Ok - motor builders aren't going to like this.

[rvaha]

Merc 1998 250 Efi. S#OG571005

2 weekends ago I lost #6 piston. It had a hole in it. I shared pics with with Don. Not sure what happened. I had a load of people and was pulling tubes and skiers. I thought it felt down on power but nothing big. Next day it seized around 4K rpm. Don and I think the damage was likely done from the previous day but not sure. I let it cool a bit and it restarted and I limped back on 5 cylinders. Water pressure good and temps looked fine

Don is thinking it may have hung a ring (from pic) but not sure. He flowed injectors last fall. It did not lose ring locator pins. He doesn't think it's a lean condition but not positive

So, I asked Don about sending it to him to rebuild. He's pretty busy and suggested I look at other options. I've spoke to Stan Carsen who I had would trust and a couple of other engine builders - not sure about them. Bottom line rebuild $4-5k.

So, I decided to rebuild just the 1 cylinder without pulling the powerhead and save some time and money. If it doesn't work then nothing Lost except some time

i pulled head. It looked fine. I pulled intake and reeds. Removed rod bolts and pulled piston. There was some aluminum transfer and minor scratching. I sealed off all holes in sleeve and used a small amount of muratic acid to clean off aluminum. I then used a hone to get rid of scratches and get cross hatching. I was very careful to keep any grit and acid out of engine. I used a lot of oil. Cylinder is round within a couple of thousands and is within a couple of thousands to the other cylinders. Cylinder looks really nice.

Resinstalled a new piston. I was very careful to make sure rod cap matched rod. I used a sharp pick till
i couldn't feel the break between the rod and cap.

Put it back together and ran it on muffs for a bit. Runs great. Running double oil. Compression exactly the same as before 102 on 2,4 and 6 and 105 on 1,3 and 5.

I plan to take it to the lake tomorrow by myself and run it thru Breakin. Hopefully rings will seat and compression will stay the same or get better.

I know the pros would hate this but thought I would share my experience so far. I remember reading that some of the 2.5 guys would replace pistons at a race without pulling the Powerhead.

I'll have the trolling motor on just in case!:). I'll post more results. If this works I'll have about $150
in piston and gaskets. Don't hate on me too much. Trying to salvage a weekend as my son comes home from college next weekend. Hoping I may get lucky and this be a lasting fix. Ill likely send injectors back to don as we need to find out why this happened.

I have before and after pics but not sure how to post. Wonder if anyone else has tried this before. Thanks. Rick. 540-521-5211

[crankshop1000]

A hole in a piston is almost always from running lean.You may want to pull the sparkplug on the re done cylinder from time to time to look for color and also for any aluminum.I'm saying good job on the fix,the only real unknown is any debris that may have gotten into the crankcase.

[rvaha]

That's what I'm thinking about the hole but Don was less convinced. That's my plan as well, keep an eye on the plugs. I have pyros to monitor exhaust temp but the senders are going bad. I have more on order. I got all the small pieces of aluminum out of the crankcase of the affected cylinder. Maybe there's some in other places - not sure. Don't think there's any steel as all rings intact. Also reeds are composite. Thx

[OldTimer57]

I have repaired one or two burned pistons multiple times over the years (using racing motors tends to make you an expert at doing that). Don't see a thing wrong with it. That being said, I've never tried to short-cut the system. I've always pulled the powerhead in my basement, separated the block halves and pulled EVERYTHING. That lets me feel confident that no grit or metal particles get into places I'd rather they not get. Most of the time I have had to replace the sleeve or sleeves that showed signs of metal transfer from the piston. Not a very hard job if your wife don't throw a fit when you bake the block a while to get the thing to release its almighty grip on a sleeve (mine was NOT happy, but that's another issue. Last time we replaced the oven, I kept it downstairs and hard-wire it to an appropriately fused connection when I need to bake the block).

I definitely agree with CS1000 above that hole is almost certainly lean. But there are exceptions. Once upon a time I had a 2.5 that was mega-strong. Lost two pistons at the same time. Running REALLY high compression heads from land and see with dual plugs per cylinder. I rebuilt the block, then went through everything looking for problems (this was a carbed racing motor). Carbs were all good, lines good, no leak around the old quick fuel line disconnect, etc. Friend of mine said bring me a fuel sample and I'll send it off (this motor required 93 octane, before ethanol became a bother). I bought some at a gas station I had not used. Tested at 86.5 octane. Of course, I would never be able to prove I bought the gas at this station, etc. Lesson learned. Other burns were from trash, etc, causing a lean condition on one cylinder. I'd certainly have the fuel delivery checked.

