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302 Gives Way - Update...Issue Finally Found

6

65fast

Member
Some specs on the motor to start off.

302
289 Heads
9.5:1
Forged Pistons
7K on rebuild
Heads were checked and block was decked before assembly
ARP Rod & Head bolts


Yesterday, I was heading to my parents house to visit my Dad and I had just gotten off the highway and was sitting at a light for a few minutes. Light turns Green, I went WOT in first, shifted to second had it wide open and was climbing past 5500 and I hear a loud boom from the motor. It quits and I coast to the side of the road. I looked in the rear view as soon as it popped and did not see smoke or anything. I had no fluids under the car either once I pulled off. I had pulled the dipstick and oil looks/ed fine.

Got the car towed home pulled the plugs to see any damage and there was none, they were just white from running a little lean. I pulled the valve covers off to inspect the valve train and nothing wrong there. I spun the motor over with the covers off and had motion with all rocker arms as well.

Compression tested all cylinders and had 0-5psi on cylinder 1,2,6,5. 140lbs on 8, 80lbs on 7, 110 on 4. I did not test 3 (was running way late at this point).


Air temps were around 92 yesterday and I had just filled the car half way with 92 instead of the usual 93. The car was not overheating at any point during my trip either.



Do you guys think one octane point could lead to a significant detonation event causing a head gasket to blow? Assuming it was det that caused the motor to blow…..I am not even sure if it’s head gaskets at this point. I plan on draining the oil Wednesday and see if I get anything obvious out.

There is no obvious metallic knocking noise when turning the motor over either……



Thoughts?



UPDATE - 7/18

I got the timing cover off and spun the motor over to TDC and the dots lined up on like they should do I went to take the cam bolt and and the cam spun, but the cam gear did not. Somehow the pin that keeps the cam and cam gear spining together worked its way out of them cam allowing it to spin separate from the timing gear...Ughhh It's always the little stuff!
 
Re: 302 Gives Way

Depending on how lean it was running and for how long, it could be holes in the piston tops. I cannot see the fuel change doing that. You would have noticed a bunch of pinging prior to it popping.

Any coolant missing? Head gaskets normally mean coolant missing.
 
Re: 302 Gives Way

You're just going to have to pull the heads to find out more. A loud boom usually indicates more than just a head gasket, unfortunately. Sorry man, that sucks.
 
Re: 302 Gives Way

Pull it apart and see what all you broke. By the sounds of things it won't be minor. No sense getting down about it. Instead, start planning the triumphant rebirth.

Sucks now but it'll get better.
 
Re: 302 Gives Way

That's exactly the way mine went down when it broke. Big bang, no smoke, no oil trail.....

On mine, the oil pump locked up and took out the cam and dizzy gears.

Pull the dizzy and check the gear. That won't affect the compression. If you cranked it forever and pumped the gas it could have washed out the rings. Shoot some oil in the holes and retest comp.
 
Re: 302 Gives Way

Even with the rings washed from to much gas, the thing should still read more than 0 compression with the valves still moving.
 
Re: 302 Gives Way

Thanks for the suggestions...

I did not check the coolant level yet for some reason (brain fart) but will do when I get to the car next. I don't *think* it is the dizzy gear, I spun the motor with the cap off and the rotor is still spinning.

I will drain the oil this week and see if anything obvious comes out. If so, I will yank the motor and tranny. If not I will pull the heads while it's in the car.

Attached is my AFR readings from the dyno, kind of hard to see the dark blue line though.
 
Re: 302 Gives Way

Sluggo,

Did yours go on the street or track?


I am looking forward to another build, but this is the second motor in about 10K mi. The first one dropped a valve. Ahhh!!!!
 
Re: 302 Gives Way

"65fast" said:
Sluggo,

Did yours go on the street or track?


I am looking forward to another build, but this is the second motor in about 10K mi. The first one dropped a valve. Ahhh!!!!
Click to expand...

Street. 10 miles after putting new cam in it.
 
Re: 302 Gives Way

climbing past 5500 and I hear a loud boom from the motor
Click to expand...

Compression tested all cylinders and had 0-5psi on cylinder 1,2,6,5. 140lbs on 8, 80lbs on 7, 110 on 4.
Click to expand...


I'm unsure what's leading you to believe it's something as simple as a head gasket? Both head gaskets blew out at the same time? That's highly unlikely.


If it were me, the engine would be coming out for a complete teardown/inspection.
 
Re: 302 Gives Way

I'm with Dave. You lost the compression on the two front cylinders on each side. I highly doubt it's something like a head gasket. That sucks man but it's time to pull it apart.
 
Re: 302 Gives Way

The thought crossed my mind that it's highly unlikely, but I was just hoping for the best (least expensive).
 
Re: 302 Gives Way

By losing compression on that many cylinders at once, I'd venture to guess its either timing chain or camshaft related. If the timing chain jumps teeth, your valves no longer open and close at the correct time which will cause numerous cylinders to act dead in a compression test. Unfortunately this can also cause valves to go through the pistons, so lets hope you are lucky and this didn't happen. Sluggo's comment about oil pump locking up may also be spot on. I doubt it's a busted camshaft since you said all valves are opening and closing. If it were my car, I'd pull the timing cover off and inspect the timing chain. Check the chain, both sprockets, woodruff keys, and then find TDC and verify that the marks line up on the chain and sprockets.


Looks like that T56 install may get put on the backburner :sad
 
Re: 302 Gives Way

Jeremy, I think you timing chain idea might be onto something.


I got to the car again yesterday looked at the coolant level and all was fine. Drained the oil and was nothing abnormal.

I am going to pull the heads next and see how bad the pistons might be damaged.
 
Re: 302 Gives Way

I'd hold off on pulling the heads until I first took a look at the timing chain. Jumping the chain a tooth is not a guarantee you did serious damage elsewhere. You may be able to get away with just installing a new timing chain. Whole lot easier to go this route than tearing the top of the engine off when you pretty much know you will have to do the chain anyway. Who knows...maybe you get lucky!
 
Re: 302 Gives Way

That sucks man.

Wish you were in this area...I know a guy that has a 302 sitting in his garage. He was building it for a project car then someone backed into the car so now he has a motor with nothing to put it in.
 
Re: 302 Gives Way

Well I got the heads off last night and there were definitely piston to valve contact on all the cylinders. Luckily none of the valve broke off into the cylinder though.

I have not taken the timing chain off yet, but I am guessing this is the culprit. This was on my other motor that blew so I am wondering if it was weakened from the previous event on that motor.

I am happy that the bottom end did not come apart!



I think I might go for some aluminum heads putting it back together and maybe a new cam.


Thanks for the offer Tim, I will let you know!
 
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