Ok, I assume there's plenty of folks that have brought up their valve shimming agonies in this forum, but I haven't found anything about this. I pulled my 996 heads and checked the valve clearances, several were off, some quite a bit, and the valve stem seals were original. There also was some wear on a few of the rockers so I'll be checking with Megacycle to see about refacing. In the meantime, since I hadn't done this before, I replaced the seals and decided to give the valve adjustment a go. All went fairly well, checking unloaded/loaded clearances, loading values in shim software, calculating new shim sizes (made sense) and selecting the new shims as necessary. I started with the vertical head, intake side, and the right side didn't need any changes, left, small change on opener. The cam was out, and I reinstalled the original shims on the right, made the change on the left (Jesus, those fiddly retainer rings suuuuccckk). Stuck the cam back in and now I cant' even fully rotate the cam, it appears that the closer is so tight that it won't rotate but about 20 degrees!?! This has to be because of the closer shims, right? I pulled the left shim stack off and with only the right shims (original) it still only rotates a few degrees before it locks. WTF? I did read about those fucking retainer rings needing to seat, push the closer down and let the closer spring snap it closed to seat, did that several times, but still no joy. In addition, the opener clearance for the right side, the one that the shims weren't changed, just re-installed, are now tighter than before I touched this infernal Italian torture machine. I'm not a complete mechanical nimrod, lots of car and bike mechanical knucklebusting in my past. What did I screw up?? Thanks for any leads, Jack
I think you are right, it must be about the closers as even if openers are installed with no clearance or even negative values, then the valve head just stays off the seat rather than jam the cam movement up. If you can get cam to TDC firing/"back" of the cam without forcing anything then check for closer clearance as this will confirm above won't it?
Thanks for your suggestion Chris, but after I started this thread, I decided I'd better go back and double check the cast info on the cam and with great red faced embarrassment, I realized I had the horizontal intake cam in the vertical cylinder. Upon switching the cams, the damn thing rotates as it should and everything looks familiar. I can't explain how I managed to mix them up, I was trying to be scrupulous in my labeling, but then again, maybe I am a mechanical nimrod! I'm not sure why it wouldn't work using the horizontal intake cam, but I'm glad it didn't, that would have been a royal FU!
It is definitely easier to do one head/one camshaft at a time. Seating the wire clips is very important as is putting them the same way back, new ones frequently change the clearance measured before disassembly. when you get it right though it is very satisfying if longwinded and fiddly
