lower unit swap on Mercruiser inline 6 outdrive

[uspoet]

I found a complete outdrive on CL ( I know) and want to swap the lower with mine. When I turn the shift shaft on mine it will go in reverse neutral and forward but will not lock. I have been reading that it's not worth rebuilding but I can't spring for the big bucks for a "factory" rebuilt at this time....big family reunion next month!!! My drive serial # is 2765230 the replacement is 3079718. Would this be a direct swap? Thanks! Sorry...both are 165 hp.

 

[alldodge]

Re: lower unit swap on Mercruiser inline 6 outdrive

I found a complete outdrive on CL ( I know) and want to swap the lower with mine. When I turn the shift shaft on mine it will go in reverse neutral and forward but will not lock. I have been reading that it's not worth rebuilding but I can't spring for the big bucks for a "factory" rebuilt at this time....big family reunion next month!!! My drive serial # is 2765230 the replacement is 3079718. Would this be a direct swap? Thanks! Sorry...both are 165 hp.

You said yours goes in FWD/N/REV but will not lock; what do you mean it will not lock? The drive gears will not lock up entirely, only in one direction for FWD/REV. What makes you think yours is bad?

 

[achris]

Re: lower unit swap on Mercruiser inline 6 outdrive

These is no detent like an outboard. The shift shaft just rotates to the correct position for that gear, the undercut on the clutch dog and the engine torque do the rest.... There may be nothing wrong with your gear housing....

Chris......

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

First, and am quite new to boating...at least from the maintenance aspect. I just bought this boat and I've had it in the water twice and it overheated both times.

I had previously pulled the lower to replace the impeller. It didn't resolve the overheating issue. I have since pull the exhaust manifold and riser and cleaned out the water passages which I'm pretty sure...judging by how much scale I removed....was the cause of the overheating.

After redocking after the 2nd overheating issue, I wanted to make sure the shifting was ok (I was pushed off the dock so didn't put it in reverse after launch). I was still tied up to the dock when I shifted into reverse and nearly tore the dock off! It immediately went to HI RPM. I untied and tried it again and it did the same thing. I started to smell rubber burning and I assumed the impeller I had just replace got cooked so today I pulled the lower to inspect the impeller. It was ok, but when I turned the prop to insure that it was in forward gear prior to reinstalling the unit the prop wouldn't lock when turning the opposite direction. When the shift shaft is turned in either direction it will move through neutral into the opposite gear. There is no "positive" engagement in either gear and the prop can easily be turned in the opposite direction. I'm not sure what the mechanism is for preventing this but it seems this is not right. Just going by the advise of internet forums that say replace rather than rebuild....less expensive. Am I worrying about a problem that doesn't exist? Thanks.

BTW anyone have an answer as to whether the drives are a direct replacement?

 

[alldodge]

Re: lower unit swap on Mercruiser inline 6 outdrive

I think you have other issues going on and may want to pull the drive totally off and check alignment and shift linkage. The burning rubber maybe your engine coupler.

This link below listed both serial Sterndrive serial numbers. Yours is listed as 67-69 Merc 160 and CL one is 70-77 Merc 165. If either link is selected it takes you to the same PDF catalog, therefore they will probably work. Only issue not clearly determined is the gear ratio. If they are not the same ratio you may need another prop.

Mercruiser help parts guide model-year-make-serial number

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

Thanks AllDodge. I was hoping the burning rubber was the impeller but since it was intact I don't believe that was what I smelled. The engine and drive haven't been separated (at least not by me). Alignment could still be an issue but the boat ran fine both times I had it in the water despite the overheating issues.

After dropping the lower and checking the impeller I later discovered...after initial post...that the lower drive shaft seal ....(I had put a new one in with the 1st impeller replacement) had been shredded. There was NO second seal.
The O-ring had been totally vaporized except for a 1/4" section. I'm hoping this was the rubber smell. I going to check to make sure the drive shaft isn't pitted where it goes through the seal when I go out to the shop oh and thanks for the link. Now to figure out gear ratios on my lower and the CL lower....

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

"This link below listed both serial Sterndrive serial numbers. Yours is listed as 67-69 Merc 160 and CL one is 70-77 Merc 165. If either link is selected it takes you to the same PDF catalog, therefore they will probably work. Only issue not clearly determined is the gear ratio. If they are not the same ratio you may need another prop."

This chart is for the engine serial number. The serial numbers I posted were the drive serial numbers. I definitely have a 165 not a 160. So if what I am reading in other posts is correct....the gearing ratios in the upper are what I need to be concerned about. But since I would only be swapping lowers I should be OK. ???

 

[ktbarrentine]

Re: lower unit swap on Mercruiser inline 6 outdrive

After dropping the lower and checking the impeller I later discovered...after initial post...that the lower drive shaft seal ....(I had put a new one in with the 1st impeller replacement) had been shredded. There was NO second seal.
The O-ring had been totally vaporized except for a 1/4" section. ....

If that is the case, then you would have lost the oil in the upper part of the drive, and it would have been replaced with water and eminently damaged. I hope that is not the case! Refer to an exploded drawing of your drive to see where those two seals are in the upper drive. I am hard pressed to believe you dont have two seals there. And based on you saying the lower seal was shredded, it sounds like the O-ring got caught in the seal during reassembly (common), causing premature failure. Word on the street is to leave that O-ring out, because it is not needed (the lower seal supposedly does the job). Of course, you have to have two seals to make it work right!

