balanced flex plate on balanced 360 cid

-
R BEE

R BEE

Well-Known Member
Joined
Nov 9, 2009
Messages
205
Reaction score
1
Location
Vermont
I have installed a b&m flex plate on my blue printed and balanced 360.
When i idle and rev her up I have a vibration through steering wheel.
The car cam was set up for circle track so it is heavy the harmonic is a balanced one.Is it possible that the flex plate is not working with the rest of the balanced combo? Just hate to crack everything open if I don't have to but it is begining to look that way .
Any input would be great. Car has not been on the road and I have only done a small burn out to make sure the transmission rebuild went well
There didn't seem to be any vibration during the burn out ????
 
Need more information mainly because all engines are balanced. Some are internally balanced while others are externally balanced. Has your 360 been internally balanced or is it still externally balanced like it came from the factory? What B&M flex plate (part #) did you use? No idea what your talking about when you say "The car cam was set up for circle track so it is heavy the harmonic is a balanced one". What does the cam have to do with balancing???? Excuse my being blunt but that's a bunch of jiberish to me! Also, better punctuation helps us older guys decipher what your saying.:banghead:

:D:D:D
 
Double check that you have the correct flex plate and that your harmonic balancer is correct as well. For instance, The 340 and 360 have different balancers and one will not work with the other. The other balancing factor to consider is the torque converter.

There are a couple ways you can go to properly "balance" the engine.
You could use a stock Flex plate on either SB engine but you would then need a balanced torque converter specific to each engine. The easiest route would be to buy a specially balanced flex plate specific to the 360, which you have done. If your harmonic balancer is correct, then Once you have the back end of the engine balanced with your B&M flex plate, you can use a neutral or zero balanced torque converter which is much more affordable and available

So,
Make sure you flex plate is for a 360 not a 340
the 340 balanced flex plate is slightly different than the 360 balanced flex plate.


Make sure your harmonic balancer is correct. the harmonic balancer for the 360 has a funky shape to it. It is "weighted" to balance the engine as it goes round and round.

If both your flex plate and you balancer are correct, then perhaps your torque converter is not the neutral balanced one you need. If it is specially "balanced" for a different set up, it would throw off your engine. In other words. If you use a B&M flex plate and the correct harmonic balancer, your torque converter should be zero or neutrally balanced.

When either of these things are out of whack you will know because the engine will wobble at higher RPMs when you are in park. If what you are feeling is a slight vibration in the wheel and not a violent shake, then your vibration lies elsewhere. You need to simply start troubleshooting and eliminating. Check engine mounts. Are the bolts all tight? Are the rubber bushings still good? Is there metal touching metal?. Are your tires good to go? Vibrations are a search and destroy symptom and take alot of patience. I found my vibration problems in the transmission mount. But you will find yours! drive on my friend.
thanks and God Bless
Keni
 
first pic shows how a B&M 340 and 360 flex plate differ.

second pic shows the 340 harmonic balancer for an externally balanced block. This balancer is different than the 360 balancer shown on the blue engine below

this is a neutral or zero balanced torque converter. Basically its just a stock converter for the 904 transmission. You can use this on either the 340 or the 360 as long as you have used both the correct specially balanced Flex plate and the harmonic balancer specific to your engine.

4th pic 360 harmonic balancer is different than the 340s
 

Attachments

  • DSC00942.jpg
    160.8 KB · Views: 920
  • DSC00955.jpg
    101.8 KB · Views: 1,030
  • DSC00938.jpg
    107.9 KB · Views: 892
  • DSC00950.jpg
    94.7 KB · Views: 852
The 360 is externally balanced,so.....
My recipe.
B&M 360 flex plate
Mopar Performance 360 harmonic balancer.
Neutral balanced torque converter.
 
R BEE said:
I have installed a b&m flex plate on my blue printed and balanced 360.
Click to expand...


