Broken rings again...

[85_prairieboy]

I took my engine apart today to freshen it up and noticed that most of the second compression rings were broken. This happened 5 years ago when I took it apart as well. Engine is a SBC 350 with forged pistons 10.5:1 and a 150 shot. What could cause this? On my last pass down the track it pushed oil out the breather and ever since then if I get on the throttle too hard the crankcase pressure builds up. All of the top rings were good

[cableguy0]

Incorrect ring gap on forged pistons will definitely cause it. Incorrect ring gap on forged pistons with nitrous will certainly cause it.

[85_prairieboy]

I was wondering that too but both times the gap was set to .028" on both rings which is what the ring manufacturer specified. Maybe I should go to .030"?

[68Gold/white]

Check w/ piston ring manufacturer, they usually have very specific instructions...

[Marv D]

JE has a chart that is pretty close to everyone else,, but like Gold/White said you should absolutely check with the ring manufacturer. But typically on a 4.030 bore with big shots of nitrous your going to want 0.026-0.027. You should have been OK @ 0.028.
There is no hint of a ridge in the block?

http://www.small-block-chevy.com/images/jering1.jpg

[Old Truck Man]

5 years on a engine that has nitrious and is run on a track sounds ok to me. we used to tear down our drag engines after about a dozen runs and refresh the rings & rod bearings. Did you balance the rotating assembly are all the combustion chambers the same CC. are all the deck heights equal. Is the block square. Was a block plate used when the cyls where bored & honed. In other words to make HP and be reliable an engine must be balanced & blueprinted.

[68Gold/white]

Honing w/ a torque plate has so many advantages, that are not always realized...

Many old timey naysayers laugh, when you tell them about a "torqueplate". I built engines for umpteen years, never used one......

Yes, the final bore will be very close to "round" when it's properly honed.

The rings sealing is the most important obvious thing!!! BUT (without a torqueplate) when you measure everything, gap the rings, put the heads on and torque the head bolts... The cylinders are pulled in at the top (how far from top down, I'm not sure), enough to unseal the rings
(@ the head bolt areas) AND narrow the ring gaps all at the same time...

Kinda poops on an otherwise well prepared engine build, and a lot don't know about it...

Not knocking ANYONE here, just saying....been there, done that...

[Old Truck Man]

Originally Posted by 68Gold/white

Honing w/ a torque plate has so many advantages, that are not always realized...

Many old timey naysayers laugh, when you tell them about a "torqueplate". I built engines for umpteen years, never used one......

Yes, the final bore will be very close to "round" when it's properly honed.

The rings sealing is the most important obvious thing!!! BUT (without a torqueplate) when you measure everything, gap the rings, put the heads on and torque the head bolts... The cylinders are pulled in at the top (how far from top down, I'm not sure), enough to unseal the rings
(@ the head bolt areas) AND narrow the ring gaps all at the same time...

Kinda poops on an otherwise well prepared engine build, and a lot don't know about it...

Not knocking ANYONE here, just saying....been there, done that...

Years ago We where building 8000 RPM all day long stock car engines & 10,000 RPM drag strip engines(big bores & short strokes). and ours stayed together. Attention to detail like making sure the bores where round when assembling and reworking the oiling system to insure the bottom end always had oil pressure had a lot to do with it. Most machine shops can do a adequate bore job for a stock engine. The only place I know of that bolts a torque plate to the block when machining it is Racing Head Service in Memphis Tenn. The book about Building the Small Block chevy By Smokey Unick Explains the how & why much better than I can.

[GMR-PERFORMANCE]

I have to wonder if maybe there is more to this... One thing that many never check is ring to piston land gap.. Some pistons have less than great ring lands. Myself dislike JE pistons for this very reason they cut the ring lands in the start where as CP will do that last. I have found that the CP piston for example has extremely close spec on these items. It has shown up with better ring seal better power less blow by and less ring flutter. On the JE piston you can see odd wear on the ring area that contacts the piston land. Add NOS to the mix and things must be even better. Low rpm engagement is another issue that will tax the pistons and entire rotating system. The piston may be pinching the ring and creating the fracture which then breaks the ring. A true NOS piston will have more area above the top ring to help with this issue. Myself feel that there are way too many variables to give you a spot on fix. Ign ping is something that will stress the crap out of the rings. Too many guys run plugs that are too hot never really check the plugs, or AFR if pump gas is in use( I say this as todays pump gas is not easy to read due to additives) But I would use a high quality piston( anti , set the ring gap up for the bottle. Ensure that the cylinders are round and straight.

Some info on why we ONLY use CP pistons. I supply tons of my buddys with these pistons .. Price wise they are not much more than JE SRP though summit and CP supplys them complete. Enough on that good luck with the build I hope that with some solid info you can solve your problem with what ever parts you use to repair the engine.




