Well just got my carbs sorted. Went for a drive and something has come unglued in the bottom of the engine. Huge loud slapping like a rod banging. Very rpm related. On the 3 4 side. No damage to the plugs. Still runs but it is clear that something is very broken. Will check valves tomorrow but I am betting the case has to be split.

Any thoughts on easy things to check or where to start?

The printed venturi's broke?

You say you got your carbs sorted. Possible they are running too lean resulting in a detonation and bent rod? Check condition of your plugs.

Nope they are perfect!

If anything plugs looked slightly rich.

I have not been lucky with this car yet!

At idel check to see if you're blowing any gas out, also pull a plug wire off each plug one at a time and if the rpms don't drop when you pull the plug wire off of one of them you may have dropped a valve seat.

Check for big exhaust leak near the heads. I had a smog injector plug unscrew itself on my turbo, sounded like a mechanical slap, turned out to be a $.50 plug...

sounds like a very loose valve rocker.

I've had that particular version of the sound a couple of times. In each case, it was a dropped valve seat... Hopefully this ain't one.

Pop the valve covers off and take a look.

--DD

Initial look with a bore sope ghrough spark plug says #4 position broken. Too much oil to see clearly. Will drain oil and look again before dropping it. F#%k.

piston?

Yep. Auto correct and being pissed are not a good combination.

Real sorry to hear that.

But at least it is a good time of year to pull the engine and have at it.

You will be back on the road for spring!

Yikes, crappy luck. It could have been worse, like internal.

Sorry to hear that. Pistons usually break because valves hit them ..................... Occasionally they go because of FOD, like a nut or bolt falling in.

The Cap'n

Could not see any FOD looking in but the valves seem to be ok. This was a new build on the top end with new jugs, pistons, valve guides, and such. I am wondering if I got a bad piston?

Be sure to check the rod on that cylinder. I have bent them during collision.

Pictures are not of good quality but this is what I see looking into the #3 spark plug hole. Looks like the piston is cracked completely across.

Click to view attachment

Click to view attachment

Any thoughts? Does not look like a valve came into contact with the piston and there is no debris that would suggest a dropped seat. Spark plug was not damaged when removed.

I have to think the piston was flawed.

Seems kind of hard to crack a piston without nitrus, boost or a foreign object.

Well it's clear you'll have to pull the engine now. You'll likely see the cause once you pull the head. I would also have the rod checked. You would be surprised the number of times I have either seen or actually discovered a bent a rod when piston damage was evident.

I find it very hard to understand also when this engine has maybe 400 miles on it since it was rebuilt. I have to think there was a flaw in the piston.

I know it looked like this when installed. Click to view attachment

If it was due to FOD there would be indications of damage to the surface of the piston. There is no indication that anything was ingested. Given the coating of burnt oil, I think that there was a flaw in the piston when it was made and it slowly spread across the piston until it failed.

Or there was a flaw in the backside of the piston in the wrist pin area. And of course there is always the possibility of the wrist pin binding and stressing the metal until it heated and cracked.

But what ever the cause turns out to be this should not have happened to an engine with 400 miles on it.

What pistons did you use for your build, any history of them failing.

Really sucks, never fun to take apart a "new" engine.

Jeff

They were 96 mm AA. Of course that makes them suspect from the beginning. But their quality has improved some. But I hope I can at least get a new cylinder and piston and get this running again.

I am dealing with the same thing on my BMW engine. never fun.... OP good luck with everything, hopefully its not as bad as it could be. Mine went back to square one. new rings, new bearings, rod bolts, etc

Started pulling engine today. Drained oil and checked strainer. No metal. That may be a good sign!

Cracked in half, that is a new one.

Sorry Mike
Could running the engine too advanced cause this?

I used AA 96mm pistons on my 'new build' ...... however before they were installed ..... the builder did an inspection of all the engine parts and one of the pistons had a casting defect on the wrist pin bore.

