[steve25]

If your considering reusing those Pistons then one of the most important clearances to check is the ring to ring groove clearance for both compression rings.
Anything over .003" and it's new piston time.

[TRADERMIKE 2012]

Originally Posted by TRADERMIKE 2012

Mikes reply:

"Why did the Top Compression ring Break into uneven parts anyway, on about 5 combos of Piston and Ring sets?

You said:

Molly face rings need to be installed very carefully, so as not to scratch their face or the cylinder wall finish. A smooth finish must be what’s needed for such a ring face.

Mikes reply:

Does that mean that after Boring or simply Honing, one would "not" cross hatch the cyl. wall?

Thank you in advance.

[Schurkey]

Boring has to be followed by honing, and honing is what puts the crosshatch on the cylinder wall.

The issue is that there's a science/art to the crosshatch. Not too aggressive, proper angles, lots of valleys but not much for peaks.

Go on Youtube and look for Lake Speed Jr. and the company Total Seal, there's multiple videos on the honing requirements of modern rings.

Examples:
Short 'n' sweet
https://www.youtube.com/watch?v=Jehtgk5cd3A

Long 'n' involved
https://www.youtube.com/watch?v=LIfbYd9cqcs

In the end, this is going to be handled by the machinist you choose, and hopefully they've got a torque plate for Pontiac.

[400 Lemans]

I think the rings broke when you knocked the pistons out and the top ridge on the cylinders was a little to big. The rings grabbed on the edge of it. Sometimes you have to use a ridge reamer when possibly reusing the same pistons.

[Schurkey]

Originally Posted by 400 Lemans

I think the rings broke when you knocked the pistons out and the top ridge on the cylinders was a little to big. The rings grabbed on the edge of it. Sometimes you have to use a ridge reamer when possibly reusing the same pistons.

I completely agree that the ridge is likely the cause of the broken rings.

To my way of thinking, a ridge-reamer is a tool for destroying cylinder walls. It's really easy to get too aggressive and carve too deeply. In my world, the pistons get knocked-out and thrown in the scrap-metal bin if they're damaged by the ridge. I let the boring-bar deal with the ridge.

MOST OEM pistons are not worth saving--they're heavy, they're cast to be cheap, they're maybe not shaped properly for optimal compression and flame travel...modern pistons can be so much better than what came in the engine to begin with.

[TRADERMIKE 2012]

Originally Posted by steve25

If you're considering reusing those Pistons then one of the most important clearances to check is the ring-to-ring groove clearance for both compression rings.
Anything over .003" and it's new piston time.

Mikes reply:

My research so far, watching a video, found this:

If you have a 4" Piston and you set your gap to 3.5 thousand /inch of the Piston diameter = .014 gap.

So, now the Piston is worn about the upper 2" of the cyl. wall from the top down, I add .014" to .003" = .017" Ring gap (measuring both compression rings, the same way) thus, over .017 ring gap and I need to replace the Pistons. Is there something called oversized rings to consider first, before discarding the existing Pistons, if they are in re-useable condition? In addition is there a tolerance from .014" to add to the original ring gap to consider in the first place? For example, .014"-.017" original ring gap.

[Gach]

Do yourself a BIG favor and replace those pistons. I know its not cheap, but think about down road having to go through all this again. There’s is so much involved trying to use those piston over. If those piston are collapsed no ring is going to seal. Without getting all the details on why a pistons collapses which would open another can of worms for discussion.

[TRADERMIKE 2012]

Originally Posted by Schurkey

I completely agree that the ridge is likely the cause of the broken rings.

To my way of thinking, a ridge-reamer is a tool for destroying cylinder walls. It's really easy to get too aggressive and carve too deeply. In my world, the pistons get knocked-out and thrown in the scrap-metal bin if they're damaged by the ridge. I let the boring bar deal with the ridge.

MOST OEM pistons are not worth saving--they're heavy, they're cast to be cheap, they're maybe not shaped properly for optimal compression and flame travel...modern pistons can be so much better than what came in the engine to begin with.

Mikes reply:

I never considered to ridge reem the top of the cyl. prior to removing the pistons. Is that Protocall when dismantling the motor? I always thought that came later, as a matter of fact one would Bore first and that should remove the ridge before Honing and lastly cross Hatching the cyl. , wall with x's.

