Early Diagnosis on My Engine

[Joe Flanagan]

Today I brought my engine, crank, camshaft, and pistons to a machine shop. The guy has been rebuilding engines for 30 years. He said the crank and cylinder walls will most likely be fine with a hone and polish. He will mike everything to make sure, though. He examined the wrist pin, bushing, and piston that was making noise (#6). He said the bushing is fine, the pin is not loose, the holes in the piston skirt are also fine. That was not the cause of my knocking, according to him. He thinks, from the marks on the piston skirt and cylinder walls, that number 6 was slapping in the cylinder and giving me that rapid knocking sound. It was slapping because it was getting hot. It was getting hot because he believes I had developed a hot spot toward the back of the engine where coolant was not circulating, likely an air pocket. The piston could very well be deformed ("collapsed" was the word he used) and might not be round anymore, but oval. He is going to mike the piston skirt and see what shape it's in. I did drain and refill the coolant several times to deal with various issues (water pump, etc.) and may have introduced an air pocket. Anyway, that's his initial diagnosis. I might get out of this for a cool 350 bucks.

[P-12 Tommy]

Let's cross our fingers and hope he's right.

Tom

[Jim Yergin]

Joe,

Which shop did you go to?

Jim Yergin

[Joe Flanagan]

The one in Woodbridge. The guy was really decent and seemed to be very interested in the old flathead. I'm not sure I agree with the overheating cylinder scenario, the more I read, but he does have 30 years more experience with this stuff than I do. It's finding the cause of the noise that I'm really concerned about. The other stuff is manageable, but I don't want to reassemble this thing and have the noise reappear.

[Jim Yergin]

Joe,

Glad to hear he can help you. I am very pleased with the work he did for me.

Jim Yergin

[greg g]

WARNING, WARNING, WARNING! Original mopar pistons were ground OVAL. The reason being that as they got hot the oval grinding left room for expansion within the cylinder wall. Make sure when he mic's that one he checks the rest they should all be oval. Unless the repacements are not ground that way to begin with. I would check the oil squirter in that rod to make sure it is clear. and the bearing was instaled so that oil was fed to the passage.

Piston slap is usually a symptom of old pistons that have worn irregularly at the bottom of the skirt, and they will uslally quiet down as they get to operating temp unless theya re severly worn.

ot saying that the guy doens't know his stuff, but maybe he isn't aware of the oval grinding deal.

[Flatie46]

Joe what oil were you using in you engine?

[JoelOkie]

Sounds like you might get out of it without being too bad Joe. Hope you have it back together in no time.

[Joe Flanagan]

WARNING, WARNING, WARNING! Original mopar pistons were ground OVAL. The reason being that as they got hot the oval grinding left room for expansion within the cylinder wall. Make sure when he mic's that one he checks the rest they should all be oval. Unless the repacements are not ground that way to begin with. I would check the oil squirter in that rod to make sure it is clear. and the bearing was instaled so that oil was fed to the passage.

Piston slap is usually a symptom of old pistons that have worn irregularly at the bottom of the skirt, and they will uslally quiet down as they get to operating temp unless theya re severly worn.

ot saying that the guy doens't know his stuff, but maybe he isn't aware of the oval grinding deal.

The out of round reference was mine. He didn't actually make the round/oval comparison. Since I posted I read about the original oval shape of the pistons. I should have said "distorted," I suppose. As I understood his explanation, the piston skirt has become out of shape in some way. He said he was going to mike it to verify if this is the case.

I was using 10W40 with a zinc additive, by the way.

[Don Coatney]

This is the oil squirt hole in the rod that Greg mentioned. Needs to point towards the camshaft.

No charge for this information:)

[Joe Flanagan]

Thanks Don. I verified the position of all the holes back when I had the pan off to install the flywheel bolts on the crank.

[gillettealvin]

Hey, Joe,

Glad you’ve found a machinist to help you shed some light on your motor. Hopefully you will pardon my possible ineptitude, (stupid question alert!) as the inner workings of these old Mopar flat sixes are “new” to this old dog. I’m wondering if the lead paragraph from the “Technical Tips” page of this board may hold a clue?

“The water distribution tube provides a vital function in cooling your engine. It directs cooling water in the upper block and valve area. Generally it is removed for inspection when an engine is overhauled, and replaced as required. However, in my experience, many production rebuilders do not perform this repair because the tube is rusted in place and difficult to remove. Failure to replace a rusted out water distribution tube will certainly lead to hot spots in the block and future problems.”

. . . I’m just sayin.’

GA

[55 Fargo]

Hey, Joe,

Glad you’ve found a machinist to help you shed some light on your motor. Hopefully you will pardon my possible ineptitude, (stupid question alert!) as the inner workings of these old Mopar flat sixes are “new” to this old dog. I’m wondering if the lead paragraph from the “Technical Tips” page of this board may hold a clue?

“The water distribution tube provides a vital function in cooling your engine. It directs cooling water in the upper block and valve area. Generally it is removed for inspection when an engine is overhauled, and replaced as required. However, in my experience, many production rebuilders do not perform this repair because the tube is rusted in place and difficult to remove. Failure to replace a rusted out water distribution tube will certainly lead to hot spots in the block and future problems.”

. . . I’m just sayin.’

GA

Yah, these need to be pulled for a thorough cleaning, just to let you know, a lot of them up here in Canada were brass, as mine was, so clean it and re-use again.

I do not think Joe missed this on his rebuild, as he mentioned about a possible "air pocket", would allow for a real hot spot, that is for sure.

Even after a very well orchestated re-build, things can and will go wrong, in Joe's case, he is gonna correct this and move forward.

This has been a bit of a bad omen for Joe, getting her going at the beginning, oil pressure worries, then spinning a bearing, I hope all is sorted out, and put back together, and hopefully Joe will put a 100000 miles on it

[Joe Flanagan]

I pulled the distribution tube and replaced it with a new one when I rebuilt the engine.