I was hoping to have the ignition fixed by now, but this whole Covid thing "zapped" any schedule I thought reasonable. With all this down time, I gotta tackle things where I can, so onward we go.
Smokey (no Bandit) exhaust - lets dive in and see whats happening
Besides the smokey exhaust, there is another indicator right under my nose telling me this engine isn't as tightly sealed as it should be. Its the vacuum pump. Its only generating about 3" in of Hg at 6k rpm and considerably less at idle. (like ZERO) In speaking with GZ Motorsports (awesome tech support BTW) I'm told if everything is sealed and in good condition, I should see 3-5" Hg at idle, and 12-14" at 6000 rpm. Since I'm no where near those numbers, I have to wonder (and I have been) why the pump inst getting a good seal. I know the pump is good. It comes with its own dyno sheet. So, looks like its time for a leak-down test.
Full disclosure - I've never done a leak down test before. Never had to. I'm not a mechanic by trade plus all my engine builds have gone exactly as I expected them to. This is the first one to smoke. I'm so new to leak-downs, I don't even have any good puns about them and that really feels like a lost opportunity. On the bright side, I get to learn something new. Lets start with a tip.
================================================== ================================================== =
Tip#17 - If you perform a leak down test and everything comes up perfectly at zero, make sure you've taken the Schrader valve out of the inlet tube you're using to pressurize the cylinder. Air enters the engine better that way. Stupid valve.
================================================== =============================================
BTW, there is no neat YT video for the particular type of tester I'm borrowing. Its not the dual gauge units like all the vids have (which are self explanatory with no need for a video IMO), its this -
Searching vids was more about getting a consensus on the proper method of performing the test anyway. (Imagine that, conflicting opinions on the internet. Who knew?) Perform @ TDC? Back off the valves? Do you connect the inlet tube when the tester is fully pressurized, or do you connect first and turn up the air after? (checked this board first and it was just as undetermined on best practice)
Turns out this particular box expects to be pressurized by shop air first, (120 psi...sharp eyes will see the box says 60 max, so don't tell anyone) and then connected to the cylinder in question. You calibrate the gauge to zero before connecting to the cylinder and you watch the gauge try to get back to zero once you are connected. Where it stops is your % of leak-down.
Most testers agreed the test should be done at TDC on the compression stroke. My thinking about that recommendation is to make sure the valves are closed and maybe give the tester a consistent bore to work with. Am I wrong? (Real mechanics feel free to chime in.) I really should ask this question in the tech forum. My testing was
not done at TDC, but the valves were all backed off, eliminating them from the equation. However, I did get different readings depending on where the piston was in the hole. I'm not really sure why. Whats worse is every time I put the cylinder at TDC thinking it might make a difference, air pressure pushed the cylinder downward, which was pretty easy given there was no spring pressure and the plugs were out. I can run the test again with the valves set to be 100% sure, but after looking at the numbers, I'm don't see a need. Check'em out.
- The dipstick is out to see if I can hear/feel any air coming out
- The radiator cap is off to see if anything is coming back through the head gasket.
Passenger side -
#2 - dry - 12%
#4 - dry - 35%
#6 - dry - 35%
#8 - dry - 15%
Seeing how off the two middle cylinders were, I put some oil in them and retested.
#4 - wet - 10%
#6 - wet - 10%
Drivers side -
#1 - dry - 4%
#3 - dry - 4%
#5 - dry - 6%
#7 - dry - 12%
Most of the air I'm hearing is coming from the gaping distributor hole, which makes sense if the rings are letting it all go into the crankcase, but honestly, the air noise there wasn't any different between a good or a "bad" cylinder. Still, putting oil in the faulty cylinders "sealed" the deal on the real culprit. Bad rings.
A compression test on those two cylinders shows consistent numbers (245psi) with other cylinders, but of course that was done wet since the oil was still in the cylinder from the previous leak testing round. (I'll check them again when the oil has a chance to settle out of the cylinder)
You want my theory on why those two are down? Doesn't matter, you're getting it anyway.
Back in 2015 when I first decided to rebuild this engine, I self imposed a budget upon...myself. Had to. The wife and I just moved into a new house and I wanted to play it safe to see how the bills went and to make sure no major surprises with the new home set us back. (say like a "new" roof leaking onto your drum set even though it was just done 6 months prior to you buying the house) Yeah, things like that. The idea was to just get the car back in working order and drive it. Then I got it into my head that I'd send the heads out for some work, and I knew the fuel system would need work..... and by the time the 4 bolt caps came into the picture (you know the story!) I was well beyond anything resembling a budget. (but had to get back to safe). The point is, not buying new rings at that time was one way to save some money. I didn't see a need. They've been in the engine for 5 years and have likely 3-4k miles on them, probably less. As long as they stayed with their respective cylinder and no honing was done, there should be no problem, right? That was until my machinist pointed out that I had initially installed two of the rings upside down. (don't recall exactly which rings they were, but I have a sneaking suspicion I now know which cylinders they're in) It was kind of a backhanded compliment too. He he told me many amateur builders usually screw up a lot more than two, so I guess that's good?? What are the odds those two rings are on right-side-up now in cylinders 4 and 6, the same two leaking down right now? Pretty good I'd say.
The big question now is, what am I going to do about it? Not a dang thing. The whole point of this test was to understand why the engine was smoking. I figured it out. Keeping it in perspective, the engine only has 90 minutes on it. I'm going to drive the car and put some hard mileage on it. (If I ever get back my distributor!) If the engine still smokes after some serious beat downs, I'll reconsider my options. If I'm being positive, I think those rings will seat to that cylinder in short order. But if i have to re-ring, I can do it in a weekend. I'll wait and see what happens instead of making that call now. Right move? Probably not, but its the way its going to be.
In parting, allow me to clarify an earlier post. At the beginning of this thread I stated new rings went into this build. I actually thought that was the true. (I still do to some degree, but the evidence is mounting to the contrary!) Its been so long since all of that happened, and it seems so absurd not to put new rings in, I thought I must have and forgotten I didn't. It was only recently when I tried to find a receipt that I had to really figure out what happened. Having only one old ring box is the real proof, as I keep all of those odd boxes for storage. Without a second box and no receipt, I can safely conclude I never had a second set of rings.