Piston skirt failure (part 2)
06-30-2006, 09:46 AM
#1
Melting Slicks
Thread Starter
Piston skirt failure (part 2)
Someone remember the piston skirt failure I had some time ago?
OK, yesterday i removed the oil pan due to a suspected blown engine.
The oil pan is now a Aluminum holder...
Pieces of pistons anywhere. I see that I have the SAME exact failure I had in the piston #8 also on additinal 4 pistons: Piston skirt failure.
All the broke piston skirt are in the camshaft side (not the pan rail side)
Also 2 central piston are broken (not only the external ones). On these cilinders the piston skirt/counterweight clearance was really large so the little clearance probably is NOT the cause of the first skirt failure as supposed.
What cause all these repeated skirt failure?...
P.S. Pete..I know you'll be there.. check your email
-Beppe-
OK, yesterday i removed the oil pan due to a suspected blown engine.
The oil pan is now a Aluminum holder...
Pieces of pistons anywhere. I see that I have the SAME exact failure I had in the piston #8 also on additinal 4 pistons: Piston skirt failure.
All the broke piston skirt are in the camshaft side (not the pan rail side)
Also 2 central piston are broken (not only the external ones). On these cilinders the piston skirt/counterweight clearance was really large so the little clearance probably is NOT the cause of the first skirt failure as supposed.
What cause all these repeated skirt failure?...
P.S. Pete..I know you'll be there.. check your email
-Beppe-
06-30-2006, 09:52 AM
#2
Beppe, I got the mail and replied. The only thing I can think of is that the piston stuck in the bore for a moment. Although a defective piston set is possible. It truly is extremely rare.
06-30-2006, 11:23 AM
#6
it is my opinion that any cast or hypo piston should not be used in ANY performance application. they just dont get the job done. every motor that i rebuild, i alway spent the extra money for a good set of forged pistons.
06-30-2006, 12:20 PM
#7
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St. Jude Donor '04-'05-'06-'07
What kind of power were you making with this engine, Beppe? I used KB hypers in my last build and had no problems. It was a stock stroke, 11.3 CR and was making 370 RWHP. It had almost 25K on it when I removed it.
06-30-2006, 12:23 PM
#8
Originally Posted by Corvette Kid
What kind of power were you making with this engine, Beppe? I used KB hypers in my last build and had no problems. It was a stock stroke, 11.3 CR and was making 370 RWHP. It had almost 25K on it when I removed it.
06-30-2006, 05:12 PM
#11
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St. Jude Donor '04-'05-'06-'07
Originally Posted by JAKE
I'd put my money on the piston to wall clearance being too tight.
Jake
Jake
06-30-2006, 05:47 PM
#12
Melting Slicks
Gotta be clearance or severe harmonics. We just finished a 383 and used KB Hypers, followed the specs exactly. Heard none of that piston slap we were supposed to hear.
BTW, the factory pistons are Hypers also. What was GM's train of thought if they're so bad?
BTW, the factory pistons are Hypers also. What was GM's train of thought if they're so bad?
06-30-2006, 06:27 PM
#14
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St. Jude Donor '04-'05-'06-'07
Originally Posted by ALLT4
Gotta be clearance or severe harmonics. We just finished a 383 and used KB Hypers, followed the specs exactly. Heard none of that piston slap we were supposed to hear.
BTW, the factory pistons are Hypers also. What was GM's train of thought if they're so bad?
BTW, the factory pistons are Hypers also. What was GM's train of thought if they're so bad?
07-01-2006, 07:00 AM
#15
Burning Brakes
Originally Posted by JAKE
I'd put my money on the piston to wall clearance being too tight.
Jake
Jake
I ran KB pistons in my .060" over 350 for about 13k miles. I made 330 rwhp, ran high 12s, turned the engine 7500 on a couple of occasions and frequently went to 6300rpm or so. I had .0015" wall clearance and when I took the engine apart the skirts were perfect. No cracks and no galling. I threw them away though and went with Mahle forged pistons because I had a terrible ring seal and too much blowby.
For what that's worth...
Dan
07-03-2006, 05:12 AM
#17
Melting Slicks
Thread Starter
Thanks to all for the interesting and usefull replies.
Here a bit of History with some reply to someone of you that asked something to better understand.
This stock 638 block had 2 rebuilds. The first from 350 to 355.
Spun bearings was the cause for the first rebuild. I used a balanced Eagle rotating assembly with KB Hyper pistons. The work was: A friend removed/reinstalled the engine and a local builder made the bore-honing and assembled the engine with stock parts (heads, cam…).
I said to this builder to do a piston to wall clearance of .00175” . He said OK, but I really don’t know if done as requested. I also said file the rings as in the KB site.
This engine started using 1 quart of oil and ended about 10,000 miles later burning 1 quart /1000 miles.
10,000 miles and 2.5 years later of normal and abused use, I bought TF heads and 219 cam, Superram…wanting to install in this 355. The new builder proposed to do a 383 and using Eagle parts. (He was using the same cast Eagle kit with KB pistons on his ‘79 corvette and done 4 of these motors with zero problems).
