DrFeelgood

Gen VI roller cam, 502 Mag MPI.

I probably opened a can of worms today that might not have needed to be opened, seems I'm good at that.

I decided to inspect the lifters, just to be sure they were all in good shape, while they are easily accessible. All the lifters look good, rollers turn smoothly, no significant wear, etc. Great.

BUT, on the port motor, Cyl #2, has a worn camshaft lobe. The worst wear is on the opening ramp, reducing to very little at the top of the lobe, and none on the closing ramp. The corresponding lifter has no signs of damage or deficiencies in rolling. I cut the oil filters open when I bought this boat 9-10 hours of operation ago, no metal was found. I also cut and inspected the filters when I had my recent stuck valve/bent pushrod issue, no metal found.

So, I don't know how long this cam lobe has looked this way, maybe a long time? Obviously the correct fix is to yank the block out and put in a new cam. I'm not going to do that at this time for a variety of reasons. I know there's a risk that this lobe is going to wear further and if that happens it could chew up the lifter, which would be bad.

My question is, what to do to mitigate the risks until I decide what my next move is (cam swap with tuning, full rebuilds, swap to some other motors altogether, etc).

I have the Isky 8005a springs arriving this week, will the higher seat pressure on these vs. stock increase the rate of wear?
Should I have the machinist reuse a stock spring on this one location to minimize that risk?
Any other words of wisdom, other than reminding me that I'm kind of an idiot?








Dial indicator shows that this lifter has 0.292 max lift. Adjacent cylinder intake valve lifter shows 0.295 at max lift.

Multiplying 0.295 x 1.7 rocker ratio gives 0.501 lift but the stock cam is supposed to be .483

TomZ

iTrader: (2)

I don’t like that at all. That’s not just worn, it’s damaged. Perhaps a bad heat treatment job. I would not use this cam.

I just sold my last MPI cam, too. Sorry man.

DrFeelgood

Yeah, I've seen similar pictures that were attributed to faulty surface treatment during manufacture. Odd, that it's one lobe only.

Ryan00TJ

iTrader: (8)

Be glad you caught it. Fix it correctly now. It will be far more $$ to repair once that lobe/lifter takes a **** and sends metal thru the engine.

Stock GM cams have this reputation.

GPM

Just think of all the metal that's probably buried in the piston skirts by now. Grinding up and down the cylinder walls.

Batmeat

I agree with others. Fix it/ clean it all and get another cam installed.

DrFeelgood

OK, OK, you guys talked me into it (I knew it was the right thing to do anyway). One of the big obstacles I was avoiding was the bulkhead under the rear seat, which I finally figured out was removable. Now that's out of the way and once I get the harmonic balancer pulled, it won't be long. I got the balancer halfway off and the puller tool stripped its threads out (the tool threads, not the crank).

SB

iTrader: (1)

Lube (grease is better) the threads of pullers.
Lube the threads of any puller
Lube thread of pullers
Lube thread of pullers
Lube thread of pullers

DrFeelgood

Yeah, there was a little bit of oil on the threads but I shoulda added more.

AllDodge

iTrader: (1)

What's the difference between the Merc 502 MPI cam and another manufacture?
Looks like several sell cams for the 502