Cylinder #4 is toast.... please help diagnose (w/ pics)

1990 120hp L-Drive

A few months back I was on the river. I just got the boat on plane and then 5 seconds later it lost power. The boat would run, but only at 1/3 - 1/2 power. I limped it back to the dock, took it home and let it sit until now.

I started simple with a compression check. Cylinder 1 (top one) 135lbs, cylinder 2 133lbs, cylinder 3 127lbs and cylinder 4..... 0lbs. So off came the head and here's what I saw






Not good!

I found some shavings in cylinder 3, but it surprisingly read 127lbs on the compression test. Not sure if the cylinder is trashed. Cylinder 4 is mega-trashed.... not even sure if it can be bored enough to rid of those gouges.

Please speculate as to the cause and requirements for repairing. Is cylinder #4 going to require a sleeve? Do the spatter marks on the head render it useless?

Also, where can I get replacement motor parts for the best price?

Thank you!

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

diagnosis...cyl #4 is toast...

since its an L-drive i would consider looking for another boat...parts to rebuild or replace head will be tough to find...repowering is more than likely out of the question on L-drives unless you close up transom and put a bracket on it and hang a outboard....but at minimum your looking at a rebuild and might as well do all 4 holes while ya at it....$1000+ if you do it yourself...$2000-$2500+ if you pay someone to do it....good luck bro

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Any idea as to possible culprit?
Leaking head gasket? I know water can do some bad things to a hot piston crown.

Also, why would the head not be usable? I cant imagine the spatter marks would change the volume of the combustion chamber? I'm no mechanic though, so I'm just asking.


thanks!

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

looks like your rings failed? theres a few possibilities.......when i said replace head i meant powerhead...

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Like sucking in air which created a lean condition causing the exhaust side of the piston crown to melt?

I've been riding & rebuilding 2 stroke motocross bikes for many years, but I've never seen a piston look like that before. At least until now.

Does anyone have any input on the head? Salvageable?

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Cheap parts...better grab 'em.........
http://cgi.ebay.com/ebaymotors/ws/e...TRK:MEWA:VRI&viewitem=&item=260174874689&rd=1

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

contractorguy said:

Cheap parts...better grab 'em.........
http://cgi.ebay.com/ebaymotors/ws/e...TRK:MEWA:VRI&viewitem=&item=260174874689&rd=1

Click to expand...

Damn!
It's local pickup only in Minnesota. I'm in Oregon.

thanks though.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Looks almost as if that piston got hammered by a loose carburetor screw being sucked in or part of a crank or wrist pin bearing that went bad due to wear failure or lack of lube. Any missing bearings for that cylinder? Pretty substantial damage. Head looks fine as long as it didn't suffer any warpage or too much damage around the gasket surface area. However,... by the pic of the powerhead, it almost looks like some blockage around the cylinder's water jacketing. If that's the case, could be a lack of cooling for that cylinder. Which...systematically leads to bearing failure. Usually the wristpin bearings first. Which of course the cylinder naturally inhales as bits of very hard pieces of metal. Hence, the dents in the piston top.
Forget resleeving...usually bucks and very difficult to do.
Search Ebay for used powerheads, motors if you enjoy or don't mind doing the work yourself. If not...probably cheaper to replace the entire motor with a used O.B.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

brandonv said:

Damn!
It's local pickup only in Minnesota. I'm in Oregon.

thanks though.

Click to expand...

I wouldn't worry about that 'local pickup' comment. E-mail the seller and tell him you'll pay him a few bucks (arrive at a price) to crate it and ship it for you. If you throw a bit of money at him.....it's not that big a deal to crate it up a bit. His concern probably lies with the type of buyer that would expect him to crate it and ship it...for free. (...not)
This minor effort for a ready to go power head will pay you back in spades for your effort.
Good luck.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Maybe this is a bit more convenient. This is a guy just north of you out of Washington State who specializes in Force rebuilds (including L-drives).
Again....good luck.



http://seattle.craigslist.org/est/boa/463616447.html

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

try this site. I just found stuff that I have been looking for for quite a while, cheap too.

Here

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Thanks everyone!

Matthew A,
thanks for the input. I'll pull the motor this weekend hopefully and figure out exactly what happened.


I've read posts from another member whom only bored 2 of his cylinders, leaving the other 2 at stock bore. Is this a viable option for me? Will the additional weight of the oversized piston cause balance issues? I hate to bore in-spec cylinders if they dont require it.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Kajun37 said:

diagnosis...cyl #4 is toast...

since its an L-drive i would consider looking for another boat...parts to rebuild or replace head will be tough to find...repowering is more than likely out of the question on L-drives unless you close up transom and put a bracket on it and hang a outboard....but at minimum your looking at a rebuild and might as well do all 4 holes while ya at it....$1000+ if you do it yourself...$2000-$2500+ if you pay someone to do it....good luck bro

Click to expand...

Rebuild parts are NOT hard to find. My brother-in-law just rebuilt my L-drive this year... The only part that he had a hard time finding was a 1" hose from the lower to the powerhead. And that he found at an autoparts store.

Total cost on my 3 cyl was around 1500.

$18 bore per hole
$40 or so machine heads
$100 to grind crank
$950 parts (gaskets, pistons, rings, carb kits, sealers, head bolts, odds & ends)
$65 or something like that to have my prop rebuilt


I am EXTREMELY happy with this rebuild. So happy, I'm gonna sell it in the spring. I'm not having ANY problems with it, but according to most of the nay-sayers here, I will. Better to let someone else have to deal with it, I guess.

