atlantadan

Had a knock when hot, and only when hot. Pulled the engine and dug into it and didn't find anything that screams "bad bearing", just some scratches from debris. Karl suggested the bearings are ok to run, so I am not going to change them out. The rods all had bordering-on-too-much side clearance. Karl said its an issue he's currently dealing with in regards to the forged Scat rods in this engine as he's building another that has "clearance that's on the high-side". He thinks that its this clearance that could be a contributing factor to the knock. The oil pump definitely has something going on with it. Turning it by hand, it is very grabby and almost feels like the pump lobes are square and unable to mesh properly. This was undoubtedly the source of the groan. I am replacing the pump.

TLDR: In the end - the issue was the Crower lifters failing, which caused a cam failure. Scroll down for images of lifter rollers and cam. If anyone has any ideas as to what could cause the lifter surface to fail in that way, Karl and I would appreciate your thoughts.

Rearmost cap has some scratches from assembly checking


Cap 2:


Cap 3:


Cap 4:


Front cap:


Rod bearings:




For reference, someone asked to see the oil pump gear on the cam. Here it is - in perfect condition:


I also noticed a lot of oil-scale on the tops of my pistons. I am going to get the heads checked out and make sure the valve seals are good.

The Crower lifters that were installed appear to have failed. I am contacting Crower to see what they think. It appears that some of the external coating on the rollers has started to flake off. Yes, you can catch a nail on these defects. These are Crower 6630 lifters.






And here is the bad lobe on the cam. (CompCams spec'd by Lloyd Elliot) All of the lobes showed excessive wear and damage, but this one was by-far the worst:

atlantadan

Response from Lloyd:

Over the years, I have talked with ppl at Comp, Lunati, Bullet, etc and they all agree that if you can feel any of those scratches with a finger nail, that it is starting to wear into the lobes and at that point it is just a matter of time until it wears past the "hardest metal" on the outside of the lobes and into the "softer metal" as it gets further inside.

If the lifters are showing signs of this also, I would expect the same to happen to them.

All it takes would be for just ONE of the lifters or lobes to wear past this hard metal on the outside and into softer metal and then you will have metal ALL in the engine as we go from smooth/hard parts contacing each other to rougher and rougher and softer and softer material as it wears deeper into the lobes/lifters.

I would say if you can feel it with your finger nail, the cam would need to be shipped back to Comp/Lunati and possibly polished if it is very slightly scratched/wounded or just get a different camshaft. Emailing them a pic of the wounded lobe might be enough for them to say if they can repair the camshaft or not and save you shipping $.

I would DEFINITELY replace ALL of the lifters since the pic looks like they are all showing signs of this happening and eventually they will take out the cam lobes.

Since ALL of the lifters look to show that wear, I would guess that the lifters are coming apart on the wheel and that wis causing the lobes to wear.

Judging by the pics, cam doesn't seem to show any wear on the signs from lifters jumping off lobes and crashing back down on side of lobes that you usually see with valve float but I would still check all 16 springs for seat/open pressure so you can eleminate that. This is just based on these pics and not having the camshaft in my hands.

EDIT: IF YOU HAVE CROWER LT1 LIFTERS, I'D ADVISE YOU TO PULL THEM AND CHECK THEM OUT This is based on input from Karl and Lloyd.

SS RRR

iTrader: (2)

How are your piston skirts and cylinder walls? That hardened steel was raining down on them from the rollers and lobes and may have caused some damage. Being me, I wouldn't use those bearings, but that's just my opinion. I would also get the block tanked if you haven't already.

97Z28SS

iTrader: (5)

I'm with SS-RRR on this one, since you know some metal circulated through the engine I would have the block hot tanked and ALL new bearings installed (including cam bearings).
I would also replace the cam/lifters ( get it on a billet core) and possibly the valve springs and I'd add an AFR Hydra rev lit for extra insurance. I'd also hot tank/clean the oilpan and replace the oil pump.

pdxmotorhead

Use a high zinc break-in oil, looks a whole lot like your pics Comp-Cams used to put out with their instructions about why break-in oil is a must on big cams.. Rubbing surfaces need zink to burnish the surface smooth on break-in.. (My past knowledge YMMV)

+1 the all new bearings, your too deep now to cheap out on a set of bearings..

Shownomercy

iTrader: (1)

I have a cam in my junk bucket that looks exactly like that!

I had LS7 lifters though, and IMO, the cam was too soft. Either the surface hardness was not up to spec or something. Comp cam here

atlantadan

Piston skirts look brand-new. Only a handful of scratches and nothing of real importance. I am ordering the same cam from Comp - but this one is on a billet core. I've heard a lot of complaints about the cast Comp cores. I hope the billet ones are better. I am going to be running the GM LT1-specific lifters, which are not LSx lifters.

BALLSS

That with a melonized gear?

Double Aught

iTrader: (5)

Concur 100%. If the hard metal has flaked, it is more than likely been run through the engine unless you have supreme confidence in your oil filter.

atlantadan

Engine has been torn down to the bare block. Spent the day yesterday power-washing everything with soap and water, then blow-dry with an airgun, then wipe down with ATF, then oil. Paid special attention to the oil passages in the block and the crank. New King bearings on the crank and rods. Installed the crank with Permatex Assembly Lube and torqued everything to spec.

Got a replacement cam, in billet, from Comp. That's going in probably this evening, along with the rods.

Had the heads checked at a local shop. They were .004 out of true, so I had them surfaced. Everything else with the heads was fine.

Thoroughly checked the pistons, rods, and pins for cracks since I thought that maybe a cracked piston near the pin would also lead to a knock. Everything was 100% within spec.

So, in the end, the bearings were all ok, crank was ok, rods and pistons were ok. The only thing I can locate that could cause a knock was one bad lobe on the piston and all the lifter rollers were delaminating.

The upside is that I was able to clean and paint the frame with POR15 and seal it, and I'll get a chance to install the Dennys driveshaft before it goes back on the road.

97Z28SS

iTrader: (5)

Did you replace the cam bearing to, you will want to do that but otherwise you are on the right track.