Customs Straight 8 Pontiac problem diagnosed - only 7 pistons working

I pulled the head off the engine today and turned it over a few times by hand with the fan and saw that only 7 of the pistons were going up and down. The third one from the back doesn't move so tomorrow I'm going to remove the oil pan and check it out from that angle. Any ideas on what I should expect to find? Will I need to replace the piston? Here's some pics....

 

a busted rod and some rod bolts!

 

A connecting rod that is no longer attached to the piston. I would guess it broke a rod.

 

And probably chunks missing out of the cylinder wall. Sorry

sent via classroom note. pass it on

 

Years ago,I had a really nice '51 hardtop that split a piston under the top ring. Good Luck!

 

In the late 60's, I stoped by a shop in Phoenix. I saw a guy under a car welding. It looked like he must be welding on the engine. Sure enough, he was putting some weld in a cylinder so a piston would not come down. He had cut the rod off. It had a bad knock in that rod and he was preparing the car for sale.

 

I thought you said it ran fine/smooth in your original thread? Impossible with one hole out. This makes it so much harder for us to help you

 

I hope you are lucky enough to find the piston separated between the wrist pin and the oil ring at the drain back groove. In which case, yes you need a new piston. Anything else and you need a lot more than a new piston. Up to and including a new block or at least a sleeve. The LS idea is sounding better and better.

 

Lord only knows right now. If you are lucky, maybe the rod cap came off and maybe no real damage was done to the block.
Piston may be OK but the rod is likely history.

 

Best Case scenario....

 

1/2 a connecting rod flailing around making that noise.

But it wouldn't be running smooth on 7 of 8 cylinders. It would be missing and horribly out of balance.

 

I would have to turn the crank over a few more times just to confirm it. I know you may have already done that....

The Previous owner was a Liar.....With that carbon...No way it's a recent rebuild. Recent gold spray paint yes rebuild..Nope

 

A low compression straight 8 with a busted rod won't necessarily shake or run as bad as a more modern V8 in the same condition. The crankshaft in that motor probably weighs in at close to a hundred pounds, so a few pounds of missing rotating and reciprocating weight is a lot smaller percentage of the total. And not throwing stones here, but from where I sit and read, the owner of the car probably wouldn't be as aware of 12.5% of the cylinders not firing, given his admission in his previous thread regarding his level of experience and comfort with the internal workings of an engine.
Hopefully the damage inside is repairable with no damage to the block or crank. FYI, I've got a pair of Buick 263 Straight Eights for sale, one of which would look right at home in that engine bay.

 

I'll keep that in mind. It looks like you're about 520 miles from Louisville. I had a '49 Buick Special several years ago with a straight 8. Is there much of a difference between the Buick and Pontiac straight 8 engines?

 

[QUOTE="Lebowski, post: 10601720, member: 161053 Is there much of a difference between the Buick and Pontiac straight 8 engines?[/QUOTE]


Yes, and mostly accruing to the benefits of the Buick...EXCEPT...when it comes to the transmission. Your Hydramatic doesn't fit the Buick and the Dynaflow isn't recommended, not the least of which is due to the torque tube driveshaft.

There are, however, adapters to fit more modern GM transmissions.
See Bendtsens in Ham Lake, MN www.transmissionadapters.com.
Not cheap, but excellent quality.

Ray

 

From what I heard last night, this is the most likely scenario.

 

Now you see why everybody was saying to turn it off and take it apart.

 

A connecting rod that is no longer attached to the piston.

 

Bad news. It appears that the oil pan cannot be removed without pulling the engine first. There's only an inch or two of room between the front part of the pan and the frame (top part of photo). I stuck my hand in there as far as I could and still couldn't even touch the front of the pan. There's no way to get a wrench in there to remove the bolts....

 

Is that an internal part lying across the drain plug hole

 

Sure looks like it....if the pistons not moving I think it's safe to say the motor is coming out anyways.


Posted using the Full Custom H.A.M.B. App!

 

Gee, I guess the president of the Pontiac club isn't quite as FOS as the armchair automotive diagnosticians thought he was.

 

Lmao !
Rod bearing and busted connecting rod are really similar noises

 

FOS?

I tried to remove the piece of metal in the oil pan with a screwdriver but couldn't. It sure looks like that mechanical genius who said it was a rod bearing was trying to rip me off....

 

I looked in my 59 edition MOTORS MANUAL, and it says the pan CAN be removed with the engine in the car; steering linkage has to be dropped and the engine raised. Your local library may have MOTORS MANUALS if you can't locate one. Yes, you have dis-articulation of the piston-crankshaft connection. I am Butch/56sedandelivery.

 

Dropping the pan in the car is another waste of extra effort. The engine will have to come out sooner or later........unless this a rare "virgin failure" (no other damage to crank or block)....

Ray

 

Yes you are well past repairing your engine without removing it. If it can be repaired at all. If you want to get a better look at that cylinder, you could drill and tap through the loose piston. Screw in a bolt and maybe use a puller to remove what ever is there. Then you could look down through the hole and see the destruction. But the engine is going to have to come out sooner or later.

 

Sometimes I feel if I look around, I will see Rod Serling, standing there with a cigarette in his hand, saying, "Submitted for your approval, Mr. Carl LaFong, trapped in an alternate universe we call......"The Twilight Zone."
OK, here goes,
1. FOS=Full of shit
2.The mechanical genius was pretty spot on. 6 grand for a rebuild is a bit high. I suspect you could do it for half, providing the damage is limited to a busted piston or a rod cap that said, "Buh By."

 

The Dude abides...............

 

There's a 1950 Pontiac straight 8 with Trans in the classifieds for easy money.
Advertised as running well, smooth, quiet, no smoke.