HELP Needed, 425 engine vibration

I just had the 425 in my car rebuilt. Starts perfect and runs wonderful. As the rpms are increased a high speed vibration starts, and is really noticable from about 1500-1800 Rpms on up. At a normal driving speed of say 45 mph, is noticable even in the steering wheel.
The engine itself was completely balanced out and internally should be dead on. it runs perfect with the exception of that dang vibration.

It was suggested that the fly wheel may be bolted on to the engine in the wrong position, and hence is putting the engine off balance.

Does anyone have any tech reports or photos to show correct positioning of the fly wheel?

 

Some people do say that,,, but ,,,, I have not been able to do that, because as you rotate the flex plate around the crank the holes will not all line up untill it is lined up right... then all,,, all,, of the bolts will go in and thread up.... I have never had one to be out of balance doing it that way.... the torque converter is balanced as a unit so it should be ok.... start checking around the front of the engine,,, fan,, fan clutch, pulleys,,, tightness of the harmonic balancer bolt... ect...

 

Good information Doc.

They will be playing with the car this week.

Mark

 

When my water pump went bad, the car had a wicked vibration at certain RPMs. My other thought would be the driveshaft.

 

My first motor I built I put the flywheel on wrong, id say thats ur problem or the balancer has slipped

 

X2

 

REv it up in natural, if its still there , its engine or parts attached, if not its drive train

 

Here you go. It will bolt up 6 ways, but only one way is right (Doc may be thinking of the 455).

Cheryl

 

I second what Cheryl says. All in favor say "aye."

 

Its not in the drive shaft, because it vibrates in park as well. Something in the engine. Its under warrenty, so they will fix it.
These are all great places for them to start looking. THANKS :beer

Cheryl, Thank you for the picture, thats perfect!!!

 

I one time in a hurry didn't torque a flywheel right had a slight vibration that wasn't in the car before as it was a clutch job I knew where it came from started over this time taking my time and vibration gone.ou:

 

aye

 

Aye!

 

aye and also to Andy as I've had water pumps failing that really felt about the same. Also, a torque convertor that missed being rebalanced after a rework

 

This is all very cool info, THANKS!!!!!!!!!!

 

There is an extra hole in the flexplate which should be lined up with a mark in the flange of the crank. The mark looks much like someone started to drill it! It is very difficult to get a good look at it while in the car but it can be done with plenty of light and an inspection mirror. Sounds very much like your problem,
Tom Mooney

 

Aye!

 

The shop just finnished the car in front of the wildcat, someone had a 69 GS 400 in there getting new engine..
I had them read this thread, plus a few of the service manuals, long story short, the engine gets pulled out monday to check the position of the flywheel.

Here is the bonus part of this, while the engine is out, I get to install the NOS fan shroud that I picked up last weekend in BG from one of our more famous and incredibly generous members.

A huge Thank you to all who helped with this issue, they will have the Wildcat back on the road next week

 

You Don't Need To Pull The Engine. Just Un-bolt The Trans. & Move It Back About One Inch Hanging On A Couple Of Longer Bolts.

 

That's what I would think, too! Unless they think it's not the flywheel installation!