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Auto Tran to Man swap violent shake

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chrizti4 View Drop Down
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    Posted: Jul/02/2019 at 9:14am
AMC Friends, I'm stumped! 1978 CJ7, removed 304 3spd swapped in running (78?) 360 out of a J10 auto. Ordered flywheel and input shaft bushing and installed working 5spd. Engine starts fine, no odd sounds from starter or anything. At 800 rpm shakes violently till around 3k (didn't go higher than that). Engine responds like its new, no blow by, no burning oil on accel or de-accel. Vac gauge at a solid stable 16lbs needle has no waiver or shake, timing and firing order checked four times, 5degBTDC with ported line attached. Changed plugs, wires, dist cap. Header temp only varies <50deg between pipes. Don't want to (shouldn't) drive it with SHAKING the whole jeep. Doesn't overheat, stays a good 165. Carb flow checked, and everything within standards. After warmed up did rev it a bit, sounds fantastic with both open headers and with mufflers installed, shaking doesn't change. But at idle smooth as a kitten and when hitting accelerator smooth as a tiger. Have built a lot of vehicles, this is second AMC build. I AM STUMPED! I know some say the 401 has a different flywheel, but I ordered one for a 360. Next step is dropping drive-train, installing the old flex-plate, building a temp rear block mount and starting the engine again. Is there anyway to tell if the flywheel is the wrong one? Thank you sir!
Respectfully submitted,
Christopher Wuertz
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 9:46am
Yes, sounds like you have an engine balance issue.
The manual flywheel (correct or not) is not going to have the same balance as an automatic flexplate.
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chrizti4 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chrizti4 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 9:47am
Thank you sir for the response, how do I fix this?
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tufcj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 9:54am
Did you use the 304 flywheel or order one for a 360?  AMC V-8s are externally balanced.  The flywheel (and harmonic balancer) have to be for your specific displacement.

If you still have the automatic flexplate that came off the 360, you can take that and the flywheel to an automotive machine shop and have them "match balanced".

Bob
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BrotherBamc Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 10:01am
Have your flywheel neutral balanced... 
A reputable machine shop that does balancing will be able to help you out with that. 

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SC397 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SC397 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 10:16am
A pleasure to meet you Mr. Stumped,
If you have the original flex plate from the 360 you could have a machine shop match-balance the new flywheel to the old flex plate.  Or, disassemble the engine and have a machine shop externally balance the rotating assembly.
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mark09 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mark09 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 11:44am
Brotherbamc there's a big difference between neutral and match balance.
V-8 's not  neutral ballance unless specifically done at a rebuild .
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 12:13pm
Originally posted by ramblinrev ramblinrev wrote:

Yes, sounds like you have an engine balance issue.
The manual flywheel (correct or not) is not going to have the same balance as an automatic flexplate.

They actually would have the same balance. When I converted from auto to stick, I had my new flywheel match balanced to the old flexplate. My engine had previously been rebuilt and rebalanced, so stock balance weighting didn't apply anymore.

I recently had a friend with a similar problem and it turned out to be the clutch/pressure plate that was the culprit. You might try it with the clutch and pressure plate removed but keep the current flywheel and see what happens.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BrotherBamc Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 12:59pm
Originally posted by mark09 mark09 wrote:

Brotherbamc there's a big difference between neutral and match balance.
V-8 's not  neutral ballance unless specifically done at a rebuild .


I stand corrected then...
I had a 360 flywheel "neutral balanced" when I put a T-10 behind my 258.
I believe that the 258's are externally balanced then..??
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tufcj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post Posted: Jul/02/2019 at 1:19pm
Originally posted by BrotherBamc BrotherBamc wrote:


I stand corrected then...
I had a 360 flywheel "neutral balanced" when I put a T-10 behind my 258.
I believe that the 258's are externally balanced then..??


Neutral balance is correct on an I-6.  Those are INTERNALLY balanced. 

V-8s are EXTERNALLY balanced and rely on the harmonic balancer and flywheel/flexplate for balancing.

Bob
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