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replacing pistons on 1986 150 merc outboard

H

harnessedenergy06

Member
hi everyone, my question is if I just do pistons and rings how in depth is that. #1 and #2 pistons are toast. I do plan on replacing all the pistons and rings. Thanks!
 
Check the cost of all the parts and compare to a reman powerhead. There is alot of labor involved for what you are doing. You may find all sorts of worn parts...crank may be scored.
 
Agree - it's rarely "just the pistons" - since you are in there you may as well do the connecting and rod bearings. And of course you will get a look at the crank and the sealing rings may be nicked, and the main bearings may have some slop - plus, of course every gasket and seal you touch will have to be replaced.

Now, there is "total rebuild" kits out there in varying degrees of "completeness" - some with just rings, gaskets and bearings, others including pistons, main bearings etc. They generally range from 700'ish to 1200'ish bucks depending on how "complete" they are - but can give you a "rebuild in a box" set of parts should you go that route.

You still have to add on honing or boring of the cylinders. I always leave that to the experts at a machine shop - unless you do it all the time it's not worth cheaping out at this point - if you are going to tear down and replace anything, have a shop look after the cylinders (average about 50 bucks a hole, so figure $300 for a 6 cylinder).

Additionally, you still need to find the "cause" of the two toasted pistons - they are the "result". Most often it's a fuel system issue that caused them in the first place (clogged carbs is high on the list).

The parts to correct the cause are not part of the rebuild kit. Even if you go for a reman powerhead you will have to swap over your ignition, carbs etc, so whatever toasted the current one MUST be corrected.

(sound like I have rebuilt a couple?) :)

All in all, doing the work yourself, you can figure on dropping upwards of 2 grand to fully rebuild/restore a 6 cylinder. Now that may sound alot but you will get a "like new" motor and it's about 1/7th the cost of a new 150.

Food for thought...
 
Thanks for advice from guyjg and galamb, yes you do sound like you have rebuild a few. you mentioned it may have been the clogged carbs. the other pistons compression were 115-120 on all 3,4,5,6 the head had a piece of what looked like a ring welded to it. Question again. If my friend never mixed oil with the gas would all the cylinders be smoked? Sounds funny but REALLY my friend not me. Lol! I lent him my boat an got it back locked. then I unsiezed it and got it to start ran for about 3 minutes. then would not start did a compression check 20psi in #1 and 25psi in #2
 
Your motor had 3 "pairs" of carbs - the top pair feed cylinders 1&2, then so on. If you had no oil in the gas (either mixed or via the oil injection) then yes, all your cylinders would be toast.

Since it's 1&2 that are shot then I would suspect 1) your top carb assembly is clogged up or 2) your cooling system (impeller etc) is partially toast - an overheat seems to take out the top cylinders first (I don't know exactly why) - but my top suspect would be the top carb pair (with the others probably pretty close behind).

If you are going to rebuild I would do all three carb pairs as well - yes, it's about 100 bucks a kit for each carb, but you don't want to toast cylinders 3/4 after you have already torn it down once.
 
...."...an overheat seems to take out the top cylinders first"

Sure, for the cooling water comes in the bottom, getting warmer as it rises in the block.

Jeff
 
Thanks again for the advice carbs and impeller. Question can I just do the top end? Is it possible to pull the block only and replace all the pistons and rings? Or do I have to take the flywheel and the lower end apart to fix that. I would clean all the carbs(rebuild them) I don't think there is anything wrong with the rods,crank,etc. It might be a stupid question. Just curious.
 
Thanks for the info about the parts place. I will go ahead and rebuild the 1986 150 at least I know it was running great before any problems. Can any body tell me were I can get the pullers to take off the flywheel,etc. I would buy them if it is not to much. If you know of a place. Napa,Autozone, Sunset marine are about the only places around for me. I have rebuilt motors before but never a boat. I like to learn new things and right now the motor not doing any good. I will keep you updated and I am sure I will have more questions.
 
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