Detonation? Pre ignition?

-
furiousgeorge

furiousgeorge

Active Member
Joined
Jul 3, 2010
Messages
38
Reaction score
0
Location
saskatoon
Hello! I've picked up an '86 360 to build for my '75 Duster, was told it ran well when pulled, but the guy didn't build it, so knew nothing about it. It has an old Edelbrock LD340 intake, dual valve springs and flat top pistons. The cam he figured wasn't stock as it had some lope to it. I started peeling it apart, and ran into two pistons (7 and 6) that look like oatmeal. All other pistons look fine. The cylinder walls and chamber/valves also look good. This will be my second rebuild, and I've never come across this. Is this detonation or pre ignition? The damaged pistons are nearly perfectly clean, while the others are dirty as one would expect. I was planing a full rebuild anyways, I'm just wondering about this. The pistons don't look broken or cracked, could it have run like this?

Also, I'm trying to figure out what cam I should use. I'm going to try to id the cam in it, but would like suggestions. The engine will be built with 9:1 pistons, is bored 40 over already, and will run the Eddie LD340 with a Carter AVS from a '70 340. The car will be a driver, no racing, stock 727 with a non posi 8 1/4 with 2.92 gears I think (off the top of my head, close to that anyways). I was thinking the stock 340 hp cam would be good?

Thanks!
 
Usually when pistons are super clean it means there was a coolant leak into those cylinders.
On top of this, that much detonation on only two cylinders is pretty much impossible.
Those two cylinders might have gotten some foriegn object in them, but you would think the heads and cylinder walls would also be beat up.
 
If they were side by side I would say a bad head gasket was allowing coolant to get into the cylinders. Head gaskets on both sides though wouldn't be to common, but possible.

A Comp extreme energy 268H would be a good cam for it. Or one with close specs. Not to bumpy and lots of grunt.

Jack
 
red cuda said:
maybe someone will tell us the difference between the 2. detonation,and pre ignition that is.
Click to expand...

Same thing "pre det", "detonation", "pre ignition"
People use different names for it, but all of them are a description for early ignition of the fuel air mix.
 
You can save a few $s with the Summit 6900 cam, $70.00 without lifters. Specs are close to the 68 manual trans cam.
 
The head gasket on the drivers side was good, the passenger side was so stuck it tore to pieces when I pulled the head off. I'll clean up the other pistons and see if I can get a clear pic of all of them (they're still in the block). Unless there was something bouncing about in there and it was removed shortly after the engine was built. But without marks on the walls and heads, I doubt that one. It seems obvious to me that this engine hasn't been apart on many years, mostly basing this off the crud being uniformly thick all over it.
Are the Summit cams good quality wise? I've always gone with major name parts, so no experience with Summit.
 
My wife just asked if its possible something got into those cylinders that was hard enough to damage the aluminum piston, but not the steel walls/chambers/valves? I doubt it, but like I said, not much experience here. She's great at pointing out "out of the box"ideas, bless her soul.
 
Since "oatmeal" isn't very descriptive, some pictures would help.
 
It amounts to the same thing, with different causes, "engine knock," ping, etc

Bad head gasket, depending on engine, can be a damaged head gasket with material etched away some, creating a hot spot

Carbon / other crud / deposits.

Sharp spot, as in a casting flaw, which runs hot

Poor piston / head / combustion chamber design / combination

Low fuel quality.

OIL USAGE, from things like the rings, cracked piston, valve guides, and in "other" than Mopar, a bad vacuum modulator or other oil-producing accessory, including the PCV system

I'm with Rob (Rusty) I've no idea what "oatmeal" "is." Antifreeze, unless in there long enough to corrode / etch the pistons, would not cause rough pistons, just wash them clean and wash off carbon.
 
Sorry, that's the closest thing I could think of! I couldn't get a decent pic with my phone of all pistons, so I got a good one of one of the buggard ones.
 

Attachments

  • image.jpg
    45.8 KB · Views: 469
Better, and looks like coolant damage to me.
Does the head look normal on those two?
 

Attachments

  • image.jpg
    57.4 KB · Views: 505
  • piston.jpg
    57.8 KB · Views: 474
The chambers and valves on those cylinders look no different then the others. I'll take a closer look after lunch to be sure.
 
Water will do that. I've seen little round dimples that look like BB shot. I'm thinking enough of them would create the texture you have there. A crack in a head could do that. Too much porting work could too.
 
