pistons are going to have dings in them. i would suggest pulling the cam and inspecting the bearings as well. it looks "off" in the picture behind the thrust plate. you may have spun a bearing.
No/Very Low Compression While Cranking
- Thread starter blackneck94
- Start date
the valve reliefs saved the pistons and you can definitely see they hit the pistons but you need to pull the valve springs and cycle each valve to actually be sure they are not catching or tweaked. being these are not angled valved like gassers, they dont always bend at an aggressive angle.
did you pull the cam and check the bearings?
looks like coating is burning off or there is pitting going on in there too on those pistons, no bueno.
did you pull the cam and check the bearings?
looks like coating is burning off or there is pitting going on in there too on those pistons, no bueno.
I’ll have to get my hands on a valve spring compressor again and check.
Removed the cam and the bearings looked good and oil holes lined up as far back as I could see. Did not see anything worrysome on the cam journals.
Thermal coating definitely looks all but gone at this point.
Wow no sign of any cause???
How many miles on the is motor?
Was the block line bored is there any chance of the gear clearance being too tight by the crank center line being moved?
How many miles on the is motor?
Was the block line bored is there any chance of the gear clearance being too tight by the crank center line being moved?
It gave me no warning signs/noises. This happened at basically idle speeds when coasting to a stop through a parking lot.
Just a hair over 3,000 miles on it.
Line bored mains, cam bore was line honed. I doubt there was any error there, the machine work was done by a trusted and competent shop.
Just thinking if maybe clearance was enough for assembly but at operating temp things got tight. Very strange failure for sure.
I am in the process of building now and had no luck finding a local machinist to do a line bore for billet caps.
I am in the process of building now and had no luck finding a local machinist to do a line bore for billet caps.
He would have lost teeth on the gear if lash became too tight but he had Larry do the machine work (same place who does all my machine work to my spec) and he’s very diligent about machine work. Doesn’t mean mistakes don’t happen but that’s why I verify everything done with mics/bore gauges/etc so it’s now had 2 eyes on it. This case doesn’t add up to that though
From the videos I saw on Instagram as he pulled it apart, it’s highly likely the bolt didn’t receive proper torque and applied as gm intended or the original tty bolt was re-used and it failed to yield the correct torque upon stretching or just was hand tighten and forgotten. Bolt goes loose, gear wallows around on the cam, eventually works the metal and breaks it.
From the videos I saw on Instagram as he pulled it apart, it’s highly likely the bolt didn’t receive proper torque and applied as gm intended or the original tty bolt was re-used and it failed to yield the correct torque upon stretching or just was hand tighten and forgotten. Bolt goes loose, gear wallows around on the cam, eventually works the metal and breaks it.
I made it a point to torque everything internal, that I am sure of. Wether or not the final torque was accurate, I cannot say. Even if in most cases threadlocker is not needed, I wish I had used it.
After studying the picture you posted of your cam and the end of my new cam I can now see how the bolt backing out could cause this.
Kind of surprised how small and thin it is where the gear mounts. Looks like the bolt is not just relied upon to hold the gear on it also supplies the majority of the support???
Kind of surprised how small and thin it is where the gear mounts. Looks like the bolt is not just relied upon to hold the gear on it also supplies the majority of the support???
Never heard of the cam failing there, much less for no reason. Bolt backing out makes the most sense.
