Post # 4 has the needed information !!

 

[BillP]

Post # 4 has the needed information !!

In your opinion for sure...but in 1991 my 65 is was a NOS 1986 commercial block on a much later factory new 1991 lower unit, carbs, fuel, electricals, etc. Your 1988 date says this doesn't match up...but it does on this one (I was going to scan and post the red tags that were wired on the parts when purchased that say what the part numbers are, year of mfg and QC person but couldn't find them - probably at my other house). I can only guess OMC put these out earlier than 1988 in the commercial engines and it didn't get documented on parts lists. Like I posted earlier, the op just needs to compare the number of splines to make sure they match.