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I have a borescope for firearms and decided to use it to see the cam bore better, this is what I found. These are very magnified, close-up pics.
The actual bore doesn't look bad, correct me if I'm wrong, maybe polish it a little.
It appears that the drivers side oiling passage isn't drilled clear through, I don't think that's babbit material, it looks like iron. You can see a circle where the hole should be.
And here's the bearing, one hole is blocked with babbit, the other is open.
OK, so here's what I want to do, tell me if I'm insane!
I was trying to avoid pulling the crank, but now I have to, for one to check the bearings. Knowing this motor was so low hours/miles I was expecting them to be good, but now with finding the bad cam bearing I need to verify the mains are good.
Two, it's a bigger pain to pull a LS crank than a SBC crank, and I didn't want to have to deal with new bearings, and bolts.
Anyway, I want to pull the crank and drill out the oil passage that goes up to that cam bearing. Then just use a small hone like a brake cylinder hone, to clean up the bore, slide new cam bearings in it and re-assemble.
So, am I crazy?
I'd hate to jump to conclusions. Let's not go there.
In any case, crazy or not, the oil doesn't flow that way. It flows from front to rear along the oil pan rail back to the filter & cooler (or bypass), then up across the rear of the block to the rear cam bearing, then along the lifter bores toward the front. At each main bearing saddle a passage goes downwards to feed the crank.
If I were the guessing kind I'd be almost willing to guess that the main associated with the cam brg is also wiped. Looks like the front one butt I could be wrong.
Thank you. I was looking at the flowchart backwards assuming the oil flowed up from the mains.
Well, I guess that cranks coming out either way, and new mains may be in my future.
I hope the cranks not hurt, I have a new cam.
As bad as this, I'm glad I caught it now. I had planned to put the cam in after installing the new pistons, that would've really burned me.
I was wrong. There is no second oil feed to the cam bearings. It looks like the bearings just have an extra hole in them. There is no passage that lines up with that hole.
I'm still in the dark as to why the bearing spun, but at least the block looks unharmed. Can see it much better with the crank out.
Should I get the journals polished? It seems that 3 is the worst.
#3 main bearing which lines up with #3 cam bearing, that spun. Some crud there.
The rest of the bearings.
I'll send it in for hot tanking and have them put new cam bearings in, polish and fit the crank, and then I'll do the rest.
I was thinking (wrong) that this was an aluminum block. Your likely ok with this being an iron block regarding the spun cam bearing. Make sure your machine shop knows about the spun cam bearing and exactly which bearing it was, wen you drop it off. They will take it from there...
LS engines have more oversized cam bearings than any other production engine ever produced. It is an issue. Block needs to come down to completely bare for cam tunnel work. Better to bore than than to hone.
I'd leave that bore alone unless I was absolutely positively undeniably most sincerely SURE it's fornicated. Which isn't all that likely. IN NO CASE would I just launch an irreversible preemptive first strike on it.
I'd leave that bore alone unless I was absolutely positively undeniably most sincerely SURE it's fornicated. Which isn't all that likely. IN NO CASE would I just launch an irreversible preemptive first strike on it.
A dial bore gauge and about 15 minutes will tell the tale, when the shop gets to it.
As soon as I can get it in to him I will. Hopefully it's OK. If so, I'll have him hot tank it and see if he thinks the crank needs polished. Then I'll have him install cam bearings and the crank with new bearings, I'll finish assembly.
I'm half tempted to return the stage 2 cam for a stage 3, and whatever rocker arm upgrade needed to run it.
Update. Just heard from engine guy, he says cam bore is within spec although towards the outer size, and mentioned GM's questionable tooling.
He is going to hot tank it, mill the head surface, hone cylinders, install Dura Bond cam bearings, line bore, polish and install crank, resurface heads.
I'll install pistons, cam, heads etc...
Shouldn't take too long, I'm between the end of the racing season and winter rebuild season.
Hate to see this. I had the #5 cam bearing walk forward on my aluminum block, Darton sleeved 427. Came forward just enough to completely open the oil orifice to the bearing journal, with no oil going to the bearing insert. Oil pressure dropped to zero immediately. As great as the LS engines are, there are two places I feel that GM dropped the ball on the LS design. Number one is having lifters inaccessible w/o head removal. Number two is no priority main oiling. My .02, but I feel your pain.....
08-05-2024, 01:52 PM
Is this why my cam bearing failed? 
