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Mercury 90 2 stroke. 87-93 vs 94-06 differences.

J

Jho88

New member
I currently run a 1995 elpto 90 and it's running great despite finding some cylinder wall scoring. I purchased it under the premise that it overheats. I solved that problem by replacing the water tube, grommet, and exhaust plate.

The scoring worried me even though it gave me no running issues on dozens of 10-18 mile runs this year but I went out and picked up an 87-93 generation mariner 90hp for $50 hoping to have a spare powerhead to build not knowing that there was a generational difference.

Can anyone tell me what parts are and are not interchangeable between generations? Trying to decide if I should keep them as 2 separate engines or have one be a donor engine. The seller said the mariner ran in the spring but had a bad starter and trim pump motor which prompted him to repower.

Thanks in advance!
 
I know that ignition systems are different. I had a 2002 90 for about 10 years It was a running dude without any major problems.
 
Texasmark said:
I know that ignition systems are different. I had a 2002 90 for about 10 years It was a running dude without any major problems.
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did you run it with some scoring in the bore? I read somewhere that it could just be aluminum piston deposits and some people run it without issues. I could just get this 75hp engine running on the stand as an entire spare and use the 90hp trim bracket if I ever blow this 90hp. I would love for the blocks to be identical though then I can save up for pistons and rebuild the 75 and drop fhr powerhead on my 90hp.
 
I never had a reason to scope the cylinder or piston sidewalls. On a couple of occasions I peered down the spark plug holes and found clean piston tops as I had expected.

I would think that some scoring of cylinder walls/piston skirts especially, being aluminum, will/can occur over time. If not too bad, I would expect the engine oil to overcome any resistance to expected performance. I mean you have a piston running up and down in a steel cylinder liner, with piston rings making the seal and aluminum piston skirts banging the sides of the cylinders. Considering the piston rings, only 2 in loop charged engines, have an expansion gap allows for some compression leakage and I would expect that that would far exceed some microscopic scoring in the cylinders.
 
Blocks ,crank ,rods,firing order and pistons all different. The 87-93 is a small bore 71 CID and the 93 is a 84.6 CID
 
faztbullet said:
Blocks ,crank ,rods,firing order and pistons all different. The 87-93 is a small bore 71 CID and the 93 is a 84.6 CID
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Darn! Thanks for the info. I guess it won't be a spare powerhead. I suppose I can fix the trim pump motor issue and starter and flip it or keep it as an entire spare motor.
 
How is the compression?
If it's within 10% between cylinders I'd pretend I never looked and just run it. Worst that happens is you drop a cylinder and run back to shore at reduced speed.
 
I never checked compression and chose blissful ignorance. I'll check it soon. I'm currently mounting it on a different boat.
 
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