Why would this happen

**Daddychatham** · 06-29-2008, 12:33 PM

Not sure what would cause this. Motor was running great, just replaced the head gaskets, put on the 40 amp charging ssytem (its a fishing boat), and added temp sensors. I am baffled

**flabum1017** · 06-29-2008, 01:52 PM

first impression is that a locator pin came out letting the piston ring rotatae and catch a port.....

**myron** · 06-29-2008, 04:48 PM

I would agree, a locator pin came out,look at the piston at the right of the "S", there is the same size and shape marks as a pin

**terry taylor** · 06-29-2008, 08:38 PM

DAMAGE HI.How long did the engine run well after replacing gasket before this happened thanks.

**Mr.Rude** · 06-29-2008, 09:14 PM

You can see the pin impressions on the piston as well part of it in the head.

**Daddychatham** · 06-29-2008, 09:46 PM

Couple Hours, I fished 3 tournaments in it before running it this weekend.

**Jay Smith** · 06-29-2008, 09:58 PM

Amazing what a $.25 locater pin failure can cause...

Jay

**Mr.Rude** · 06-29-2008, 10:17 PM

why is the far piston from the damaged one different? It does not have the S designation or the center raised boss. Is this a previously repaired powerhead?

**Daddychatham** · 06-30-2008, 04:15 AM

Originally Posted by Mr.Rude

why is the far piston from the damaged one different? It does not have the S designation or the center raised boss. Is this a previously repaired powerhead?

I cannot explain that. I do not believe this motor has blown up before, I bought it in Feb.

**TheRickster** · 06-30-2008, 06:03 AM

Looks like a lot of pin material embedded. I would say a roller pin from a plastic caged rod bearing. ..

Rick

**terry taylor** · 06-30-2008, 07:13 AM

WHY HI. To me the whole bank appears on the lean side no real residue. Would this come into the assessment ? thanks.

**trashy** · 06-30-2008, 07:32 AM

I'm still learning about these motors, and am wondering about a couple of things.

To me the major damage appears to be at the exhaust side of the piston. What would be the reason for that, and where on a piston is the locater pin?

**YELLOWSS** · 06-30-2008, 07:46 AM

the locater pin is what holds the ring in place... it is in the side of the pistons.. that way the rings can move on the piston..... the new improved pistons pin come from the top of the piston down through it to hold the rings in place.... it looks like that little pin was in there a while before exiting out the exhaust...... i will never run side pin pistons in a merc hipo motor.... JMO
it does look like someone replaced a piston before...

**trashy** · 06-30-2008, 07:52 AM

Originally Posted by RWR

the locater pin is what holds the ring in place... it is in the side of the pistons.. that way the rings can move on the piston..... the new improved pistons pin come from the top of the piston down through it to hold the rings in place.... it looks like that little pin was in there a while before exiting out the exhaust...... i will never run side pin pistons in a merc hipo motor.... JMO
it does look like someone replaced a piston before...

Perhaps you misunderstood my question. I know what the locater pin is and what it is for. I was wondering if it is physically located on the exhaust side of the piston or maybe the 12:00 position, etc. I figured part of the reason for more damage to the exhaust side was because it was pushed there while trying to make it's exit.

**YELLOWSS** · 06-30-2008, 09:01 AM

no it is not... a "star" piston has the pins located at 12 o'clock, and 3 o'clock.
a "port" piston has them at 12 o'clock and 9 o'clock.
a top pinned piston only has one pin the ring gaps are aligned, but it doesn't seem to effect it...

it looks like it could have been running lean too... which would cause the exhaust side to get hotter...

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