VibrationAugust 13 2017 at 1:13 AM
|John UK (Login johncougaruk)|
I seem to have a slight vibration just off throttle on my 428 C6 cougar. Paranoid that I'd wiped another cam lobe I've pulled the valve covers and all seems fine. I have a weighted flex plate but I'm not sure whether I should have an unweighted or not.
I do not know the build spec so I'm not sure what crank I have. I simply plan to swap the flexplate for an unbalanced to see if the problem goes away. Anything else I should look out for?
|August 13 2017, 2:37 AM |
unless its been converted to internal you may do more damage with a 390 unbalanced flexplate
make sure its a 428 crank and no heavy metal in one of the throws
|August 13 2017, 6:14 AM |
Excuse my unfamiliarity but how can I tell it's a 428 crank, by measuring the stroke?
Extra weight on crank
|August 13 2017, 9:08 AM |
When/If you have the pan off, there will be an extra weight cast near the center of the crankshaft. It looks sort of like the external hatchet weight that is used near the harmonic balancer on the snout of a SCJ crankshaft, except it's cast onto the crank.
The stroke can also be measured.
1967 Galaxie 500 Red original Q code 428
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|August 13 2017, 5:13 AM |
A couple things to check for vibration.
Try removing the belts and see if that changes the vibration.
Look for dirt build-up inside the crank pulley.
All stock 428 cranks use a weighted flex plate.
I once had a 428 that someone installed a 390 flex plate. It shook pretty bad.
|This message has been edited by galaxiex on Aug 13, 2017 5:15 AM|
|August 13 2017, 6:16 AM |
Definitely a 428 flexplate with weights, bought specifically for the engine. I'm assuming it's a stock crank too.
Where did you get your flex plate ?? Installed one for a buddy and
|August 13 2017, 7:15 AM |
had vibration. Replace with a stock plate and vibration vanished... Lot of poorly made parts being sold.... JMHO
|August 13 2017, 8:12 AM |
I bought it from NE Performance Mustang
|This message has been edited by johncougaruk on Aug 13, 2017 8:13 AM|
My aftermarket flywheel was "supposed to match stock"
|August 14 2017, 1:17 PM |
but come to think of it, i believe the weight on it was smaller than a stock flywheel, that could be part of my problem.. I rushed and did not get it all balanced. I should have maybe.
|August 13 2017, 8:16 AM |
The flexplate can only be bolted on one way if my memory is correct?
Correct n/m KS
|August 13 2017, 9:45 AM |
If it needed a zero flywheel, you would KNOW IT.
|August 14 2017, 10:00 AM |
You would not be on here posting 'slight vibration' you would be saying Holy Sh*t i cant see out of my rear view mirror or hold the shiftier, i think it is going its fall off!
Measure your stroke, if its 4 inches+/- you probably need a flywheel weight. But as noted, someone may have fussed with the balance, and the parts may not be 100% matched. My 428 engine is like that. Its all 'stock' parts supposedly, but i can feel a shacking at 900 and 1800 that i did not have on my professionally internally balanced 410. 2500 RPM cruise is good, almost perfectly smooth, although not like butter that my 410 was.
|August 16 2017, 7:14 AM |
Thanks for the response, I'm going to try everybody's recommendations this week. The engine builder dyno'd the engine and made no mention of a slight vibration (feels like a miss), I'd hope he wouldn't of released it to me if it had. Which makes me hope its a pulley or gearbox (C6) derived problem.