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CSI Seattle: 318 Forensic Analysis...

Flathead38

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Location
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This should be fun... I provide the clues, and you pick your favorite explanation for what I found... See my intro post, "Wakening a 1969 Charger from a long slumber", and "Newbie 318 questions" if you want more background.

Update on '69 Charger resurrection... Original "675" heads failed magna flux; they had multiple cracks between valve seats and/or valve seat to spark plug hole. So began a search for rebuildable heads.

We bought a cheap tired 318 long block as a spare, minus the valve covers, intake and push rods (Clue #1), because the heads were also "675", the same as our old engine. For grins, ran a leakdown test on the spare engine. Most cylinders were around 70/80 (Clue #2), with the sound indicating that worn rings were causing the majority of compression loss.

Then we pulled the heads. We saw valve to piston contact on EVERY valve (see attached pictures, Clue #3). That's the mystery part. What's your favorite explanation for how this likely happened? I can think of a few plausible scenarios, but it will be more fun if I don't provide them... Also curious to hear, based on your favorite theory of how this happened, what other damage I might expect to find as I continue the disassembly.

The good news is that this engine is all 1970, and appears never to have been opened up since new. Lots of original paint on the exterior. Cylinders measure out at STD +.002, and the walls look decent. I haven't pulled the valves out of the heads yet, but anticipate that I may see bent valves, and possibly cam damage, although the cam looks very tired and likely junk anyways. No hardened valve seats is also consistent with untouched 1970 heads...

If the head castings are rebuildable, I figure what I paid for the spare engine is probably fair. If the block can be rebuilt at .010" over, or maybe .020", I would consider it a pretty good deal.

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Somebody bricked it because they actually believed the myth that 'you can't blow up a 318'?

Seriously though, it could have been over-revved to the point that the springs couldn't keep things happy. If it was a singular failure (like a popped pushrod/rocker/lifter) it shouldn't have caused contact on all 8 like that. Timing chain/sprocket failure also a maybe.

I figure what I paid for the spare engine is probably fair. If the block can be rebuilt at .010" over, or maybe .020", I would consider it a pretty good deal.
Was it free:D
 
Those don't look like factory head gaskets.
And the pistons look pretty clean for a smoked motor.
How loose was the chain?
 
With every piston being hit something was very wrong on cam timing. Someone may of goofed on an adjustable timing gear set. To long of push rod at one time. Without seeing the timing chain and gears along with the heads it is hard to say. But for sure something was not compatible. The way you bought it it will almost be impossible to correctly say.
 
Timing chain broke or skipped due to slop in chain and/or original coating from cam gear coming off.
 
Timing chain broke or skipped due to slop in chain and/or original coating from cam gear coming off.
That was a thought I had but I have never seen a small block timing failure with the valves getting bent. All those pistons are pretty evenly hit. My experience when you see even one piston hit you will also see a bent push rod and broken rocker. One I could see but not all 16. Pretty hard for both intake and exhaust to both hit.
 
This should be fun... I provide the clues, and you pick your favorite explanation for what I found... See my intro post, "Wakening a 1969 Charger from a long slumber", and "Newbie 318 questions" if you want more background.

Update on '69 Charger resurrection... Original "675" heads failed magna flux; they had multiple cracks between valve seats and/or valve seat to spark plug hole. So began a search for rebuildable heads.

We bought a cheap tired 318 long block as a spare, minus the valve covers, intake and push rods (Clue #1), because the heads were also "675", the same as our old engine. For grins, ran a leakdown test on the spare engine. Most cylinders were around 70/80 (Clue #2), with the sound indicating that worn rings were causing the majority of compression loss.

Then we pulled the heads. We saw valve to piston contact on EVERY valve (see attached pictures, Clue #3). That's the mystery part. What's your favorite explanation for how this likely happened? I can think of a few plausible scenarios, but it will be more fun if I don't provide them... Also curious to hear, based on your favorite theory of how this happened, what other damage I might expect to find as I continue the disassembly.

The good news is that this engine is all 1970, and appears never to have been opened up since new. Lots of original paint on the exterior. Cylinders measure out at STD +.002, and the walls look decent. I haven't pulled the valves out of the heads yet, but anticipate that I may see bent valves, and possibly cam damage, although the cam looks very tired and likely junk anyways. No hardened valve seats is also consistent with untouched 1970 heads...

If the head castings are rebuildable, I figure what I paid for the spare engine is probably fair. If the block can be rebuilt at .010" over, or maybe .020", I would consider it a pretty good deal.

View attachment 1455836

View attachment 1455837

View attachment 1455838
Oh well, it's all moot really. Machine shop, and new parts. That's the way I see it, after that after action report.
 
