Stuck another one....

[flabum1017]

Stuck another piston in the same hole. Pro-Marine piston, 15 hours of break-in, opened her up a few times and the third time after a minute of runnin, stuck it. No detonation...top of piston looks perfect, skidded at 4 o'clock and 11 o'clock on the skirt. This is the second piston to do this in the same hole.... bottom starboard (#3). Using Merc Premium Plus at 50:1 and high test. The aluminum transfer did not get to the ring area, still have 125 - 130 psi. The motor still runs great, but had a rattle after it stuck. Going to pull the piston this weekend and do some measuring....

Anyone got any ideas?

Here is a pic of the first piston that stuck.... I'm sure the second one looks the same:

[Jay Smith]

Can't tell how big the bore is BUT I never run any engine that has a 3 1/2" bore or more any less than 40:1 on oil ratios...

Good luck,
Jay

[flabum1017]

It's an OMC crossflow 3.5" running 5600 rpm. 50:1 should have been fine for it.

[afr]

i say the cyclinder is out of round or changing with heat
somthing is flexing

[Greg Moss]

have you changed the rubber water deflectors?

50-1 is fine for that motor

What motor is this? Is it a 235 or just a flat back?

[flabum1017]

have you changed the rubber water deflectors?

50-1 is fine for that motor

What motor is this? Is it a 235 or just a flat back?


it's a v-4 crossflow bubbleback. All cylinders were bored .030 over by a reputable machinist. All deflectors are new. New exhaust stuffer, new exhaust housing, all new bearings, all new Pro-Marine pistons. Carbs completely gone thru twice. Stock fuel pump, QL77JC4 plugs, new packs and stator, timing at 24*, 22" Raker prop running 5600 WOT and a so-so holeshot. This is a complete rebuild with no expense spared. I have built litterally hundreds of these with no problems. This is the first one I have had a problem with.

I will do a bore measurement this weekend.

[afr]

do a hot and cold bore measurement

[Airboater]

time for a looper

[baja200merk]

time for a looper
:iagree:

my friends cross flow had one hole so out of round the piston barley came out and then i tried sticking an new one in for kicks and it wasnt even close :p that block went in the garbage as expected:D

[flabum1017]

time for a looper


I was actually leaning that way.... can the 60* V-4 be modded well or should I stick with a 90*?

[baja200merk]

I was actually leaning that way.... can the 60* V-4 be modded well or should I stick with a 90*?

90* is the way to go.. read every post laker has ever made then build it:p

[flabum1017]

90* is the way to go.. read every post laker has ever made then build it:p


Time for a frankenrude......

[flabum1017]

Back to the question at hand..... why am I sticking in only one hole?

[sosmerc]

Is this a dual pack motor? If so, maybe you need to index the flywheel to confirm that timing is consistant on each cylinder. Maybe step up a main jet size on that cylinder. Got the cooling hose deflectors in the proper location?
Are you running stock thermostats and poppet housing?

[JUPITER PULSARE]

It's time to come over to the Dark Side!!;)

[lokinutz]

Fresh .030" bore, everything else is new and to stock specs...no porting or anything worked on, I think it's a cooling issue in the block.

[Greg Moss]

Well are you sure you have the deflectors in the right spot?

If it was my motor I would cut about 3 turns out of the T-stat bypass springs and gut the t-stats also. You live in an area that the water is warm most of the time.

Check the bore very well. If the cylinder is round then you really have a cooling problem. If the timing or fuel was bad the top of that piston would be melted. Stick a bend-a-light in the big water passage in the top of the block and see if when you look into the water passages if you see good light. You should be able to tell if you have any blockage that way.

[CharlieB53]

Measure your bore, then torque the head down and remeasure the bore from the bottom, you want to see if there is any change.

I haven't heard any of you mention torque plates during boring and honing. They aren't needed for simple fishing motors but I would expect scream n fly guys to be far more particular.

[Greg Moss]

Measure your bore, then torque the head down and remeasure the bore from the bottom, you want to see if there is any change.

