reason for 90 hp v4 pistons failure

[JoshKeller]

posting this for an older guy without internet that is in my bass club. this is a late 80s 90 hp 'rude. all 4 pistons and rings were replaced in 2016 due to a broken ring. he was fishing today, and lost power. brought it over, and the two starboard side pistons had a ring failure. top still had 90 psi with a broken ring, buttom zero psi. pulled head and found ring dents. pulled powerhead, disassembled and this is what we have found.

bottom (with 0 compression).
https://vgy.me/ThQpZK.jpg

https://vgy.me/jNq5nu.jpg

https://vgy.me/XVFwy6.jpg

top cyl with 90 psi, but still a broken ring.
https://vgy.me/sCtJfr.jpg

https://vgy.me/jpKdwS.jpg

i am going to help him rebuild this motor, as he cant afford to have a shop do it, but id like to insure it doesnt go down again, so im asking for opinions on why she blew. being both on the same side, it has me thinking of a possible overheat. i would think detonation wouldnt happen over both carbs on one side. possibly bad pistons? given he told me it started idling poorly and coughing a few weeks ago, im thinking the rings broke then, and just now sent one though the combustion chamber. im also wondering if perhaps the shop that did the rebuild, or perhaps vibrating after running has changed the timing?

[flabum1017]

Ring caught th port, possibly port was not chamfered properly......

[JoshKeller]

its already bored .030 over. is the block likely scrapped now? its pretty easy to find an old v4 block that hasnt been bored over as much.

[racervboat]

Looks like it got hot? wiseco makes .064 over pistons if its not that bad a lot cheaper than a sleeve.

[JoshKeller]

edit - figured it out.

[JoshKeller]

come to find out, the motor previously broke the same two cylinders last time it went out. this rebuild lasted 1.5 years. i did notice the lower water diverter is gone - would that cause them to fail again? here are the bottoms of the failed pistons if that helps any..

https://vgy.me/koBKw0.jpg

[flabum1017]

Missing water diverters will make hotspots..... yup

[flabum1017]

Your's looks more like a ring caught the port ............here's what mine looked like from overheat:

404719

[powerabout]

Your's looks more like a ring caught the port ............here's what mine looked like from overheat:

404719
not seen one look like that after an overheat?

[flabum1017]

bottom cylinder kept over heating due to a blockage in the block

[spybot]

bottom cylinder kept over heating due to a blockage in the block
How did you fix the blockage ???
Run a hose to flush out the block in the opposite direction ???
I think i have the same problem in a motor i have just stripped down. Number 3 piston cooked and blcok scored. When i took of the l/u i found some bits of the impeller stuck in the water pick tube. Just at the point of entry. I will have to figure out if its lodged any parts in the block and the only way i figured was running a hose in the oipposite direction of the flow.
Is there a better way ??

PS dont mean to high jack this thread

[racervboat]

Usually the pieces of impeller will go up the water tube and get stuck in the adapter plate and block off water flow.

[spybot]

Usually the pieces of impeller will go up the water tube and get stuck in the adapter plate and block off water flow.

Cheers Ken
I will have a look today
Would the reverse flow idea work to remove the "Stuck/Blocked" pieces?

[racervboat]

????? you might have to remove the side plug on the adapter plate.

[JoshKeller]

im guessing these horrible ports are to blame?

https://vgy.me/eBk2Lq.jpg

https://vgy.me/SN0a65.jpg

[racervboat]

Yeah they don't look like they were chamfered , wiseco also makes .044 and .064 pistons you might get buy ?

[JoshKeller]

Yeah they don't look like they were chamfered , wiseco also makes .044 and .064 pistons you might get buy ?

im assuming all 4 would need replaced, and not just the two blown ones? its certainly an option, im just trying to help the guy get a reliable running motor, and thus far, hasnt proven to be one.

[flabum1017]

How did you fix the blockage ???
Run a hose to flush out the block in the opposite direction ???
I think i have the same problem in a motor i have just stripped down. Number 3 piston cooked and blcok scored. When i took of the l/u i found some bits of the impeller stuck in the water pick tube. Just at the point of entry. I will have to figure out if its lodged any parts in the block and the only way i figured was running a hose in the oipposite direction of the flow.
Is there a better way ??

