to balance or not to balance: 360

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   Your problem is mis-matched parts. So you need to get a 360 balancer and flex-plate for starters. It will run with a 304 flexplate, may or may not cause a noticeable vibration. The motor mounts will absorb some, as will the damper on front, but there will be a vibration going through the crank and that will eventually destroy the bearings -- thrust part first apparently. The thrust bearing is one of the main bearings, #2 or #3. 

Your first problem is the flex plate. Did you install the 304 flexplate? If you know for sure it's a 304 flexplate (engine swap?) and it wasn't altered when it was installed, you should be able to just get the correct 360 flexplate and balancer and call it good. A stock to mild build 360 will be fine for over 100K miles, no other issues withstanding. 

Is it a good idea to balance? Well, it doesn't cost that much any more, and it will add some life to the engine (mainly bearings) even with a stock rebuild. Not sure I'd do a full balance on a stock rebuild that wouldn't see hard use, but would do a "poor man's balance" even then -- during a rebuild with the engine apart. That's just making sure all the pistons and rod ends are within a gram or so of each other (weigh all, match to the lightest weight). It helps and is cheap and easy, just takes some time. I wouldn't disassemble a low mileage engine and do that or any balancing unless I was going to spin it at high rpm (5000+) often though, or I was unsure of what was done with the mis-matched parts, as may be your case.

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farna Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19689	Post Options Post Reply Quote farna Report Post Thanks(0) Quote Reply Topic: to balance or not to balance: 360 Posted: Feb/11/2019 at 6:32am
	Your problem is mis-matched parts. So you need to get a 360 balancer and flex-plate for starters. It will run with a 304 flexplate, may or may not cause a noticeable vibration. The motor mounts will absorb some, as will the damper on front, but there will be a vibration going through the crank and that will eventually destroy the bearings -- thrust part first apparently. The thrust bearing is one of the main bearings, #2 or #3. Your first problem is the flex plate. Did you install the 304 flexplate? If you know for sure it's a 304 flexplate (engine swap?) and it wasn't altered when it was installed, you should be able to just get the correct 360 flexplate and balancer and call it good. A stock to mild build 360 will be fine for over 100K miles, no other issues withstanding. Is it a good idea to balance? Well, it doesn't cost that much any more, and it will add some life to the engine (mainly bearings) even with a stock rebuild. Not sure I'd do a full balance on a stock rebuild that wouldn't see hard use, but would do a "poor man's balance" even then -- during a rebuild with the engine apart. That's just making sure all the pistons and rod ends are within a gram or so of each other (weigh all, match to the lightest weight). It helps and is cheap and easy, just takes some time. I wouldn't disassemble a low mileage engine and do that or any balancing unless I was going to spin it at high rpm (5000+) often though, or I was unsure of what was done with the mis-matched parts, as may be your case.
	Frank Swygert

Trader Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6910	Post Options Post Reply Quote Trader Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 9:10pm
	The torque converter is a hydraulic motor/pump, it does not balance the engine. If someone previously "balanced" the engine for the 304 flex plate that does have balance weights then any new flex plate will have to be match balanced to it. If the 304 flex plate was balanced to what a factory 360 flex plate is, then you don't need to do anything but change them. If you don't know, match balance the old flex plate to the new. The balancer if original, can be replaced or repaired. If being repaired - match mark the inner hub and outer counterweight. Then when it comes back you know it is exactly in the same alignment.

purple72Gremlin Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16614	Post Options Post Reply Quote purple72Gremlin Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 8:24pm
	get the correct 360 flexplate....the 304 flexplate will not work.....

WesternRed Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5808	Post Options Post Reply Quote WesternRed Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 7:11pm
	If you were happy with how it ran before, just change the balancer and be done with it. A stock balancer is directly interchangeable with another stock balance for the same engine capacity.
	I've finally given up drinking for good...........now I only drink for evil.

Softbuster Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Nov/08/2014 Location: Pennsylvania Status: Offline Points: 116	Post Options Post Reply Quote Softbuster Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 7:07pm
	The torque converter of the trans bolts to the flexplate and is full of fluid, should't the fluid find the imbalance and alleviate some of it?

Softbuster Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Nov/08/2014 Location: Pennsylvania Status: Offline Points: 116	Post Options Post Reply Quote Softbuster Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 7:02pm
	The balancer is original to the 360, my only concern with rebuilding it is that it comes back exact so that i dont end up with timing (and balance) off. So a good rebuild place is what i'm looking for. How would i check end play? Where is the thrust bearing and how do i check it. The 360 is on a stand and i can do some things but it will not be coming apart simply to balance the rotating assy.

motorhead_1 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/16/2014 Location: AZ Status: Offline Points: 1007	Post Options Post Reply Quote motorhead_1 Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 6:23pm
	the 304 flexplate on the 360 likely already destroyed the thrust bearing. been there. done that. didn't get a tshirt. got a rebuild instead...... what's your crank end play? is the balancer 360 or 304?
	69 SC/Rambler tribute 401/th400, 68 Rebel SST LSA, 66 F100 460/c6, 88 Merkur Xr4Ti, 71 Jaguar XJ6 LS1, 08 Supercharged Tundra

BDCVG Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Dec/19/2007 Location: Endless Mtns. Status: Offline Points: 993	Post Options Post Reply Quote BDCVG Report Post Thanks(1) Quote Reply Posted: Feb/10/2019 at 6:09pm
	Definately get a rebuild from Damper Doctor or Damper dude and if You can afford the balance it's worth it. Probably contribute to longevity too.
	1970 AMX 390 5 spd full Control Freaks front and rear suspension 2014 E63 AMG-S wagon 1965 Austin-Healey 3000 MK III

wheelz Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Jan/29/2019 Location: NJ Status: Offline Points: 101	Post Options Post Reply Quote wheelz Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 6:03pm
	rebuild the original damper install and be done with it in this application. Likely not enough difference in piston weightto have a great effect under 5k rpm . The 304 flexplate could be a bigger problem but unsure

Trader Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6910	Post Options Post Reply Quote Trader Report Post Thanks(0) Quote Reply Posted: Feb/10/2019 at 4:46pm
	First question I would have is did the engine run smooth when it was running at all RPM ranges you took/take it to? If the engine ran smooth, then you really only need to match balance the changed components. In your case the balancer and flex plate if you are changing it. I currently have a 401 that I have overbored and am changing pistons, rings, wrist pins and doing new bearings. It turns out that the new pistons, rings and wrist pins, total each, are only 1.5 g different then what was currently in the motor. A shop (unless a very, very expensive shop) cannot balance a V8 to show that 1.5g difference. It's not being re-balanced. We use to balance everything at my old workplace, every time we worked on it. Records would show that 10g either way would not show, 15g and you see a spike develop. Nascar, will overbalance an engine for high RPM running. A diesel truck engine should be under balanced. I'm not stating that balancing is not important - it is, but, if your talking bolt on components that can be matched to original components, it is not worth the cost of re-balancing everything. My opinion.