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Author Topic:   Mercury 200-HP Lower Unit
TampaTom posted 02-21-2004 12:43 AM ET (US)   Profile for TampaTom   Send Email to TampaTom  
I'm going through a 1997 200 Merc that is new to me. I think that I have already established that an occasional knocking sound was coming from the gearcase which was filled with seawater instead of oil. I ran it the other day with moderate success except for overheating at higher RPM. I changed the impeller today but I'm unable to get the lower unit back on the motor. The shaft passes through two frame supports then into the crank. I shined a light up there. It seems that a ring/collar is between the top frame bulkhead and the crank. It's floating around up there and I can't line it up to pass the shaft through it. What is it? A seal that should be on the otherside of the crank endcap? Do I need to pull the powerhead?

Please don't tell me that I'm trying to run the shaft up the water tube.

Clark Roberts posted 02-21-2004 08:18 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Tom, first make sure it's in forward and that throttle lever is also in forward (this to ensure that shift is in proper position)! Get someone to help you hold and steady the thing and line up drive shaft in crank socket (there should be nothing floating around) and make sure that up tube from water pump aligns properly. At this point lower unit should be about half inch from home. Push and slowly turn prop shaft (this will turn drive shaft since unit is in forward gear) until splines align and she slips home. Hope this works for you. Happy Whalin.. Clark.. SCN
TampaTom posted 02-21-2004 08:36 AM ET (US)     Profile for TampaTom  Send Email to TampaTom     
Thanks Clark.

I'm not even getting close to home (still 2" to go) The shaft is being blocked by an object that the shaft had gone through before I pulled the lower unit off. Not easy to see, but looks similar to the shaft seal in the water pump. I've also tried to pull this "ring" out, but it will not pass through the top support hole.

Clark Roberts posted 02-21-2004 06:16 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Tampa, I've removed and replaced lower units on 200-HP and other Merc V-6's dozens of times and never had a situation like yours. Are you positive that you are inserting the drive shaft into correct location? Now just reevaluate the whole thing, start over and look up into head area and look for the splined crank. Insert into opening that is farthest forward in housing. There is nothing that can come off like you are describing... get someone who has done it before to help. Wish I was closer as I would come right over. Good luck... Clark.. Spruce Creek Navy
Dick posted 02-21-2004 09:41 PM ET (US)     Profile for Dick  Send Email to Dick     

Clark has described the assembly as well as possible and I can't add anything there.

Has anything been done to address the problem of sea water in the lower unit lube? If not, that should be the first priority. Find out why water is getting in and correct the problem. Gears have a tendency to blow when run on water or a mixture of water and lube.


Sal DiMercurio posted 02-21-2004 10:09 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Tom, Clark covered it very well so no need for me to go farther. My concern is you are saying you ran it the other day at higher RPM and she heated up. I really hope you're not running that engine on the hose at high RPM because that's a huge No-No.
If the boat was in the water, in gear, and she heated up, I'd change the thermostats first thing, because at high speed or high RPM the water is forced through the engine not by the water pump, but by just plain pressure from the boat moving forward at high speed.

What I'm saying: high speed heat-up's normally indicate bad thermostats, before water pump.

jimh posted 02-22-2004 08:37 AM ET (US)     Profile for jimh  Send Email to jimh     
I believe that the V-6 Mercury cooling system uses a poppet valve in the thermostat. This keeps the engine warm at low RPM by reducing cooling flow, but the poppet valve opens at higher RPM to increase cooling flow. If the poppet valve is not opening you may experience overheating at higher RPM.

Wrestling with the lower unit of a large engine when trying to re-assemble it can be a chore. Good luck in resolving the mysterious floating seal problem. Please let us know what it turns out to be.

