What's shaking!!

[Jack A.]

I have had a 65 corvette for about five years. It is a 275 H.P. 327. The whole time I have had it I've had a problem with a vibration that is quite noticable. Like something is out of balance. Through the years and with a lot of effort eliminated some of the more obvious possibilities. Tires, wheels, driveshaft, rear end etc. What Ive come to is it must be in the engine itself. What I was wondering is the engine internally or externally balanced? It would help if I knew that.

Thanks,

Jack Alexander

[Wayne W.]

Re: What's shaking!!

I have had a 65 corvette for about five years. It is a 275 H.P. 327. The whole time I have had it I've had a problem with a vibration that is quite noticable. Like something is out of balance. Through the years and with a lot of effort eliminated some of the more obvious possibilities. Tires, wheels, driveshaft, rear end etc. What Ive come to is it must be in the engine itself. What I was wondering is the engine internally or externally balanced? It would help if I knew that.

Thanks,

Jack Alexander

...
Internal

[Terry M.]

Re: What's shaking!!

I have had a 65 corvette for about five years. It is a 275 H.P. 327. The whole time I have had it I've had a problem with a vibration that is quite noticable. Like something is out of balance. Through the years and with a lot of effort eliminated some of the more obvious possibilities. Tires, wheels, driveshaft, rear end etc. What Ive come to is it must be in the engine itself. What I was wondering is the engine internally or externally balanced? It would help if I knew that.

Thanks,

Jack Alexander

Jack 327 cid engines are statically balanced internally. At some point small blocks were also dynamically balanced using weight addition to the harmonic balancer and weight removal (by drilling) on the flywheel or flex plate -- I am not sure when the dynamic balance began and may not have been done on your engine. Others will have to provide that detail.

You may also read a story in the current Restorer about a member who chased a vibration and finally found it in the front bearing of his transmission. I am not sure if his symptoms mimic yours, but it might be enlightening to read the story.

[Timothy B.]

Re: What's shaking!!

Jack,

If the problem exposes itself when driving don't overlook a front wheel bearing. Sometimes the vibration/feel will go away when you turn left or right because the bearing is not loaded.

If your confident it's there when not moving don't overlook front engine parts like fan clutch etc. I once had a water pump blow up in my face because someone installed a fan clutch with 3/4" bore hub on a C2 water pump and the excentric (sp) pounded the water pump, finally the casting just broke. I was not a happy camper!!

[Donald L.]

Re: What's shaking!!

I had the rubber on the balancer go bad and giving a vibration. Run down the road at the point of the most vibration, let off the gas and push in the clutch. If it stops it is could be in the engine (balancer)

[Jack A.]

Re: What's shaking!!

Hi Guys,

Great suggestions! I will chase them down. If anyone else has anything please let me know.

I appreciate the time you have taken to reply.

Regards,

Jack Alexander 35730

[John D.]

Re: What's shaking!!

Hi Jack,

Do you know anyone who works at a car dealer or repair shop who may have access to an EVA (see below) ? It measures the vibration frequencies to help narrow down where the vibration is coming from.
It's normally used once the usual suspects tires,wheels etc. are eliminated.

Here's the technical jargon from the service manual:

The J-38792-A Electronic Vibration Analyzer 2 (EVA 2) , is a 12-volt powered hand-held device, similar to a scan tool, which receives input from an attached vibration sensor or accelerometer and displays the most dominate input frequency(ies) (up to three) on its liquid crystal display. The vibration concern frequency(ies) are obtained through the use of the J-38792-A Electronic Vibration Analyzer 2 (EVA 2) while following the Vibration Analysis Diagnostic Tables. The frequency(ies) obtained, when applied to the Vibration Analysis Diagnostic Tables, are used as a primary input to help determine the source of the vibration concern.

[Edward J.]

Re: What's shaking!!

Jack,As Don says I think I would be chasing after the harmonic balancer, ,if the vibration is sensative to engine rpms that could be the problem.

Drive the car to when the vibration begins, put car into netural and coast to see if vibration is gone, or still there, that would indacate a driveline problem, Note the engine rpms when the vibration occurs ,you maybe able to duplicate the vibration in netural at the same RPM ,which leads to the engine.

[Duke W.]

Re: What's shaking!!

Jack 327 cid engines are statically balanced internally. At some point small blocks were also dynamically balanced using weight addition to the harmonic balancer and weight removal (by drilling) on the flywheel or flex plate -- I am not sure when the dynamic balance began and may not have been done on your engine. Others will have to provide that detail.

Terry, this is new information to me, and I'd like to learn more from any source. I have a video tape of early SB production, and it shows a final adjustment to the crankshaft end masses just prior to installilng the oil pan on the assembled engine, but I don't know how long this procedure endured.

This operation eliminates as much as possible the first order rocking couple that is present on cruciform V8 crankshafts. If one does a precision restoration of a vintage SB or 427 including balancing, this operation is performed on the crankshaft alone after inputing the masses of all the rotating and reciprocating components, and I highly recommend this for all engine restorations; 454s require statically unbalanced front dampers and flywheels/flexplates, and I'm not sure if current machine shop practice is to make the final adjustment on the crankshaft end masses or the damper and flywheel/flexplate.

If what you say is true it means that dampers/flywheels/flexplates on "internally balanced" engines are not truely interchangeable since each would be "tuned" to a specific rotating/reciprocating assembly.

Duke

[Clem Z.]

Re: What's shaking!!

later SBC when they went to one piece rear crank seal used a external balanced flywheel because they had to removed the balancing weight from the flywheel flange. the damper was not changed

[Duke W.]

Re: What's shaking!!

So that would have been sometime in the eighties(?).

Duke

[Jack H.]

Re: What's shaking!!

Great suggestions! I will chase them down. If anyone else has anything please let me know.

How did you determine the tires & wheels were not the problem?

[Clem Z.]

Re: What's shaking!!

So that would have been sometime in the eighties(?).

Duke

yes the 80s for the change

[Clem Z.]

Re: What's shaking!!

Great suggestions! I will chase them down. If anyone else has anything please let me know.

How did you determine the tires & wheels were not the problem?

shut of the engine in neutral and coast

[Clem Z.]

Re: What's shaking!!

I have had a 65 corvette for about five years. It is a 275 H.P. 327. The whole time I have had it I've had a problem with a vibration that is quite noticable. Like something is out of balance. Through the years and with a lot of effort eliminated some of the more obvious possibilities. Tires, wheels, driveshaft, rear end etc. What Ive come to is it must be in the engine itself. What I was wondering is the engine internally or externally balanced? It would help if I knew that.

Thanks,

Jack Alexander

if the vibration is there when revving the engine in neutral i would suspect the clutch pressure plate