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79 AMX Spirit 304 lessons learned |
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jdlmodelt
AMC Fan Joined: Jul/08/2020 Location: Durango, CO Status: Offline Points: 10 |
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Posted: Mar/25/2023 at 10:38am |
Good morning from Snowy SW Colorado! My son has a 79 Spirit AMX with the factory 304 and a 4 speed manual behind it. We overhauled the engine in summer 2019 I think it was, covid messed the timeline up the past 3 or 4 years. Anyway, we installed the engine back in the car and she started up great but, there was a vibration around 2500-3500 rpm. After checking with a lot of local mechanics and lots of internet searching, we determine it had a 360 flywheel on it that the PO had installed. I order 2 different flywheels online giving the seller very specific instructions regarding the measurement of the colar on the flywheel that fits to the end of the crankshaft. We also discovered, the crank in this engine is an older late 60s early 70s crank with the slightly smaller diameter that the flywheel connects to. Anyway, when we finally got a flywheel that would actually fit properly, it was for either the 6 cylinder, or a 360. We tried for hours to magically put weights on the flywheel to balance the engine to no avail. So, we finally bit the bullet and pulled the rebuilt engine and tore it all the way down, took the flywheel, crank, harmonic balancer, a piston, rod, ring assembly to our local shop for a balance. We expected he would hand us the externally balanced solution. When we go to the call to come pick it up that it was ready we were in for a surprise. The stars where aligned. He was able to zero balance the flywheel, crank, harmonic balancer all individually. No more engine tear down if we ever have to replace the flywheel. Now, engine is all back together. It has an Edelbrock intake manifold and carburetor. It ran smooth throughout the RPM range before we pulled the engine back out to get it balanced except the vibration. Now, It runs rough, studders, and with the advance vacuum connected on the distributor, it runs pretty lean. I'm wondering if we have an intake manifold leak this time. I've tried several combinations of meter rods and orifices in the Edelbrock carburetor and no fix. It ran quite decent before the balance. I think I'll be pulling the intake manifold and reseating with new sealer today. It's been a crazy run with this one. We have learned a lot. I've rebuilt several engines prior to this one but this one has been a whole new learning curve for me. The ignition is all new including distributor. Two new fuel pumps so make sure the first pump wasn't faulty and not delivering enough fuel. The vacuum gauge shows steady strong vacuum at idle. If you drive it with a light foot, it's pretty smooth, but if you put your foot in the pedal, it acts starved when the secondaries open up.
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1969redamx
AMC Fan Joined: May/05/2012 Location: Sun city az Status: Offline Points: 4 |
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Quick way to check for vacumn leaks is to take brake cleaner and spray around the carb and intake while the engine is running. If it runs smoother after spaying a particular area,that is probably where you have a vacumn leak.
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BassBoat
AMC Addicted Joined: Aug/29/2008 Status: Offline Points: 1713 |
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vacuum gauge would help diagnose a vacuum leak. I am curious about your comment "it runs lean with vacuum advance connected" That tells me the timing isn't right as normally vacuum advance wont affect rich/lean. If the vacuum advance was bad, and you were inducing a vacuum leak connecting the vacuum advance, maybe.
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73hornut
AMC Addicted Joined: Jul/03/2007 Location: Southern Oregon Status: Offline Points: 3132 |
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I don't believe, that you can zero balance the balancer, or the crank, without adding expensive mallory?
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71 Javelin
74 Gremlin 79 Spirit AMX Rogue Valley Rumblers Like Us on FB https://www.facebook.com/groups/1602825606650796 |
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Boris Badanov
AMC Addicted Joined: Dec/14/2013 Location: NH USA Status: Offline Points: 4209 |
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Did you disconnect the vacuum advance when you timed it.
I'll bet it has nothing to do with a vacuum leak. It's inadequate ignition advance or a blockage in the carb. So, In my not so humble opinion the issue is a lean bog or (more likely) improper ignition timing.
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Gremlin Dreams
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jdlmodelt
AMC Fan Joined: Jul/08/2020 Location: Durango, CO Status: Offline Points: 10 |
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I guess we got lucky. I tried posting the printout of before and after balance numbers but I couldn't import the pictures on here. |
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White70JavelinSST
Supporter of TheAMCForum Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4867 |
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Quote : Quick way to check for vacumn leaks is to take brake cleaner and
spray around the carb and intake while the engine is running. If it
runs smoother after spaying a particular area,that is probably where you
have a vacumn leak. unquote If you spray CRC Chemicals brake clean into the engine such that it burns, beware that burning this chemical creates phosgene gas as a by product and will kill you if you breathe the wrong amount of fumes. quote : guess we got lucky. I tried posting the printout of before and after
balance numbers but I couldn't import the pictures on here. unquote 30 points (or posts) are required in order to post photos. Once you get that many posts you can use the post photos icon.
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70 Javelin SST, second owner, purchased 1972
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White70JavelinSST
Supporter of TheAMCForum Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4867 |
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It sounds like your problems began with a rebuilder that thought he was doing a small block chevy engine. AMC engines are detroit balanced, not neutral balalnced. The entire rotating and reciprocating assemblies have to be balanced together. 6 cylinder engines and their flywheels are neutral balanced. 72 and later V8 engines can use a 72 and later 6 cylinder flywheel, but it must be match balanced to the engine. A 360 flywheel is a different balance than a 304, however the crankshaft and rods are the same, pistons are not. Finding the shop that knows about AMC is more difficult today than ever. I trust you observed oil being squirted into the timing chain distributor gear area by looking through the fuel pump boss without the pump installed and turning over the engine. Timing gears are not always made correctly for AMC V8 engines these days. There are several other problems that arise with rebuilds due to incorrectly manufactured parts and lack of knowledge about AMC engines. But hey, don't blame the SBC rebuild guy, he doesn't know any better, after all he isn't smart enough to build anything other than a SBC ha ha ha ha This forum is your friend. There are dozens of extremely knowledgeable people on this forum. Ask as many questions as you need, some one will respond. Good luck with your endeavor.
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70 Javelin SST, second owner, purchased 1972
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Buzzman72
AMC Addicted Joined: Sep/15/2009 Location: Southern IN Status: Offline Points: 2713 |
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Building a SBC:
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Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.
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jdlmodelt
AMC Fan Joined: Jul/08/2020 Location: Durango, CO Status: Offline Points: 10 |
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The oil pressure is healthy, 40-60 psi with a stock oil pump. As for crank balance, he ended up with left plane 3.34g, center plane 1.51g, and right plane 3.04 g. The right and left tolerances were 10.64g for both left and right planes. The engine is smooth now, I'm just trying to figure out this timing issue. It backfires on quick acceleration. Everything I read and talking with some mechanics indicated it was running lean. I have an Edelbrock 2131 intake manifold with an Edelbrock 1406 carburetor and factory rods and orifices currently installed with this backfire and missing issue. I have a second 1406 carburetor I plan to try tomorrow with a new gasket set so see if it still backfires and misses. I've done new spark plugs, wires, distributor, ignition module. Yesterday I replaced the intake manifold valley tin and reinstalled the intake manifold.
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