Engine Vibration

[jhorton3]

I fired up Midgie about two weeks ago and discovered a strange engine vibration. It doesn't happen at idle, but around 2500-2900 RPM, then it disappears as RPMs increase. Could this be an issue with the crankshaft damper pulley, or should I be looking at something else?

 

[David_Doan]

I know this is an ancient post, but I have the same issue. Any words of wisdom?

 

[Billm]

It is highly unlikely (but still possible) that the pulley damper is causing a vibration that you could easily detect while driving (unless it is almost ready to fall apart). It is far more likely that it is the flywheel incorrectly located or more likely that it is the fan belt too loose and vibrating at a given RPM or the water pump about to die.
BillM

 

[David_Doan]

Thanks Bill, I will check out the water pump this weekend.

 

[Guest]

Is it running evenly on all cylinders when this happens?

 

[David_Doan]

As far as I know, yes. Compression is good on all cylinders (165,170,170,175), and everything in the ignition has been, checked/replaced.

 

[JPSmit]

could this be caused by a bad motor mount?

 

[jlaird]

About all I can think of JP.

Check fan belt, fan, pulleys and such as well.

 

[Guest]

could this be caused by a bad motor mount?

Yes and when mine runs lean it'll vibrate.

 

[David_Doan]

Troubleshooting the vibration got sidetracked by having to replace the fuel pump - converted to electric. I did check the water pump and generator, both seem to be OK. While I was in there I replaced the 20 yo belt.

The motor mounts are all snug. I'm starting to think it might be misfire related. While idling, It did pull each plug wire one at a time. At first the back two had less effect than the front two. I tweaked the idle screw on the back carb and now pulling any wire has the same effect. When I have more time, I need to go through the whole carb balance procedure again.

I want to repeat the spark plug wire test at speed running on 3 cylinders. If the issue is related to one cylinder, when that one is disconnected, there should be less change than the others. (got this tip at spritespot)

While driving around tonight, it seemed like the vibration got worse when the engine was completely warmed up with the water temp at about 180 degrees.

I still need to dig into checking the 1/4 marks - I'll have to get the manual out to see what they are.

This is not a huge problem, the car is very drivable. I'm just trying to learn about what's normal and not normal for a 50's technology engine. I wish I had another sprite to drive for comparison.

Thanks,

David

 

[jlaird]

50's engines are happy little engines. Should be smooth as silk and quickly responsive.