6# 7 share the same intake runner a vacuum leak on this runner can lean out these cylinders ,intake gasket sucked in / rubber hoses missing on vacuum tee on this runner ,and I've seen valve seats drop and spit metal between these cylinders sharing runners. just something else to think about.
 
furiousgeorge said:
Are the Summit cams good quality wise? I've always gone with major name parts, so no experience with Summit.
Click to expand...

I've had the 6901 kit in the 318 Demon for a while. No problems. You may want to consider it as well. It's fairly tractable on the street and does not require exotic springs on the valves. Several others on FABO run it and are pleased with their purchase.

I'm not aware of any Summit production facilities (maybe it's next to the Kenmore appliance factory. lol)so I assume that someone is producing the cams for them. The box was generic except it did say "Made in USA". The instructions illustrated a Crane Fireball cam, the card with the specs looked like a Crane card. I deduce I probably have a cam made by Crane. I was unaware of this up front, so I chalk my find up to dumb luck.
 
It would be difficult to get coolant/water to completely cover 2 pistons, on opposite sides, in a V-8, unless it was sat on it's side..

Detonation damage is usually found around he circumference of the piston,, with most damage occuring on the side of the piston opposite the spark plug..

Ping/pre-ignition and detonation are not the same..

Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.

Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition.

The two are completely different and abnormal phenomenon.

With ping,, the pressure shockwave is slow and is created before the piston reached TDC.

Detonation is a sharper/higher pressure wave at, or after TDC..

hope it helps
 
Thanks everyone for all the great help! After lunch I went out to check things over, and one thing led to another, and I now have one of the offending pistons sitting on the bench. Unfortunately, that cylinder (#7) has a vertical crack down abouts halfway, 1 1/2" - 2" long, on the outer side of the cylinder. I'm not sure how I missed it, perhaps just the light and angle I initially looked at it. I didn't bother taking out the other piston. Is it a dumb question to ask if it can be welded and bored round again? The block has already been bored 40 over, how far can it go before it's not reliable anymore?
 
inertia said:
It would be difficult to get coolant/water to completely cover 2 pistons in a V-8, unless it was sat on it's side..

Detonation damage is usually found around he circumference of the piston,, with most damage occuring on the side of the piston opposite the spark plug..

Ping/pre-ignition and detonation are not the same..

Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.

Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition.

The two are completely different and abnormal phenomenon.

With ping,, the pressure shockwave is slow and is created before the piston reached TDC.

Detonation is a sharper/higher pressure wave at, or after TDC..

hope it helps
Click to expand...


x2^

It looks like that piston pictured had some issues. If it was me I'd pull those two rod/piston assemblies and check the rod and main bearings. Straight away figure on replacing the rings and bearings. If the pistons are that beat on top, the ring lands and rings are hammered too but the ring lands may be usable - just not great.
 
It's possible to have that cyl sleeved,, and the other if nec.. But the entire engine should be thoroughly inspected first, as I suspect there may be other issues..

My #s matching 69 340,, has had 3 sleeves to save it,, while running 12.5 pistons as well.. (less now)

hope it helps
 
I'm not sure I'd bother getting sleeves put in, as 360's are still relatively easy to find. I did email a few machine shops around, so I'll wait and see what they come back with. At the very least, I did get a good LD340 intake, the dual valve springs and perhaps and aftermarket cam. And most of the other parts (lifters, oil pump, valve train parts etc.) look good, just the block and maybe heads (they air injection heads anyways) are no good. Still worth what I paid for it I guess, just disappointing. I messaged the fellow I got it from, told him what I found, but I really doubt I'll get anywhere with him. I took a chance and got nailed. I really appreciate the help and suggestions!
 
That LD 340 is a very desireable manifold, and the other goodies have value for sure.. A used block, or even motor shouldn't be much..

good luck
 
Also, I'm trying to figure out what cam I should use. I'm going to try to id the cam in it, but would like suggestions. The engine will be built with 9:1 pistons, is bored 40 over already, and will run the Eddie LD340 with a Carter AVS from a '70 340. The car will be a driver, no racing, stock 727 with a non posi 8 1/4 with 2.92 gears I think (off the top of my head, close to that anyways). I was thinking the stock 340 hp cam would be good?
Click to expand...

I would 2nt finding a 360. longer stroke will be much better at leaving that traffic light, with your freeway gear ratio.(2.92:1)
 
You could probably replace the damaged pistons, ring and bearing it, and be done. Not sure this needs all kinds of replacement or full boogie...
 
You must log in or register to reply here.
-

Back
Top