lower unit 1970 20 hp mercury

[fd203]

just looking for opinion, I have a 20 horse that when running and in neutral the prop turns slowly, not fast and if you apply a Little pressure to it it does stop spinning but when pressure is removed it will spin slowly again, not sure how bad of symptom this is or if this could be normal. also after it is used in the lake lower unit oil is a little milky so Ive been changing it after every use, am I damaging the lower unit to bad by running it this way? as you can tell I am very green when it comes to outboards but am trying to learn all I can. Thanks for the Help.

 

[Gerald K4NHN]

Re: lower unit 1970 20 hp mercury

I have a 1972 model and the prop turns when it's in neutral when it on the muffs but doesn't' turn when it's in the water.

The milky oil tells me that the seals in the lower unit is letting water into the lower unit. I would think that it's coming from the seals around the water pump where the drive shaft is...

problem had the same proplem years ago because the shaft had pitted over time where the seals are located. A couple of years later they started to use a S/S drive shaft. I didn't it replaced and didn't have any more leakage.

I've had to go back to another old lower unit with a pitted shaft because my son hit a stump and bent the prop shaft about 6 months ago. :'( I'll have to run it until I can locate a prop shaft to put in the lower unit that I have with the S/S drive shaft.

I don't keep the gear oil changed so you don't have the bearings going bad until you can get it fixed. Gear oil is cheap.

Any one have a K4NHN Cayce laying around that I can get.

Gerald K4NHN
Cayce, SC

 

[Gerald K4NHN]

Re: lower unit 1970 20 hp mercury

When I spell checked my last posting it really messed it up. I'll try it again. I don't know how to delete it.
Gerald........

I have a 1972 model and the prop turns when it's in neutral when it on the muffs but doesn't' turn when it's in the water.

The milky oil tells me that the seals in the lower unit is letting water into the lower unit. I would think that it's coming from the seals around the water pump where the drive shaft is...

I had the same proplem years ago because the shaft had pitted over time where the seals are located. A couple of years later they started to use a S/S drive shaft. I had it replaced and didn't have any more leakage.

I've had to go back to another old lower unit with a pitted shaft because my son hit a stump and bent the prop shaft about 6 months ago. I'll have to run it until I can locate a prop shaft to put in the lower unit that I have with the S/S drive shaft.

I would keep the gear oil changed so you don't have the bearings going bad until you can get it fixed. Gear oil is cheap.

Any one have a prop shaft laying around that I can get.

Gerald K4NHN
Cayce, SC

 

[Motor Boater Bill]

Re: lower unit 1970 20 hp mercury

fd203: prop turning some in neutral is probably OK, just the drag of the LU oil can cause this. Keep that oil changed until you can get the seals done.

Gerald: Have you looked into having a sleeve put on your shaft? May solve your problem. If you have a good drive shaft on one unit and good prop shaft on the other you may be able to swap them out.

 

[Gerald K4NHN]

Re: lower unit 1970 20 hp mercury

Yea, I've thought about the sleeves and checked into that. They were $29 each and it would take 2.

I may just marry the 2 together. It's always nice to have a good spare lower unit around because the boat is used in the Santee swamp and it get a lot a stump knocking down there.

Gerald K4NHN
Cayce, SC

Gerald: Have you looked into having a sleeve put on your shaft? May solve your problem. If you have a good drive shaft on one unit and good prop shaft on the other you may be able to swap them out.[/quote]

 

[Motor Boater Bill]

Re: lower unit 1970 20 hp mercury

I found a propshaft on eBay a while back, ended up getting it for about $25-30 with shipping, if I recall. Don't see them too often. Marrying the two you have will buy you time to hunt for one. Good drive shafts seem to be the scarcest part out there, I'm still hunting one for my "spare" lower. The rocks, trees and stumps of the Cumberland River here make the spare lower seem like a good idea to me, too!

You might also see if a machine shop can straighten the propshaft you have, if it's otherwise good.

 

[Motor Boater Bill]

Re: lower unit 1970 20 hp mercury

fd203: You can drop the lower unit and pressure test the lower unit with air to see where it is leaking. Drain the oil, make an adaptor, give it 15 psi and put it a bucket to see where the bubbles come out. It may only need one seal to fix it up. At least you'd know where you stand. If you pull the water pump housing you can inspect the shaft seal surface there to see what kind of shape it's in.

I've also heard some folks suggest using Lubriplate 105 in a leaking lower unit, since it is thicker and will resist leakage better than LU oil. Everyone seems to agree that it is best to fix the seals.

In the meantime, changing oil after each trip will keep corrosion from setting up in the LU. If you are getting a lot of water in it there is the danger of not having enough lube but if it just leaks a little you should be fine. To see how much it is leaking, keep the oil you drain and let it settle for a few weeks in a glass jar, you'll see the water puddle in the bottom of the jar. Don't let it freeze with water in it or you can bust the LU housing.