Rebuilt 360 cranks and then stops

Rebuilt a 79 360. Stock crank, scat rods, speed pro pistons.

Already fired up and ran for 10 minutes. Ran great. Turned her off normally, went inside and ate dinner, went out to start her back up, she started, I pushed the clutch in, she died, and now she will crank a partial turn. I can get underneath and turn it in reverse by the flywheel, and when I turn the key to crank her, she will turn a revolution, and then stop.

I pulled plugs thinking maybe a hydrolock situation, but the spark plugs are bone dry.

Swapped starters thinking maybe a bad starter, but same situation.

Before I tear my hair out, what could possibly be my issue?

Been a long week, so not gonna mess with it until morning...

Edit: oil pressure was 50psi confirmed with a mechanical gauge.

Turn it by hand forward and see what happens.

Agreed, pull the plugs back out & grab your 1&1/4" socket/breaker bar. Post what happens. EDIT After rereading I hope it is something external with the clutch (my guess) as opposed to something internal maybe with the thrust bearing (just thinking out loud).

Turning it forward by hand/1-1/4” produces the same result.

If I turn it back, and then forward, the motor eventually gets “tight” and doesn’t turn anymore.

The block was line honed, and when I assembled it, I rotated the crank every time I installed a piston. No binding at all.

Check your torque convertor bolts, sounds like one has loosened and backed out.

Did you try turning it with the plugs removed as suggested? My thought was a leaking head gasket that didn't seal and you have a cyl. full of water.

He did say he removed all the plugs and they're bone dry.

Checked flywheel bolts as I rotated the crank backwards by hand. Looking at the back of the crank flange. I can see all the bolts and that they are all the same depth.

Clutch to flywheel bolts are the same. They are all tight.

I did remove the spark plugs and they are dry, though I did not try cranking it with them removed. I was thinking that since the plugs are dry, no water present, and no hydrolock...

I will pull them again and see if it spins over freely.

Almost sounds like a standard main bearing is in place where the thrust bearing should be. But that would have been thumping I think while it was initially running.

When you get to the tight spot, does the crankshaft still have endplay?

Does it get tight, or stop? Does it always stop at the same spot (put mark on damper). May be valve stuck open hitting piston. Might pull valve covers to check.

^^^ X2!

Took valve covers off. Found these on the passenger rear (#8)

Cam and lifters are 508 Mopar Performance purple shaft. Pistons have valve reliefs. Springs are iskendarian....

Rest of the rockers look great.....

Gonna throw the borescope down this cylinder. See what I can see.

Even with plugs pulled, motor does not rotate.

Stay tuned kids!

Take a rubber mallet and give a good whack to each valve on the cylinder to see if they are free. That head is probably going to have to come off. Hopefully the piston and cylinder wall isn't damaged.

P/V collision I am thinking (sumpin dont quite add up tho). I would pull the rockers/pushrods & see if it is (now) free.

Whacked them all and they all are free.

Borescope down the cylinder shows no damage...

Ordered new pushrods and have spare rockers from another motor.

Rotated the motor by hand and the rest of the rockers and distributor cap turn, so it’s srill all connected. I have a cloyes true double roller on there....

Motor still hits when turn backwards....

^^^ & that is whith all the pushrods out?

Stock rocker arms will be punched thru by the pushrod went a stiffer valve spring is used...

MP made or makes a heavy duty non adjustable rocker arm to correct that problem. Still for sale at Mancini Racing..

A dropped bolt or nut in the intake which finally made its way into a cylinder and now jams between a piston and head?
Or a piece of ringland has broken off and is jammed?

I would check all cylinders with the borescope, but the fact that one cylinder has both rockers broken through tells me there's something wrong there.

The saga continues...


Pulled the rocker off to replace pushrods, and......

Looking down the guide, the valve is laying on the piston...

Dunno if it dropped now, or dropped earlier....

Heads coming off after the rains.....

Thinking this is easy...you cant use valve rotaters with that big of a cam. I would say valve spring coil bind.

And in my opinion your cam, lifters, pushrods, rockers. valves, and keepers are all junk now. You will also need new springs and retainers that are for whatever cam you use. Did you tell whoever did the valve job what cam you had. No excuse for this if you did...

Yes. Everything was supposed to have been spec’d out for this cam.

What springs/retainers/pushrods/valves/etc should I go with?

Stock stuff will work ok for valves, keepers, and retainers, just no thick rotating retainers. Springs should be what cam company recommends, or something similar. You also need to check retainer to guide clearance. Whoever did the heads is at fault no question, but doubt they admit it as you are the final quality control person.

What part number valve springs are those?

You were getting coil bind on both intake and exhaust valve springs, proof is both rocker arms failed. You'll most likely find a bunch of bent pushrods.

I've seen the stock rockers due that many times. Put a new pair on and go as long as the pushrods are straight. Now why doesn't the motor turn? related ? Maybe?
Doug

Do not run or rotate this engine anymore until you pull heads and correct retainer to guide clearance about .060, check for coilbind, and check piston to valve clearance. It is not normal for pushrods to go thru stock rockers with that cam. I have done it, and gone thousands of miles no problems with that cam and correct springs.

Be sure to check the piston height in the hole with the dropped valve. You may have bent the rod.

Run it or replace it?

I'd replace it. Be sure to check the rod too. But most importantly, why did this happen in the first place?

How does the cylinder wall look?

Replace it. Part number for a single is WH116CP 30. Less than $50 on Rockauto, $75 from NAPA.

It's the W in front of the H that makes it a single piston although Rockauto seems to be breaking up sets and selling individually.

It's a hypereutectic piston although there's a difference between a Keith Black and a Sealed Power hypereutectic. The Sealed Power alloy is closer to the eutectic point and thus more ductile. Yet I don't like that gnarly black spot that looks like it goes quite a way in.

R.

Yeah, I was afraid replacing it was going to have to be done.

Got this one from Bob mazzolinni years ago.

As far as why it happened, I think everyone is right about coil bind. When the heads were put together, everything measured out tight but fine.

The piston sits in the hole same as the others, so no bent rod. Gonna replace the bearing just to be sure as well...

Off to the parts store....

So are you thinking the coil bind is your only problem? It looks like the valve was tagging the piston too. Did you check P-V clearance and degree the cam? What does the head look like? Any sign to piston-valve contact on any other cylinder. You don't want to go through this again. It could have been much worse.

^^^ agreed, I would mockup with a pair of light springs & go thru all of the clearance checks

Changing piston and bearing is smart.

As long as the only difference in the pistons is how they I.D. them on top, you should be fine.
No flame intended, no matter how careful, we all over look things, and I've had catastrophes too but with the failure pointing to coil bind, one wonders what else may have been missed. i.e.
Ring end gap (which can be checked when you pull that slug)
Bearing clearances
Rod side gap
Piston to valve clearance
If you had coil bind with that combination, check bottom of retainer to top of guide clearance too.
My process after events like this......
1. "Well this happened causing that"
2. "How did this get over looked?"
3. I either didn't know to check, or forgot to check.
Most of us even check the work/measurements of a trusted machine shop on returned parts.