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#1
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Motor to Transmission
Hello all. Hope everyones doing good.
I just installed my newly rebuilt engine in my 73 Charger. Its a 360 with a 727 trans. It has a vibration when driving. When I took it down to get a front end alignment. The mechanic (he owns a 68 Charger) noticed it alot. He pointed out a really mangled trans mount, and said that might be the problem. so Ive replaced that with some good poly bushings from "Just Suspension". But in case thats not it, and out of curiosity. My question is when bolting the Flexplate to the trans torque converter there are 4 bolts (hence 4 ways to bolt it together) How do you know which way to bolt the two together? I would assume the flywheel is balanced because there are balancing weights welded to it. Please dont say "Mark em BEFORE you take em apart" Cause I foolishly Didnt Thanks in advance for any help and or thoughts... Craig |
#2
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The flex plate only fit one way, the hole centers are not the same distance from each other, one is offset. A stock 360 has externally balanced damper and flywheel or converter. If you have used different weight pistons or some other parts, it's possible that the engine isn't in balance anymore, should have hat the recopricating assy balanced. What kind of flex plate are you using, is it the stock factory unit? How about the converter, is it the old one? Is the damper the correct one for your engine?
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#3
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Thanks for your reply.... the flex plate, converter/flywheel, and damper are all the original parts before the rebuild. The pistons are new. The engine runs smoothly in idle but when I drove it the first time it seemed very rough, with what seems like a vibration.
I dont know if the place that built the engine, balanced the engine or not. He is very reputable. I do know I put the damper on when I got the engine back from him. |
#4
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There should be no need to balance the engine for a rebuild like that...
The pistons would come at least 'batch balanced' as they come in a set. That is to say, they are sorted by weight and all pistons in a set would be (as I said, at least...) within a few grams of each other. Plenty for most use... and certainly nothing that would show up in noticeable vibrations. This wouldn't seem to me to be a balance issue as in that the bits aren't in balance... it's a matter, I would say, of something not correctly assembled. |
#5
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Most cases yes............
But still the pistons may be balanced together but that doesn't mean they are balanced to the crank. If weight is changed significantly, the crank may no longer be balanced to the rec. mass.
This engine was not balanced as they didn't have the balancer to include in the process. If they balanced it with a different balancer it could be off because of stupidity. If that's the case, I wouldn't trust them to put in a set of rod bolts. |
#6
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You did press on the dampner, right? Hammers and them don't go well.
Other than that, unless something is loose in the driveline, or you didn't index your driveshaft (make sure the u joints line up) IDK what could be causing it. Are the pistons right on the rods? IE, the valve cutouts in the right spots? Dead cylinder? There's alot of things it could be... Jay |
#7
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SixGunner is right about hammers and balancers not getting along well. Seen many a balancer ruined by guys hammering it on.
Moparots does it vibrate in neutral when you hold the rpm's up? If it dosen't that would seem to put the engine/trans. in the clear and point to a problem with the driveshaft/rearend. Back when I was a kid I rebuilt an engine on a budget and used some valve springs that were supposed to be good but one wasn't and it ran smooth at idle but started missing at about 2000 rpm and the missing cyl. made it feel like a vibration. Just an example for thought. |
#8
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Does your balancer have a big ass weight built into it, and has writing on it stating is is only used for a certain motor? If you put that balancer on after he balanced the motor you are out of luck. If it looks concentric,symetrical..round then you are OK at least in the sense that the balancer is usually "neutral" and ypu are adding it to a now neutral balanced motor. 360's were "detroit" balanced off the assembly line, the whole reciprocating mass was spun and then balanced as a unit, could not really mix and match components. Neutral balance motors were put together with balanced assemblies, kinda like a bunch of zeros added together would still be zero or close enough for Ma Mopar. Internally and externally balanced were also phrases used for Neutral and Detroit.
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#9
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Thanks for all the imput guys.
