swingingdart
Well-Known Member
I have a 318 with a 340 crank in it.Since the 340 crank is internally balanced, would a 318 harmonic balancer work? Or is that a bad idea?
340 crank with 318 harmonic balancer?
- Thread starter swingingdart
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Neutral balance is neutral balance. So yes, the same harmonic balancer will work on a 318 or 340.
swingingdart
Well-Known Member
Okay, second question.
If the harmonic balancer spun on the rubber, is it junk?
Yes
But you must remember the neutral balance harmonic balancer prior to 70 had the timing mark in a different place than the 70 and 71
But you must remember the neutral balance harmonic balancer prior to 70 had the timing mark in a different place than the 70 and 71
Did you put the 340 crank into your 318 or are you just going off the casting numbers on the crankshaft. A 340 has heavier rods and pistons than a 318 so it is balanced different even though it is neutral balanced.
swingingdart
Well-Known Member
It is a 340 crank shaft in a 318 with all 318 rods and pistons.
However they all spent time in an engine builder's shop together and he did his magic to make sure they would all work together.
I thought the harmonic balancer off the 318 was fine (thanks for verifying what I was hoping) but at some point with checking the timing I realized it spun on the rubber. And driving it i feel a vibration, its hard to describe, but it starts small then vibrates up harder, then drops small and vibrates up harder, over and over and over and the instances increase with RPMs.
Caused by bad harmonic balancer?
Plymouth 65
I'll be in the shop
Please replace the torsional vibration damper before the inertia ring flies off and kills someone. 65'
Here is my thought on your vibration. The vibration is being caused by the 340 crank not being balanced to the 318 rods and pistons. And I say this because your harmonic balancer is neutral balanced even if the ring slips it's still neutral balanced. Your vibration is going to knock out your rod bearings and you're going to have a piece of junk for a motor sitting in that car if you continue to run it with that vibration. I think you need to pull the motor apart and have it balanced
The reason I asked about the casting number is the 318 and the 340 use the same casting numbers even though they were balanced internally different.
swingingdart
Well-Known Member
I bought it off another member on this site years ago. It is definitely a forged crank and he said it was out of a 340.
I'll be giving the engine shop a call come monday and see what he did to balance them all together. Sounds like I'll end up having to pull the engine like you said.
This is annoying.
I started building this car when I was 16, and I think had the engine work done a couple years after that. So I was leaning heavily on older dudes that "knew what they were doing". And I only got the thing drivable 3 years ago or so. And have barely drove it. I replaced a transmission mount and that's when I really started to notice the vibration. The new mount was a touch taller than my other, and I dont think it put the trans touching the floor board, I had wondered if it did and that's what caused this vibration. It also only does it while driving. It doesn't just sit there and vibrate while iding or revving. (That I can tell, it idles and revs nice)
That's what made me create this post, because I have several suspicions of the cause, but even if the trans was touching I dont think this should be a vibration that exists.
But I know even idling and revving without vibration isnt proof its balanced.
Sounds like engine shop time.
I would rule out driveline vibration before pulling the motor. My experience is if the motor is out of balance it will shake with the car setting still and it may be more noticeable at certian rpms.
Plymouth 65
I'll be in the shop
If the inertia ring slipped the damper itself is likely out of balance. This will cause vibration and will be related to the engine RPM. Before you do all that work of pulling your engine, refer back to post #7. 65'
Are you sure the damper has slipped and isn't just marked for a different timing tab location? My experience is if they have slipped they will continue to slip. Mark the balancer from outer ring to inner hub. In a safe place rev the motor aggressively several times then check your marks.
I would replace the harmonic balancer after checking top dead center and making sure that the Mark is off. But you've thrown a different iron in the fire now with the transmission mount. If it's up against the floor it could be your U-joint causing the vibration.
While you have the engine at tdc check the position of the tdc mark on the balancer and see if it is in the position of the alternate timing cover mark. If so you can remark the balancer tdc mark with a line that passes from outer ring to center hub so you can monitor it for slip.
Do u have the cast or aluminum water pump? Which side is the timing tab on? Is it at 2 o’clock or 10 o’clock? If the balancer mark is opposite of the timing tab u have the wrong damper. That would be hell to balance with the 340 crank in a 318. Also check the pinion and trans angles. Kim
swingingdart
Well-Known Member
I'll try this, but if memory serves we had the timing mark to start with, then it went away. Lol
So I assume it spun.
I'll try this marking and see what happens.
I messaged the engine shop and they reassured me that the engine was balanced correctly for the rods and pistons. They said they deal with this all the time.
I'll order a new transmission mount, I went ahead and bought a 73 spool style trans cross member to replace the current 72 one.
What is the max angle you can have on the driveshaft?
I have the cast water pump/timing cover. It has the timing Mark's on the right 2 o'clock. What year of 340 cranks wont work with this timing mark?
'72 and newer 340 cranks were external balanced!
Hence you need the proper weighted front balancer and a properly weighted Torque Converter or the proper weighted flex plate to a 904 or 727 automatic. The weighted flex plates are different for the 904 and 727.
☆☆☆☆☆
Hence you need the proper weighted front balancer and a properly weighted Torque Converter or the proper weighted flex plate to a 904 or 727 automatic. The weighted flex plates are different for the 904 and 727.
☆☆☆☆☆
perfacar
Well-Known Member
if it doesn't vibrate running in shop, it's ok, if it vibrates driving, then it's in drive train the rear trans mount has changed drive shaft angle, install the correct mount,. 73 to 72 mounts are different, .
lemondana
BlackDart
Early 72 340's were steel cranks.
Yes. And if you keep on running it, the damper will eventually just come apart. Not good.
BTW, I'm running a 1965 273 harmonic balancer on my 340. Also a 1965 273 timing cover. Reason being it's a late 340 block (71) and its original timing cover and damper have the timing marks in the wrong place for an early cast iron water pump and radiator - at least if you don't want the timing marks hidden by the lower radiator hose. According to my white book, damper pn 2658458 was used on 273, 318 and 340 from 66 through 69 (with the short cast iron water pump and driver's side lower radiator hose). The 64-65 273 damper has a different part number, but will fit 318/340, at least if you use a 273 crank pulley. For some reason there is another 66-67 318 damper, pn 2658459. Have no idea why (C body maybe?).
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cudamark
Well-Known Member
If it's not vibrating with the car stationary and engine revving, it's not likely an engine balance problem. Check the drivetrain items already mentioned, and also how the exhaust system is mounted and the clearance around all it's components. Solid mounts anywhere can cause a vibration.
swingingdart
Well-Known Member
Will do, I fell victim to the Headman header sales pitch. lol
So some parts have 1/16" clearance that could close with engine torque. (Ugh)
I'm considering the 340 manifolds and ditching the headers. But those are pricy....
Did the shop have the balancer when they assembled the engine? It sounds like they knew what they were doing from what you said.
I sold my early 340 manifolds for enough to buy a set of TTI's.
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