PS dont mean to high jack this thread

the blockage turned out to be an impeller blade stuck in the passage between the port ans starboard banks.... there is a small ( 1/2") diameter plug on the side of the block just above the bottom that is pressed in......, I drilled out that plug and found the blockage.

404757

[71V153]

Only have to replace/rebore the bad holes. No need to do all 4.

That one pic looks like the ring locating pin fell outa the piston?

[Markus]

im assuming all 4 would need replaced, and not just the two blown ones?

No need to fix what is not broken. Just fix the bad holes. Whoever rebuilt it probably saved some time by not chamfering the ports after boring the cylinders.

Different OD bore sizes is not a problem.

OD pistons are designed to have the same weight as stock, but balancing pistons and rods is of course a good thing to do when the engine is apart.

(Also, bear in mind that this is a V4 OMC. Precision manufacturing is not the first term that comes to mind when trying to describe them...)

[frank jackson]

Personally , look for a used v4 looper , ready to go . Sell the remains of the crossflow the dollar difference will be made up for in a much better motor .....

[Umassot50]

The Piston top shows detonation and overheating. Which leads to ring land pinching. Also the black char on the bottom of the Piston done shows overheating leading to detonation. The cooling problems would cause that.

[JoshKeller]

Personally , look for a used v4 looper , ready to go . Sell the remains of the crossflow the dollar difference will be made up for in a much better motor .....

dont think thats an option unless his jet unit will bolt up.

[JoshKeller]

The Piston top shows detonation and overheating. Which leads to ring land pinching. Also the black char on the bottom of the Piston done shows overheating leading to detonation. The cooling problems would cause that.

so you believed its totally a cooling issue and not a port issue?

[roadkill636]

The crank is fried in post #15 top pic

[FMP]

Where, only seeing about half the journal? That color is the table through the front of the block?

[roadkill636]

Ohhhh. I see now. I was seeing the brownish part on the left side. I guess it is the background. My bad

[FMP]

That table needs a coat of paint

[racer]

Personally I dont see detonation but due see a lean engine that looks to have been run on poor quality oil or fuel. Other items that can cause these issues that were not mention are cylinder wall clearance and ring tip clearance. Also once and engine start to leave aluminum on the bore the ring continuing to go over this will damage the ring and ring gland.

[Steve Pope]

If the damaged"cylinders bore to .040"up then you could fit WSM pistons. They make a plus 40 cast item. Make sure all the ports have a good chamfer. Looks like you are on top of the heating issue, possibly what took out those cylinders originally ???

[JoshKeller]

well guys, another twist. my older friend found an 85 hp powerhead for cheap, we checked it out, and threw it on his mid section.. i put a new water pump impeller in to be sure. a month and a half later, he calls me distraught saying its running rough at idle and coughing again. i took a comp test and hot port of 108, 110, starboard 95 and 100. pulled the head and exhaust cover and found the same exact thing that happened to the last powerhead. im thinking possibly a intermittantly bad thermostat, even though i tested them? what else could it be? lyckily it was caught before the rings broke, so a hone job and new pistons and rings should fix it, but what could be going on here? this block has never been opened up best i can tell, and for sure has never been bored over.

https://vgy.me/cimTHJ.jpg

https://vgy.me/4oJ5P7.jpg

[Motv18]

Blow another power head put a water pressure gauge on it. He could be running it dry.

Also the ever popular forgot oil.

The new ph more or less eliminated everything but that and supper common omc issues.

[gotboostedvr6]

Crossflows are everywhere and often very cheap. Find another ph or complete motor and get him a water pressure gauge.

Several plaques around the boat that remind him to add oil will not hurt.

[JoshKeller]

is there anything in the mid section that could cause an issue? i did flush the water tube out before we swapped the powerheads - but two powerheads with the same issue is baffling me. is there a test to verify the overtemp sensors work properly aside from just the horn test?

[racervboat]

Its an old used powerhead with years of time on it.They are notorious for carboning up the rings and sticking then they catch a port and its all over. I only rebuild about 10 a year so I don't know what the heck im talking about.?