I haven't heard any of you mention torque plates during boring and honing. They aren't needed for simple fishing motors but I would expect scream n fly guys to be far more particular.
I don't know if a torque plate would do alot of good on an outboard. On car motors the head-bolt are right next to the cylinder walls. On an outboard there is a water jacket in between the head bolt and the cylinder wall. I have thought about it many times but just don't think it would be that much of a difference because of the water jacket spacing.

[Riverman]

And the open deck of the block!

[Paul Vaillancourt]

Could it be a "cold sieze" ?

[racer]

Clearance or cooling issue, make sure the engine is running between 125 and 140 degrees if your clearance is at .0065.

[Specialized P4-12]

just sosmerc said.. we have been finding that the triggers on mercs have to be checked at full advance timming for every cylinder.. i dont know about the omc stuff... but john marles told me he was having people sticking pistons for no aparent reason and so he started checking timming on all 6 and recomended we do the same.. so now we just buy new triggers and go from there...

[flabum1017]

The cooling system is all new, new springs, valves, t-stats and even a new housing. Deflectors are all new and in the right places. Remember, the t-stats are usesless after 2,000 rpm on these motors since the releifs open up and you have basically a free-flow of water. Both are opening well. The use or no use of a torque plate has no bearing on this problem since it is sticking at the bottom of the bore. the top of the bore is fine, in fact, my compression is at 125-130 all around.

New piston is on it's way and I will pull it apart tommorrow and let you know what I find. The powerhead is sitting in the back of my truck right now.

Someone told me to check the powerhead mounting bolts for length, seem he came across one that someone had put longer bolts in and the bolts bottomed out against the bottom sleeve pushing it out of round. The cylinder I am having problems with is #3, and all the bolts on that side are stock, so it's not that. Just thought you guys would like to hear of that type of problem.

[flabum1017]

Is this a dual pack motor? If so, maybe you need to index the flywheel to confirm that timing is consistant on each cylinder. Maybe step up a main jet size on that cylinder. Got the cooling hose deflectors in the proper location?
Are you running stock thermostats and poppet housing?

I'll do the indexing when I get it back together, but I doubt that has anything to do with it since the tops of the piston looks perfect.

[E-tec1]

running pre mix i assume

[flabum1017]

running pre mix i assume



Stuck at 4 o'clock and 11 o'clock, I'm betting an egg shaped hole down low.

[flabum1017]

Most mercs do not have any top piston damage either when they have a timing problem, you need to index EACH CYLINDER, and check again. Alot of scratched heads have come from here. Darrell


Plenty of scratching here.... I will take all advice and do everything even if I think it has nothing to do with this failure. One thing I am not afraid of is work.....

[flabum1017]

Well, got it apart, everything was well coated in oil. All the bearings are perfect, the other three pistons are perfect......

[flabum1017]

Claened up the bore and used a bore gauge on it....


The first pic is of the top of the bore, the second is bottom..... as you can see, the taper gets bigger down low. I did this check all around the clock and have no out of round, only a slight taper that gets bigger at the bottom. The only thing I have come up with is maybe the port are too sharp, seems the scuffing originates at the port edges and they feel a little too sharp for me. So I'm going to do a good honing and soften up the port edges a little more and slap a new piston in and see what happens.

[afr]

hummm
well you know there has to be a mark on it right out of the box
fire it up load test it and take another look before you go to the point of sticking another one

[faztbullet]

Silly question, How do you bore a tapered hole with a boring bar. When I bore a block, my top and bottom are the same size. Maybe I am doing something wrong ..Kwik-way FwII.:confused: :confused:

[flabum1017]

Silly question, How do you bore a tapered hole with a boring bar. When I bore a block, my top and bottom are the same size. Maybe I am doing something wrong ..Kwik-way FwII.:confused: :confused:


I don't know, but you see the numbers in my pics. This hole has 100 hours on it since a re-bore. Unusual to see the bottom of the bore bigger than the top.

