VIBRATION

[GEOFF289]

Hi everyone,

Looking for some help sorting out a vibration in my 66 coupe. It was there when I bought a car a little while ago but I wasn't too fussed as I bought the car for the excellent body and numerous new parts and plan some major driveline changes anyway. Those changes now have to wait a year or so due to some other developments so I've been trying to sort out this vibration.

The car has the original or replacement 289 that apart from a Pertronix and dual exhaust (after the standard manifolds) it's standard 66 C code. C4 behind it. It does have after market aircon fitted.

The vibration is not what I'd call severe and only appears from about 1,000 revs to maybe 1,700 or so. It's not there at idle, which is nice and smooth and disappears once it has a little bit of speed up. While the engine's a bit tired, at idle and above about 1,700 it runs smoothly and pulls as strongly as such a basic little motor should. Things I think can be ruled out are:

- uni joints and tailshaft as the vibe is there when the car is stationery and in park
- engine and trans mounts which are new and torqued correctly
- a misfire situation as there is no stumble during this vibration phase of the rev range
- aircon compressor, I wondered if the pulley was out of alignment even though it looked OK but removing the belt didn't change anything.

Yesterday I pulled the inspection plate off the front of the bellhousing to check the convertor bolts. These turned out to be nice and tight. However, I discovered the nice shiny new flexplate has a dirty big weight welded to it and seems to be a 50 oz job rather than the 28 oz one that should be there. I haven't been able to figure out how to insert pictures here but it looks the same as images of 50 oz plates I googled, and way different to an old 28 oz one I have lying around.

If the harmonic balancer isn't also 50 oz maybe this is the answer. However, I can't see how such a mismatch would lead to a vibration only in a pretty narrow rev range. I would have thought this would cause a problem right across the rev range, get worse as revs rise and be way more severe than my problem. Is this right?

If such a mismatch is the problem, is it possible to determine the imbalance of the harmonic balancer visually? If so, what am I looking for?

I'm thinking that replacing the balancer would be easier than replacing the flexplate. I've done the latter before and it's a pain and I'm pretty sure on this car I would have to cut the exhaust system.

Finally, while I know that describing it as not too severe isn't real precise, what might be the implications of just continuing to drive it for another year or so? - no more than 90 days and only a few thousand k's in total at most.

Grateful for any advice and suggestions. Thanks in anticipation.

[flatchat]

What condition is the harmonic balancer ?
Otherwise it sounds more like tune problem  -- like a lean out between idle jets and main jets change over ??

[GEOFF289]

Thanks for the response flatchat. Visually the balancer looks fine but I'm no expert. Nothing obviously wrong like bits of rubber hanging out or anything. I'd be pretty happy if the vibration can just be tuned out of it. I'll see what others have to suggest but will look into that idea.

[peter9231]

The weights on the balancer and drive plate are to externally balance the engine.
This is due to the compact design of the engine hence there is insufficient weight available on the crankshaft to balance the engine internally.
If you are running mismatched drive plate and balancer you will have this problem.
The same will occur if you have 50 ounce balancing components on a 28 ounce engine.
Crankshafts are very strong when all is in sync with balance and vibration dampers.
You need to correct this issue or the torsional vibration may well break the crankshaft.
Remember if you get a crankshaft balanced it is to the gram, yours may well be 20 ounces out of balance.
Peter.

[GEOFF289]

Thanks. I understand that but it makes me think this isn't the problem. As you say, it would be 22 oz out and I would have thought the vibration would be quite violent and present right across the rev range rather than just in the narrow rev range where I'm experiencing it.

[peter9231]

Harmonic vibration is just that a harmonic.
It may well occur at that rpm.
More than likely it will smooth out and then come back at twice that rpm
And continue this cycle.
I am not trying to be smart here,just trying to help you avoid engine damage.
Peter.

[shaunp]

Most early engines 289s had 3 bolt pulleys on the on the front, so if this is the case to balancer is likely 28oz. If the vibe is in the engine I'll bet the flex plate is wrong or balancer very common mistake.

[GEOFF289]

Thanks peter9231. I do appreciate you sharing your knowledge and think I understand. Shaunp, the balancer is a 3 bolt one so it's starting to look a lot like the problem is the flexplate. Also that if that's 50 oz then replacing the balancer with a 50 oz one isn't necessarily a good idea even if it is easier.

Think I might just try to figure out how to bring forward my crate motor and T5 swap instead.

Happy to have any other input from anyone.

[peter9231]

Geoff,
All good.
You engine will be a 28 ounce imbalance engine.
You need to make sure you have a 28 ounce Harmonic balancer and flex plate.
You can't change the harmonic balancer to 50 ounce to suit the flex plate or you will still be out of balance. (the 289 is a 28 ounce imbalance engine)
The five litre roller cam engines are 50 ounce imbalance.
Peter.

[lukep6470]

I ran a 28oz flexplate on a 50oz balanced motor (For a very short time)  and the vibration only showed up in a narrow range as well.

[shaunp]

I'd say the box is coming out and new flex plate.

[GEOFF289]

Always a good day when you learn something. Thanks to everyone. Looks like it is the plate and the box will have to come out.

[66FBK]

Geoff, a common problem even for the guys that have been around these motor for a while. Had the same problem also. Mine was a 4 bolt (50 oz harmonic balancer) on an early 28 oz 302 Windsor. Had vibration around 1500 and after 2500prpm.  Around 1985 Ford changes the 302 Windsor from a 28 oz to 50 oz balance and also the firing order changed to the 351W. This and a roller cam and a few other little changes made a nicer little motor that Ford ran right up to the AU Falcon in 2002. If you have a nice new shinny flex plate than it might be the later 50oz number. They don't convieniently stamp these things them to show you either. A flex plate change is not a huge exercise but will make a heap of difference to the running of your motor.

Dave 

[GEOFF289]

Thanks 66 FBK. I had another look under the car last night and compared the weight on the plate with the old 28 oz one I have from the old car and the one on the car definitely has a bigger weight. What I've learned from this post is that my assumption that such a mismatch would cause a constant vibration throughout the rev range is wrong. As I said above, always good to learn something.

As noted, I've changed a flexplate before so comfortable I can do it, was just hoping to avoid it but seems clear I can't.

Thanks again to everyone.

[GEOFF289]

Happy camper here!

Today I completed the process of replacing the flexplate with the right 28 oz one, fired the old girl up for the first time in a month and she's as smooth as silk right across the rev range.

I managed to do the job without cutting the exhaust which makes me even happier. Just disconnected the pipes at the manifolds and used a long lump of wood to lever and hold the pipes down a couple of inches. This still wouldn't allow the trans to come right out but was enough to move it back and down enough to get the plate off and the new one on, including getting the torque wrench in there.

This also meant I could avoid the messy business of dropping the pan off the trans to completely drain it. They've always leaked on me after this in the past. With the front wheels on ramps and the back on jack stands I removed the driveshaft then lowered the back to drain as much fluid as would come out the back, then jacked it back up level, drained the converter and then kept the trans level as I moved it back and down a bit. I lost a little bit from the coolant lines and dipstick but only a spoonful each. Plugged the dipstick and speedo cable holes while I was moving the trans (Clark Rubber is your friend) and of course the extension housing where the driveshaft goes.

As noted, vibration gone! I have a small new problem with the NSS now needing adjustment after disturbing the shift linkage but will sort that out tomorrow morning and then go and drive it somewhere as the forecast is fine.

Thanks to all who responded to my original post. As usual this forum has been a godsend to rank amateurs like me.

[mojocoops]

Good work!

[peter9231]

Glad you got it sorted
Peter.