CAM AND BARREL
The Cam is the shape around the skirt of the piston and the barrel is the
sha
pe from under the oil ring to the bottom of the skirt. Extensive research
and development has been done to find the optimum skirt shape for each
piston. These shapes have been found to seal up cylinders and reduce
harmonics in the bore better than ever before. Depending on the forging and
application, different cam and barrel profiles are utilized for maximum
performance. Having the correct cam and barrel on a part promotes the
following:
1. Tighter clearances
2. Less noise
3. Better ring seal
4. More power
5. Increased durability
ANTI DETONATION GROOVES (CONTACT REDUCTION GROOVES)
Also know as contact reduction grooves, which limit the
piston/c
ylinder contact during high temperature and high RPM.
These grooves also protect the top ring by disrupting detonation
waves.
ACCUMULATOR GROOVE
V-shaped groove machined in the 2nd ring land that adds to the
volume between the top and second ring.
This groove accumu-
lates residual gasses from combustion which alleviates top ring
flutter and premature second ring wear, improving ring seal.
CP Groove
CP Groove stands for Constant Pressure Groove. This groove is
used as a channel on the lo
wer part of the top land and equal-
izes pressure to the top ring groove. When used in combination
with lateral gas ports, the CP groove helps keep gas ports clear
of carbon build up. In addition, the CP groove prevents the top
land from smearing into the top ring if the land rubs the cylinder bore.
DOUBLE PIN OILERS
Double Pin Oilers (opposed to single pin oilers), in conjunction
with our annular reser
voir, can add twice the amount of oil from
the cylinder wall to the wristpin bore. This is a standard option on
any piston that receives forced pin oiling.
BROACHES
Broaches are horizontal slots in the pinbore designed to allow oil
to enter between the wristpin and pinbore.
Broaches are also
used to accommodate the wristpin shape under compression, as
it can become somewhat oval and needs room in order to allevi-
ate galling.
PIN FITTING
The pin bore is precision honed to attain an exact pin clearance. Depending on
the a
pplication clearances typically range from .0003 to as much as .003
between the wristpin and pin bore.
COMBUSTION TROUGH
A term used to describe a feature on the piston crown between
the intake and exhaust.
Ignited air/fuel mixture on flat top and
dish pistons typically have better flame travel than a dome pis-
ton. Flame travel on dome pistons can be improved with “fire
slots” and/or a combustion trough.
PLUG RELIEFS AND FIRE SLOTS
Various machined slots and reliefs that are used to promote
c
learance for the spark plug. The plug relief is generally a
plunged ball end mill, where the fire slot is a trough in the pis-
ton that helps move the spark towards the exhaust side of the
chamber.
CLIP CUTS
Additional cuts that are on the edge of the piston (generally near
the valve reliefs) and used to deburr or un-shroud the valves
while still on the CNC machine.
STRAIGHT CUTS
Cuts that are used to create the deck surface on a piston. These
are generally used on 4 valve pistons and the compression
height is genera
ted from this cut.
SLANT CUTS
Cuts that are used over the valve reliefs in order to un-shroud the
area around the valve.
PLUNGE POCKET(S)
Valve reliefs that are machined in a plunged or circular fashion,
designed to lea
ve a boundary around the perimeter to achieve
higher compression.
TULIP POCKET(S)
Valve reliefs that have a protrusion in the center of the valve
pocket to ma
tch the underhead shape of the valves. This helps
when max compression is the goal.
RADIUS VALVE RELIEFS
A Radius valve relief is created by using a form tool (or done in
a 3D fashion) to roll the edge of the valve relief.
Often times we
generate radii from valve relief to valve relief (see VR Sweep) as
well and this is used to improve flame travel and cross flow in
the combustion chamber during the overlap stroke.
VR SWEEP
Swept valve reliefs relieve fuel puddling and shrouded valves for
a better fuel cur
ve and allow the engines operation to improve
during the overlap stroke.

[85_prairieboy]

The engine is booked in for some machine work. I can't see or feel a ring ridge. One thing the machine shop pointed out is that the rings may have never been broken in properly. The second ring looks like it has been overheated and may have been doing most of the sealing. He could be right. I also measured the deck height on all pistons and was surprised to find one piston .045 down and then all pistons higher sequentially to .012 on the highest. Similar measurements on the other side. He will square the deck. I've always been just an engine assembler rather that a builder but seeing my block that far out of square has me convinced to spend more time. By my calculations the worst cylinder was 10.1:1 and the highest was 11.0:1. The shop will be using a torque plate for honing my cylinders. I'm also getting them to short fill my block for a better ring seal. I should measure the ring to land clearance. Something caused this to happen both times and I don't want it to happen again. It makes a decent amount of power but the engine likely doesn't make much more than 400 hp based on weight and 1/4 mile time.

[71Dragtruck]

If an option have it broken in on a dyno, money well spent as they can put a proper load on the engine and hold it where it needs to be for break in.

[85_prairieboy]

Quick update. Cylinders are now round and block is machined square. Was about to start measuring ring gaps and decided to measure ring to land clearance. A .015" feeler gauge slid in easily. I have been using 1/16" rings in a 5/64" groove. When I bought my pistons they were supposed to have 1/16" grooves and I never tbought to check. Embarrassing to admit but glad I found something.

[85_prairieboy]

Thanks for bringing it up GMR

[moggey01]

Another trick to the torque plate hone in the hone angle. With the new sunnen hone you can vary stroke speed. It changes the angle on the hone pattern. There is a good bit of power in it when its right.