The defect was detected under very high magnification ..... the builder let me see the defect on the inspection bench and sure enough it was there plain as day ................ so I took the defective piston back to AA and they gave me another one ..... which had to be machined and balanced to match the other three.

Moral of the story ...... if I had run the defective piston ...... the wrist pin would have eventually pulled through the bottom of the piston ...... not that all possible bad has been prevented, but I am very happy that defect was found before putting the engine together ...... that 'find' alone was worth the extra dough paid to this experienced and renowned builder .......

I am sure that is not a good thing but I think it causes more concerns for valves than pistons.

Detonation (caused by too much advance) typically burns a piston or blows a hole right through it if left to run like that for too long.

Got the head off. Not the piston. No scratches in cylinder wall.

Did not feel excessive travel on wrist pin. Filled ports in heads with solvent. No leaks.

But still only have about 70 psi compression. Did notice some ware on intake push rod where it meets the lifter but nothing else.

I guess I will pull the 1 2 side head and check it and then put it back together and check compression again. Thoughts?

Push rod. Odd marking on end that sits in the lifter.

Click to view attachment

Have you looked at the lifter associated with that pushrod? Crazy stuff there.....

Push rod scratch is from the wire retainer not being put in properly and rubbing the push rod, it happens and would eventually ruin the push rod.

Also, maybe one or more of. The push rods was not properly seated into the lifter, which would cause the valve to never really close all the way....

When you put it back together, as you are seating the rocker assembly, keep turning each push rod and look at the angle of the push rod, they should all spin freely with your finger when the rocker set is torqued to spec....

The push rod tube retainer spring (properly notated for the Cap'n) will not touch any push rod, it will push against each push rod tube, and it will sit in the bottom of each rocker stand bolt holder retainer thingy...there is a slot for that spring.

This will make you redo your carbs again....once the motor is running (and pumping air) properly, so don't be stubborn, trust that your carbs are probably wrong and you need to start over to tune them.

That seems to be a very substantial piston failure not to be " just a piston failure." But I'm a lover not a pro engine builder.
Konrad

Wish I had seen this earlier. You know now, but that 'crack' in the first pics is the valve relief pocket.

Well it is official. I am a dumb ass! Found the problem and it was FOD.

Click to view attachment

Lost this while installing the throttle linkage. Thought I heard it hit the ground. But I removed the intakes and searched the intakes with a mirror and magnet. Nothing!

But somehow I missed this and it went in. No real damage. Minor nicks but the cylinder had 120 psi compression so do I put it back together?

Click to view attachment

Yup.

buy a lotto ticket now you lucky bastard

I once sucked a screw into my Mopar 383. Slammed into the brand new aluminum head and stayed there. It was the loudest racket I've ever heard from an engine.

I pulled the head and found a nice forging of the screw. Removed the screw and reassembled. No bent valves. No catastrophic damage. Never had a problem after that.

It did cost me my pride and a gasket set...

what is that? one of the tiny screws for the helper springs?

Nope! It was the cable anchor for the Tangerine throttle linkage. The small set screw came out and made a few dents before exiting. The big silver steel thing on the upper right hand side of the head is what was sucked in.

Whew! You already know this, but you got lucky Mike! Love it when it works out like that!

FWIW, whenever I have my carbs off, I am *meticulous* about preventing foreign objects from falling down the intakes. I always make sure I have nothing rolling around on the rear deck or roof, collect each piece of hardware as I remove it, and as soon as I pull one carb off, I use aluminum foil insulation tape to close up the top of the intakes.

You're not a dumbass, it can happen. You did luck out on that one, minor damage and all. Put it back together and you'll be wiser for it next time!

All things considered I am pretty lucky. But now I am faced with the desire to get it running again versers doing all of the things I said I was going to do the next time I had the engine out like put in the stainless steel fuel lines. If I do that I would remove the tank. While I had the tank out I could install my sway bars........

It never ends!

Definitely the time to do it Mike. You could (and should) get both of those done before lunch. If I was closer, you know I'd be there to help

Do the ss lines while the engine is out. It's an easy afternoon project, even for me.