Jimmid

I recently had my 1967 corvette 427/435 engine rebuilt from two different speed shops. They replaced the crank, pistons, cam, lifters, push rods, front balancer, flywheel, clutch, and pressure plate. They both balanced the engine, but it has a vibration starting at 2200 rpm, and gets stronger as the rpm increases. The only rotating parts not replaced were the rods, but they both reconditioned them. Anybody have any suggestions on where to go from here? Jim

jrm5657

Well, without knowing the details of how they balanced the components and certainly why 2 shops have been involved, the first place I would look would be to make sure you have a 427 balancer and flywheel which are way different than the balancer and flywheel used on 454's. If you post pictures of what you have, it is easy to tell which ones you have.

Nowhere Man

Did you check the drive shaft? Does it do it in all gears? Clutch in or out? Like said above check that out

warrenmj

Are the motor mounts good?

Jimmid

I ran the engine without the balancer and without the clutch and pressure plate. The same vibration starts at the same RPM. I bought an aluminum flywheel from Summit Racing for that engine, still the same, and this is not going down the highway. This is sitting on blocks. I have new motor mounts in it also.

jrm5657

Not sure why you replied and then crossed everything out, but running without a balancer and changing flywheels, oh boy, what a mess. You need to take a step back and figure out what you have as a starting point before you go changing out parts and pieces.

babbah

427's are internally balanced and require a internally balanced harmonic damper. If you have the externally balanced balancer on the crank you will be in trouble.

DansYellow66

Has anyone bought a quality motor mount lately? GM still offering them?

SledgeHammer 2.0

I am no engine builder, but when you balance an engine isn't that so all the parts, no matter where they came, when bolted together, don't vibrate?
If so, If you had two different machine shops hand you back your engine saying "it's balanced" You would think one of them got it right.

Maybe you have a engine miss that starts at 2200 rpm and gets worse.

ptjsk

Can anybody provide pictures of the two different balancers?

Jimmid

I only have one balancer in my possession, and I got it from ecklers ,they balanced it also. It is for the 427 8"

Nowhere Man

Who balanced it?

Jimmid

The speed shop did, and this is the second balancer. I forgot to say that the vibration is worse when under power. If I coast with the same rpm, and speed when under power, I don't feel it! I feel the vibration the most on the steering wheel, and clutch pedal. When I push in the clutch, and let off the gas the vibration goes away on both.

Crunch527

Jim,

Although scratched out, you said you ran the engine w/o the balancer and have the same issue. Good, you have eliminated the balancer (which I didn't think that was the issue anyway).

What are the details the flywheel? Part number?

Clutch? (although, this shouldn't matter)

Did you swap out the flywheel and go to an aluminum one after you had experienced the vibration?

I can't really tell what is going on?

Not ideal, but the next thing you could do is to remove trans and flywheel/clutch and run it (briefly)...see if the engine itself has an issue.

I assume neither shop ran this engine on a stand/engine dyno before you put it in the car?

Frank

DansYellow66

You could be dealing with a driveline vibration. Have you checked the rear bushing and yoke in the transmission for wear and looseness. I had a vibration in mine that was traced to that eventually. When I grabbed the u-joint at the yoke and pushed and pulled it laterally I discovered a lot of play. Once the bushing was replaced and a new yoke installed it was fixed, although my 427 isn't the smoothest reving motor I've experienced.

Also check the driveshaft for damage or signs a balance weight might have been knocked off.

I would still like to know if anyone has bought a decent quality motor mount for our cars lately.

Jimmid

Now that winter is almost here the 67 is going back on blocks and the trans, clutch, and flywheel are coming off again just to narrow the vibration to just the engine or not! The problem is there even when the car is not moving. One person said that all the 437s have vibration. I had a 66 427 and it ran smooth! The last speed shop ran the engine on a stand and didn't notice any. But maybe he didn't run the rpm up long enough. Noticed also that when the oil gets hot, I can feel it more! That's for everyone's comments!!

Westlotorn

Don't be offended but are you absolutely positive the spark plug wires are routed correctly and the fire order is correct.
You might have 2 wires switched that are close enough to run but not run smooth.
You might have wires cross firing sparking the wrong wire at the wrong time.
You might pull the plugs and look for anything unusual.
If your clutch was balanced with the engine as it should have been in a balanced engine is the clutch mounted with the alignment marks in the right place?

The 427 is not known to have vibration issues, for two shops to "balance" your engine wrong would be a 30,000:1 chance. Wild guess on that number of course, but not likely at all. I would look outside the engine for answers. All the bolt on parts. Maybe the harmonic balancer is wrong but it should have been balanced with the crankshaft and flywheel.
What city or area of the USA are you in? I would bet some on this forum may have experience with your engine builders that could be shared.

plaidside

427:
http://www.dormanproducts.com/p-2222...cer&origin=YMM

454, notice the counter weight on the inside:
http://www.dormanproducts.com/p-3490...cer&origin=YMM

Patman65

You should look into the fan and fan clutch. I watched someone rebuild a L79 engine twice because they could not determine the cause of the vibration. The vibration showed up after the first engine build. At any rate the fan clutch never looked wobbly when running but apparently there was some washer/bushing or shim that wasn't installed and caused the vibration starting at about the same RPM your reporting issues.

Hope this helps it's easy to remove the fan from the system and check.

jost6453

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