Let’s track down a vibration

DorianL

solid fixture here in the forum
Staff member
Ok. I just swapped a worn performance cam for a stock cam. The cam had a few worn lobes which I thought were leading to a less than smooth operation.

Well, I swapped the cam and, what seems like a mild vibration is still there. I think I can hear it and I can see the steering wheel shudder a bit. It feels like it’s slightly out of balance.

My sense is now, beware of what you suspect more often than not, it can be something completely other. But it feels like something out of balance :D

So the things is could be:
- inconsistent ignition
- worn mounts
- clutch assy wasn’t properly aligned
- vibration damper is dead
- rotating assembly is out of balance
- accessories and water pump

How does one check these things ?

My ignition looks new under there. I’m going to put a temp gun onto my exhaust headers to see if one is running cold.
 
I’m betting motor mounts. All the other rubber is perished.
 
well, is it more pronounced sitting still at idle or when driving and does it get changed as the car accelerates, decelerates ,
when you go into reverse, turn corners, does it change if you use the brakes, etc?
if your running at lets say a constant 40 mph and push the clutch in and hold it does it change?
have you checked for loose motor mounts, transmission mounts, ball joints?
did the damper look worn?
if the vibrations only while moving,
have you checked the cars 6 u-joints and trans yoke?
those u-joints may need replacing or the drive shaft may need to be balanced

carefully slide the yoke into the trans tail assembly, until it bottoms out, then back it out about 3/4"-1"
you want a minimum of 3.5-5" of spline engagement, if thats available to handle the torque loads, more is better,
as long as theres about 3/4" of room for the yoke to slide in further during suspension movement without bottoming out and binding,
and the u-joint will ideally be resting about 1"-3/4" back out of the tail of the trans to allow for suspension movement ,
if the yoke u-joint is mounted where it located back several inches during the cars operation,
your exerting unwanted extra stress leverage on the trans tail shaft

http://www.grumpysperformance.com/transpline1.jpg
 
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Thanks. Lots of tests to try out this weekend !!!

Will report back
 
I need to put that hood back on and stop that oil leak.

Say... should I wait 100 miles before changing the oil and the filter ?
 
your car of course, but I'd drive it for at least several days and at least that 100 miles,
before the oil and new oil filter change, and I'd cut open the filter and inspect it

Rgr that.
 
Mmmm. I think I might have found the vibration. There is a visible slight wobble to the lower pulley on the crank. I’ll briefly run the engine tomorrow without the lower pulley. Hopefully it’ll be that
 
its very un-likely to be the pulley
its more likely to be related to a defective damper/balancer,
you might want too get a new fluid-damper ,
designed to match the intended application,like RICK DID.
http://www.fluidampr.com/contact/

Font Slope Screenshot Document Electric blue



Font Parallel Technology Diagram Electric blue



Font Line Auto part Parallel Technology


Phone: (716) 592-1000
https://www.summitracing.com/parts/flu-62260d

https://www.summitracing.com/search...geSize=100&SortBy=Default&SortOrder=Ascending
 
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The damper seems to be spinning smoothly. The pulley on it is wobbling.
 
If I remove the pulley... is there any way to test the damper to see if it’s the culprit and failing ?
 
I wonder if that also contributed to the leaking timing chain cover ?
 
The crankshaft pulley on a Small Block Chevy is pretty stout.
I do not see how it can bend unless someone had the engine out and the Pulley stuck something hard or was set on the ground hard coming off a Cherry picker engine hoist.
 
If you pull the pulley off then there is no good seating area for the crankshaft balancer bolt.
Start the engine and the balancer make work its way off. Go flying off.
 
If you have a timing light hook it up on #1 spark plug wire, shine it at the pulley and balancer.
See if the balancer hub is OK with the stroboscopic light flashes.
 
There are like a zillion SBC balancer styles.
If you know what year the SBC engine it will help knowing if the balancer is right or not. Confirm by pictures looked at.
400 SBC is no mistaking for. Its 8 inches in diameter. Has a counter weight on the inside.
Very thick also.
 
Lowest cost options on Summit Racing.
Made by Dorman. As long as you do not spin the engine over 5700 RPM it should Be Ok stock replacement.

If the crank pulley is bent you will need the 2 letter code off of the GM Pulley to match up with used replacement.
Or Find a new match somewhere.
 
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