[rvaha]

Thanks Old Timer. I've had a couple of 2.4s apart so I know the routine. I've never had one in the oven. Brand new oven so I hope I don't have to go that route! I agree on the correct method. Seems I've seen posts on Scream and Fly where guys replaced a piston with powerhead on but that was during a race condition

From the pics Don thought it may have gotten too hot. He was also thinking cold seize but the air temp was in the 80's (humidity about 50% that day) and water temp about 88 and I'm pretty good about letting it warm up. He said that specs of aluminum will cause detonation.

I buy 87 with 10% ethanol either from Sheetz or Kroger on the way to the lake as I always tow. Both are very high turnover. I may bump it to 89. I'm taking it out today for testing. I may do a quick WOT and cut and then read the plugs.

Thanks all for the input. Like I said I know the correct way is to remove the powerhead and split the block. I may regret my shortcut (don't most always cost us!) but maybe I'll get lucky. I guess time will tell. I'll know more later today if it was a very short fix! If anyone wants or could post pics i would appreciate it. Many thanks. Rick. 54-521-5211

[nightbasser]

Was you running premium fuel with that big load in the boat? I would always run 93 if you are gonna be loaded heavy especially in the heat of summer

[jethro1]

Detonation or pre-ignition can both hole a piston without the mixture being lean at all. In fact, if a cylinder is lean enough it will run cooler than a normal cylinder. Think of a failed injector. As lean as it can be. No fuel, no power, no temperature build up.

Get a bad batch of gasoline, use old gasoline, carbon buildup on the top of the piston or combustion chamber, get a hot spot glowing in a combustion chamber, be over propped on a hot day, hammering down on the throttle at take off, etc., etc., and some bad stuff can happen. Detonation and pre-ignition are the ugly twin red-headed step sisters of engine damage. One can lead to the other. Both can destroy a motor. Before it is known to be happening.

[NoodleRodDude]

I have the same basic problem, No hole do you have an up date on your repair? thanks Dennis

[crankshop1000]

Detonation (preignition if you prefer) usually causes damaged ring lands,snagged rings and erosion to the exhaust edge of the top of a piston on a two stroke.Could be lack of octane or timing issues.A hole eroded in the middle of a piston is 99% always lean condition.Could be not enough fuel or an air leak.

[rvaha]

Update - I replaced #6 and it is doing fine. Ran it thru breakin by myself for a couple of hours last weekend. Compression is the same as before. But, I have an issue with #3 with a slightly turned sleeve and lost a ring locating pin that I need to address. I believe the sleeve was turned before breakin (but not positive as I didn't pull the starboard head). So, i think #6 and #3 likely occurred at a similar time during heavy loading with a boat full of people and and a bunch of tubers. I'm thinking it may have overheated. I didn't get any alarms and gauges were normal so I guess I missed it.

After 2-3 hrs of breakin I did a quick WOT and cut the engine and trolled back. Checked plugs at home and they all looked about the same (mostly black)

My next course of action is considering how to best fix #3, and after that I'm replacing water pump and going to check poppet. Also in the future I'm going to limit either people or tubes or how hard I pull (it pulls very hard with 19pitch prop) I think it was around 10-11 people with a few guys around 250lbs. This probably makes bass guys cringe!

Im happy with the repair on #6 as it did fine during breakin. I should have pulled the starboard head before the breakin run. I'll post more as I make progress. Time has been tight for boat repairs lately. Thanks for the replys and advice. Rick

[NoodleRodDude]

Thanks for the reply. The shop I took my motor to wants to replace the power head, retired so I cant do that. My motor is a 200 efi 2004 with 350 hrs on it. I am going to do the same repair you did. I will wait until spring, want to look at other options. Dennis

[NoodleRodDude]

Have you run the engine any more? I would like to know how its doing. Thanks Dennis

[rvaha]

Dennis - I got the cylinder spun back in place last weekend. I used an Inferno propane torch to heat it up enough to spin the sleeve. I haven't put the piston back in yet. Maybe this weekend. Thx.

[Savage]

Did you re-position the sleeve with the rest of the motors cylinders intact, pistons installed?

[NoodleRodDude]

Thanks for the up date. I think I broke a ring, what kind of money do you have in yours for the repair? Thanks Dennis

[rvaha]

Around $150 for the repair on #6. Includes piston and rings and cylinder head gaskets.

[NoodleRodDude]

Thanks vary much rvaha for the up date. Keep us posted. Dennis