Merc 200 lower unit

Hello members. Newbie here. I just purchased a 1966 14' jon boat with a 1967 Mercury 200 20hp motor on it. The history/condition of the motor was unknown. With the plugs pulled and the shifter in gear. I could turn the prop and motor over. So it isn't locked up. Only thing I know is the boats registration ran out in 2000. The guy said the motor was stored inside a shed. The boat, motor and trailer looked in really good condition considering their age and espically for $200. I get it home and start doing some PM on the motor. I knew that I at least needed to change the lower unit oil and install a new impeller before attempting to start it. So I removed the upper and then the lower fill plugs and only about 1/4 cup of water came out. No gear oil at all. I don't know if the oil was drained out a long time ago or if it has a bad seal somewhere and it leaked out. I think it's a neet looking motor and would like to keep in matched up with the boat. So I would like to know from someone with more wisdom on this issue on how to precede with this motor.

Check the compression first to really see where to start or if it is worth the expense. Next, put in some new gear oil. Then check to see if it is getting gas to the carbs when turned over. If it starts, don't let it run very long and shut it off to change the seals and the impellor in the lower unit. Clean and adjust your carbs and try to budget out for electrical parts where the wiring insulation is rotten. The boat is worth 200 so if it needs to be sold for motor parts, you will not be hurt. Great little motors if it can be restored, do it. Price a new one.

Checked the compression. Got 115 both cyl. That was in neutral with the control in the shift position. Before I had messed with anything on the boat I had went around it and sprayed things with Kroil. I had also pulled the plugs and sprayed some in the cylinders. It was shifting kind of hard so before I did the compression test I pulled the lower unit off. I wanted to have a look see on the inside of it. It was nice and clean.

After spraying some lube into the vent hole and letting it drain. The oil is coming out a brownish color. This indicates some rust on the inside. So a couple of questions to determine which direction I'm going to go.
#1 How tolerant are these lower units with having some corrosion in them. I'm sensing it needs to be torn down and cleaned at least. What say you?
#2 How hard should these things be to pull start? After the compression test I put the plugs back in. I had the wife pull it to see if she might even be able to start it in case of a emergency. She had a hard time pulling it and doubt she could start it. I just may have to go get an electric start motor.

I took the top off the water pump and pulled a vacume test on the lower unit. It did not hold and I could here it sucking air on the top. Trying to get the water pump base off. It appears to be stuck on by the gasket. Nowhere to pry on the front. Any tricks to get it off? The wife said go get a electrick start motor. Weather I keep or sell it I want to tear the lower unit apart to look at it at least. Are there any write ups on how to dissemble it.

Got the lower pump housing off. I didn't know you could access the front of the housing joint from the inside. Tapped a log thin flat screwdriver in and was able to break the front seal. Then with a soft touch and and a lot of gentle persuasion it came off. I think if I had a radio in the shop I would have played it some Marvin Gaye or something. The top bearing had some rust on one side of the bearing carriage. Going to have to take it apart.

tasthree said:

I took the top off the water pump and pulled a vacume test on the lower unit. It did not hold and I could here it sucking air on the top. Trying to get the water pump base off. It appears to be stuck on by the gasket. Nowhere to pry on the front. Any tricks to get it off? The wife said go get a electrick start motor. Weather I keep or sell it I want to tear the lower unit apart to look at it at least. Are there any write ups on how to dissemble it.

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I would need a Mercury manual for that kind of repair. Try Ebay. I would try to get it running before you overhaul the lower. That would be the only way to know what the complete assessment of your "gift" really is.

I got the lower unit apart. All the gears and all but the top bearing are ok. Going to order a new bearing, seal kit and a impeller.

Check the driveshaft where the seal touches. If it's rusted or pitted, you'll need to install a Speedi-Sleeve or the new seal will leak.

Jeff

fastjeff. Thanks for the heads up. Haven't worked on it much today. Been painting some and looking up parts. I took a better look at the drive shaft. There is about 1/8" of smooth surface above the bearing. Then a tiny groove which I can't hook a fingernail on. I'm assuming thats where the seal rode. Then there is about 1/16" of smooth surface before it starts to pit a little. I think a hit of emery and it should be ok. There are three shims in between the lower water pump housing and the bearing. Could I remove one of those shims to let the WP housing and seal sit lower? Just in case where might one get a speedi-sleeve. So far I've been putting parts into the Sierra cart. It's the only place I've found that has all of what I need

You'd have to find one for your shaft size on line.

From your description, I think you might get away with the shaft as is. Removing those shims raises the bearing, so you don't want to do that.

Jeff

Just wanted to update this. Got it back togeather. Actually last weekend. Well almost. Need another seal for the water pump. Ended up only ordering one the first time. Darn parts list on the site I ordered from skipped a number and I didn't catch that I needed two. While I was waiting for the seal I moved on to the upper. One cyl didn't have spark. Removed the flywheel. Somebody did a tune up on it. They put in one of the condensers so the wire rubbed on the inside of the flywheel. Waiting on new condenser also.

God protect us from such "mechanics!"

Jeff

Just wanted to update and finish this off as a succesfull thread. I've been working on others things while waiting on parts. Redid the transom on the boat. I cleaned and painted the trailer, rewired it including new lights, put new skids on the bunks, and put new wheels and tires on it. I got the last seal in and LU back on, new condensers installed, points set, new fuel line on, the carb and fuel pump rebuilt. Rigged it up on a stand with a water tub then hooked it up to the fuel tank. With reserved anticipation I started pulling on it. Within about a hand full of pulls it fired right up. Wahoo. Let it run for about five seconds and twisted it down to idle and it runs purrrrfectly. It shifted into gears solid also. I can hardly believe how well it runs after sitting for who knows how long. The boats last registration ran out in 2000. I'm just stoked and a very happy camper. Thanks for all your advice and what not. Now to finish rigging up the boat, get my numbers. sticker and hope for some nice weather to get it on the water.

Thank YOU for resurrecting another great old Merc.

Jeff

Agree! The classic 20Mercury (67+/- to 1980) was "King of the Road" in its day!!, Better than the 18 or 25 Evinrude or Johnson, IMHO, LOL's!!

The driveshaft, if a 67, is all carbon steel, if you can find a stainless steel later year replacement, I would swap it out next time it leaks. I think you want 76 and up and pretty sure the 76+ will interchange, check though.

Enjoy, nothing like a 20 Mercury!