TampaTom posted 02-22-2004 03:16 PM ET (US)     Profile for TampaTom  Send Email to TampaTom     
Thanks for your comments. Like I said its a new engine for me and I will be going through it systematically. First cleaned the carbs, found some wires pulled off the switch box, changed the gear oil (I did not run it with out oil.)
When I put it it the water to check how things were working, the temp alarm went off. Right back up on the trailer. My plan is to go through the poppet/thermo, however, stalled on this present problem. I've looked in manuals and have gathered other comments. Something is not right. I could probably get this object to line up with the shaft but since it shouldn't be there I won't. I'm taking it to a tech tomorrow and will report back.

Thanks again.

captreils posted 02-22-2004 10:02 PM ET (US)     Profile for captreils  Send Email to captreils     
I have seen this problem before.It is your lower crank seal that has come loose and is not allowing your shaft to go all the way up. Yes you have to remove the powerhead to replace the seal. At least while you have the powerhead off you can get a good look at your upper motor mounts. I recently worked on a 1996 200 Merc that needed upper and lower mounts.
TampaTom posted 02-29-2004 11:00 PM ET (US)     Profile for TampaTom  Send Email to TampaTom     
A tech stopped by and took a look. Its the oil seals but still don't get how the came past the end cap. Maybe it wasn't rebuilt correctly. Haven't been able to break the powerhead off the mid-section, so I'm going to turn it over to the pro this week.
Bigshot posted 03-01-2004 02:51 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Tom....not always easy to "pop" the head from the mid. Try rocking side to side, should go being foot is not on. I bet they forgot to tighten lower seal when they had it apart. Once head is off, put it on bench and rip the heads off and clean everything, etc. If she has been rebuilt, nothing should break coming apart. Get some never-seize for reassmbly.
TampaTom posted 03-01-2004 08:16 PM ET (US)     Profile for TampaTom  Send Email to TampaTom     
Thanks Nick. My wife told me I'm not allowed to yell at it anymore. Go finish the 20 other projects I've got going. I dropped it off today with the mechanic that has been advising me (friend of a friend deal). He took another look up there and said it looks like the spines are worn off the crank (we'll know more when he splits it.) He thinks water has been getting up there and causing major corrosion issues. Told me he will give me a rebuilt crank for $500 and put it in for $300 with new lower bearing and seals. Sounds like a deal to me. Hope that it stops there.

Steve Leone posted 03-02-2004 01:35 AM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
I know you found the problem but there is another scenario with the Mercs that is equally frustating. Sometimes an extention kit is added to make a regular shaft outboard a longshaft. These conversion kits come with a driveshaft extension piece. Its only about 5 inches long. If you remove the lower unit and the shock of shaft does not come with it it can be a bear to re-align. On another note when installing a kit for the first time it is necessary to ream the intermediate out in order to clear the shoulder on the extension piece. Its either that or remove the powerhead and stack it from the top. The price you had quoted sounds very reasonable. Thats about 18 hours of flat rate work. Steve
Bigshot posted 03-02-2004 11:09 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Sounds fishy....$800 is DAMN cheap and how can he tell the splines are worn from looking up the mid. Make sure you see that crank before he rips it down and make sure he is on the ball.
TampaTom posted 03-03-2004 02:59 PM ET (US)     Profile for TampaTom  Send Email to TampaTom     
$800 is damm cheep, thankfully, I won't have to pay that. You are correct, as usual, he couldn't see anything and the crank is fine. It was not oil seals but was a water seal. He had to put a torch on it to get it to split. Get it back tomorrow and I will do the thermos and poppet valve.

armrey posted 12-18-2008 07:21 PM ET (US)     Profile for armrey  Send Email to armrey     
[This thread was dormant for almost five years before being revived --jimh]

[Is there a diagram that illustrates the technique used] to replace the seal kit on a 200-HP Mercury outboard?

jimh posted 12-19-2008 08:42 AM ET (US)     Profile for jimh  Send Email to jimh     
Usually the service manual has a diagram or illustrated procedure that shows how to perform part replacements. Investing in a service manual is usually worth the cost when planing on doing repair work on an engine yourself. You can get some exploded view diagrams of Mercury gear case assemblies from on-line websites such as Mercury Parts Express.

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