Mercury 2.5 questions

Hey folks

So you may remember me from last year. I have an ole JohnnyRude 150/175 that just never would live up to what it should be. Some suggested that it has a porting issue, and after finally getting the jetting dialed in, it still won't do what I want. I'm pretty sure those who said the exhaust ports may have been altered are probably right. It's sad because it's a solid runner in the low to mid range. Just falls off on the high end.

So... after a TON of help from RJ getting the jetting figured out (I'm forever in his debt) I gave up.

I'm coming to the dark side. Last weekend I picked up an old clapped out Stratos Fish and Ski with a 2.5 Merc on it. SN: 0G216747.
I got it cheap... and found out that the headgasket is blown on cylinder 1 giving me 65psi of compression on that cylinder. All other cylinders are 110. (15 degree ambient temps)

Cylinder 1 has a very light rust trace, but you can't feel anything with your fingernail. The middle cylinder has a very small amount of scoring, that again you can't feel with your fingernail.
I was thinking I'd order new rings and just regasket it, hone it and rering it.

So I measured the bores with a spring T-bar and a dial caliper (I know not the best, but it's what I have)
I only have the bank one head off, and they measure 3.501 3.502 and 3.502.

I intentionally didn't look up specs because I didn't want to mentally sway what I found. I tired to look up specs tonight and I found 3.494, meaning from what I can tell, if I hone it, I'll need to go to a .010 over piston. But then when looking for pistons I found a couple listings that said ".010 over piston for a 3.5" bore"

Wait... if it's a 3.5" bore... then I should be more than good to just hone it and rering it.

So to make a short story long....What REALLY is the spec? If I hone and re-ring it is pretty reasonable for cost, but adding 6 pistons and possible machine work is quite a bit more...

What do you guys suggest?
Slap a set of gaskets in it and run it for the season?
Hone and Re-ring what I have?
Or do I actually need to start eating Ramen and order up some pistons?

I know it will be asked, so I'll note it again here... Serial: 0G216747

Thanks guys!

Put some head gaskets on it and run it. Get some satisfaction. Enjoy it for the next season while making a plan.

3.501 is correct bore. The piston is what measures 3.494. Personally I would hone and re-ring as long as I was sure the scoring would not morph into an issue. If you just throw a couple head gaskets at it and run it with "light scoring" you may damage an otherwise decent block. If scoring is in any way substantial the correct way is bore and go with new pistons. Good luck and welcome to the dark side.

Rock

Attachment 480362Attachment 480363Attachment 480364

The 3 pics... first one is Cylinder 1 with the blown gasket. I'm guessing when it popped it drained some water into that cylinder causing the rust. The picture actually turned out really good, it's kind of tough to see really.
Second pic is the middle cylinder. I ran my finger all over those scores, I don't feel anything at all. I'm thinking because of those, I may do the hone and re-ring. I'd like to pull that piston and see what the cause is, and correct it. If it's just carbon, great. Easy fix. If I have to find one piston, that's not the end of the world either.

But like you said.. I'm a little worried about that one giving me more issues down the road with that light scoring turning into bad scoring.

Clean it up with a brass or stainless brush. Check for pitting. Gasket and run.

streaks don’t mean scoring they can hide it though.

a proper. Fix would be pulling it apart looking for corrosion in the wrist pins and such.

clean and run should be fine though.

That middle cylinder looks like the skirt of the piston rubbed.... maybe overheat..... I'd at least pull that piston and have a look.

Can you see any damage on the piston through the exhaust port?

Quote:

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Originally Posted by flabum1017

That middle cylinder looks like the skirt of the piston rubbed.... maybe overheat..... I'd at least pull that piston and have a look.

Can you see any damage on the piston through the exhaust port?

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I measured the bores. 3.501, 3.502, 5.502 for that bank.

At the point I can re-ring it for $425 in parts... so I think to be safe, I'm going to pull it down for a full inspection. If I need one piston... thats a whole lot cheaper than needing a sleeve, or worse a whole powerhead.

I'm hoping to pull it all down in the next couple weeks.

I'll keep everyone updated here as well.

Diesel, did not see any water diverters in your pictures. Maybe they are in there, but if not put them in.

https://www.screamandfly.com/showthr...ight=diverters

Quote:

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Originally Posted by rjdubiel

Diesel, did not see any water diverters in your pictures. Maybe they are in there, but if not put them in.

https://www.screamandfly.com/showthr...ight=diverters

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I didn't know anything about those!

I'll look for those and reach out for more info if I don't find them.

Any other things like this, that I don't know about that should be done on this motor while it's down?

You just need to decide if your going to re-ring it OR put new head gaskets on and run it! haha. It should be killer VS the OMC crossflow of last year running heavy tournament load, full fuel, full livewell to keep the fishies alive, all that.

At this point, I'd like to do it once, do it right and be done... but. Economical.

I think doing a re-ring is the best and probably the most logical step. So... providing I don't find any major issues when I pull it down, that's the way I'm going to go.

That scoring bothers me. If it's nothing... great. If the cylinder got hot and messed up the piston skirt, that could be bad down the road.

It's a nice motor. I dont want to put a hole in it! Lol