sbc 400 engine vibration - Team Camaro Tech
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post #1 of 15 (permalink) Old Mar 13th, 10, 11:26 PM Thread Starter
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sbc 400 engine vibration

Hi, I recently installed a new scat 9000 cast crank and new bearings in my 400 sbc. I now have a vibration ( on scale of 1-10 about a 6) that shows up at about 2200rpm. It then gets better once the rpm increases. It does this with the transmission in any position, even park or neutral or while driving. I installed this crank because the stock crank had excessive wear on the thrust plate. I didn't rebuild the engine, therefore did not take it all apart. I installed the flexplate with the dowel pin holes lined up. There was no dowel pin though. I also had a new TCI torque convertor installed. I have the correct harmonic balancer and the correct weighted 168 tooth flexplate for the 400 sbc. Do you I need to have the dowel pin installed to balance the components? Should I have had the parts balanced by a machine shop? If so, what parts do I need to take to have them balanced properly? Any help would be appreciated!

James
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post #2 of 15 (permalink) Old Mar 14th, 10, 05:18 AM
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Re: sbc 400 engine vibration

crank NEEDS to be balanced with the balancer and flexplate installed.


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post #3 of 15 (permalink) Old Mar 14th, 10, 06:37 AM
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Re: sbc 400 engine vibration

I would guess that SCAT crank is internally balanced, and you need a neutral balanced flex plate and harmonic balance wheel now too, not the original 400 which is externally balanced.

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post #4 of 15 (permalink) Old Mar 14th, 10, 06:50 AM
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Re: sbc 400 engine vibration

so first you gotta find out which crank you have then go from there.


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post #5 of 15 (permalink) Old Mar 14th, 10, 07:58 AM
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Re: sbc 400 engine vibration

Quote:
Originally Posted by dawg View Post
crank needs to be balanced with the balancer and flexplate installed.
x2
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post #6 of 15 (permalink) Old Mar 14th, 10, 12:09 PM Thread Starter
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Re: sbc 400 engine vibration

The crank is an externally balanced crank from Scat. Im not an engine builder, so I appreciate any help. Is it common practice to have a new crank balanced with flexplate and flywheel? Does the dowel pin in crank have to be installed to be balanced?

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post #7 of 15 (permalink) Old Mar 14th, 10, 01:35 PM
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Re: sbc 400 engine vibration

yes and definately yes


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post #8 of 15 (permalink) Old Mar 14th, 10, 01:50 PM Thread Starter
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Re: sbc 400 engine vibration

Thanks for the reply Dawg! I will take crank out and take crank, dampner, and flywheel to machine shop. any other suggestions or info I need to give to machine shop?

James
Espanola, New Mexico

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post #9 of 15 (permalink) Old Mar 14th, 10, 03:25 PM
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Re: sbc 400 engine vibration

I had something similar (vibration at low RPMs) and took me about a month to find it.... found by accident too

While under my truck for a problem, the exhaust sound was off and I couldn't figure it out.
Long story short... broken exhaust valve spring killing A/F mixture

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post #10 of 15 (permalink) Old Mar 14th, 10, 04:30 PM
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Re: sbc 400 engine vibration

Quote:
Originally Posted by james_m_ag View Post
Thanks for the reply Dawg! I will take crank out and take crank, dampner, and flywheel to machine shop. any other suggestions or info I need to give to machine shop?
If you're taking it that far apart, take the NUMBERED pistons/rods and have the whole shebang balanced.


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post #11 of 15 (permalink) Old Mar 14th, 10, 06:55 PM Thread Starter
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Re: sbc 400 engine vibration

Well, I do have the six inch scat rods sitting on the shelf. I was buying parts slowly so I could rebuild it right next summer. I'm thinking that the rebuild time is now. Any suggestions from you guys which pistons to get. I have the 400sbc two bolt main. Scat 9000 stroker lightweight crank for the 400sbc with a 3.75" stroke and 5.7" rod length. . Scat forged I-beam connecting rods 6" . A new Comp cams part # cs xe262H-10 camshaft and lifter kit. How do I figure out which pistons to get. Being that the crank is for a 5.7" rod and I am going to use 6"rods. I got crank and rods on craigslist for $250 all sealed and brand new in boxes. Any idea would be greatly appreciated. Also, what would the combo produce as far as cubic inches and compression ? Any concerns with this build? As for heads, I am using some stock 76cc heads, but plan on upgrading to some aftermarket heads in the future. Can't afford it now, but I understand how a good set of heads would make a huge difference. The pistons would have to be able to clear these stock heads for now. My car will be mostly street driven, weekend strip occassionally. I like to have the power when I want it, but it needs to be streetable. Thanks for any info.

James
Espanola, New Mexico

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post #12 of 15 (permalink) Old Mar 14th, 10, 07:12 PM
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Re: sbc 400 engine vibration

James,
The Scat 9000 cranks are not balanced at all from the factory. YOu need to have the crankshaft balanced to the weights of your parts (pistons, rings, rods etc) You dont actually have to have the dowel pin, but it makes certain that you install the flywheel in the proper position.

Any good machine shop that does engine balancing should be able to tell youexactly what you need to do.

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1971 Chevelle "Heavy Chevy" original owner


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post #13 of 15 (permalink) Old Mar 14th, 10, 07:16 PM Thread Starter
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Re: sbc 400 engine vibration

Thanks for the help Bill. I will dissassemble and take in. Once again, thanks!

James
Espanola, New Mexico

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post #14 of 15 (permalink) Old Mar 14th, 10, 09:07 PM Thread Starter
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Re: sbc 400 engine vibration

I am going to start a new thread on perfomance, thanks for the help guys.

James
Espanola, New Mexico

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post #15 of 15 (permalink) Old Mar 15th, 10, 08:42 AM
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Re: sbc 400 engine vibration

This is a long-shot, but I once solved a vibration problem by inspecting the radiator fan. The previous owner had installed an aftermarket flex fan and half of one of the blades was missing. Swapped for a factory 5 blade fan and she smoothed out perfectly.

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