1968 Bad Vibes

[franklinair]

My fresh 302 engine (stock, .030" over) has a vibration @1,100RPM:
New (crate) engine, Edelbrock Performer Intake & 600CFM 4BBL, Pertronix Ignition.

Idle (650RPM, MAP 15") is smooth. Moving throttle up, a stong vibration occurs (not a miss) @ 1,100RPM. Advancing RPM above that point, engine smooths out to normal again.

I'm going to try a new harmonic balancer in place of the original (104,000 miles on it + 40 years) although it appeared OK, and was OK on the old, original 302.

Neil

 

[CougarCJ]

New crate engine......... fresh 302 .030 over? begs the obvious question Neil, which one is it? Is it new, or rebuilt?

Next question, are you using the correct flex plate for your year of engine?
They have a couple of different ones 28oz and 50oz.

What about your firing order? early or modern (351W firing order) Most new cams use the 351w firing order. Is this an E303 cam?

 

[GTCSMustang]

I had a similar problem and it was the flywheel. Took it to a machine shop and had it balanced and the problem went away.

Scott

 

[admin]

Original 40 yr old harmonic balancer is a good place to start, even if it's not your immediate problem. The rubber inner ring gets brittle and the bond to the metal breaks down over time. Even if it looks good the outer ring may still slip on the inner ring, which at the very least will play havoc with your timing.

 

[franklinair]

My terminology re: 'fresh' engine refers to overhauled engines, as opposed to 'new' engines (zero time, zero miles/hours). This comes from my aviation terminology concerning aircraft engines. This engine was built (stock) to 1968 parameters. I agree the flexplate may very well be the culprit, but I thought I'd start with the easiest part to change out (not crazy about pulling the C-4 for access).
Ignition, timing, carburation are all correct. (Checked & rechecked)
I've got a spare harmonic damper, but it's also OLD. I've heard that someone refurbishes these, but don't know who. Most expeditious would be to just buy a new one. If this doesn't cure the problem, then I'll tackle the flexplate. Yuk!

Neil

 

[robert campbell]

Neil.
Damper first, but sadly I predict no joy. I had an experience with a 250 6-cylinder engine. It came with a flex plate but I changed to a 4 speed. Long long story, but wrong balance on the flywheel I got. Motor did exactly as you described. Not bad at idle. Very bad just off idle and then it would smooth out above. Never very good anywhere, but REAL bad just off idle. Motor was about ready to jump out of car.

So at this point the flex plate is unknown? I take it that they supplied you with it? You did not have them rebuild a known engine you had already?

Don’t you just want the person who gave you the wrong part come over and lay under the car while you hand them wrenches! Have ATF drain down their armpit!!! At least pay you for your labor. I got a defective torque converter from TCI recently when I upgraded my 1957 Station Wagon. Weld leaked around the input snout to the crank. Sure, they replaced the part, but nooooooooo, help from them of course.

Gosh, I really hope it is the damper!!!

Rob

 

[franklinair]

Yeah, I'm thinking along the same line. But being inherently lazy, I'll try the easy one first. Which brings me to another question:

1.) What determines the use of the flexplate weight of 28 or 50 oz weight? I've got 2 or 3 flexplates gathering dust over the years.

2.) Should I just take one & have it balanced? (I think they came off of 289's)

3.) Also, isn't there a different tooth count for A/T versus M/T? (Even tho I don't understand the logic for that) The ones I have were all A/T cars.

We're just finishing up an engine installation on a Cessna 182 & installing an engine analyzer system. Then I can get back to the IMPORTANT stuff of working on my cars!

Neil

 

[robert campbell]

Neil,
1963 to 1980, 289/302, C4 applications say 28 oz and 157 tooth. Should not need to be balanced unless you balance the whole engine.

This assumes that you have stock internals to the above years with a matching vibration damper.

Rob

 

[franklinair]

Thanks Rob. Good info. Engine IS stock, so the 28 oz flexplate should be OK.

Neil

 

[teamlo]

Damper Doctor is a good source for a rebuild. Reasonable price and quick turnaround. Just had the one for my J-code 302 redone.

Terry

 

[franklinair]

Just finished installing the NEW harmonic balancer - no joy. I even ran it for a few minutes without the Alternator & P/S pump hooked up, just to eliminate those possibilities.
I've got a brand new flex plate to try, but I'm having a hard time convincing myself that this could be the culprit. I had re-installed the original flex plate when putting things together, and it was fine in the original engine.
Well, razzelfratz,#%&@*^#. Up goes the car, and out comes the tranny, and in with the new flex plate

Neil (knucklebuster)

 

[di81977]

Neil,

Did you change out your torque converter? I still think the flex plate is a good possibility.

 

[robert campbell]

Neil,
Sorry to hear that.... Flex plate change sucks.... Wish I was there to spin a wrench with you. It would be fun if we did it together. Want to fly our in one of your planes and fly me back? Sure Rob, anything for a free flight....

Rob