lower end won't drop 75hp 1985 merc 2stroke. 4cyl

happysteve · Aug 29, 2012

1985 merc 75hp 2stroke, 4cyl. serial A169314
Lower end won't drop. I have the service manual and a mechanic helping me. searched you tube, iboats, and even justanswers.com mechanic couldn't help so far. I bought this Proline 16' w/75hp Merc a couple months ago. It had been moored in salt water. the motor wouldn't start. replaced starter and cleaned carbs. It ran for an hour then motor bog to a complete stop, limp home idle only. Replaced fuel pump, fuel lines, fuel tank, fuel. Not fixed. ran 3 min., motor bog to completer stop, limp home. Motor would pee, but never very strong stream. Learned that worn out impeller may cause motor bog. (As well as stator)
Attempted to remove lower unit. removed 3 bolts forward and 4 bolts aft including anode. This model does not have a shift shaft nut to remove. I don't think there is anything to disconnect on the shift shaft? Or is there? Pry'd the lower unit down enough to get a putty knife, then 2 screw drivers, then barely the end of a crow bar. and still only an eighth inch gap, daylight all the way through. Then wedged chisels between forward stud nuts and cranked on nuts to force the lower unit downward, nothing advanced, still barely an eighth inch gap. what am I missing?
Have read that the drive shaft splines may be rusted to power head? If so, how the heck do you get it loose? Drive wood wedges a little more each day? & Hammer down on the torpedo? Can you get to drive shaft from the power head? & hit it down? Remove carbs? and access drive shaft with PB Blaster?... If someone has successfully removed a frozen lower unit, please help. Thank you, and God Bless!

Lyle29464 · Aug 29, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

1. Don't hit nothing.
Do a search on here. Maybe 10 things you can try. Some are easy some are wild. It would take me an hour to explain all of them.
Keep in mind if you ruin the crank it's over.

aussieflash · Aug 30, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

Keep going with the wedge evenly on both sides,your seized on shaft will eventually let go.Make sure 2 nuts still on loose so you dont smash on the ground when it lets go.Dont forget to rattle and shake the leg now and then with wedges removed for a little play.
Careful hitting the foot and if you must,use a rubber mallet.
Patients required.

jslu · Aug 30, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

(un) happysteve,

I had a very similar problem with a purchaseof a 1985 35 hp salt water merc.

I found that wooden wedges (even hardwood) did not work because the wedges distorted rather than exerting the much needed additional force. I finally resorted to opposing metal wedges (thin cold chisels) inserted as near as possible to the drive shaft and gently beat on them each day. After a week of this patient process it finally popped loose one day.
The drive shaft splines were definitely rusted to the crankshaft which created a tremendous expansive binding force.
Good luck,

John

happysteve said:
1985 merc 75hp 2stroke, 4cyl. serial A169314
Lower end won't drop. I have the service manual and a mechanic helping me. searched you tube, iboats, and even justanswers.com mechanic couldn't help so far. I bought this Proline 16' w/75hp Merc a couple months ago. It had been moored in salt water. the motor wouldn't start. replaced starter and cleaned carbs. It ran for an hour then motor bog to a complete stop, limp home idle only. Replaced fuel pump, fuel lines, fuel tank, fuel. Not fixed. ran 3 min., motor bog to completer stop, limp home. Motor would pee, but never very strong stream. Learned that worn out impeller may cause motor bog. (As well as stator)
Attempted to remove lower unit. removed 3 bolts forward and 4 bolts aft including anode. This model does not have a shift shaft nut to remove. I don't think there is anything to disconnect on the shift shaft? Or is there? Pry'd the lower unit down enough to get a putty knife, then 2 screw drivers, then barely the end of a crow bar. and still only an eighth inch gap, daylight all the way through. Then wedged chisels between forward stud nuts and cranked on nuts to force the lower unit downward, nothing advanced, still barely an eighth inch gap. what am I missing?
Have read that the drive shaft splines may be rusted to power head? If so, how the heck do you get it loose? Drive wood wedges a little more each day? & Hammer down on the torpedo? Can you get to drive shaft from the power head? & hit it down? Remove carbs? and access drive shaft with PB Blaster?... If someone has successfully removed a frozen lower unit, please help. Thank you, and God Bless!

