340 cam question

[Cliff Ramsdell]

Engine has been run with this combo and no signs of piston/valve contact so all good about that. Now I have found that cam is 4 deg retarded and I want to change that to 0 deg so will have to check clearance again after that. Anyway, how can pistons be "leaned" to the left?

Good point about the banana cuts, will look for them! The non locking OEM has already been changed, but thanks!

I misread the original question. I thought it was left to right bank and not left to right side of the piston in the bore. Maybe the piston rocking in the bore, don’t know if have ever seen it like that though. Once apart look at pin and bushing wear that would allow the piston to move that way.

Cliff Ramsdell

 

[BSB67]

Like the initial cam measurements, I suspect it's mostly in the measurement method/technique. I can see daylight between the piston and the straightedge on the high side. Properly clean the piston top and use a dial indicator on a deck bridge and the results will be different.

That said, I have seen a deck taper of 0.015" from front to back.

 

[Curiousyellow71]

The worst engine that we ran into was a 67 383 the back of the block was higher then the front by .1, not sure what happened that day at Chrysler. Thankfully, never seen another that bad. It's much more common to be off like BSB67 mentioned.

With those pistons and 65cc eddy heads it should be close to 10:1 150psi seems pretty low. It may need rings?

I would advance the cam 2 degrees if it were mine.

 

[HP2]

The worst engine that we ran into was a 67 383 the back of the block was higher then the front by .1, not sure what happened that day at Chrysler. Thankfully, never seen another that bad. It's much more common to be off like BSB67 mentioned.

With those pistons and 65cc eddy heads it should be close to 10:1 150psi seems pretty low. It may need rings?

I would advance the cam 2 degrees if it were mine.

The problems are that the pistons are not square. The tops leans to one side. I have never seen anything like it but it might not be an issue. I haven't taking them out but I will so I can get a closer look at them. And the rings as you say, they might be bad. A little strange though that all cylinders had 150-154 psi. If the rings were bad I feel that the numbers would have been more different from cylinder to cylinder, all rings wouldn't be the same?
Measured the head gaskets and they are not .039 but .055 so I will use thinner gaskets to get better ratio.
2 degrees advanced would also bump cyl pressure up some.

 

[HP2]

I misread the original question. I thought it was left to right bank and not left to right side of the piston in the bore. Maybe the piston rocking in the bore, don’t know if have ever seen it like that though. Once apart look at pin and bushing wear that would allow the piston to move that way.

Cliff Ramsdell

It has nothing to do with rocking or un-normal side movments.
Hard to explain but the piston tops seems to have been milled in an angle, and all 8 look the some...
If every piston shows that same offset the issue is the top surface of the pistons not being perpendicular to the bore. The deck being a little out of square isn't going to show up with the same offset on each piston inline with the crank.

 

[Curiousyellow71]

If it had detonation. It's not uncommon that ring tension is gone equally among all cylinders, especially moly rings. If you pull a piston out and the rings don't expand...they are done. It's been 2 long since I had our 340 apart to remember how the pistons set in the bore. All I remember is they were out of deck slightly.
Anyhow...not sure if I would worry about the pistons. But if your engine is apart this far, it sounds like it has some good parts and it's new to you. Rering, bearings and piston inspection would be a good peace-of-mind.