351w engine rectification

[olddog]

Since he said shave off the top of the piston, I would assume he was trying to gain some piston to valve clearance, which is very common with larger cams. I didn't see the cam specification in your list.

If that is the case, it makes perfect since. Having worked with language communication misunderstandings, make it fit does not necessarily mean fit in the block. I fit may mean no collision of parts, when it rotates.

Back to your original 0.040 overbore. That is commonly done, but most people choose to bore no bigger than they have to, so they have some room to bore again on the next rebuild.

0.040 overbore is a general rule of thumb that almost any engine can be bored that far, with out any issue. Today it is easy to check cylinder thickness with ultra sound before you bore. Back in the day before ultra sound was invented, shops were confident that you would not get into trouble at 0.040, and in the rare case that you did, it was a bad block anyway.

Drag racers used to bore engines 0.060 back in the day. The problem with boring more is if the cylinder walls get too thin you can have problems with the engine overheating. They don't run long enough to overheat in a drag race only situation.

[blykins]

Originally Posted by olddog

Since he said shave off the top of the piston, I would assume he was trying to gain some piston to valve clearance, which is very common with larger cams. I didn't see the cam specification in your list.

If that is the case, it makes perfect since. Having worked with language communication misunderstandings, make it fit does not necessarily mean fit in the block. I fit may mean no collision of parts, when it rotates.

Back to your original 0.040 overbore. That is commonly done, but most people choose to bore no bigger than they have to, so they have some room to bore again on the next rebuild.

0.040 overbore is a general rule of thumb that almost any engine can be bored that far, with out any issue. Today it is easy to check cylinder thickness with ultra sound before you bore. Back in the day before ultra sound was invented, shops were confident that you would not get into trouble at 0.040, and in the rare case that you did, it was a bad block anyway.

Drag racers used to bore engines 0.060 back in the day. The problem with boring more is if the cylinder walls get too thin you can have problems with the engine overheating. They don't run long enough to overheat in a drag race only situation.

Shaving material off the top of the pistons would only be to increase compression ratio, or trying to make a 9.500" piston fit into a 9.480" block. Increasing piston to valve clearance would be considered "fly cutting" the valve reliefs.

It's also a wives' tale to say that overboring a cylinder causes the engine to overheat. That is pretty far from the truth. The only issue that extreme overboring causes is a thin cylinder, which decreases ring seal.

I've sonic tested two 351C blocks recently with less than .050" cylinder wall thickness, as they came from the factory, standard bore. The only detriment there is cylinder weakness.

Combustion heat takes place in the head. That's why you can put block filler in an engine block and the water temperature doesn't increase. The oil temperature will go up, but the engine will not overheat.

[olddog]

Originally Posted by blykins

Shaving material off the top of the pistons would only be to increase compression ratio, or trying to make a 9.500" piston fit into a 9.480" block. Increasing piston to valve clearance would be considered "fly cutting" the valve reliefs.

Bad day, typo, I don't know, but taking material off of the top of the piston will decrease compression not increase it, just to keep us all honest and factual. That or pop up pistons are for low compression.

I do believe "fly cutting" the valve reliefs may well translate from one language to the next as shaving material off the top of the pistons, when a person cannot think of the correct words. French is sometimes lacking technical words in mechanical terms. I work with a sister plant in France. I could be flat wrong, but offered it as a possibility. I wish I could recall an example. We have had some big misunderstanding when everyone thought we were clear.

Originally Posted by blykins

It's also a wives' tale to say that overboring a cylinder causes the engine to overheat. That is pretty far from the truth. The only issue that extreme overboring causes is a thin cylinder, which decreases ring seal.

Well I have questioned the overheating claim in my own mind. I assumed the less cast iron, the less mass to make a thermal flywheel - so to speak. Under steady state conditions it make no difference, but in a short burst of maximum power, the temperature spike would be shorter and higher with less mass. It is hard to see how a few thousands of an inch would matter, so I accept that I have continued to pass this old wives tail about. Guilty as charged.

Originally Posted by blykins

I've sonic tested two 351C blocks recently with less than .050" cylinder wall thickness, as they came from the factory, standard bore. The only detriment there is cylinder weakness.

Combustion heat takes place in the head. That's why you can put block filler in an engine block and the water temperature doesn't increase. The oil temperature will go up, but the engine will not overheat.

I read a bit on that on your C website. I wondered if you could put an epoxy filled block on the street. Sounds like you can.

By the way thanks for the free education. I appreciate all you do for this forum.