I would check with the person that balanced your engine and see what balancer, flex plate and or torque converter that needs to be used. There are too many variables to just start guessing.
 
fishy68 said:
Need more information mainly because all engines are balanced. Some are internally balanced while others are externally balanced. Has your 360 been internally balanced or is it still externally balanced like it came from the factory? What B&M flex plate (part #) did you use? No idea what your talking about when you say "The car cam was set up for circle track so it is heavy the harmonic is a balanced one". What does the cam have to do with balancing???? Excuse my being blunt but that's a bunch of jiberish to me! Also, better punctuation helps us older guys decipher what your saying.:banghead:

:D:D:D
Click to expand...
Sorry I wasn't more clear . Let me try again with my 52 year old brain.
The motor was used as a late model race engine running circle tracks throughout New England It was designed to run at 7500-8000 rpm's.
It was internally balanced and externally balanced. By saying heavy on the cam I meant high lift and does shake some. As for punctuation sorry
but you get what i have to offer.Thanks for Reply
 
kenicb said:
first pic shows how a B&M 340 and 360 flex plate differ.

second pic shows the 340 harmonic balancer for an externally balanced block. This balancer is different than the 360 balancer shown on the blue engine below

this is a neutral or zero balanced torque converter. Basically its just a stock converter for the 904 transmission. You can use this on either the 340 or the 360 as long as you have used both the correct specially balanced Flex plate and the harmonic balancer specific to your engine.

4th pic 360 harmonic balancer is different than the 340s
Click to expand...
Great pictures thanks I did install the 360 flex plate and my harmonic is a special liquid filled . I am going to take off the clutch fan and see if that gets it . And check all points of tie down.Thanks for your help it has given me some ideas to look for and try

R BEE
 
attachment.php
 
I would say if it was a race motor it is usually internally balanced and you have a external flexplate on it. You need one for a 318 they are internally balanced
 
R BEE said:
Sorry I wasn't more clear . Let me try again with my 52 year old brain.
The motor was used as a late model race engine running circle tracks throughout New England It was designed to run at 7500-8000 rpm's.
It was internally balanced and externally balanced. By saying heavy on the cam I meant high lift and does shake some. As for punctuation sorry
but you get what i have to offer.Thanks for Reply
Click to expand...

Ok Bee. The cam comment threw me but I understand now. Here's the thing, an engine can't be internally and externally balanced. Has to be one or the other, no iff's and's or but's. Using the B&M flexplate designed for an externally balanced 360 combined with a fluid damper (balancer) may be the issue because the B&M plate is for an externally balanced engine and most fluid damper's are for internally balanced engines, if they are for an external balanced engine they need to be for that specific engine as different engines require a different ammount of balance weight. Like Brian T asked what were you told you needed to run for a flexplate and balancer when you bought the engine? Was either the flexplate or balancer you have on it now on it when you bought it? If I were you I wouldn't run it anymore than needed for testing purposes (no more burnouts for sure) until you have the vibration solved. A harmonic vibration like you described can wreak havoc on engine and trans. components. I've seen cranks, torque converter snouts, and trans. input shafts snapped right in half because of a harmonic vibration. At the least it'll take a lot of life out of the bearings.
 
I agree. More than likely, if it is a balanced race engine, and it had the Fluid dampner on it when you got it , it is internal balance. I would again, ask the guy you bought it from what flex plate/convertor combo he was running. Hopefully, you can get a way with just running a nuetral balanced flex plate.

I built a hot little 340 one time and used my existing 318 flywheel, so I know the vibes you are feeling. As soon as I got the correct flywheel on there, it was as smooth as glass and rev'd to the moon. Until you get it figured out, I wouldn't drive or rev it any more than absolutely necessary.

Let us know how this turns out.
 
The hard thing about contacting the builder is the motor was built 12 years ago and has been put up .Thanks for the external,internal explannation guys this makes understanding and reminds me of what was forgotten.When I was racing I ran both 340"s and 360"s . I am the one who put the flex plate on ,this was a manual engine and I hooked it to a auto . That is why I asked about flex plate cause it was me that made the change . My builder is long since gone from the area but if I ever do bump into him the questions will fly. I still have bodywork to finish so not running car until I change flex plate is easy. Just finding time is the problem.
thanks
R BEE
you can check out car at my 73 restoration by R BEE there is a sound clip on page 2.
 