happysteve · Aug 30, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

Thanks Guys, been reading posts here for over an hour. lots of good helpful hints.
Will do the wedges, PB Blaster and patience?. Hot & Humid working conditions in South GA. Inhaling the knats & feeding the Giant Stripped Mosquitos really sucks too! 'fraid I'm gonna beat the crap out of this LU before she gives!
Also got this tip: Unbolt Fly wheel nut, attach sliding hammer and slam it up! This will loosen the splines on drive shaft.
Then if all that don't work over this lovely Labor Day weekend, I may hang it upside down, (with a noose,by the neck!) spray PB, and continue with wedges.
The Wedge is the most powerful force we have. (Unless your Yoda, Darth Vader or that kid in the Volkswagen commercial) lol.
(not so happy yet) happysteve.

jslu said:
(un) happysteve,

I had a very similar problem with a purchaseof a 1985 35 hp salt water merc.

I found that wooden wedges (even hardwood) did not work because the wedges distorted rather than exerting the much needed additional force. I finally resorted to opposing metal wedges (thin cold chisels) inserted as near as possible to the drive shaft and gently beat on them each day. After a week of this patient process it finally popped loose one day.
The drive shaft splines were definitely rusted to the crankshaft which created a tremendous expansive binding force.
Good luck,

John

bigtrout1949 · Aug 31, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

Had success with this problem by inverting the engine and dribbling P.B. down the shaft and letting it soak. Go easy with the hammer!! Good luck

wn6ngp · Aug 31, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

bigtrout1949 said:
Had success with this problem by inverting the engine and dribbling P.B. down the shaft and letting it soak. Go easy with the hammer!! Good luck

I've got the same thing going with 90hp merc. Only difference is that I can see some slight separation mostly on the trim tab end and enough for a feeler gauge on the transom end. I have some wood splitter steel wedges that I could push in from both sides a little at a time. I've just been reluctant to use them as I figure they will bugger up the castings. However, they are like 3 inches wide so at least the force will be applied over a wide area. I sprayed a bunch of wd40 in there earlier. Like others have suggested I'll just have to go slowly. Shouldn't be out on the water over Labor Day anyway.

As others have mentioned wood just splits.

Reason for removal is to replace the water pump.

thanks for the tip on putting the nuts on there so it doesn't fall out and hit the ground all of a sudden. (don't I wish)

don

silvereagle · Aug 31, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

I too have the same issues,just got a saltwater 45hp,and everything seemed to come off easy as far as the 1bolt next to trim tab and the 1 bolt next to that,and the other 2 on each side,unless there are more?I can actually get a 1/4to1/2 inch gap and no more?I kinda gave up

wn6ngp · Sep 1, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

I have an official merc manual and it only mentions those 5 nuts. I am thinking about making 2 steel wedges and then slowly pressing those 2 into the gap with a large C clamp. I could also gently tap with a hammer. but....I'm still thinking...I don't want to mess up something.

This motor has been in salt like 20% of trips but normally sits on a trailer in my backyard. There probably is some corrosion but I wouldn't think a lot. I think my problem is that its 2000 model and never been apart.

happysteve · Sep 1, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

LU Not dropped yet.

Made the slide hammer for flywheel, Removed the fly wheel nut and threaded the slide hammer down on it. Hit it up (NOT DOWN) so many times that the threads stripped out of the threaded rod's... double nut welded to the 5/8" nut that goes on the flyweel. No damage to flywheel threads . Made a 4x4's pounding frame mounted around the torpedo. Put a scissor jack under transome mount to shore it up (boat on trailer was bouncing when we hit down on the LU.) Simultaneously Beat down on both sides of the torpedo 4x4 frame with 4lb mauls. Not budging yet. sprayed Penetrating oil up in upper exhaust vent, attempting to spray the drive shaft splines. Cranked stud nuts against the exhaust housing in order to push the LU down. not using wedges, just the forward stud nuts cranked against exhaust housing. Letting it sit now. will go beat on it some more tomorrow. Going to have to weld a beefier slide hammer connection with more threaded area than just one 3/8" nut receiving the slide rod welded to the 5/8" nut that goes on the flywheel shaft. Like a long coupling nut. Thinking about third guy to simultaneously smack UP on slide hammer as we hammer down on 4x4's around the Torpedo LU. This a killer job in this South Georgia Heat! Trying everything possible before cutting a hole in exhaust housing and either heating and pounding the drive shaft down, or just cutting it in two as last resort.
(not happy yet)
happysteve