That's another reason why I remove my whole drive to do impeller replacement (along with other annual stuff). On reassembly (if you just dropped the lower), you cant see the "finished product" (i.e., the shaft where it penetrates the lower seal) to make sure it is OK. Of course, the post assembly pressure test would also indicate a problem if there was one. You do perform a post assembly pressure test, right?

 

[alldodge]

Re: lower unit swap on Mercruiser inline 6 outdrive

"This link below listed both serial Sterndrive serial numbers. Yours is listed as 67-69 Merc 160 and CL one is 70-77 Merc 165. If either link is selected it takes you to the same PDF catalog, therefore they will probably work. Only issue not clearly determined is the gear ratio. If they are not the same ratio you may need another prop."

This chart is for the engine serial number. The serial numbers I posted were the drive serial numbers. I definitely have a 165 not a 160. So if what I am reading in other posts is correct....the gearing ratios in the upper are what I need to be concerned about. But since I would only be swapping lowers I should be OK. ???

Sorry grab the wrong link it is
Mercruiser Sterndrive Modelliste I would post but the PDF file is over 3MB.

 

[achris]

Re: lower unit swap on Mercruiser inline 6 outdrive

The serial number of the drive only really applies to the upper (drive-shaft housing). Although most lower (gear housing) units will fit on most drive-shaft housings, there are a couple of different ratios. Only counting turns (or dis-assembly and counting teeth) will tell what the ratio is.

The correct ratio for a gear housing on your engine is 1.65:1. Just make sure the ratio is the same. (BTW, for a 165 the drive-shaft housing ratio is 1:1, so the overall ratio is 1.65:1)

HTH

Chris.......

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

Thanks ktb. I a newbie and still trying to learn and decipher what I am looking at and visualize how the parts go together when I look at a parts diagram. I initially thought the 2nd seal in the upper unit was supposed to be installed just like the 1st (not having one to see the difference). It just dawned on me that the seal goes around the upper gear that the shaft from the lower slides into duh! Yep! I'd have oil all over the place if it weren't there like I originally thought...Thanks for setting me straight!

After replacing the lower seal and impeller the first time I didn't do a pressure test...didn't know about it then but I will when I get the new seal in this time! Thanks again!

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

Thanks for the link AllDodge.

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

achris are you saying that the forward and reverse gears in my lower may be different than the one i would be replacing it with?

I should be able to compare revolutions of the drive shaft to determine if there is a difference shouldn't I? If there is, do I need to do anything?

Thanks

uspoet

 

[achris]

Re: lower unit swap on Mercruiser inline 6 outdrive

There are 2 different ratios used in the earlier Gear housings, 1.65:1 and 2.0:1. I have attached a chart showing all the possible ratios with all the different combinations...

Yes, you count turns on one shaft and the other.... If it's not the ratio you need, you have 3 options.
1. Move on, find a drive with the right ratio.
2. Change the gear set in whichever housing they are different to what you want.
3. If the ratio difference is in the direction favourable to your boat, change prop.

Chris........

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

Wow!!! Complicated!! It may take me a while to figure this one out. With all this new information I'm going to have to make room for this in my head and dump something....hope I can remember where I parked my car!

Since the replacement drive is both upper and lower would I be better off just swapping the the whole thing rather than just the lower? If I do that, any issues I should be concerned about?

Thanks achris

uspoet

 

[achris]

Re: lower unit swap on Mercruiser inline 6 outdrive

Wow!!! Complicated!! It may take me a while to figure this one out. With all this new information I'm going to have to make room for this in my head and dump something....hope I can remember where I parked my car!

Oh, we haven't started on 'complicated' yet... I have a wiring schedule from one of the junction boxes of one of the machines I work on (my paid employment)... I keep asking Don if I can post it, he keeps telling me 'NO'... Apparently he thinks it will make people's heads explode... You might just be my guinea pig...

Interested in seeing it????

Chris......

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

If I put my motorcycle helmet on I may be able to take a peak at it for just a second. If you don't hear from me within a minute or two SOMEONE will have a mess to clean up:joyous: My ex won't get any money when I retire....and she will hunt you down! You will be setting off a whole chain of events...butterfly flapping its wings....
If you think you are prepared bring it!

uspoet

 

[achris]

Re: lower unit swap on Mercruiser inline 6 outdrive

Ok... Don't say you weren't warned...

This is the drawings for one of the junction boxes on one of the machines (there are 10 pages in this drawing set). This machine has 3 like this (each with its own 7 page drawing set) and a 'control can' with the subsea computer in it... (that drawing also runs to 10 pages). And then there's the circuit drawing for each of the PCBs in these boxes... :facepalm:

Good luck....

https://docs.google.com/file/d/0B6Fkgjcx_cpaUzBTVGpOdmFXQnM/edit?usp=sharing

 

[uspoet]

Re: lower unit swap on Mercruiser inline 6 outdrive

achris when I clicked on the link it says that "This sites security certificate has expired"... I'm on a computer at work so apparently the administrator doesn't want me to see it. Whew!!! That was a close one!!! I think you are indebted to me now for saving you from committing homicide:laugh:
I'll check it out when I get home

uspoet