Some suggestions and questions for you. Do you have access to a surface plate? You can roll the cam on it to determine if the journals are in line. Did you measure the cam bearing ID after installing them? It seems like too little clearance if you eliminate lack of oil at all bearings as the root cause. Did the timing chain feel tight? What's your cam bearing clearance?
Was the timing chain very tight? I had one that was and took out four sets of cam bearings ( two engine builders before me) and I installed the fifth set but the timing chain was SO tight that it would not fit onto the cam stub with"screwing" it on with the cam bolt. I ended up going with a used chain that had "some" play and 7 years later the engine is still running flawlessly.
Smoking Gun?? I think I have figured out the problem (well, YOU all figured it out). It is the timing chain being too tight. When I reported earlier that the timing chain went on without much effort, that was relative to what effort is to me. Meaning I did not have to hit it with too big of a hammer and once I got it started I was able to walk both sprockets back into place. Chain was tight but given no take up, I thought nothing more of it (now I see I’m darn lucky to not have popped out the rear cam plug last time)
Fast forward to today…. A lot has been suggested and I have done a ton of research and ruled out a lot of suspects. So finally I got everything clean (AGAIN!!) and also extensively measured/mic’d to assess clearances. Started re-assembling the short block, cam bearing in, cam in, crank in. All feel and rotate good. Now I get to the timing chain, one of the prime suspects. I can’t get it to go on by hand. Fiddle with it and not going to happen. Did not want to pound it on like last time, so I pulled up on it with a ratcheting strap from the ceiling to the cam sprocket. Started ratcheting and eventually got it to slide on the cam shaft. I had enough force to get the front of the engine hoist off the ground. Once on I was able to slide the sprockets back without tools. The chain is tight, too tight. See pic. I have 3/32” deflection, and now that I am really thinking about what is happening, there is absolutely too much down force and the weakest links are the babbit cam bearings.
Again really thinking about it, you want no/minimal tension between cam and crank, just enough force to give a good chain tension. I never even rotated the motor this time, as I think it might damage the cam bearings.
Note that the #5 cam bearing last time was not nearly as damaged as the first four so these seems more plausible
So I have to figure out what to buy now. This is a Comp Cams timing set (CCA-2120) of course so maybe it’s defective like all my other Comp parts. Or is my crank/cam centerline off for some other reason. Block was align honed but that should make it looser if anything?
Confidence is way up now bit I am still being vigilant every step of the way. Can’t work on the motor for a couple weeks so it sits bagged, but I’ll report back.
Timing Chain wide1.JPG
Timing chain measureed.JPG