I picked up a 350 roller block out of a van recently. I'm gonna use it for my buildup instead of the other block I bought online a few months back thinking it was a roller block. Anyways, this engine looked like it had either detonation problems or debris fell in two cylinders. Not sure which of the two.

 

That was the fourth cylinder on the passenger side. Here is the third cylinder on the driver side. Its not as bad as the other cylinder though. When I pulled the heads off, some small metallic pieces fell out of the intake port on one of the heads. Also, the spark plug on the cylinder in the first pic had no gap. That cylinder would obviously have had detonation problems, I just don't know if that would be its only problem.

 

I pulled the oil pan off, and took the rod cap off on the piston in the second pic. This is the first time I take a look at engine bearings, so I don't know what to make of this. It has some marks that are discolored, and a couple of tiny spots that are shiny. It feels completely smooth though.

 

Sorry, heres the pic...

 

wow, can detonation really cause that much damage?

 

That's what pistons look like when debris or hardware falls down through the intake.
The bearings don't look all that bad.
At the very least, you'll need a rebuild kit with a new set of pistons. Possibly a rebore.
Check the oil pan and filter for metal particles. If there are none then that would mean that the damage was most likely limited to the top end.
But to play it safe, it's a good idea to check everything in the rebuild process. But that's what you should do anyhow.

 

Last piston I saw that looked like that came out of a motor that ran lean at the track due to tuning, broke off a piece of piston, ruined the #5 piston, and then jumped over to #7 and killed it as well. They were TRW forged ones too... He ran WAY lean!!!

 

This is what less than 3 seconds of detonation did to a forged piston (they have been on the shelf for a long time thats why its rusty)

 

wow ate them up pretty good.

 

I was planning on changing pistons, rings, and bearings regardless. I also have a set of x rods that I will be using. There is no ridge whatsoever on any of the cylinders, but the two with the damage I would have to take a really close look at. I haven't pulled out the pistons, but judging by the top of the bore, it looks like it would be fine just honing out the cylinder. Atleast one cylinder HAD to be detonating because the spark plug electrode was touching. There was no gap whatsoever. I just can't picture detonation making a square imprint on the piston everytime.

 

Looks like years of detonation to me. I'd like to see what the underside of the heads look like. That'll tell you if something like a bolt done the damage.

If you're replacing bearings anyway, what counts is what the crank journals look like, not the old bearings. I'd mike out those cylinders too. Most wear occurs about 2" in the hole, so check the tolerance there. Doesn't hurt.

Good luck with it!!

 

Gaaaa! stupid POS computer cut off 2/3 my post.

 

Wow... thats pretty sobering. Ive done alot of tuning mods and believed that my low compression and knock sensor would, at least in part, help prevent any serious detonation that would damage the motor. Guess I aught to think again.

 

That piston wasn't damaged by detonation. That's from a foreign metal object running around in there. Detonation erodes the edge of the piston under the spark plug, it doesn't put nice cute metal stapmpings in the side opposite the plug and leave the rest of the piston top entirely alone. Notice how all of the damage is confined to the area where there's no combustion chamber. The loose object broke the spark plug off. The small amount of damage right under the plug is from when the foreign matter wandered over to that side and got stuck under the plug boss.

The bearing looks mostly OK, obviously a little stressed, maybe from being used as a stamping press; but nothing really disastrous.

 

So, is detonation what killed my motor?

 

Zepher:

If your detonation was a piece of something rod-shaped, straight, about 11/32" diameter and about ½" long, then maybe so.

 

I think a piston ring came apart and did all that damage, but I gave the motor away before taking it apart.

 

I've had engines that had a serious serious detonation problems. Street driven, CR too high, slightly out of tune. They would ping any time my foot was into the gas enough to make the vaccum ga drop to 10" or lower, at between 2000-3000rpm. That's typical low rpm pinging that street engines experience.
Basically... these were motors that would ping all the time, cause they were originally designed to be used with leaded gas.
When I rebuilt these engines, there was no visible damage to the cast pistons.

In race motors or with a power adder things are a lot different, detonation can be the cause of immediate destruction.

Point is, if you're driving in the street, and your engine pings at part throttle, it's not a good thing, but it isn't gonna kill it right away. It could reduce your engine life a bit tho.

On the track at WOT is where detoation is really something to be looked out for. That's where you'll see pistons that are busted or melted from 3 sec of detonation.

 

This is what detonation (pre-ignition) does to pistons.

 

That picture of the bearing looks exactly like the ones that came out of my L98. I thought they looked trashed, but my bro who is a mechanic says they looked alright, not good but alright. The main bearings looked near perfect. And the cylinder walls still had the cross hatches in the a 123,000 miles. Maybe the bearings says I ran the poop out of it?