I didnt really HAMMER the balancer on, I tapped it till I could get the bolt in and tightened it on. Do ya suppose that might have ruined the balancer? I prolly ought to get another.... how do you know what to get... do all small block balancers balance all small blocks? Ive heard about the fluid types whats that all about? Tracy, I broke in the cam at 2000-2500 rpm for 20 mins and the Engine purred like a kitten. Sooooo possibly driveshaft... rear end? I do remember when I installed the driveshaft It barely fit. I really had to force it into place, there was no play left in the trans yoke. Which I thought was strange because I use all the same parts. Id like to take the car out today, to test the new trans mount bushings, to see if that is the problem, but cant cause Im working on other things like new K member bushings and new lug nut/bolt combos for mag wheels (70s style Slots) Sorry if Im asking alot of questions that may sound simple to yall. This is a hobby to me and I havent been doing it as long as you guys have been doing it probaly for a living. Im pretty good at the wrenching just not at the diagnosing. I think every one on this site is very knowlegable and generous with that knowledge. OK OK enough of the sappy sensitive stuff.... |
#10
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No play in the yoke? You gotta have at least 1/2 inch play at the trans slip yoke because the driveshaft cant compress! when the rear end squats, the distance between the diff and the trans reduces because you are now closer to a straight line connection. Also when you romp on it, you are winding up the diff against the leaf springs. Your tires resist moving down (forward motion), so your diff tries to move up, (for every action there is a reaction...) that also reduces the distance. You need some play! I cut a driveshaft too long and my car wouldnt sit right, the rear propped up because it had no where to go! Here is a stretch...You are could be feeling the U joints sinusoidal rotational transfer as it has no where to go except against your trans tail shaft. It is not a linear transfer but has a fast and a slow rate that gets worse with a larger pinion angle, that is why you phase a driveshaft so the two ends cancel each other out.
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#11
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If you just tapped lightly on the balancer then pulled it down with the nut your probably ok. It's when guys beat them all the way on with a hammer that they smash the metal so much it don't transfer harmonics correctly. No all small block balancers don't interchange. You need one specifically off a pre magnum 360. The fluid balancers are supposed to absorb more bad harmonics than a stock type balancer. I have never ran one but remember when they first came out I saw a article where one was tested and showed an actual gain (although slight) in horsepower just by using one.
I agree with Pishta. If you don't have at least 1/2" play in the driveshaft yoke that could be the problem. If it's all the original parts that came off I'm not sure what to say could have happened. Is it possible to mix up the motor mounts from side to side that would cause the engine to be set back a little?? If so that would also throw off the trans. mount also. Did the bolts for it line up correctly? If so that would rule out the possibility of motor mounts being switched. I'd get that driveshaft issue resolved before thinking it's an engine problem. |
#12
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You answered your own question.......
If the drive shaft came out of the car without a problem, and has to forced in, something is wrong. There should be at least 1 inch to 1.5 inches to allow for movement when the springs compress due to driving or taking off. Failure to do this properly can result in a BUSTED transmission. Driving the car in that condition will result in an expensive repair. Fix it now.
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#13
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moparots, did the car have a 904 in it before? The 727 case is longer (3"?) and would certainly pose a driveshaft problem, if indeed you could even get it installed. Just a thought. As to the vibrations, I went through the same diagnostic headache. Had a 360 built by a quality shop, and balanced during the process. A very sloppy trans mount hid most of the vibes until I replaced it with a new urethane unit. SCARED the S--T out of me when I fired it up!! Long story short, after installing a proper B&M 360 flex plate, a new (360) harmonic damper and a neutral-balance converter from a 318, the shakes were still there. It seems that when having an externally balanced engine (which our 360's are) rebalanced the tech needs both the harmonic damper and the flexplate or flywheel, as well as the crank assembly, as they are both offset-weighted, which my builder did not have available.Plus, aftermarket cast pistons will not necessarily weigh the same as the factory units and may necessitate a re-balance. All that said, if your harmonic damper doesn't have an offset cast into the hub - you have the wrong one and that might be your problem. Me - I have a new winter project. It's called "Pull the engine and .........."
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#14
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Once again, a new set of pistons (as long as they are a set) shouldn't need any form of balancing...
The balance of pistons is in relation to each other, nothing to do with the crank. |
#15
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Whereas it's true that pistons are batch matched to each other as a set, if they aren't weighted properly for the offset imballance built into the dampener/flexplate (in an externally balanced engine), they could cause an imballance in rotational mass, thereby creating a vibration.
