Hot Rods 327 Humming Me To Insanity

Am I to understand that the broken pushrod was about 65K miles ago and you have been aware of the vibration for maybe 45K miles? And now this is a problem when it wasn't during the time it took to drive it about 45,000 miles?

 

So you have over 65k miles on a sbc of unknown build, Id be happier than a fox in a hen house on a build like that.

And, you have driven it for the last 45k miles with the "vibration"?
Its a sbc, drive it till it dies.

 

Thank you for the thorough advice! Much appreciated

 

It's been a problem since I began paying enough attention to things. It took 45k for me to finally tuck my tail and come for some advice, and attempt to solve it on my own in the interim

 

I wouldn't say entirely unknown, as it was a build done by my father. But over the past 26 years, he can't clear the fog enough to remember exactly what went in it. I put a lot of faith in this motor, it's already taken me well over 100k all over the country. I suppose I'm becoming more concerned as the miles rack up, and the work I've done over the last 45k hasn't helped any. I've received a bunch of good advice so far, so I have faith I'll come to some sort of a solution before she goes sky high

 

Being somewhat of a 327 nerd I'm thinking the motor is telling you
"hey man, I've given it my all and I need a little love".

 

I once encountered a 283 that had a quite a strange sound coming from it.

It otherwise ran just fine, and went everywhere.

It sounded like it was coming from the entire top-end, but it turned out to not be under the valve covers. It was under the manifold.

The baffle/oil separator had broken free from the retaining tab, and it was vibrating against it.

Might not be it, but if you are already in there, check it.

 

At 100k it's probably ready for a tear down

 

Could it be in the exhaust? Could you unhook the exhaust after the headers/manifolds, tie it up so it won't drag, then roll it outside and revitup, or even drive it? You probably won't be able to hear any vibrations, but maybe you and the girlfriend can feel them (or not feel them).

 

The Chevrolet 400 small block uses an external balance configuration, unlike all other SBCs which are internally balanced.

I'm bringing that up because a 400sb flywheel and harmonic balancer will bolt onto a 327 and give you problems a bit like you describe, although I wouldn't expect it to be "smooth" at any RPM. Maybe dad grabbed any ol balancer from the parts pile and ***umed it would work? I'd take a look.

 

So you replaced the rocker arm and the pushrod? Is the new pushrod long slot ( like a corvette) or not. If it needs long slot rockers and you replaced it with a short slot rocker arm that could be a problem. If you are running molly pushrods and one stock pushrods that could make the valve train behave differently in that one valve. If you replace the rocker with a stock rocker and the other are longer ratio (1.5:1 V 1.6:1 for example) that could also cause you a problem. This is ***uming that the broken pushrod is the problem to start with.

 

I only read the original post so I apologize if you figured it out.
My first thought is the harmonic balancer. Check it thoroughly for any slop or cracks, etc. Good luck

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Why you go abreakin ma heart?

 

It's been nearly identical between the prior axle dump, and the now bumper dump. But, stranger things have happened

 

I see no weights, nor any cutouts. I haven't retrieved a PN from either, so I guess in all reality I can't be 100% certain. She's pretty damn smooth down low, but once on the highway, different story.

 

I'm NOT an engine builder...so this is more a question to more knowledgeable people than a suggestion to you...but would the change to forged pistons require a rebalance of the rotating bits?
Just wondering if this might be a case of needing one but not getting it...and now, as the engine wears and gets looser, the inbalance is getting more pronounced?

Just a dumb thought...

 

The balance doesn't change as it wears, it will change if some component changes weight ie a piston skirt broke.

 

Makes sense...
Does changing from cast to forged usually require a rebalance though?

 

A cylinder pressure imbalance i.e. From Wear will cause noticable roughness in the engine. And it might be just fine until the RPMs Come up.

Not to be confused with a dead cylinder.

 

At least the new pistons. But why stop there at that point and not supply all the rotating parts?

 

I had a ever so slightly bent valve in a 440 that idled and ran perfect below 2500, above that it ran goofy and vibrated.

I could drive it around, just above that it ran weird. It had a bent pushrod too that I replaced but when replacing it didn't fix my problem I dug deeper.

Not sure that's your problem, just a thought.


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I have a similar problem with my 301 SBC. I have found my pulleys not to be running true. My harmonic comes in a bit earlier than yours. It appears better with the belt off and you can see the bottom pulley (flat 283 type) is running slightly eccentric, and the top pulley has a miss stamped V causing the belt to move up and down in said V. As I drive faster I can still just feel it but it smooth's out some what. JW