Piston Pictures

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   Anyone know what causes damage to a piston/cylinder that looks like this:

Piston/Cylinder Pics

These are pictures of #1.  #5 looks almost as bad and it seems to get gradually better towards the rear of the engine.  This is a PCM 351 out of a '79 SN.  The engine has 1100 indicated hours, but I've only owned it since last August so I am unsure of all the history.

I'm amazed at how good the boat ran last season for how bad the cylinders look.

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AWhite70 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: March-05-2004 Location: United States Status: Offline Points: 242	Post Options Post Reply Quote AWhite70 Report Post Thanks(0) Quote Reply Topic: Piston Pictures Posted: March-10-2004 at 12:18am
	Anyone know what causes damage to a piston/cylinder that looks like this: Piston/Cylinder Pics These are pictures of #1. #5 looks almost as bad and it seems to get gradually better towards the rear of the engine. This is a PCM 351 out of a '79 SN. The engine has 1100 indicated hours, but I've only owned it since last August so I am unsure of all the history. I'm amazed at how good the boat ran last season for how bad the cylinders look.

66polyhead Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: December-20-2003 Location: United States Status: Offline Points: 171	Post Options Post Reply Quote 66polyhead Report Post Thanks(0) Quote Reply Posted: March-10-2004 at 12:33am
	Look's like you engine got hot for some period of time, and your oil rings collapsed. Note the varnish above both sets of comprssion rings. The grooves on your pistons and cylinder block are from the piston canting, or tilting sideways in the bore. Usually on a auto motor the rear cylinders will be progressivaly worse, but on a marine motor, when they get hot, they get real hot! Check your main bearings, and your wrist pins, and bushings.

danman Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: February-04-2004 Location: United States Status: Offline Points: 56	Post Options Post Reply Quote danman Report Post Thanks(0) Quote Reply Posted: March-10-2004 at 12:43am
	awhite70 - The reason your cylinder walls look like that is probably because the rings are so worn, that the piston itself is actually starting to ride against the cylinder wall. take a compression ring off the worst cylinder piston, place the ring down into that cylinder bore squared evenly with the deck, and measure the ring gap with a feeler gauge set - post this measurement...

AWhite70 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: March-05-2004 Location: United States Status: Offline Points: 242	Post Options Post Reply Quote AWhite70 Report Post Thanks(0) Quote Reply Posted: March-10-2004 at 2:16am
	I'l measure the ring gap and post it eventually. I haven't gotten to the main bearings yet, but the rod bearings looked really good. I don't expect the mains to be much different. The engine has always had good oil pressure. Last season aside from a tick the engine ran great, good power and didn't use oil. Now that I think about it the boat had a new raw water pump when I bought it. I wonder if the old one went bad and the engine overheated?

Morfoot Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: February-06-2004 Location: South Lanier Status: Offline Points: 5320	Post Options Post Reply Quote Morfoot Report Post Thanks(0) Quote Reply Posted: March-10-2004 at 11:56am
	Do you not have a temp gauge in the boat that you could monitor as your boating? If not then once the repairs are made would you attempt to install one? I agree that your oil got too hot which is proven by the varnish on the pistons.Oil pump bad? How about the Oil Pressure during ops? Was it normal or do you not have one of those either? I don't know much about earlier SN's.
	"Morfoot; He can ski. He can wakeboard.He can cook chicken.He can create his own self-named beverage, & can also apparently fly. A man of many talents."72 Mustang "Kermit",88 SN Miss Scarlett, 99 SN "Sherman"

tryan Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: November-12-2003 Location: United States Status: Offline Points: 345	Post Options Post Reply Quote tryan Report Post Thanks(0) Quote Reply Posted: March-10-2004 at 2:29pm
	could have been a big dust storm on the lake or someone munched an impeller and kept on going. not you , but a PO. look for chunks-o-rubber in the heads. i think you should have chrome upper ring and oil control RING to handle a motor that is run without an air filter. IMHO. are those ductile/moly rings in the photo? this is an interesting aspect of breakin' one in.moto man
	promo #2

AWhite70 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: March-05-2004 Location: United States Status: Offline Points: 242	Post Options Post Reply Quote AWhite70 Report Post Thanks(0) Quote Reply Posted: March-10-2004 at 4:56pm
	Oil Pressure was always good, and the temp gage never went over 160. The boat was never overheated or run low on oil since I've had it, but I don't know the history before last August.

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