Those don't look like factory head gaskets.
And the pistons look pretty clean for a smoked motor.
How loose was the chain?
I haven't seen the timing chain yet, I'll let you know... and I cleansed some carbon off the pistons, but it was suspiciously light... maybe that's another clue. I don't know what factory head gaskets look like, but I was curious if someone else did. Thanks for the input!
 
That was a thought I had but I have never seen a small block timing failure with the valves getting bent. All those pistons are pretty evenly hit. My experience when you see even one piston hit you will also see a bent push rod and broken rocker. One I could see but not all 16. Pretty hard for both intake and exhaust to both hit.
No broken rockers. ALL the pushrods were MIA...
 
Somebody bricked it because they actually believed the myth that 'you can't blow up a 318'?

Seriously though, it could have been over-revved to the point that the springs couldn't keep things happy. If it was a singular failure (like a popped pushrod/rocker/lifter) it shouldn't have caused contact on all 8 like that. Timing chain/sprocket failure also a maybe.


Was it free:D
Not free... I guess a bargain is in the eye of the beholder. LOL
 
That was a thought I had but I have never seen a small block timing failure with the valves getting bent. All those pistons are pretty evenly hit. My experience when you see even one piston hit you will also see a bent push rod and broken rocker. One I could see but not all 16. Pretty hard for both intake and exhaust to both hit.

The scenario I'm thinking about is the chain was skipping and grabbing due to extreme wear or partial breakage and someone kept cranking the engine over in a no start condition. I just can't think of anything else.
 
The scenario I'm thinking about is the chain was skipping and grabbing due to extreme wear or partial breakage and someone kept cranking the engine over in a no start condition. I just can't think of anything else.
Perhaps afterwards they took the heads off, cleaned the pistons off and tried to revive the engine with poor results.
 
Looking again the valley looks pretty clean as well.
Most carbuerated V-8's from the period with worn out rings would have a good layer of black sooty buildup in there.
So this part doesn't add up that the rings are wiped more likely the valves were all leaking from the collisions.
 
This is obvious to me. When I was 17 I had a 70 duster with a 318 stickshift. I would repeatedly floor it till the valves floated and side step the clutch! Went through 3 engines 2 transmissions and the rearend. 8 3/4 fixed that. Dumb kid stuff but boy was it fun smoking those n50 15s!
 
Too long of pushrods? Perhaps someone tried to get more giddy up from the motor with a higher ratio rocker & required pushrod change and took his buddy's advice on what to put in instead of actully measuring...or his buddy gave him the parts to try..
My guess anyway.
 
No broken rockers. ALL the pushrods were MIA...

Speaking from personal experience, if you experience piston to valve contact there's going to be bent pushrods. Mine was caused by a catastrophic timing gear failure.
 
Look inside the fuel pump hole in the timing cover. You will be able to see the camshaft gear with a flashlight. If it had the plastic coated gear teeth that fell apart you will be able to see the metal teeth and some leftover plastic on the gear.

In high school I bought a Magnum off a classmate because it quit running while he was driving it and would not start. Engine cranked over and had spark and fuel but was very low compression on all cylinders. I took it apart in auto shop class. Found the cam gear plastic had fallen apart and timing chain jumped. No damaged rocker arms or pushrods. All valves were just slightly bent. I used the shop valve grinder to grind the valves and recut the valve seats in the heads. Put it all back together and it ran and drive excellent.

Now, I fully admit it was not a proper repair. The valves should have been replaced, but it was a cheap project for a dumb kid.

When pistons have valve notches that match the valve angle properly, any contact is usually strait on the valve head and that puts lots of force up into the pushrod and rocker arm. More likely to bend a pushrod and damage a rocker arm.

With no valve notches at all, like these flat 318 pistons, most of the force of the piston contacting a valve is on a side or offset angle that easily bends the valve head, so less force is put up into the pushrod and rocker arm. Combine that with tons of valve clearance and you get just minor contact when the chain jumps, but enough that it bends the valves.

Sorry for the long post but I had to make it long enough to be worthy of the Forensic Analysis title of this thread.
 
I like the idea of looking through the fuel pump hole. I will try that. All the valves passed the machinist inspection and will be re-used. He also said the 1970 vintage heads had virtually no wear evident. I needed some good news...
 
The scenario I'm thinking about is the chain was skipping and grabbing due to extreme wear or partial breakage and someone kept cranking the engine over in a no start condition. I just can't think of anything else.
This scenario seems likely to me. Might even be that someone replaced the timing chain and got it off.
 
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