Still no resolution on the vibration. I was really hoping motor mounts would clear it up. They were dry rotting. So, again, it was good maintenance, but not the cause of the vibration. For the hell of it, I swapped the plugs out, and the old ones looked ok. Definitely a colder heat range than optimal on the street, but they weren't fouled, and again no change in vibration.
I noticed the timing is a bit jumpy when the spout is in. i.e. I'll set the gun to 40*, free revving, the timing comes on up, but a once every second or so, it pops to a different timing. Seems a bit erratic. However, with the spout out, it's totally smooth and stays at 10*. And, the vibration is still there, regardless. It sounds perfectly fine. High load, low rpm (maybe 1600-ish) WOT in 6th gear is perfectly smooth. Tried bypassing the MSD, too. I'm not totally satisfied with the timing jumping like that with the spout in, but that really doesn't seem to have anything to do with the vibration.
I test drove it and decided that if it was gonna let go, then so be it. Feels strong. Can powershift and turn the tires over. I can bounce the car off the limiter for 10+ seconds in 2nd gear. So, I really don't understand what's doing this. My best guess is maybe it is flywheel or clutch imbalance related since I installed them in January about 7k miles ago, but I just don't understand why it got worse recently.
I called my local machinist. I'm gonna bite the bullet start the 306 build. I have a spare OEM block with rotating assembly on the garage floor, some good top end parts, and I've been jonesing to get into it for a coupme years. The machinist thinks he can get to work on it in October.
That's fine by me. I'll keep trying to work through it, but as long as it doesn't get any worse, I'll take my chances to run Larry at foxtoberfest, this year. If it blows, so be it.
Edit:
I thought a pilot bearing might explain things, but after rethinking it, I'd expect to detect differences when in vs out of gear. Oh well... Will keep noodling.
I went back through the EEC tests today and, once everything was set up correctly and fully warmed up, the results were pretty clean.
81/82 and 44/94 are Thermactor/smog-pump related. All of that equipment is gone, so those are expected and irrelevant.
I also got the cylinder balance/contribution test working after forcing the transmission strategy to neutral because of the T56 swap. For anyone who has to do this witgout a T5, you have to use the quarterhorse to set the TRLOAD scalar to 0, which forces the computer to see 'neutral'. Anyways, it came back 9, so the EEC did not identify a weak cylinder. I ran that test 3 times, twice back to back, and then another time after playing with the idle tune for an hour. I guess that rules out ignition and injectors.
The only code I still have any interest in is the 95/96 secondary fuel-pump circuit fault. I have a FP Guage on the A-pillar & fuel pressure is not doing anything wrong. Plus, the Walbro 255 LPH pump sounds normal, so I still need to determine whether that is just related to the pump-monitor circuit/wiring or whether there is actually anything worth chasing.
As for the vibration, I had been seriously considering pulling the transmission, clutch and flywheel and tearing into that next.
I've decided I'm not doing it... I really think it's one of those or maybe the tid bit of grinding I did on the crank around the pilot bearing was enough to throw things off, but I'm already gonna do most of the work when I swap motors, anyways.
I'm moving ahead with building the other motor. When that engine is ready, everything has to come apart anyway, so I'm giving myself permission to quit obsessing over this in the meantime.
Worst case, if there really is something wrong in the current engine and I hurt it, I'm probably risking something like $2,500 in used-engine resale value. I'm willing to accept that rather than tear the car apart twice chasing a vibration I still haven't conclusively identified.
So until the new motor is ready, I'm going to act like the vibration doesn't exist and drive it like I stole it.
If it gets dramatically worse, breaks, or finally gives me an unmistakable clue, then I'll know what it was. Otherwise, I'm going to enjoy the car. So, I invite all of ya to come to foxtoberfest and watch the fireworks!