This will take us a bit out of the forum but I think the moderator will allow it to run.
Orich, Jeff, Hio, help me out.
A while ago my son and I pulled down his 351W that had a bad rap, sounded like a rod. Four pistons were cracked on the bottom of one bank.
We have since replaced the engine after a rebore and replaced the Carter 625 AFB. All is well and back in and running but I am still scratching my head.
The block and water jackets were fine. A smart guy suggested a carb leak that rinsed away lubrication on one bank on the bottom.
What do you guys think?
Have you ever experienced this?

 

My 1st reaction was piston slap. But that usually breaks piston skirts. It's really stretching but the only other thing I can think of is whomever bored the block out .30 over might not have had the block in their machine clocked quite right doing that bank. So the pistons were rocking when coming back up from BDC. The piston skirts would be out of and below the cylinder at that time.

 

Excellent. Nobody thought of that or told me that thought.
My next question is:
When they re-bore, do they follow the old hole out or do they start over and re-index?
The block was re-bored from .030 to .040 but Jeff has made me think that the problem will come back.

 

I can only assume the person who bored it out to .030 before had a machine somewhat like below. Didn't program it quite right,mount the block correctly, or whatever. So the latest person who bored it .040 hopefully straightened it out. It's the only thing I can think of that all 4 cylinders and their pistons have in common. I am also curious to know Orich's and Hio's thoughts, but also Bobby's,351's,and Tro's.
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Not all engine machine shops use torque plates when boring/honing the block but really good engine machine shops will.

A torque plate simulates the stresses the heads will have on the block when the heads are bolted down.

The block will have some distortion when the heads are put on and bolted down. If torque plates weren't used to simulate the stress, during the machining process, there's a good chance the rings will not seat as they should and it can cause piston scuffing or piston slap.

Torque Plate Honing | Accurate Performance Machine

NASIOC - View Single Post - Torque Plate vs Non Torque Plate Motor

Introduction To BHJ Honing Plates (Torque Plates) and Options: BHJ Products, +1 (510)797-6780

 

Excellent stuff, UR.

 

2x block shift or screw up poor alignment.

If you still have the old piston check wrist pin location for it's off set amount. If they match the other four. Who built the engine ?

I've found you have to tell them to use torque plates when honing for size.
A good piston will are all the same OD size and when done with torque plates right the piston will not need any cylinder fitting needed.

I have even come across once a engine with one bank where one row of pistons in backwards causes a lack to the wrist pin oil. Wrist Pins started to gall scuffing pistons an walls.
Don't know who built it like this but good reason to be in PnP JY

How many miles were on this motor john?
orich

 

Orich, the engine had about 60k miles on it but it was old. I re-built it back about 1990, had it bored to .030 by what I thought was a competent shop. I knew nothing about torque plates then but I do now.
The engine was in a '70 Mach 1 and was hammered now and then- stoplight stuff- but never beated.
Anyhow it is now out to .040. Seems fine but we shall see.
Thanks, guys.

 

I ran all this by my son. Smart guy, good engineer and fair mechanic. This is what he said:
He saw the block up on the boring machine with the torque plate installed. The guy who did the .030-.040 re-rebore almost certainly straightened out any crooked holes on the first bore. The shop is reputedly one of the best in the Bay Area, racing engines and all that.
The manifold that came off was a Holley single plane. Any fuel that leaked past the float and down after shutoff would pool on the bottom side of one bank if the car had a tilt. Hence, rinsed piston bottoms on one bank, no lube on start-up on that side, cracked rings and pistons.
What think you guys?
I love these puzzles but I do not like the wallet hit to solve them.
Let us add this to our collective experience.

Semper Fi

 

....another reason why I prefer (Ford) direct port sequential fuel injection. There's no fuel administered into the intake tract. The fuel stream is sprayed directly into the combustion chamber and, only the required amount of fuel is metered out.

A carburetor is just basically a (somewhat) controlled leak.

 

Gas washing down the intake runner should have been cleaner then the of side of the engine. I'd also think they're would not have any carbon build up at the top above ring travel. A very close inspection of parts while pulling it down. Checking head gasket for carbon build up. How clean the ring groves & inside piston pin area lack of oil.



I had a Shop here in San Jose the builds mostly racing type to stock motors do my engine work. They squared the block bored it.
And rebuild the rods with new pin bushing..

Okay I've learn to never trust a shop yrs ago as anyone can screw up..

I found the 4 of the piston pin bushing were a 1/3 off center on the oil hole.

If, I hand not checked, I am sure the pins would have had a short life and then gall up mess up piston & score the skirts or worse.

I returned to that well known M-shop and inform the was I only came to their shop so, I would not get work like this..

A few red faces from embarrassment. would correct the screw up.

In the mean time of waiting I just went ahead and bought H-bean Rods.

I then sold the rebuilt rods on ebay at about a 50 dollar loss but could not wait 2 weeks waiting for them to correct them.

I then took my heads to the shop in Clarks shop in Cupertino won't ever go back V' in s bay.

A small shop has to many irons in the fire and to many interruptions having to answer the phones

An forgetting what they were going~~~~~to do.

orich