Compression on the M129 was 120, 125, 110, 135, 130, 125 with the lash done and the cam changed. No real improvement from the original cam was in. The car starts brilliantly, first crank, but max vacuum is 15, it goes no higher, it does have a steady needle, so valves aren't the big issue. It doesn't backfire or sputter anymore and it builds some power at high RPMs. Vacuum holds at about 12-13 at 1200 rpm, try to knock the idle down, it's like someone shut off the key. Carbs are dialed in, they are pulling uniform now. Idle tubes are clear. Cover 1 (either) carb, and the revs climb; (Weird) - cover them both, it dies. The floats have been reset now 3 times; - first to spec, then high, then low, and now back to factory, no difference at all. Throttle response is instantaneous, and good; - no flat spot anymore. Take it for a drive, and it pulls pretty good; loping along in 3rd gear it surges a bit, which matches the miss in the exhaust, so I think there's at least one burnt valve.
It's running better now than it ever did, but it still will not idle. The old cam was wiped, the blowback and spitting through the carb has stopped, as has the backfiring. There's now just a miss, which was there when I got the car.
According to what I've read in the various Zenith troubleshooting guides, if there isn't at least 15 inches of vacuum, the carbs will not function. At engine speeds of less than 1200 rpm, the vacuum falls off instantly. And yes, I did spray it down, checked for leaks, throttle shafts are tight, heat risers are free, spacer plates and heat shields are flat and in good shape, carb bottoms are flat, and intake gaskets were replaced. I cannot find a vacuum leak. Maybe the head gasket is gone, but when the cam was changed, I retorqued the head.
So I'm done with it; - the parts I've pulled off exhibit far more wear than the supposed 70,000 miles. It's more like 170,000 miles. I'd rebuild the M129 but I read that they have head issues and parts are even scarcer for them, so that's why I went to the 230, which coincidently is the original block to the car.
The head on the 230 was redone before it was parked. Of course I would get it gone through again before I put it back together. The compression is apparently no good on this thing either, but it ran smoothly and just smoked like the Titanic. Thanks for confirming that oversizes do exist, from what I've heard, these 230 (M180) engines in 1966 had a taper problem, they cut the taper wrong at the factory and so the rings fail prematurely on them. To correct that will likely need a bore and an oversize. So who sells pistons and rings? I can't find anyone that has them.
Good thing I have the flywheel, clutch and balancer to the 230. I'm just not sure I have the right transmission for it, so will it fit the M129's transmission? They look the same...
Yeah, I knew this was going to get expensive; - but the body on the car is perfect, there is no rust at all on it. If it had any rust, I probably would have cried a little and scrapped it all rather than sinking a ton of money into it.
There are none of these cars around here anymore, they all dissolved back in the 90s. This might be the last one in the Edmonton area. As I said, I'm no stranger to rebuilding engines, I've done dozens of Buicks and Oldsmobiles, (I've been into collectable cars for 40 years now) and they aren't cheap either. (I seem to have a knack for buying them, beautiful body but exhausted mechanicals, it never fails!) They're a lot easier to rebuild though. And the last set of Nailhead pistons I bought were about $150 a hole. So while these are double, there's only 6.
I do have the factory manuals, and yes, I only want to do this once.
