1991 Force 90HP - What Special Tools Are Required?

[Teddy78758]

Hi All,

New to the forum, and about to completely tear down and rebuild a 90HP 1991 Force OB (906F91A) - both the powerhead and lower unit. My question: what 'special tools' are absolutely necessary and why?

Some background: compression-tested the cylinders and got 100-70-70. Oil drain on lower unit produced a drip of light brown sludge. Looking at this project as a challenge - it was my grandmother's boat, who has passed, and has been sitting up for > 7 years. Would be really cool to restore.

Looking for people who have actually worked on these motors to give some friendly advice. Thanks in advance.

 

[roscoe]

Welcome to iboats.

Not going to be able to help much with the tool question.
But a good torque wrench and a puller to get the prop shaft bearing out.

But, it all depends on what the damage is?
Does it really need a rebuild?
Head gasket may be cause of low compression.
Or broken rings.
But did they damage the cylinder walls?

Lower unit, I would flush out, then do a pressure test, less than 5# of air, to check the seals.
All may be good after a good flushing and fresh lube.

 

[jerryjerry05]

Compression and a spark test first.
Pull the plugs and check for rust?

The low readings on 2 cyl. next to each other could be the head gasket bad??
The 100-70-70
That shows the test wasn't done right or the gauge might be faulty.
Good gauge= 150+/- 5#

Special tools: the 91 connecting rods need a special holder to install the new piston/wrist pin/bearings.

Get a FACTORY manual, the aftermarket ones help but don't really have the detail.

Lower unit: pressure test.
Lots of times the drain plug seal can be the problem.

U-Tube has a lot of Force videos that cover repairs.
The first 4 post in this forum have tips and procedures for some repairs.