That is a problem if you don't know how to contact the builder but like Brian said if the balancer was on it when you got it it's probably right and the flexplate is most likely the culprit. It makes sense that they'd internally balance it for the RPM they were spinning it. Not that you can't spin an externally balanced engine that high, they just live longer when internally balanced so most shops that build an engine for real high RPM internally balance them. With that said I bet the problem is the flexplate. You probably just need a neutral balanced flexplate like a steel crank 340 or 318 would use.

p.s. what torque converter are you using? Does it have a weight(s) welded to the front (engine) side? Like it was mentioned earlier it can also figure into the equation.
 
fishy68 said:
That is a problem if you don't know how to contact the builder but like Brian said if the balancer was on it when you got it it's probably right and the flexplate is most likely the culprit. It makes sense that they'd internally balance it for the RPM they were spinning it. Not that you can't spin an externally balanced engine that high, they just live longer when internally balanced so most shops that build an engine for real high RPM internally balance them. With that said I bet the problem is the flexplate. You probably just need a neutral balanced flexplate like a steel crank 340 or 318 would use.

p.s. what torque converter are you using? Does it have a weight(s) welded to the front (engine) side? Like it was mentioned earlier it can also figure into the equation.
Click to expand...
I believe you are right and plan to split and install neutral plate. Torque converter came with car 904 . Only thing done to transmission was rebuild kit so it would be a stock converter I believe. This vibration is with car in park. The vibration changes speed with morer RMPs.(vibrates faster) Sorry about spelling and gramer .I need to figure out spell check . And thanks for you help How old are you?
 
R BEE said:
I believe you are right and plan to split and install neutral plate. Torque converter came with car 904 . Only thing done to transmission was rebuild kit so it would be a stock converter I believe. This vibration is with car in park. The vibration changes speed with morer RMPs.(vibrates faster) Sorry about spelling and gramer .I need to figure out spell check . And thanks for you help How old are you?
Click to expand...

Ok. If your engine has a big cam in it like you said is that stock converter going to work ok? I have yet to see them work right with a big cam. Just sayin... If you do keep the converter you have make sure when you get it apart it doesn't have a weight or 2 welded to the engine side of it. They'll usually be about 1-1/2~2" long by a 1/4~1/2" wide and located between a set of bolts. If it has a weight or 2 there that means it was for a externally balanced engine such as a late 340 or a 360 and you need to knock them off. If it vibrates in neutral and gets worse with rpm's it's definetly something to do with the flexplate or balancer and since the balancer was on it when you got it that should rule it out. Don't worry about the spelling/grammer thing. Your new and I didn't understand what you were meaning and thought you were using some kind of shortcut like so many use when texting and such. I'm only 48 but get thrown easily, LOL... Wish I could figure out spell check on my new computer too. My old one had it and it sure was nice. This one has it in a word document but I can't for the life of me figure out how to get it to work on the internet.
 
Well once again I need to go backwards in order to go forward.The flex plate will be a wall ornament soon.

R BEE
Thanks to all for advise.
 
Ok well after sucking it up I went back out to the shop and split the engine/trans pulled the flex plate put the one on from the engine I pulled from the car and that seems to be what it was . I want to thank all here that helped me get up the go go to split the E/T I have to admit I was not a happy camper while pulling apart but now that it is better so am I.Thanks
R BEE
 
R BEE said:
Ok well after sucking it up I went back out to the shop and split the engine/trans pulled the flex plate put the one on from the engine I pulled from the car and that seems to be what it was . I want to thank all here that helped me get up the go go to split the E/T I have to admit I was not a happy camper while pulling apart but now that it is better so am I.Thanks
R BEE
Click to expand...

Glad ya got it worked out Bee. Happy motoring :burnout:
 
You must log in or register to reply here.
-

Back
Top