I will say this -- many of the parts for the power head are interchangeable with the outboards, so rebuilding the engine will be relatively the same as a regular outboard.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Ray Charles and Stevie Wonder could see what the problem is.

You melted a piston due to detonation, due to a lean run condition. If both carbs had gone lean, the engine would have lost power and speed. Because of the lost speed and power, detonation would probably not have occurred. You would have limped back to the dock and started looking for the problem. The problem is that you did not have a fuel filter between the fuel pump and the carbs, so, assuming you did not monkey with the needle adjustment, a piece of crap got into the lower carb and caused the bottom two cylinders to go lean. The top two pistons carried the engine through detonation until the #4 piston was so bad that the engine practically would not run. This was probably a few seconds timewise--certainly not more than 20. It doesn't take long and if you do hear the detonation, by that time, it is too late. I did not
see the #3 piston but I'll bet there is at least some minor melting on its crown too. It usually happens that way: one piston is real bad and the other not too bad and probably useable in a pinch

Now: The head is dented both from the shattered ring pieces that the piston pushed into it and from the detonation forces. However, the damage is not that deep and the head is about 1/4 inch or so thick at this point so it is still useable. Not the best, but useable. See: the head never gets as much damage as the piston because it is cooled.

You can bore to .040 (that works out to .020 on each side) and that is a lot. From the photos, it looks like that would clean up the cylinder. If it does not, Wiseco has cylinder liners available to re-sleeve. Liners cost about 100 labor another 200. Pistons are available with .020, .030, and .040 oversize. Your piston is so badly damaged I can not tell if it is a 3.3125 or a 3.375 bore. Makes no difference, pistons are available for both.

The pistons are machined to proper clearance size so the cylinder is bored exact to the oversize needed. The machine shop will tell you what you need. Just for an example: If the bore is 3.375 and you need .020 to clean it, then the machine shop bores and finish hones the cylinder to 3.375 plus .020 or 3.395. A good machinist won't need to worry about tolerances--He will be able to get to within a couple of 10,000 (.0002). First let the machine shop bore it, THEN order the pistons.
Now: From the little bit of it I did see, I did not see much damage on #3 cylinder BUT if it is worn out of round or tapered more than .002, it also must be rebored. You CAN rebore and replace just one or two piston(s)/cylinder(s). Since replacement pistons are balanced to factory specs, the engine won't even notice them. That's if money is the primary governing factor. If you are going to bore 2 cylinders, and a couple of hundred extra won't bankrupt you, then go for all four and essentially have a brand new engine. The amount of work to do 2 and 4 is damn near the same--still need to disassemble and reassemble the engine.

If you are going to do the work yourself--and it is easy--, 4 pistons, 4 overbores, Clymers manual, and gaskets will cost around 1,000. Do yourself a favor and disassemble and clean both carbs before using.

Also, when you disassemble, the gaskets on the reed blocks and manifolds will almost certainly be destroyed so get new ones. The exhaust cover gaskets are also not usually reuseable as is the engine base gasket. As a matter of fact, factory gaskets all had a sealer on one side and it will be the rare gasket that comes off in one piece.

At any rate, your engine is rebuildable depending upon how much work and money you are willing to put into it.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Full gasket sets for rebuilding the powerhead on Ebay for 78 bucks. Include all gaskets neccessary for a rebuild.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Clymer's manual is a nice thing to have....

But Frank Acampora's endless knowledge is a MUST HAVE. The guy knows things that no one else knows. I think the guy should have a website, or a 900 number to be able to ask questions, for his input.

"I can't get my engine to idle..." or "What should the timing be for a '79 Dodge Dart?" or "What should I get my wife for our anniversary?"

Just don't ask him math -- 'Quick... What's the square root of 7?'

...'2.... point.... uh.... niner.... B....'

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

contractorguy said:

Cheap parts...better grab 'em.........
http://cgi.ebay.com/ebaymotors/ws/e...TRK:MEWA:VRI&viewitem=&item=260174874689&rd=1

Click to expand...

Yeah, that's a deal if you can arrange for shipping!

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Many thanks for the replies.

I will rebuild over the winter, so you'll certainly be seeing more posts by me. I just dont have time to strip it at this time between work, family and racing this weekend.

Many thanks to Frank A for the diagnosis. I've only had this boat for a few months and have not touched a thing. I did run the gas tank dry that day, so maybe it sucked something from the bottom of the tank as it was scavenging for fuel. I dunno....

If anyone runs across parts locally or on ebay then please PM me if you're willing. I would certainly be appreciative!

thank you!

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

NEVER,NEVER,NEVER run a marine engine out of gas, those few seconds as the carb fuel level is getting low the cylinders lean out, the cumbustion temp skyrockets and begins to melt pistons. Engine speed and horsepower starts to climb and in just a second, it's rebuild time.

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

If you are going to have to bore the sleeve oversized then you should do ALL the cylinders. Not just one or two. If you do, the engines displacement will be out of "square" and the rotating mass will be out of balance significantly. The slight difference in weight with one larger piston will create a substantial vibration at rpm's above 1,200 and possibly even lower. The, "only do the cylinder/'s that are bad", is not a good fix unless you are wanting to off the boat to some sucker.