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OK, I looked at the cams again, and I do see more wear than I did originally. In the first photo, the image of left cam shows the concentric wear pattern on the tip very clearly (circled). The right is actually very similar but does not show in the photo.
I did a quick and dirty measurement of some intake cam lobes:
OK, I looked at the cams again, and I do see more wear than I did originally. In the first photo, the image of left cam shows the concentric wear pattern on the tip very clearly (circled). The right is actually very similar but does not show in the photo.
I did a quick and dirty measurement of some intake cam lobes:
Base circle: 33.97mm
total lobe height: 42.45mm
So, lift would be 8.48mm
Good? Bad?
Bill,
The info I have on file is:
Stock S-4
Inlet 236* .354" or 8.99mm
Exhaust 223* .314" or 7.98mm
Yeah, my vague recollection is intake = 9mm lift. So I've lost 0.5mm. I need to repeat the measurement more carefully and over more lobes.
Yes, 9mm is correct. Assuming that the lobes are all similar, then I think it depends on what your goals are. If the lifters are OK then I think you could button it up and they would be just fine for another 100K or so. They are worn but I am not seeing any signs of distress.
The problem is that this is the edge of a very slippery slope. The bearings are probably worn as well, if you pulled the rod caps you would probably decide to replace those also. Same with rings and bores, no sense in taking things that far apart and not refreshing them. And on, and on...
What I would suggest is to button it up and drive it. Keep using the same oil (or something else with good ZDDP), change every 4-6K and send off a sample to Blackstone with very change. Keep an eye on iron (cams), aluminum (bores) and lead and copper (bearings). All should be ballpark 10ppm or less. We've got ~80K worth of samples for our GT if you want to compare notes.
Measuring a few more lobes, I am seeing 0.3mm loss of lift for intake. The exhaust cam lobes I measured are showing no loss.
For the short term, I am going to button it up. When I get some fresher S4 cams, I'll do them.
I do plan to do the rod bearings soon. I'm not quite set on the process of doing them if I leave the engine together. Given the three thickness varieties that are said to be randomly placed in a standard bearing set, I'm not sure how you go about it. I have no plans to pull the heads and do the rings. My leakdown is less than 5% and compression is 190-195.
Anyway, I do plan to measure all the cam lobes over the next few days. WIthout replacement cams in my hands, I'll button it back up until after Sharks in the Park.
Measuring a few more lobes, I am seeing 0.3mm loss of lift for intake. The exhaust cam lobes I measured are showing no loss.
My leakdown is less than 5% and compression is 190-195.
The now obvious question is why have the inlets gone and not the exhaust?
On a separate issue [if i may]- I note with interest your compression pressure is a bit higher than mine- [a constant 185 psig]. Is there any reason my compression should be lower in the 90 S4 motor I run other than something being a bit worn? My leak down figures were very good at about 99% all round and I carefully checked I had the correct procedure. I assume the 89 motor has the same compression ratio pistons but...?
I'm not sure the pitting on mine is as bad as the lobe on the right which damaged the lifter quite a bit. But I really won't know until the cams come out. I do plan to replace them with Jeff's cams if they are better than mine, as they should be, with new lifters. But for the next few weeks until I get the cams and new lifters, I'll drive as is. Thanks for all the input so far. Oh, if the current exhaust cams and lifters all look good, I may leave them alone.
As to why the exhaust cams look better than intake, they sit in a pool of oil at the bottom of the head. That's my guess anyway.
FWIW I just had WebCam re-grind my 944-4v cams (they had the same lobe pitting) and it came out to $500/pair. Stock profile but I had them adjust the lift a little.
05-17-2016, 06:02 PM