[TRADERMIKE 2012]

Originally Posted by Gach

Do yourself a BIG favor and replace those pistons. I know it's not cheap, but think about down the road having to go through all this again. There’s is so much involved with trying to reuse those pistons again. If those pistons collapsed, no ring is going to seal. Without getting all the details on why pistons collapse, which would open another can of worms, in this discussion.

Mikes reply:

I have the time, what is a piston collapse and how does that affect the combustion process? If you don't explain this event, I will just have to look it up, you got me curious.

Furthermore, what is your take on the reuse of the Rods and Crank, in this case.

[Gach]

When piston collapses it will eventually effect ring seal. I’ll explain it the best I can pistons all pistons are tapered. When they collapse the tapered goes way. If that block has a ridge. Most likely it was caused by mileage and or a collapse piston or both. Looking at those piston and ridge I would definitely check to see how much of a over bore would be need…..030 over bore or .060. Most with that king of ridge need a .060 over bore. Running a Dial bore gauge though will tell you how much it needs.

[Gach]

Just trying to hone and put news rings in is a Band-Aid. Work for a while but won’t last long.

[tom s]

With custom pistons you dont have to pic 30 or 60,big advantage for not HAVING to overbore what is needed,just pic a size where you can buy a good ring pack.Tom

[Gach]

Originally Posted by tom s

With custom pistons you dont have to pic 30 or 60,big advantage for not HAVING to overbore what is needed,just pic a size where you can buy a good ring pack.Tom

Tom I think that would be big bucks. Its just cheaper to do 030 or may need .060 what ever it needs. I’m sure Butler has a .030 or 060 over for a 428 block.

This would be my next steps, get crank check out and see what it is, then get a nice set of steel rods and forged pistons and ring pack.

[Schurkey]

Originally Posted by steve25

one of the most important clearances to check is the ring to ring groove clearance for both compression rings.
Anything over .003" and it's new piston time.

Originally Posted by TRADERMIKE 2012

Mikes reply:

My research so far, watching a video, found this:

If you have a 4" Piston and you set your gap to 3.5 thousand /inch of the Piston diameter = .014 gap.

So, now the Piston is worn about the upper 2" of the cyl. wall from the top down, I add .014" to .003" = .017" Ring gap (measuring both compression rings, the same way) thus, over .017 ring gap and I need to replace the Pistons. Is there something called oversized rings to consider first, before discarding the existing Pistons, if they are in re-useable condition? In addition is there a tolerance from .014" to add to the original ring gap to consider in the first place? For example, .014"-.017" original ring gap.

What you're describing is not at all what steve25 is telling you to measure. What you're describing (cylinder wall wear) is a valid concern, though.

Steve25 wants you to cram a .002--.0025--.003 feeler gauge blade into the ring grooves of the pistons--in several places around the circumference--with the ring in the groove. There needs to be no more than .003 gap between the ring and the ring groove, or the ring groove is worn-out and the pistons are junk.

Fifty--sixty--seventy years ago, there were lathe tools to re-cut the ring grooves so they were "square" again, and steel spacers to take up the excess clearance in the machined-oversize grooves. That crap is DONE now, nobody is going to do that any more. They'd tell you to buy new pistons that don't have worn-out ring grooves.

As for what you're saying--that your cylinders have wear towards the top (typical bellmouth wear, common as dirt) there's a limit to what's acceptable. When I was in trade school, dinosaurs roamed the Earth, and some of them were driven to church and the grocery store by grandmotherly types who never went over 30 mph, ever. For those folks, I was told that cylinder bore wear of .007 taper was the absolute limit of acceptability.

Keep in mind that .007 taper leaves a ridge of .0035. It's REAL easy to find ridges bigger than that, and if your ridges broke the rings, you've almost certainly got more ridge than .0035. You are almost certainly going to bore that engine, and again you're needing new pistons.

The most-recent engine I put together has a "service limit" spec of .001 bore wear, but actually had .0015 taper. The ridge would be about .0008-ish. I put it together like that, and "so far, so good".

You can check your bore wear with feeler gauges and a non-broken ring, and a clean flat-top piston. Put the ring inside the cylinder, push it towards the bottom of the cylinder with the piston, so it's sure to be square in the bore. Measure the end-gap with the feeler blades. Bring the ring half-way up the bore, square it up with the piston, and measure the end-gap. It'll PROBABLY be the same as the measurement farther down in the bore. Then bring the ring up to the underside of the ridge. Measure the end-gap, which is probably going to be bigger than the two previous measurements. Subtract the small end gap measurement from the big end gap measurement, and divide the difference by 3.1416.

