Need to rebuild 90 HP lower unit - Help

111torrance111

Petty Officer 1st Class
Joined
Jan 8, 2006
Messages
275
Mercury 90 HP in-line 6, serial# A903298 (84-86)<br /><br />Removed lower unit, will not go into forward gear, nutural/reverse work fine.<br /><br />How hard is it to replace the gears on this unit, should it be attempted by somebody with moderate machanical skills or left to the experts?<br /><br />During a trip last weekend the boat was working great then acted like it spun a prop, it got me back to the doc just very slow.<br /><br />Please Help.<br /><br />Jerry
 

ZmOz

Captain
Joined
Aug 13, 2003
Messages
3,949
Re: Need to rebuild 90 HP lower unit - Help

I think it's rather difficult to rebuild if you've never done it before and don't have all the tools. I had a similar problem last year, I got a late 80s model lower unit on ebay for about $300, then I sold the old one listed as-is/broken...it sold for over $200. :)
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,780
Re: Need to rebuild 90 HP lower unit - Help

Getting the hub nut off (the big guy about 4" in diameter) is your first challenge and then getting the gears out (except R...it comes out with the hub). On going back together, the gear lash between the drive gear (off the input drive shaft) and the F-R gears has to be set. Need instruments for that. Use shims to get the correct clearance.<br /><br />However, if you just have to work on the prop shaft; like replace the clutch dog, or tension spring, your main obstacle is getting the nut off. I made a tool to get mine off and used a lot of penetrating oil. Also got a scribe and cleaned out the threads to help it unscrew once I got it loose.<br /><br />Drain your fluid first.<br /><br />You can always attempt it yourself and if you fail take the box of parts to your local marine mechanic. Usually they are pretty understanding and usually are busy and don't mind the fact that you tried it yourself.<br /><br />HTH.<br /><br />Mark
 

BF

Lieutenant
Joined
Apr 8, 2003
Messages
1,489
Re: Need to rebuild 90 HP lower unit - Help

I replaced the broken driveshaft and all the bearings on my V6 150... Figured I had nothing to lose... I had to make up some "special" tools, took some head scratching, but nothing was terrible.<br /><br />For the big 4" nut holding the bearing carrier, I used a blunt chisle tapping with a 3 lb hammer (not whacking hard). Move the chisle to other slots... came out fine, didn't wreck the nut. It didn't seem like it was too tight to start with. There are probably better ways to do it (I thought about making some kind of bar that fit across that nut), but this ugly way served the purpose.<br /><br />I made a bearing carrier puller from a couple of long threaded hooks that I hooked around the carrier... then put threaded ends through holes near the ends of about a 6" piece of bar stock. The stock sat across the prop shaft (across the prop nut). Tightening the nuts on the threaded hooks pulled the carrier back.<br /><br />I sacrificed a curved pry bar/nail puller, and ground the nail pulling end to fit into the slot for the shift linkage nut... The shifter rod fit between the 2 fingers (where the nail would normally slide in) and then I was able rotate the whole thing to take out that funny round nut.<br /><br />Lastly, I had to grind the sides off a wrench (make it thinner in profile) to get it to fit on the pinion nut properly. <br /><br />It was kind of an ongoing project for a couple weeks... I'd hit a snag then try and figure out what I needed to get the next piece off. A few skinned knuckles and brews later and it was back together. I think it's been 3 seasons of use since then.... still working fine. The parts still cost me ~$500, but it would've been around $2K if I had taken it into a shop. Timewise it was about a wash because the shops were so busy they wouldn't even commit to looking at it for a few weeks.<br /><br />Good luck..
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,780
Re: Need to rebuild 90 HP lower unit - Help

Amazing the work that can be performed when a person is relaxed and working at a reasonable pace and has a couple of brews to take the edge off. BTDT many times.<br /><br />Mark
 
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