wn6ngp · Sep 4, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

sorry to hear about your headache happysteve. I got lucky yesterday. Turns out that I had 1 mounting stud that was corroded in place. With a small axe and a wood splitting edge, PB, Mapp torch, another wedge drive and a C clamp I was able to eventually pry it apart. This happened over several days. It took lots of heat.

Are you really sure that your spline is frozen to the crank? Reason I ask is that when I got mine apart there was still a lot of grease on the end of the spline. I think many of your bolts are corroded in place.

after all this when I got it apart the water pump looked fine, even after 12 years. Go figure. Good thing I did it however, if I'd waited much longer I'd have never gotten it apart. They really should say to drop the lower unit every 2 years, and put back.

I think the root cause of the problem is that the hole that was corroded showed no signs of every being painted. All the other holes had the merc black paint in them. So now I need to decide what to put on the bolts when I put it back together. Maybe RTV or blue threadlock to keep the salt water from getting in there so much.

BTW, its 102 deg here in central Texas too. Anxiously awaiting the next cold front so the bass will get going and get some rain.

happydon

happysteve · Oct 5, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

Lower end FINALLY DROPPED! SOOOO... Three cans of PB Blaster, Removed pin from tilt and raised LU as high as it would go, put a piece of wood against transome for steering thing to rest on. Started 2 weeks ago with steak knives as wedges. Advanced to Butter knives, then double butter knives, then I sharpened my 2 hand axes and evenly pounded them in, then 2 chisels front and back, then 7 days twice a day of spraying penetrating oil, and pounding the axes in with a two pound maul. Crazy tough being patient. got it to about 1 full inch gap. Couldn't stand it any more! sank a 4x4 in the ground behind my boat, backed up, wrapped my cable come-along around LU and 4x4 and started cranking cable tight while pounding axes in. POW! I WIN! Drive shaft splines were just bone dry (no grease) and dirty, no rust 'cause it's SS. No guide pin on the top of my either. Took Impeller apart, it is bad, ordered parts. Hope this solves the motor bog problem or I'm attacking the Stator next.
happysteve, much happier!

wn6ngp · Oct 8, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

congratulations Steve, you have a right to be happy. you are a patient man.
I am guessing that it was stuck due to corrosion around those studs? You did not mention using heating. I am surprised. I am now a believer in PB too.

On mine it was just one stud and it appears that it did not have paint in the hole so I got some zinc chromate and merc paint and painted it after I cleaned it. Now that lower unit is going to come off every 2 years just to be sure there is no repeat of that problem.

My water pump was actually ok, but I replaced all the parts of it anyway. The pressure is a little higher at idle.

If you still have a problem with bogging down, my guess is that its due to carbs gunked up due to gasohol. I've had this problem periodically and have solved it with putting carb cleaner straight in instead of gas or using a very strong mixture. I think Sea Foam is ok to use as a gasoline replacement. At least it seems that I have not damaged anything. Ideal solution would be to tear down those 3 carbs but that would be a long tedious job.

Don

merc850 · Oct 8, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

Go to a Merc dealer and buy the Anti-corrosion grease put it on the studs, bolts, splines reverse locks etc. it works and is salt waterproof.

happysteve · Oct 8, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

Thanks guys, 1st: Don, no, I'm guessing it was the splines on the drive shaft were just dry and stuck, 'cause all the studs were out. I was using the stud nut to push the stud down and it stripped it out of the LU.
Also I never could see where to point my torch so I just never tried any heat for fear of burning it to the ground! It's also my first motor of this size so I didn't know what the LU looked like inside, and couldn't find any clear pics looking down in the LU. I was guessing where exactly to spray the PB Blaster, turns out I was close enough. Thanks Don.
Merc850: I have a 16 oz jar of Loctite "Thread Sealant with PTFE" So, while it don't say "Marine" here's what it says: USES: threaded metal and plastic pipes and flanges for steam systems and portable water systems for plumbing, heating, air, irrigation, appliances, swimming pools, and hundreds of other applications.... sooo is it the same thing as Anti-corrosion grease in a different bottle? jus askin"?
And while I'm jus askin.... I got from Fastenal (love that place)... CRC copper ANTI-SEIZE and Lubricating Compound. I was considering coating the threads of the studs and just about everythng threaded with it before re-assembling...wadda-ya think?
thanks!
happysteve

