79 F350 460 4x2 C6

so the truck has had a really rough idle, the kind that shakes the cab and bounces the mirrors. When I'm at a stop, at idle, I can see the corner of the hood rise and fall and see the side mirror bounce up and down. When the RPMs are raised, it smooths out.

This doesn't seem to be a miss, an idle mixture setting or ignition timing, as it smooths right out at 1000 rpm, whether in park, neutral or drive

i popped the hood and started looking at belts. The a/c belt was fine, as were the idlers. The power steering looked good, as did the alternator. Then I looked down...the main pulley (crankshaft pulley) was wobbling like 1/8"!

i figured it's likely the harmonic balancer, and started tearing into the front end. I got the fan and belts out of the way, and then remembered I could take video. Duh. So I fired it up, and the main pulley looked good


i continued on, breaking loose the bolts that hold the pulley to the balancer. I don't think I lost count going around, as I can count to four, but it seems like one was already loose. And it's possible I lost count. But if one was loose, that'd certainly explain a lot


after I pulled the pulley, I pulled the balancer. It doesn't look awful, but the elastomer is forty years old...



I think I'll just replace the balancer and make sure the pulley has all four bolts tight

As always, I look forward to suggestions and advice. Thanks!

 

Hey papa bear. Can you post a longer video? It was awful short I really couldn't see to much movement. What kind of balancer are you planning on getting?

 

Thanks for looking-I appreciate the eyeballs!

I forgot to roll video when all the belts were in place. But the wobble was very apparent at that time.

I didn't want to run the engine very long without the belts/water pump/fan hooked up. So I only rolled a few seconds, but didn't see the wobble

Now everything is apart, and it's really hard to see anything off just the snout. It seems straight, and the truck doesn't rock like it was doing.

I think one bolt was loose, and the pulley was flexing, but didn't see any sign of fatigue when I pulled it off. But I think I'll replace the balancer. Summit has the stock style for under $60

If you like, I can get another video of the snout tomorrow afternoon, but you really can't tell anything from there...at least I couldn't!

 

No need to roll another video. For what I saw the snout did look true. The rubber does look deteriorated. I wonder if one loose bolt can cause a wobble if all the others are tight? Can't wait to see the truck all fixed

 

That thing is lunched. Are the timing marks shifted? Even so, it ain't doing any vibration absorbing. Though I don't think it would make the idle vibration problems you describe. Maybe.

They absorb torsional vibration, the heavy weight leads and lags under/off load and prevents resonance (bad) at certain RPM. The crankshaft itself can twist up 2°, so the heavy, elastomeric mounted weight soaks that up, through the elastomeric/weight. Without it, a crank can crack, or even break. The rubber bonding dries out from heat and ozone becomes stiff and cracks, so no vibration damping. Eventually the outer ring may slip off completely. Every now and then they'll end up on the side of the road, with a detour through the radiator &c.

 

Maybe if the bolt is sticking out enough, it could throw off the balance?

If the engine is cold, you can safely run it for a minute or two without coolant circulating.

 

A vibration could have loosened the bolt, not a wives tale. The cause of the vibration would be 180* away from the loose bolt.

 

I too just bought one too for my 460. I bought the Powerbond which does look like stock for $65 I think. I bought it because I put their better one on my 445 and it seemed nice and made in Australia if I recall. Little did I know since then Dayco bought them and now made in China. I guess I shouldn't be surprised.

 

Thanks guys!

I'm going to order a new balancer today. Summit seems to have the best price, and they have inventory ready-to-ship:

 

TWO different harmonic balancers used in 1979 460, one is used with internally balanced engine, one is used with externally balanced engine.

D4VZ-6316-A .. Harmonic Balancer-Use with internal balance with block casting number: D1VE-6015-AB or A1B or A2B / Obsolete

1974/78 460; Some 1979 460.
-----------------------------------
D9TZ-6316-B .. Harmonic Balancer-Use with external balance with block casting number: D9TE-6015-AB / Obsolete

Some 1979 460.

The flexplate is also specific to internal or external balance.

 

Went to the UPS store and picked up my care package from Summit. The Dorman harmonic balancer is actually spec'd for 80-95, but appears identical to the one I took off. I installed it today, and it seems fine.

I also bought a timing tape. The scale is a hair off, but I centered it at 14 degrees BTDC. Next time I break out the timing light, I'll take another looksie.

 

I recently replaced mine and bought a new timing light. Tried to buy a timing tape and most of the stores don't carry them anymore I guess. Tried looking for one online and couldn't get my size, which I thought was odd for a 351m. So i found some that you can just print off and tape on but I keep hoping I find a nicer one than that.

 

$5 at Summit. Available in various sizes. Clean the balancer with brake parts cleaner to degrease before applying

 

Did it solve your vibration issue?

 

i don't think so. The vibration was sporadic. It didn't do it on the first run after replacement, but it's doing it again-but not as bad

the vacuum is 16 at a reasonable idle-I'll check it for vacuum leaks again tomorrow

I'm open to other ideas...