Compression issues on merc

[theboatman69]

Hello all,
I have a 87 merc V6 135hp black max. Recently i was on the water and my power dropped down a thousand rpm. I believed at that point I lost a cylinder, went to shore and loaded up the boat. So when i got home i decided to do a compression test. All was good until i got to cylinder 2. That cylinder has No compression what so ever. Not even a little blip. I put my thumb over the hole to test and no air whatsoever. So where do i start guys? Do you think its possibly a reed valve issue? The boat has ran good all season until now so im at a loss and dont know where to start. Maybe there are some tricks I dont know about? Thank you

 

[flyingscott]

Not a reed valve issue pull the head off.

 

[ondarvr]

Major internal damage, reeds have nothing to do with compression.

 

[theboatman69]

Thank you. OK so I took the head off. You guys are right. A chunk of piston broke off........sh#t. So I guess my question is now is it worth getting this beast bored and fixed? What would have caused this? I was looking at my oil injection and nothing seems out of place...

 

[theboatman69]

Can anyone guess a price for it?

 

[ondarvr]

It's not worth just doing one cylinder and piston, if you do it, do a complete rebuild or don't do anything. Probably a grand or so.

 

[theboatman69]

So it involves stripping the motor down to the block, taking it to a machine shop, getting all 6 bored and new sleeves. The new pistons, rings etc? Is this a correct assumption? Winters in canada are long... might be a nice project for me.

 

[ondarvr]

No new sleeves, that would add significantly more money, just bored.

 

[theboatman69]

Would i have to get bigger pistons if this happened?

 

[ondarvr]

Yes, all new pistons, rings, bearings, seals, gaskets, etc. it adds up fast.

 

[flyingscott]

I believe you have a 2.0 block so look at this kit. http://www.ebay.com/itm/Mercury-Mar...ash=item5419b79428:g:7qMAAOSwHptY-Iyf&vxp=mtr

 

[theboatman69]

Really appreciate all your help guys. I'm going to try to rebuild it. Engine ran so good when it was working. I will post when I can about progress.

 

[racerone]

Remove oil pump and driven gear.---See if the plastic oil pump driving gear on the crank is damaged / stripped.----Where in Canada ?

 

[444]

What kind of shape is the cylinder in? Sometimes it's still ok and you can get by with just doing a piston. If the rest compression tested good and you don't have $ to burn, I would probably do just the one if I had to. One these two strokes, as long as the compression tests out good, IMO your time and effort is better spent focusing on making sure your engine is sealed well, good crank seals, etc. I have several OLD two strokes that I have pulled apart, resealed and put back together with the original pistons.

 

[theboatman69]

I'm in Alberta, Canada. The piston chipped half off the top......really sucks and the sleeve got wrecked as well unfortunately. There are a lot of scratches in it. The sad part is I've been on kijiji and seen engines for cheaper than I fear the rebuild will be. Every cylinder is good the oil injection seems to be working....I wonder if there was just a bummed piston....I really love this engine I have done a bunch of electrical to it. Just sucks.

 

[ondarvr]

When one set of piston and rings go, the rest may not be far behind, especially on a 30 year old motor, so doing one doesn't make much sense, all the other costs and labor are the same

 

[theboatman69]

I have been looking for a cylinder block and bloody hell they are expensive. I'm trying to get in touch with a rebuild shop (for the bore) and nothing yet

 

[444]

That sucks. If doing a rebuild is beyond your mechanical abilities I don't think it would be financially viable to have this one rebuilt. A full rebuild would probably be around 1k in parts and you will get killed on labor. If you just drop off your engine I can't see walking away for less than 3-4k. Chances are you would be better off parting out your engine and buying another one.

If it was my engine, I would pull it apart and bring the block in to the machine shop to have them see if they can bore out the bad cylinder. I *think* yours is the 2.0 V6 with the iron cylinders so it can be bored. How mechanically inclined are you? I could go into detail about how I would just do the 1 cylinder but if pulling apart an engine is more than you can tackle then it doesn't matter.

I would try to think about why this piston went boom. Pistons don't usually let go for no good reason. Usually it's because you're low on oil or more often, leaned out at high speed. Bad crank seals, leaking crank case, leaking intake manifold/carb can allow too much air in and nuke your piston. I've overhauled a lot of two strokes that were just old from age and wear and only needed the crank seals replaced and crankcase resealed along with a fuel system overhaul. I've also scrapped some where the return on investment just wasn't there.

 

[Faztbullet]

Advance module did it

 

[theboatman69]

As I research more and more I do believe it overheated. It happened at WOT which really sucks. I am mechanically inclined and a piece of me wants to break it down. I have it off the boat sitting on my bench now but I don't know if I want to break it down. I guess worst case is I part it out all my power packs are new and so are the coils and stator/ trigger is in good condition. I think I'm going to try your suggestion and take it to machine shop and see what they say. The breakdown will start next week I'll let you guys know how it goes with pics. I know cars well, how hard can it be for a outboard? (That's just a bad joke btw) also I think your right when you say the advance mod is part of the problem.