I was excited. He made the engine in a week and found the old KB pistons and rings perfect. Only some main bearings were a bit scored in the old crank with a little bit of copper exposed.
With new heads (read: new seals, new guides) and a new engine I was also curious to see how the oil consumption was. I was not impressed by the SOTP performances and the oil consumption was horrible. Asked for piston to wall clearance used and he said that he only slightly hand honed with a fine grit the cylinder walls and put the new (same +.030” pistons) in the bores, just because he found the walls finish good for a 10,000 miles engine. I performed on the next months 2 compression tests with good results and also a leak down test with very good results. I was not happy with the SOTP performance… but I have to say that this car was fast ..fast as a new 2005 Viper on the 1/8 (even better) and with a better MPH on the end of the 1/8…
The month ago I discovered a missing skirt on the #8 piston and 2 weeks ago in a 1/8 mile run I heard a noise at the end of the run and found the #8 spark plug with the gap zeroed(!) and with microscopics particles of melted aluminium on it, but not smashed. I babied to home (with the gap restored…) and in the middle of the trip I had an instantaneous 180 deg coolant increase to 230 deg and stopped the car. Later I discovered tons of coolant in the oil pan.
During the disassembly of the pan I see the others pistons skirt on the pan.
I don’t know if the skirts problems are related...but I think that the problem was detonation.
With all this oil in the combustion chambers the gas is more prone to detonation. In addition when 2 month ago I removed the Superram, I noticed an incredible carbon buildup on combustion chambers and all around valves as a 200,000 miles engine.
This week the engine will be down and I will discover if the heads are cooked also.
Zeroed spark plug gap (from .040”) without hammering signs, is typical of detonation?
-Beppe-
Thanks for your help!
Here a bit of History with some reply to someone of you that asked something to better understand.
This stock 638 block had 2 rebuilds. The first from 350 to 355.
Spun bearings was the cause for the first rebuild. I used a balanced Eagle rotating assembly with KB Hyper pistons. The work was: A friend removed/reinstalled the engine and a local builder made the bore-honing and assembled the engine with stock parts (heads, cam…).
I said to this builder to do a piston to wall clearance of .00175” . He said OK, but I really don’t know if done as requested. I also said file the rings as in the KB site.
This engine started using 1 quart of oil and ended about 10,000 miles later burning 1 quart /1000 miles.
10,000 miles and 2.5 years later of normal and abused use, I bought TF heads and 219 cam, Superram…wanting to install in this 355. The new builder proposed to do a 383 and using Eagle parts. (He was using the same cast Eagle kit with KB pistons on his ‘79 corvette and done 4 of these motors with zero problems).
I was excited. He made the engine in a week and found the old KB pistons and rings perfect. Only some main bearings were a bit scored in the old crank with a little bit of copper exposed.
With new heads (read: new seals, new guides) and a new engine I was also curious to see how the oil consumption was. I was not impressed by the SOTP performances and the oil consumption was horrible. Asked for piston to wall clearance used and he said that he only slightly hand honed with a fine grit the cylinder walls and put the new (same +.030” pistons) in the bores, just because he found the walls finish good for a 10,000 miles engine. I performed on the next months 2 compression tests with good results and also a leak down test with very good results. I was not happy with the SOTP performance… but I have to say that this car was fast ..fast as a new 2005 Viper on the 1/8 (even better) and with a better MPH on the end of the 1/8…
The month ago I discovered a missing skirt on the #8 piston and 2 weeks ago in a 1/8 mile run I heard a noise at the end of the run and found the #8 spark plug with the gap zeroed(!) and with microscopics particles of melted aluminium on it, but not smashed. I babied to home (with the gap restored…) and in the middle of the trip I had an instantaneous 180 deg coolant increase to 230 deg and stopped the car. Later I discovered tons of coolant in the oil pan.
During the disassembly of the pan I see the others pistons skirt on the pan.
I don’t know if the skirts problems are related...but I think that the problem was detonation.
With all this oil in the combustion chambers the gas is more prone to detonation. In addition when 2 month ago I removed the Superram, I noticed an incredible carbon buildup on combustion chambers and all around valves as a 200,000 miles engine.
This week the engine will be down and I will discover if the heads are cooked also.
Zeroed spark plug gap (from .040”) without hammering signs, is typical of detonation?
-Beppe-
Thanks for your help!
07-03-2006, 06:21 AM
#18
Burning Brakes
Well, sounds like you have a number of things going on there. But one thing I didn't mention explicitly is that I had alot of oil consumption with my KBs also, which is caused by the blowby from the poor rind seal. I too had good compression test results (~215psi) and made good power. The blowby does two things. It makes the oil get really dirty very quickly after an oil change because you're getting carbon in the oil. And it pressurizes the crankcase to the point of over-coming the capabilities of the PCV system. That crankcase pressure forces oil down the valve guide which gets into the combustion chambers and in the intake manifold. The spark plugs are always black and oily.