Anything over about .002 is grounds for rebore. Unless you're Grandma, going to church at 15 mph.

BEWARE of "stock replacement" or "rebuilder" pistons. They are almost always SABOTAGED with a low compression height. Used to be that .020 too-short was common, now I see many that are "only" screwed-up by .010. Low compression height affects piston-to-head clearance, which affects "squish" or "quench", which affects the speed of combustion as well as compression ratio. You do not want short pistons. Getting pistons that are properly-made may cost more than the "rebuilder" junk products.

Originally Posted by TRADERMIKE 2012

I never considered to ridge reem the top of the cyl. prior to removing the pistons. Is that Protocall when dismantling the motor?

Some guys do, if the ridge is big enough to cause difficulty removing the pistons. The point of ridge-reaming is to save the pistons from damage during removal.

"I" get a bigger hammer, and pitch the pistons in the scrap bin. I have seen too many blocks damaged by heavy-handed ridge-reaming.

Originally Posted by TRADERMIKE 2012

what is your take on the reuse of the Rods and Crank, in this case.

Haul them to your favorite automotive machinist. Let an expert examine the crank and rods.

First Guess: Nothing wrong with the crank that a regrind won't fix. Nothing wrong with the rods that an inspection and MAYBE resizing won't cure.

Someone is sure to say that "by the time you replace the rod bolts, and have the rods resized, you could buy brand-new rods from XXXXXXXXX company and be better-off." Well, yes. How high are you going to spin this engine? Do you NEED new rod bolts? IF (big IF) the RPM is modest, and the rods are inspected and found to still be round...why resize them?

But maybe you plan to beat on this engine, in which case upgrading the rod bolts and resizing after close visual inspection is probably warranted. (If the cast-iron rods and cast-iron crank were cracked...they'd probably be broken already.) I don't trust bottom-feeder Communist Chinese rods or cranks. Not everyone feels that way. And--supposedly--there's some Communist castings/forgings that get proper machining and QA here in America. How fat is your wallet? What are your goals for this engine?

Originally Posted by Gach

I would definitely check to see how much of a over bore would be need…..030 over bore or .060. Most with that king of ridge need a .060 over bore.

Have a professional, experienced eye examine the block; .030 is kinda routine for overbore, but if it can clean-up with less, bore the minimum amount. If it takes more, do what it needs. If one or two cylinders are especially bad, consider having them sleeved.

[tom s]

Lou,custom is custom,no more to order 35 over than 60 over especially if your ordering a dish.Tom

[TRADERMIKE 2012]

Originally Posted by Schurkey

Boring has to be followed by honing, and honing is what puts the crosshatch on the cylinder wall.

The issue is that there's a science/art to the crosshatch. Not too aggressive, proper angles, lots of valleys but not much for peaks.

Go on You tube and look for Lake Speed Jr. and the company Total Seal, there's multiple videos on the honing requirements of modern rings.

Examples:
Short 'n' sweet
https://www.youtube.com/watch?v=Jehtgk5cd3A

Long 'n' involved
https://www.youtube.com/watch?v=LIfbYd9cqcs

In the end, this is going to be handled by the machinist you choose, and hopefully they've got a torque plate for Pontiac.

Mikes reply:

https://youtu.be/LIfbYd9cqcs

https://www.youtube.com/watch?v=cRINK2O63GM

https://www.youtube.com/watch?v=-LnyqSXi65Y

https://youtu.be/zj7PN6LjN20?si=zMogQAvq48y6nOQw

https://www.youtube.com/watch?v=L9uXFeAnsoQ

[Gach]

Originally Posted by tom s

Lou,custom is custom,no more to order 35 over than 60 over especially if your ordering a dish.Tom

I got you tom. Its all going to depend on how much its going to take to clean it up. I’m sure Butter has them for .030 or .060 not sure if he’d have one for .035. Either way Machine shop is going to be the one that actually determines that.

[TRADERMIKE 2012]

Originally Posted by Schurkey

What you're describing is not at all what steve25 is telling you to measure. What you're describing (cylinder wall wear) is a valid concern, though.

Steve25 wants you to cram a .002--.0025--.003 feeler gauge blade into the ring grooves of the pistons--in several places around the circumference--with the ring in the groove. There needs to be no more than .003 gap between the ring and the ring groove, or the ring groove is worn-out and the pistons are junk.

