68 merc lower unit won't come off

[fmfmedic]

I am trying to remove the lower unit from a 1968 merc 650. Have removed all the bolts and nuts from front and rear (trim tab bolt, bolt under the trim tab and the nut under the mount), and loosened the two in the middle (they won't come off until the unit is free, not enough room). The long bolt at the front, under the mount, appears to be frozen inside the shaft. The lower unit flexes at all places except the front when I pry on it or use the two middle nuts to put pressure on it. I have used heat on the housing without effect. I've put the nut partially back on and hit it with a wood shaft and hammer without success. I have also soaked it with penetrating oil. What can I do next?

Thanks for any advice!

 

[steely51]

Re: 68 merc lower unit won't come off

My best guess would be the drive shaft is frozen into the end of the crank shaft There is not much of a way to get penetrant or heat where you need it. in my mind, what there is left of it, Mercs are well known for this malady. among others like, frozen props to propshafts. always grease or neverseeze when assembling and on a yearly schedule....

 

[aussieflash]

Re: 68 merc lower unit won't come off

So your saying still one bolt seized on, holding housing together?Can you post a picture?

 

[fmfmedic]

Re: 68 merc lower unit won't come off

So your saying still one bolt seized on, holding housing together?Can you post a picture?

Here are the pictures. The first has an arrow pointing to the bolt that appears to be stuck in the housing. The second shows the gap between the exhaust housing and lower unit, with no gap at the bolt area and up to 1/4 in at the other end. The drive shaft is near the middle and appears to move at least a little, while the front won't move at all.

 

[aussieflash]

Re: 68 merc lower unit won't come off

Doesnt look like drive shaft stuck though could be shift shaft seized as its located at front.Cant believe that stud is located in such a tight spot.Did the nut come off OK?....I would get a wedge on the front and close gap at rear to level surface and start hammering.

 

[fmfmedic]

Re: 68 merc lower unit won't come off

Excellent Idea! There is a place above which will support a wedge and I can reach it with a dowel or socket extender. I never thought of wedges, just direct force and levers. I'll try it and let you know what happens. Thank you!

 

[fmfmedic]

Re: 68 merc lower unit won't come off

Well, that didn't work. The only place to put a wedge, or prybar, was a crossmember for the engine mount. I put enough force on it that I was afraid of damaging it, without effect on the bolt. I'm going to soak it again in penetrating oil and then put a long rod on the end and start pounding with a BFH. IF something breaks, well, I can't run it the way it is anyway. Thank you all for your help.

 

[Moody Blue]

Re: 68 merc lower unit won't come off

Wedges are the right approach. Your implementation is wrong.

Use wooden wedges (door jam shims or window shims) and place them strategically in the gap between the LU and the exhaust housing on each side of the LU. The idea is to provide equal force all around so that you don't bend or break something. Once the wedges are in place tap them in a little at a time equally with a hammer. If needed, you can stack two wedges together to increase the angle. You will be able to impart a tremendous force between the two housings without directly prying on anything. Leave the wedges in place and keep putting the penetrating oil to it.

 

[stormmnv]

Re: 68 merc lower unit won't come off

I have found that plastic logging wedges, used for falling trees (not splitting wood) work great for this. They can be cut to any width and stacked. They can be ordered on-line if you do not have a logging shop in your area.
I had one 50hp that I tried everything on, including drilling a hole in the scag and using a axle remover hammer, and still could not get the main shaft to release. Note: I also placed some spacers between the flywheel and upper housing to help reduce the pressure off of the crank bearings during impact. I have had (I worked on the coast) and heard of this problem on many Mercs. (mainley those in salt water) but with preserverance, penetrating oil and patience they all came apart in due time. Good luck

 

[fmfmedic]

Re: 68 merc lower unit won't come off

Sorry it took so long to get back. We had some spring projects for me to do. I got the lower unit off yesterday. I've been putting penetrating oil on it periodically since my last post. Yesterday, I used a 16 oz ball peen hammer and a rod and pounded on the stuck bolt and nut, after heating it with a propane torch for about 10-15 minutes. Left the torch on it while pounding and it finally started moving down until I could put the wedge idea into play. It came off, not easy, but it did come off. Thank you to Moody Blue and Stormmnv. The wood wedges just peeled against the aluminum edges but composite wedges worked great! It was the bolt holding things up with heavy electrolysis corrosion. I might even be able to reuse it! Reminder to self...use grease on bolts when reassembling! Now just need to remove drive shaft, replace worn gears and shift assembly, water pump seals etc. Compression is 120 on all cylinders so it's well worth working on. Thank you all, this forum is a lifesaver!

 

[chum1]

Re: 68 merc lower unit won't come off

use some of this stuff or similar when installing nuts and bolts, you will be glad you did later

Permatex 80071 Anti-Seize Lubricant - 4 oz.