Also, if you are using the elastomeric (factory type) dampener (harmonic balancer) you should know that they can slip. The outer ring can "spin" in relation to the inner ring (not freewheeling but enough to misallign) which creates more, in stead of reducing, vibration. A tip is to mark the inner and outer rings of the dampener with a line of high contrast paint (white on black etc.) and to put degree tape on the outer ring. That way, if the rings slip, you can tell. |
#16
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True Ray Bell........
That the pistons won't require rebalance but if the pistons are 300 grams each lighter than the stock, this will cause a major imbalance in the BOB weight and the balance of the crank to bob will be off.
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#17
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fuktifino (just figured out that handle) and tarrbabe - thanks for explaining better than I did. Raybell, I'd agree, but I've had techs tell me that you could only get away with a very small piston weight difference. I gotta hope I dont have pistons 300 grams lighter than stock - that's better than a pound each!! I have my balance card somewhere and when I find it, I'll post the bob-weight values. Maybe someone has comparative values for a stock engine and we can see the diff. Moparots hope we're not scaring you here!
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#18
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I'm sure if you didn't ask for light weight pistons....
yours are near the same weight. But it still should be checked when building an engine. You can get away with a lot of things but if you want it to work right you have to pay attention to the details. That's why everyone tells everyone, yes you can use a 318 or 273 crank in a 340 but it MUST be re-balanced. The difference in piston weight is too great.
A lot of people have replaced stock pistons with trw forged and got away with out re-balance but the trw's are heavier. I'm using the Ross 514 gram pistons and wouldn't dream of not re-balancing. Stock 340 pistons are over 800 grams. |
#19
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So how does the shop set about balancing the crank?
They can't stick it on the dynamic balancer with a bunch of rods and pistons bolted to it! Surely the crank can only be balanced on its own or with the necessary attachments (harmonic balancer/flywheel/flex plate) in place? Also, please tell me, are harmonic balancers for these engines eccentric in their weights? I've always understood that harmonic balancers are balanced in themselves, that their purpose wasn't to offset weight out of place along the rest of the crank, but to cure harmonics by 'balancing' the ends of the cranks, that is giving the light end of the crank some weight so that its inertia was similar to the heavy (flywheel etc) end. |
#20
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Machine Shops use.........
a balance machine that comes with BOB weights. After weighing the pistons/rings/pins/rods and bearings. This amount of weight is added to the crank to all the journals to simulate the rotating mass. The crank is then turned for the machine to check the amount of miss match. The machine tells the machinest how much to add/subtract and where.
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#21
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OK, I dug up the balance card for my 360 with cast aftermarket 9 to 1 +030" pistons and stock rods. Weights in grams as follows: Piston- 579, pin- 154, rings- 56, total rod- 747, insert- 50, rotary- 1134, reciprocating- 1022 (50% factor) bobweight- 2156. My shop manual shows piston weight for a stock 80 360 pass. car as 584 grams. I don't understand some of the terminology so hopefully one of you guys can enlighten us further? (Plus, if there's only a 5 gram weight diff. from a stock piston why the vibes? Would my orig. 79 truck piston be heavier?) Also, Ray Bell, yes the harmonic dampers for externally balanced A engines have an offset weight cast or bolted in
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#22
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If you have ever seen a crank balanced, it is pretty cool how they do it. The shop I watched measured all the rotating stuff, rod, pin, piston, ring pack, and bearing shells, then added 3 (I think) for oil. They took that measurement X 2 and filled 4 clamshell looking things with the same weight of lead shot and then clamped them over the rod journals. They put a magnetic piece of tape on it for a reference and spun the entire thing up to speed and stopped it. The machine told them where the weight needed to be added or removed (hopefully) as they hand turned the crank, just like a tire balancer. They removed the weight by drilling out the counterweights or added by filling the hole with a heavy metal (Mallory or Malloy, seen it spelled both ways). The damper and flex are balanced by themselves. I dont know how they balance the TC unless they do it empty, holding the vanes still while spinning the shell. Oh yeah, you cant balance a Fluid damper, you have to trust the maker?
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