Fifty--sixty--seventy years ago, there were lathe tools to re-cut the ring grooves so they were "square" again, and steel spacers to take up the excess clearance in the machined-oversize grooves. That crap is DONE now, nobody is going to do that any more. They'd tell you to buy new pistons that don't have worn-out ring grooves.

As for what you're saying--that your cylinders have wear towards the top (typical bellmouth wear, common as dirt) there's a limit to what's acceptable. When I was in trade school, dinosaurs roamed the Earth, and some of them were driven to church and the grocery store by grandmotherly types who never went over 30 mph, ever. For those folks, I was told that cylinder bore wear of .007 taper was the absolute limit of acceptability.

Keep in mind that .007 taper leaves a ridge of .0035. It's REAL easy to find ridges bigger than that, and if your ridges broke the rings, you've almost certainly got more ridge than .0035. You are almost certainly going to bore that engine, and again you're needing new pistons.

The most-recent engine I put together has a "service limit" spec of .001 bore wear, but actually had .0015 taper. The ridge would be about .0008-ish. I put it together like that, and "so far, so good".

You can check your bore wear with feeler gauges and a non-broken ring, and a clean flat-top piston. Put the ring inside the cylinder, push it towards the bottom of the cylinder with the piston, so it's sure to be square in the bore. Measure the end-gap with the feeler blades. Bring the ring half-way up the bore, square it up with the piston, and measure the end-gap. It'll PROBABLY be the same as the measurement farther down in the bore. Then bring the ring up to the underside of the ridge. Measure the end-gap, which is probably going to be bigger than the two previous measurements. Subtract the small end gap measurement from the big end gap measurement, and divide the difference by 3.1416.

Anything over about .002 is grounds for rebore. Unless you're Grandma, going to church at 15 mph.

BEWARE of "stock replacement" or "rebuilder" pistons. They are almost always SABOTAGED with a low compression height. It used to be that .020 too-short was common, now I see many that are "only" screwed-up by .010. Low compression height affects piston-to-head clearance, which affects "squish" or "quench", which affects the speed of combustion as well as compression ratio. You do not want short pistons. Getting pistons that are properly-made may cost more than the "rebuilder" junk products.



Some guys do, if the ridge is big enough to cause difficulty removing the pistons. The point of ridge-reaming is to save the pistons from damage during removal.

"I" get a bigger hammer, and pitch the pistons in the scrap bin. I have seen too many blocks damaged by heavy-handed ridge-reaming.


Haul them to your favorite automotive machinist. Let an expert examine the crank and rods.

First Guess: Nothing wrong with the crank that a regrind won't fix. Nothing wrong with the rods that an inspection and MAYBE resizing won't cure.

Someone is sure to say that "by the time you replace the rod bolts, and have the rods resized, you could buy brand-new rods from XXXXXXXXX company and be better-off." Well, yes. How high are you going to spin this engine? Do you NEED new rod bolts? IF (big IF) the RPM is modest, and the rods are inspected and found to still be round...why resize them?

But maybe you plan to beat on this engine, in which case upgrading the rod bolts and resizing after close visual inspection is probably warranted. (If the cast-iron rods and cast-iron crank were cracked...they'd probably be broken already.) I don't trust bottom-feeder Communist Chinese rods or cranks. Not everyone feels that way. And--supposedly--there's some Communist castings/forgings that get proper machining and QA here in America. How fat is your wallet? What are your goals for this engine?


Have a professional, experienced eye examine the block; .030 is kind of routine for overbore, but if it can clean-up with less, bore the minimum amount. If it needs more, bore to what it needs. If one or two cylinders are especially bad, consider having them sleeved.

Mikes reply:

You said:

"Some guys do, if the ridge is big enough to cause difficulty removing the pistons. The point of ridge-reaming is to save the pistons from damage during removal".

Mikes reply:

The next time I take an Engine apart, perhaps I would remove the Crank first and pull the Pistons out the bottom by pushing the Pistons toward the top out of the way, sounds easy, but I suspect that is harder than it sounds like?

[TRADERMIKE 2012]

Originally Posted by Schurkey

What you're describing is not at all what steve25 is telling you to measure. What you're describing (cylinder wall wear) is a valid concern, though.

Steve25 wants you to cram a .002--.0025--.003 feeler gauge blade into the ring grooves of the pistons--in several places around the circumference--with the ring in the groove. There needs to be no more than .003 gap between the ring and the ring groove, or the ring groove is worn-out and the pistons are junk.

