I am having my motor worked on and we are having problems finding a piston for it.It is a 1997 200 mercury efi.I need the port side and it has to be 30 over.If you have one or know of a good place to get one please let me know.

Are you just doing that one hole? 30 over is a big bore. What happened?

Yes sir just the one hole is all thats needed so I am told.Said it looked like a fuel problem.It just ate that piston and tore that hole up.All the other ones cleaned up.

is it common on boats to only do 1 cylinder?

The 1 cylinder with a larger bore will create an imbalance issue due to piston bieng heavier. Also, an increase in bore will increase compression slightly unless the manufacturer modifies the pistons. this would cause a vibration.

I answered on S&F 'bout tha piston. Not really 'bout tha balance if your not turnin' tha thing 7grand plus, but more about a lean condition on a hole that big. Depends on tha ECU. There is a reason Merc doesn't offer that size piston for tha EFI's. Ya might wanna check into it a little more. Just hate ta see ya end up with tha same thing down tha road..........T

Please tell me more.I am being told its not a big deal to go 30 over.This isn't a high performance boat but I would like all the info I can get.What questions should I be asking?Is it a bad idea to do 1 hole,should it not be bored 30 over, please tell me all you care to type.

Might not be a big deal ta some guys but it is ta me and a few more. If ya got a shop doin' tha rebuild and says they will stand behind it (30 over on an EFI) then let 'em rip. Most of the ECU's will stand a 15 over but I don't trust 'em (ECU's) anymore than that. Like I said, Merc bulids lots of big pistons for carb motors (15 & 30) but not offered for tha EFI (only 15) even though they can use tha same piston. On a carb ya can run it and rejet if its lean. EFI is dependent on tha ECU. Has anyone said anythin' 'bout what caused tha burnt hole and what ta do 'bout fixin' it or were ya gonna just put it back together and hope it don't do it again?

I'm not sayin' yours WON"T run tha 30 over but it will be "on tha edge" and any kinda hic-cup in fuel delivery at high rpm could cause tha same thing ya got now.............T

Ok, partial rebuilds don't last long. If the engine is newer or has really low hours, and you can get away with a partial rebuild. But even then, 30 over on one hole is really pushing it.

However, on an engine that is 10 years old, and assuming it has normal hours, 300-400 for that model, then I wouldn't do a partial rebuild. Here is why.

You punch one hole 30 over. That is a big difference. You are now having one hole, not just up to factory specs, but beyond it.

The labor to break down the block, and put it back together are the same. They have to tear it all the way down, and send it to the machine shop. It is the machine shop that will eventually call the mechanic back to tell them what they really need to do once they determine how bad the block is hurt. What you save are boring fees (normally less than $250-350) to bore out the entire block vs. one hole. The other parts you need are the pistons, rings, bearings, new con rod, ect. Those are within $800-1000 for the remainder of the engine.

So what you're saving to do a particial is about $1200-1300. Sounds like a lot of money. But, I'm telling you, a 30 over on one hole is a big difference. I would be worried about how thin that sleeve is getting.

Plus, let's say they put EVERYTHING back to factory specs. Why would you put one fresh hole in with 5 tired ones? One of the other's will eventually fail. Especially trying to keep up with one fresh hole that is now putting out about 125-130% of a factory hole.

I tell people doing a partial is like giving a 75 year old man a 30 day perscription of Viagra, and a 21 year old bluxom blond. The heart and mind of the 75 year old man may keep up, but either his heart or his pecker is going to peter out.

In the end, you will have a motor that has been patched back together. A few months after getting it back, one of the other holes is going to let go. Then you have to do another partial. Then you get it back again, then another hole drops out of it. You see where this is going? Eventually you will have to rebuild them all. You can either build it 2-3 times and have 2 times the money in an over all rebuild, or you can build it once right, and if the right mechanic does it, it will be better than a factory motor.

Do the smart thing, build the whole thing. You will eventually save money in the long run. Call around to some other mechanics. They will tell you the same thing. Even if you have to bring it to Fort Worth to get fixed, it might be worth it. You drag your boat more than 2 1/2 hrs to go fishing more than likely. So dragging your boat 2 1/2 hrs to get it fixed right, might well be worth it.

But call around in your area first. I don't know anybody out there, so I can't recommend anyone. Gary is in littlefield I believe, but I dont know how far he is from Abilene.

Going 30Ths on one hole and all the others being standard is not really a big deal. The problem you will have is a lean fuel condition on that particular hole thats the reason Merc only offers a 15 over and as mike mentioned sleeve getting way to thin.The 2.5 litre 150,175 and 200 EFI come out of the factory as lean as possible to run on a stock bore and still live.Via Mercury, The weight of an oversize piston is approximately
the same as a standard size piston; therefore,
it is not necessary to re-bore all cylinders in a block
just because one cylinder requires re-boring......One other thing make sure they find out what caused the failure if not it will happen agian ....OPTI

Now thats scary! ole timey hot rod guy n a Merc mechanic agreein' on somethin' ..........T

Ok I definitely understand what you are saying about it running lean,so what should I do if the machines shop says its gonna take that much to clean the cylinder up.Find a new block?Sleave it?Is it junk now that it needs that much I guess is what I am asking.

It would be best to re-sleeve that cylinder.

I agree with resleeving the bad cylinder on EFI`s or any fuel injected outboard and always replace all pistons. Its about 2&1/2 hours from me too. Go with the best warranty.