 

And this is what happens when you break a valve at 6000!

 

Looks fine to me. What am I supposed to be looking for?

 

That'll buff right out, and any good shop can straighten out the rod. . .

I had a motor drop an exhaust valve at high RPM, wasted everything, block, crank, cam, head. . . Had 7 good rods & pistons and one good head left over.

RBob.

 

And yet, people think they're going to "save money" by cheeeeping out on valve springs..... which is of course what most likely broke in Zepher's motor, not the valve itself. There's enough risk of that happening without tempting fate by using inadequate springs.

{edit} Oooooops, I meant RWB's motor.

 

The only parts that survived this, was the intake and the crank!

 

I'm leaving the engine assembled for now. As soon as I finish working on the heads and siamesing the manifold, I'll take it all apart and then worry about any machine work. As long as I leave it assembled and with oil, there isn't much of a worry about rust developing in the block.

By the way, now I am thinking... What the hell happened to whatever fell inside the cylinders?



Did it completely disintegrate? I didn't see any debris inside when the head came off, even though I did notice several small metallic pieces fall out of the intake port. Whatever was in the cylinder can't work its way back into the intake port, so what fell out of the head was a separate issue.

 

hey Zepher. maybe it was all those worms on the motor that killed it...ohhhh I guess thats a chain...

 

Looks like from the picture of that piston that suffered from the broken valve that the rod bolts held. (ARP?)

 

At least the rod didn't break. LOL

 

Yep. ARP all the way Plus amasingly the rod and wrist pin still move freely in the piston! I guess that and alittle bit of luck is what saved the crank.

 

OMG I feel bad for you guys.

 

Man that brings back bad memories. I destroyed a small block 400 down to the exact same parts left ( 7 good rods and pistons, good crank, good intake, and one good head). I managed it from having a bad wrist pin though. The piston skirt disentegrated and that was the end of that motor. It also ripped the oil pan open like a can opener and threw 5 quarts of 10w-40 all over the interstate! My connecting rod didn't stay in one piece though. It was bent over at a 90 and torn in half about halfway up the beam. The bottom half of the rod was still bolted nice and tight to the crank though. There was a hole punched through the cylinder into the water jacket of the block and a nice hole punched in the flat part of the combustion chamber on the head too.

 

when I bought my full size blazer, it had 2 broken rods, melted crank, cam broken into 3 pieces, 2 broken pistons, cylinder walls in those 2 had large chunkls missing, and a trashed moroso 7 qt oil pan (that i had to beat with a hammer to unbolt)


















the truck is still using the heads, intake, RRs and headers

 

Here is a picture of a main bearing out my 406 with about 12,000 miles on it. Im not sure what caused it other than i found my oil pump pickup clogged with gasket material, but still had good oil pressure.... and the bottom end was not balanced. I belive there was some kind of debris in there too not sure what. This was the only bearing in the whole motor that looked like this. both top and bottom bearings look the same.

 

here is my oil pump right after removing the oil pan, I used a little bit too much RTV on the oil pan gasket..... ill use it sparingly if at all next time around... i learned my lesson. New crankshaft and a full rebuild again.

 

Omg, how did I know the rtv in your pic would be orange? I'm betting you used that Ultra Copper high temp crap huh? I tried the same stuff on my first oil pan gasket years ago with the same results. My engine didn't blow, but I had pieces of it on the pump pickup too. That sealer is worthless. The best stuff I've found is "the right stuff" that comes in the can and is black. However, nowadays you just buy the one piece oil pan gasket which doesn't need any sealer at all, unless you want to put just a dab in the corners for extra insurance. I'll never use a four piece oil pan gasket again when the one piece gaskets are so easy to install without leaks.

 

Im certainly no engine guru, but maybe the problem was caused by either incorrect clearancing or an out of balance rotating assy? The pickup doesnt look clogged enough to cause much trouble.

 

yeah im pretty sure the pickup wasnt clogged either, i still had good oil pressure. The clearance was right i checked everything when it was put together, my guess is that i got some kind of debris in there, and i know the bottom end was not balanced, i had it balanced before i did grinding on the rods for cam clearance, and i also changed from an manual to automatic which means i had to swith from a flywheel to flexplate, and my 406 is externally balanced.

 

Here are my thoughts. The top pictures are not caused by detonation. That was an object ingested by the piston. Could have been caused by a broken valve spring. Something went back up into the intake from the really bad piston into the one that doesn't look so bad. It can happen.

305s always detonate under a heavy load when it is hot outside. Besides a minute amount of carbon my pistons looked brand new in mine when it got pulled apart at 150,000 miles so I don't think detonation caused that. I discredit the lean theory because you would have atleast 4 pistons. Those two pistons share a common intake runner so that why I think their was a foreign object ingested.