Fifty--sixty--seventy years ago, there were lathe tools to re-cut the ring grooves so they were "square" again, and steel spacers to take up the excess clearance in the machined-oversize grooves. That crap is DONE now, nobody is going to do that any more. They'd tell you to buy new pistons that don't have worn-out ring grooves.

As for what you're saying--that your cylinders have wear towards the top (typical bellmouth wear, common as dirt) there's a limit to what's acceptable. When I was in trade school, dinosaurs roamed the Earth, and some of them were driven to church and the grocery store by grandmotherly types who never went over 30 mph, ever. For those folks, I was told that cylinder bore wear of .007 taper was the absolute limit of acceptability.

Keep in mind that .007 taper leaves a ridge of .0035. It's REAL easy to find ridges bigger than that, and if your ridges broke the rings, you've almost certainly got more ridge than .0035. You are almost certainly going to bore that engine, and again you're needing new pistons.

The most-recent engine I put together has a "service limit" spec of .001 bore wear, but actually had .0015 taper. The ridge would be about .0008-ish. I put it together like that, and "so far, so good".

You can check your bore wear with feeler gauges and a non-broken ring, and a clean flat-top piston. Put the ring inside the cylinder, push it towards the bottom of the cylinder with the piston, so it's sure to be square in the bore. Measure the end-gap with the feeler blades. Bring the ring half-way up the bore, square it up with the piston, and measure the end-gap. It'll PROBABLY be the same as the measurement farther down in the bore. Then bring the ring up to the underside of the ridge. Measure the end-gap, which is probably going to be bigger than the two previous measurements. Subtract the small end gap measurement from the big end gap measurement, and divide the difference by 3.1416.

Anything over about .002 is grounds for rebore. Unless you're Grandma, going to church at 15 mph.

BEWARE of "stock replacement" or "rebuilder" pistons. They are almost always SABOTAGED with a low compression height. It used to be that .020 too-short was common, now I see many that are "only" screwed-up by .010. Low compression height affects piston-to-head clearance, which affects "squish" or "quench", which affects the speed of combustion as well as compression ratio. You do not want short pistons. Getting pistons that are properly-made may cost more than the "rebuilder" junk products.



Some guys do, if the ridge is big enough to cause difficulty removing the pistons. The point of ridge-reaming is to save the pistons from damage during removal.

"I" get a bigger hammer, and pitch the pistons in the scrap bin. I have seen too many blocks damaged by heavy-handed ridge-reaming.


Haul them to your favorite automotive machinist. Let an expert examine the crank and rods.

First Guess: Nothing wrong with the crank that a regrind won't fix. Nothing wrong with the rods that an inspection and MAYBE resizing won't cure.

Someone is sure to say that "by the time you replace the rod bolts, and have the rods resized, you could buy brand-new rods from XXXXXXXXX company and be better-off." Well, yes. How high are you going to spin this engine? Do you NEED new rod bolts? IF (big IF) the RPM is modest, and the rods are inspected and found to still be round...why resize them?

But maybe you plan to beat on this engine, in which case upgrading the rod bolts and resizing after close visual inspection is probably warranted. (If the cast-iron rods and cast-iron crank were cracked...they'd probably be broken already.) I don't trust bottom-feeder Communist Chinese rods or cranks. Not everyone feels that way. And--supposedly--there's some Communist castings/forgings that get proper machining and QA here in America. How fat is your wallet? What are your goals for this engine?


Have a professional, experienced eye examine the block; .030 is kind of routine for overbore, but if it can clean-up with less, bore the minimum amount. If it takes more, do what it needs. If one or two cylinders are especially bad, consider having them sleeved.

Mikes reply:

The number 8 cyl has a suspect (deep dime size) area at the top wall that might come out when bored, however what caused the anomaly in the first place? Lou said it looks like someone hit the cyl. wall with a ball-peen hammer.

If this is the result of poor machining or a cast sand event is questionable, it sure did not seal good at that location, JMO.

P.S. Are these grounds to sleave this cyl.?

I am concerned with what this area looks like behind, as viewed from the water jacket area!

Behind this problemed area, is there a chunk of cast material missing or rusted, is there a way to inspect this area from behind using one of those cameras on a flexible wand, like used by a swat team?

Extra video of finishing a Bore texture honing.

https://www.youtube.com/watch?v=sBcFDoG89R8

[tom s]

Mike,just have all cycs sonic check!Tom