Engine Vibration - Flywheel Balance?

[stu in wichita]

Okay, I need help again. After the Ranchero's maiden voyage, I noticed a vibration at about 2000 rpm. I'm sure it was always there, but I had never noticed it until I drove it. The engine is a 1964 170, all stock with about 50k miles. I bought it used, but knew the owner - he changed his Comet to a V8. It seems like a great motor - starts easily, runs nice, no smoke, no noise.

At idle, there's no perceptible vibration - it runs like the proverbial sewing machine. As rpm increases, the vibration becomes noticeable. It's definitely not a misfire. it's pretty harsh, like something out-of-balance or bent. Revving the engine in neutral, it vibrates worse the faster it revs. Same thing if I rev it In gear with the clutch in. That kind of eliminates the transmission or dirveline. Now I need to figure out which end of the engine it's coming from.

My plan is to first remove the drive belts to eliminate the driven components (bent water pump shaft or damaged fan maybe). If it still vibrates, I guess I have to move to the other end of the engine. Not sure what to look for, but maybe something loose or damaged on the pressure plate. The flywheel and PP were used parts, but looked good when I installed them.

A few questions before I start taking things apart:

• 1. Is there more than one 8-1/2" recessed flywheel for these engines? If so, maybe I have the wrong one? The bolt pattern only allows it to mount one way. Are these flywheels "neutral balanced" or what?
  
  2 Is it possible that the crankshaft balancer could be the culprit? The timing marks line up close, so even if it has slipped, could it be that far off?
  
  3 Any other ideas on how to identify what's shaking?

Thanks in advance for any help.
-Stu

 

[JackFish]

I guess I'd start with the balancer.
Take a white marker and draw a line across it's face.
Give the engine a few hard revs.
If it's slipping the line will separate.

I had one that wobbled in and out but didn't really slip.

 

[MustangSix]

Make sure you didn't lose a PP bolt. One of those could be enough to cause that kind of vibration.

 

[CobraSix]

Yes, all 8.5" flywheels should be neutral balance.

Also be sure to check your motor mounts, but as others, I suspect something around your flywheel. Do you know how old the balancer is?

But if the engine was running well prior to your install, I have to agree that something is up with with the PP, Flywheel, or clutch disc.

 

[stu in wichita]

Yeah, that makes sense to me. I pulled the drive belts and the vibration is still there, so that eliminates bent water pump shaft, fan, etc. It's hard to imagine that the balancer could cause it. I've seen balancers split completely apart without creating any noticeable vibration. On an internally balanced engine, the the damper is neutral balanced just like the flywheel. In other words, there isn't any eccentric weight designed into the balancer, so even when they slip, there usually isn't a lot of vibration.

The best description I can give is that it seems like a higher frequency vibration than a misfire would cause. My thinking is that a misfire would pulse every two revolutions, where an out-of-balance condition would pulse every revolution. Another puzzling factor is that the clutch is pretty nice and smooth - no chatter or added vibration when I engage it.

Looks like I'll be pulling the tranny to see what I can find. I'm betting that it won't be anything obvious. I'll bite the bullet and get a new pressure plate (about $200, OUCH!) and get the flywheel surfaced and balanced with the PP.

Meanwhile, thanks for the ideas. With your help, I'll stay on it until it's fixed.
-Stu

 

[MustangSix]

If its a misfire you should be able to see that on a spark plug. Or you can touch a damp rag to each exhaust port. The bad one won't sizzle.

 

[CobraSix]

You can also try pulling each wire at idle and see how the engine responds. If the engine doesn't change much when you pull the wire, you've likely found the culprit cylinder to narrow the search down to.

I do agree, I don't see the balancer doing that much, but if it's managed to slip a few degrees, it can make a difference.

Its just you've eliminated the obvious answers already.