wn6ngp · Oct 8, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

OK, Steve, yeah, you could not have used heat if it was not the studs, no way you could get heat up to the end of that drive shaft. Its such a long..........way up there. Despite being 10+yrs old the upper end of my drive shaft still had grease so I was lucky that way.

My local Merc guy also said to use thread loctite red/blue on the water pump bolts which I did. That seals the threads off more than lubricates I think. Interestingly, the water pump itself came apart easily once I got the lower unit off.

One of my other friends had a 3 year old similar model and he had the same problem. Corrosion in that stud near to the transom. His boat was not heavily used in salt regularly and went to the lakes frequently. I think the problem is that the salt water gets trapped in there and if the aluminum was not painted well you are in deep yogurt. He had to go thru a similar pound/pry/heat/PB effort.

I slathered on a lot of waterproof grease over those studs and of course the drive shaft. But you can bet that I won't wait so long to break it loose next time even if the water pump is fine.

merc850 · Oct 9, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

The anti-seize should be used on all stainless steel fasteners to prevent galling, I use Merc products because they're made for Mercs and to support my local marine dealer. They also make an A-Corrosion spray.

halmc · Oct 9, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

About three years ago I pulled so hard on the lower end that it pulled the drive shaft out of the beveled gear down in the gearbox itself. in other words the shaft ripped out of the bottom end. When there was nothing other than the shaft sticking out of the power head it finally came loose with an improvised slide hammer (pulling the shaft down) when it came loose, it sounded like a rifle shot. Immediately thereafter, I could stick the shaft back into the end of the crank shaft and remove it by hand. There was no evidence of rust or grease!

I was reading this thread because I have yet another new-to-me 50 hp 4cyl, two stroke merc (serial # 6540519) which if I read correctly, is an '84. I'm about to try to remove the lower end from this fresh water motor so as to treat it to a new impleller, but I'm not sure anyone answered steve's questions about whether one must do anything to liberate the bottom parts of the shifting mechanism from the top.

SO: must I do anything with the shifting mechanism before I undertake to remove the lower end, and thanks in advance for any help.

EDIT: After making this post, I decided, post shower, to go out and try my hand at removing the lower end. Remembering that it took me nearly a full day of hammering, chilesing, and cussing to remove one from another engine a couple of years ago, the gods were apparently smiling this time.

And BTW, the shifter pretty much takes care of itself.

wn6ngp · Oct 12, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

you answered your own question.

glad this was a fresh water usage only. I've seen props corroded onto the splines from salt usage and no washing afterwards.

the only thing to watch for on the shift mechanism is to not lose that little coupler. could easily happen if you are seriously banging and pulling on things.

were you able to make the old one work without needing to replace parts? That is scary how that shaft held on there so hard.

Don

halmc · Oct 13, 2012

Re: lower end won't drop 75hp 1985 merc 2stroke. 4cyl

I was able to use the old pieces. Fortunately, the shaft that ripped out of the beveled gear (in the final drive) is secured by a very thin 3/8 locking nut. The threads on the shaft were apparently more hardy than the threads in the nut, so they (the threads on the shaft) survived. The little pin that secures the wp impeller on the shaft took a toll on the water pump housing, so I did replace it. I had to order a pack of six of the bevel gear reaining nuts. There was some damage to the face of the castings where I drove in chisels, and ultimately, ax heads, but since none of those are water tight surfaces, they were not pretty, but maintained good alignment of the guts. I sold the engine to a friend (after repowering my boat with a smaller four stroke) and it is still delivering good service.

I have to add that had I had the benefit of this thread, things might not have been so dire. There are several ideas expressed here that I might have tried to my advantage, befor breaking out the big hammers and wedges.

lower end won't drop 75hp 1985 merc 2stroke. 4cyl

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