When I switched to the Mahle pistons I lightly re-honed the cylinders, with a torque plate (this is important beyond what most people understand). I now have >7000 miles on the Mahle pistons. After 500 miles on the last oil change the oil is still looking very clean. My spark plugs are dry and tan colored. And I picked up 18rwhp with no other changes.
Detonation will certainly exacerbate the problem with the piston skirts you are having. And with bearings worn to copper, coolant in the oil, and spark plug gaps closing up, you've got something serious happening and I hope you get a handle on it. It's probably all related to detonation. I'd definitely go with forged pistons if I were you.
Are you running a knock sensor?
What is your static compression ratio?
Do you know what your DCR is?
Good luck,
Dan
When I switched to the Mahle pistons I lightly re-honed the cylinders, with a torque plate (this is important beyond what most people understand). I now have >7000 miles on the Mahle pistons. After 500 miles on the last oil change the oil is still looking very clean. My spark plugs are dry and tan colored. And I picked up 18rwhp with no other changes.
Detonation will certainly exacerbate the problem with the piston skirts you are having. And with bearings worn to copper, coolant in the oil, and spark plug gaps closing up, you've got something serious happening and I hope you get a handle on it. It's probably all related to detonation. I'd definitely go with forged pistons if I were you.
Are you running a knock sensor?
What is your static compression ratio?
Do you know what your DCR is?
Good luck,
Dan
07-03-2006, 07:00 AM
#19
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Broken piston skirts
This suggestion is based on 40 year old 'technology' so may not apply to newer Corvette engines. And please don't take offense about the incorrect assembly possibility - my son and I missed it. Please benefit from our hard earned experience.
The connecting rods aren't symetrical. Where the bearing cap mates to the rod, there's a very small 'V' shaped groove for oil to squirt out and lubricate the opposite cylinder - on one side only. If say the #7 rod is installed 'backwards' (V pointing down rather than up) then the #8 cylinder will not get adequate lubrication and eventually suffer wear, oil consumption, loss of compression and skirt breakage. It cost us a very nice 400+hp engine and lots of looking.
Do the new engines lubricate similarly?
Check out the rod/cap mating surfaces looking for an asymetrical 'V' and make sure that groove is 'up' during assembly.
Hope this helps,
Respectively...
The connecting rods aren't symetrical. Where the bearing cap mates to the rod, there's a very small 'V' shaped groove for oil to squirt out and lubricate the opposite cylinder - on one side only. If say the #7 rod is installed 'backwards' (V pointing down rather than up) then the #8 cylinder will not get adequate lubrication and eventually suffer wear, oil consumption, loss of compression and skirt breakage. It cost us a very nice 400+hp engine and lots of looking.
Do the new engines lubricate similarly?
Check out the rod/cap mating surfaces looking for an asymetrical 'V' and make sure that groove is 'up' during assembly.
Hope this helps,
Respectively...
07-03-2006, 08:01 AM
#20
Melting Slicks
Thread Starter
Originally Posted by danno85
Well, sounds like you have a number of things going on there. But one thing I didn't mention explicitly is that I had alot of oil consumption with my KBs also, which is caused by the blowby from the poor rind seal. I too had good compression test results (~215psi) and made good power. The blowby does two things. It makes the oil get really dirty very quickly after an oil change because you're getting carbon in the oil. And it pressurizes the crankcase to the point of over-coming the capabilities of the PCV system. That crankcase pressure forces oil down the valve guide which gets into the combustion chambers and in the intake manifold. The spark plugs are always black and oily.
When I switched to the Mahle pistons I lightly re-honed the cylinders, with a torque plate (this is important beyond what most people understand). I now have >7000 miles on the Mahle pistons. After 500 miles on the last oil change the oil is still looking very clean. My spark plugs are dry and tan colored. And I picked up 18rwhp with no other changes.
Detonation will certainly exacerbate the problem with the piston skirts you are having. And with bearings worn to copper, coolant in the oil, and spark plug gaps closing up, you've got something serious happening and I hope you get a handle on it. It's probably all related to detonation. I'd definitely go with forged pistons if I were you.
Are you running a knock sensor?
What is your static compression ratio?
Do you know what your DCR is?
Good luck,
Dan
When I switched to the Mahle pistons I lightly re-honed the cylinders, with a torque plate (this is important beyond what most people understand). I now have >7000 miles on the Mahle pistons. After 500 miles on the last oil change the oil is still looking very clean. My spark plugs are dry and tan colored. And I picked up 18rwhp with no other changes.
Detonation will certainly exacerbate the problem with the piston skirts you are having. And with bearings worn to copper, coolant in the oil, and spark plug gaps closing up, you've got something serious happening and I hope you get a handle on it. It's probably all related to detonation. I'd definitely go with forged pistons if I were you.
Are you running a knock sensor?
What is your static compression ratio?
Do you know what your DCR is?
Good luck,
Dan
Yes KS installed and working (but I can't run all the time with the laptop on the passenger seat..)
Compression ratio should be around 10.8:1 with 64 cc heads and flat top pistons with 383 c.i.
Dinamic should be in the medium-high side because the int valve closes a bit earlier on a 219 LPE cam in respect to another more duration cam.
-Beppe-