[j_martin]

Silly question, How do you bore a tapered hole with a boring bar. When I bore a block, my top and bottom are the same size. Maybe I am doing something wrong ..Kwik-way FwII.:confused: :confused:

Part of setting up a boring tool is figuring out how much both the tool and the piece being bored will move.

If the cylinder is free at the top, and solid at the bottom, and the boring bar doesn't flex much, it's likely to be a bit big at the bottom because the top of the cylinder flexes away from the tool as it's coming by.

Close tolerance machining, to my eyes, sometimes resembles magic.

John

[sosmerc]

I would assume the other 3 cylinders would exhibit the same dimensional characteristics as the cylinder in question. Yet, you didn't see any problems with their pistons. That leads me to believe your problem is elsewhere.
At the very least I would put a slightly fatter main jet in the carb that feeds that cylinder. I would also look very carefully for anything that might cause an air leak into that cylinder, such as a bad transfer cover gasket, or warped intake, loose reed block, etc.

[Greg Moss]

I would spend extra time looking at the water passages. You have a cooling problem with that cylinder. Don't know what it is but I would be alot of money on a passage bad or one of those deflectors being in the wrong position.

[GTO GEORGE]

The greater clearance in the bottom of the bore didn't cause it to seize, and the top of the piston rules out leaness or too much advance. If you're only turning it 5-6k the 50:1 should be OK. The only thing left is cooling; there's a hot spot somewhere.

[flabum1017]

I'll be taking a real close look at the cooling again. I did mention earlier that the ports are a little sharp. I'll be chamfering them some as well. Deflectors are new and in the right place.

[FlowMaxx]

Good luck finding the problem. This should be a solid, long life motor. My two suggestions are: Chamfer the edges and upjet that hole 2 sizes to be safe. Never seen a piston damaged in that way before. A bigger jet in that hole will cool it down a little. Also, you may want a washdown button for deceleration after high speed runs.

[racer]

I mentioned cooling as it is important to get the engine to temp before running above 1500.

Cant tell from the photos, but when it was bored did they go beyond the recess at the bottom, if so and the recess was not cut back in very tough to hone to the very bottom.

[scott reierson]

I had a xflow that did that. Drove me nuts until I found it.

Did all the new stuff. I finally pulled off the stat housing off under the bubble and pulled all that stuff out. End of problem. The motor had some light salt use that caused the stats to stick shut.

I can't remember what I left in the housings, if anything , or what I used as a restrictor if anything. But after that I always checked this area in my xflows before I ran them. Getting that stuff back in with lower cowl on was next to impossible

I've had some other V4 140's with the same issue. Since your in the warm you may be able to run without them.

Racer can give you some insight on that. Hope its that simple for you.

Scott






Fresh .030" bore, everything else is new and to stock specs...no porting or anything worked on, I think it's a cooling issue in the block.

[FlowMaxx]

GOOD POINT. Pull off the water jacket covers. I had a salt set once. opened it up just to be safe. Completely plugged with salt.

[flabum1017]

Ok guys, the ones who stressed checking the cooling system were right on. I started putting it back together and went through the block with a fine tooth comb. I found some silicone stuufed deep in the water jacket under #3 (the hole in question) right near where the water comes in, I found a couple of pieces of inpeller in the cross-over in the bottom of the block. This crossover is a blind passage that delivers water to the port side of the block and has a plug on the sterboard side where they drill it from. A bent piece of copper tube and 160 PSi of air pressure blew the impeller parts out and a long hooked pick got the silicone out. Where this stuff was, you had to really look for it. This block I got from a local dealer and had been a problem ever since I got it.....seem the problem is solved.

I have been a marine mechanic for 25 years and the one thing I have learned is this, when you are really scrathing your head for answers, don't be afraid to ask. And don't pass on reccomendations just because you think it couldn't be it.

Thanks guys.

[afr]

hahaa
see i was right

lol
it heated up warped out of round and bam

[lokinutz]

Glad you got it figured out. I have been keeping an eye on this thread to see what it ended up being. Cooling issues can cause major headaches. Hope it runs good for you for a long time, after what you have gone through.