Match balance a 390 flywheel

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   I was on the phone with Tony last night and I mentioned that I bought a complete 390, totally worked over, Milodon oil pan, Indy oil pump system, aluminum heads, roller rockers, the whole enchilada, and then he dropped the mic with this one, "Did it come with the flywheel?"Do I have to tear this complete running motor down and have the rotating assembly balanced with the flywheel I have? The flywheel is from my original 390 motor. He said you can't do that unless they are balanced together. Am I screwed? Every time I take a step forward with this car, I take 9 back. It's starting to get old. 

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Deans69 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Nov/24/2016 Location: Corpus Christi Status: Offline Points: 140	Post Options Post Reply Quote Deans69 Report Post Thanks(0) Quote Reply Topic: Match balance a 390 flywheel Posted: Jul/21/2021 at 10:34am
	I was on the phone with Tony last night and I mentioned that I bought a complete 390, totally worked over, Milodon oil pan, Indy oil pump system, aluminum heads, roller rockers, the whole enchilada, and then he dropped the mic with this one, "Did it come with the flywheel?" Do I have to tear this complete running motor down and have the rotating assembly balanced with the flywheel I have? The flywheel is from my original 390 motor. He said you can't do that unless they are balanced together. Am I screwed? Every time I take a step forward with this car, I take 9 back. It's starting to get old.

RandyB Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Nut Joined: Aug/04/2020 Location: Florida Status: Offline Points: 462	Post Options Post Reply Quote RandyB Report Post Thanks(0) Quote Reply Posted: Jul/21/2021 at 10:42am
	Can you call the previous owner and get details, else you have to balance?
	Randy B 68 Javelin SST 343 73 Charger Rallye 340 triple Blk

Heavy 488 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/27/2019 Location: In the Status: Offline Points: 3557	Post Options Post Reply Quote Heavy 488 Report Post Thanks(0) Quote Reply Posted: Jul/21/2021 at 10:47am
	Options are balanced at time of build Matched to an existing flywheel/ flexplate that came off of that engine

mbwicz Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Feb/20/2019 Location: Buffalo, NY Status: Offline Points: 2001	Post Options Post Reply Quote mbwicz Report Post Thanks(0) Quote Reply Posted: Jul/21/2021 at 10:57am
	I would also confirm if it has a factory harmonic balancer on it. If it has a neutral balance harmonic balancer on it, there is a chance that the system was built for a neutral balance flywheel. Pull off the oil pan and see if there are slugs of heavy metal in the counterweights. This is common when converting a crank to internal balance. The engine builder would normally fill out a balance card for the engine as well. This would include weights for the piston, pin, rings, and rods. This would be used to calculate the bob weight. See if you can find this balance info in some paperwork, there may be a note on what was used when balancing the crank (harmonic balancer and flywheel). If you can't find the paperwork, maybe reach out to the engine builder and see if they have any info in their files that may help. Mike
	1970 AMX, one step forward, one step back. Both steps cost time and money.

Deans69 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Nov/24/2016 Location: Corpus Christi Status: Offline Points: 140	Post Options Post Reply Quote Deans69 Report Post Thanks(0) Quote Reply Posted: Jul/21/2021 at 11:09am
	Bought the motor years ago and I have no paperwork with it. Looks to be a factory balancer, nothing fancy about it.

SC397 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5479	Post Options Post Reply Quote SC397 Report Post Thanks(1) Quote Reply Posted: Jul/21/2021 at 11:40am
	Pull it back apart and do it right. It will cost you a balancing fee, gaskets, and labor. The bonus is that you can correct all the things that the previous builder may have forgot like blueprinting the oil system to the distributor gear etc..

Deans69 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Nov/24/2016 Location: Corpus Christi Status: Offline Points: 140	Post Options Post Reply Quote Deans69 Report Post Thanks(0) Quote Reply Posted: Jul/21/2021 at 11:48am
	With a home remodel, 6 car projects and 3 children, the "labor" part is worth more than it's weight in gold. I just have zero wiggle room to deal with surprises. This is an astronomical set back in my world. As for the bonus, the guy had 2 g's just in the oil system, seriously doubt there is any meat on the bones to improve anything. I really didn't want to tear into this thing. I literally couldn't touch this car for 2 years, finally make amazing progress because I had some time, and then the hot rod gods just took a huge dump on my head. So yea, it stings.

BassBoat Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Aug/29/2008 Status: Offline Points: 1719	Post Options Post Reply Quote BassBoat Report Post Thanks(1) Quote Reply Posted: Jul/21/2021 at 12:09pm
	Any chance that with all that work it was internally balanced? That is the only way conscionable that somebody could sell an engine without a flywheel. Is the harmonic balancer truly a stock external balance? Look at it carefully. But you really need to pull the pan and see what you have. Could be all stock cast pistons and really just fancy go fast parts bolted to it. In my opinion not well matched at all. Could be all lightweight forged pistons and H-Beam rods which is what you need to do now while you are taking it apart. I wish you luck, plenty of help on here to help you figure out what you have, which probably is what you need to do and probably not what you want to hear.

Deans69 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Nov/24/2016 Location: Corpus Christi Status: Offline Points: 140	Post Options Post Reply Quote Deans69 Report Post Thanks(0) Quote Reply Posted: Jul/21/2021 at 12:17pm
	It does not need H-beam rods. I'm not going balls out and doing some insano custom engine work. I tried that with Bulltear and they ripped me off on $900 pistons. There is nothing wrong with putting aluminum heads on an engine regardless of the pistons.

scott Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/10/2007 Location: Wildwood Pa. Status: Offline Points: 3502	Post Options Post Reply Quote scott Report Post Thanks(1) Quote Reply Posted: Jul/21/2021 at 12:59pm
	In another thread you started, you say the engine is installed in the car, with transmission, and is running. So, how does it run?? Is it as smooth as polished glass all thru the RPM range?? Or does it shake like a 3 legged washing machine on spin cycle with an out of balance load?? If it is smooth as glass, I'd run it as is. If it shakes, well, others have said what to do.
	"Prolly" is not a word.