HELP 408 stroker bad vibration

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arh

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i just fired up my 360 stroked to 408. it started as a 1979 360 block. i bought a harmonic balancer from napa(external balance). i used the crank and water pump pulley from the original 318 that had a/c and power steering
from the 69 barracuda. i started it, broke in the cam, set timing dialed in the carb and it vibrates abnormally. the crank pulley from the 318 almost seemed like it was weighted, thick rubber around it. is this my problem? i also used the 904 from the 318 that had an aftermarket torque converter and a mild shift kit.

HELP,

adam
 
I'll jump in here and make a guess. I would think that if you are using the torque converter from the original 318 ,unless you are using the special B&M flexplate, that could be your problem. I know that torque convertors are different for externally balanced engines like the 360. 318's are internally balanced.

I'm sure someone who knows more will jump in here soon with us!
 
Did you use the stock flex plate and the 318 convertor? If so that is your problem. You need a counter weighed convertor for your 360.
 
I agree with the others. I'm not a mechanic, but there are usually 3 things to look at. The harmonic balancer, flexplate, & torque converter for those symptoms.
 
The stroker I built required adding mallory metal to the crank for internal balancing. Did you have the assemble internally balanced? If you did you need an early balance that came off a internally balanced engine.
 
You need to contact the engine builder and find out if your stroker was internally balanced or not. Then you can go from there as to which harmonic balancer and torque converter to use. A lot of these 4" stroker cranks are internally balanced and if you use an external balance damper and converter you will have problems like you describe. If you mix and match you will have shaking too. You need to use both damper and converter that is internal or external balance.
 
the engine builder told me it was externally balanced. the dampner i bought is for ext. balance. i re-used the torque converter and flexplate from the 318 so i hope that is all i need to change.

thanks for all the input.

adam
 
Ours uses neutral balance damper and external balanced flexplate . If your stroker was assembled wo balancing ,there is your problem. Strokers need balancing by a machine shop.
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Kinda need more info.Did you have the motor balanced?

Is there a neutral balance tq behind the motor?

Is your firing order right?Lol,I've seen it where one plug wire was not on quite right or a couple were incorrect.It's enough to cause a shake at idle.
 
it was an assembled short block from "blueprint engines". i called them and they told me it was externally balanced. i bought an external balance harmonic balancer from Napa. i saw in the summit racing catalog a flexplate for a 360 external balance, part #bmm10239. is that all i need or do i need a new torque converter also?
 
Yes, either a weighted flexplate or a 360/904 torque converter with your existing flexplate should do the trick. You do not need to internally balance a 360 stroker. Although it is a good idea.
 
To be honest, they shoudl have sold you the dampner and the flex plate they balanced it with if that were the case. External means you need those parts. The same brand, the same configuration. You should have a 360 balancer, and that 360 flexplate.
 
moper said:
To be honest, they shoudl have sold you the dampner and the flex plate they balanced it with if that were the case. External means you need those parts. The same brand, the same configuration. You should have a 360 balancer, and that 360 flexplate.
Click to expand...

I agree with Moper,and who is Still externally balancing engines???
 
340srule said:
I agree with Moper,and who is Still externally balancing engines???
Click to expand...

i still have mine externally balanced. even ehrenberg says their good to about 450hp. ideally, yes i would like to internally balance it, but can't afford the forged crank. if i am going internal, i am not going to add mallory to my cast crank.
 
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