F engine at 3,000 rpm

[brider]

Just TODAY I started my '71 Pig up and drove it out of it's winter resting spot, and let it idle until warm. Runs just like it always has, kind of stumbly at idle, but the vac guage is always practically motionless at 21 in. Hg. Revs up and down smoothly, good oil pressure.

But today I revved it up and held it at 3k just to hear what it sounds like at 70 mph (33" tires, 4.11 axles), and it was VIBRATING significantly. Kind of scared me.

Didn't mind revving that high, but the vibrating started in around 2.8k, and I didn't go any higher than 3k with no load.

Does this sound like a normal 4-main bearing F engine? I've read that the 2F's are much happier at higher revs, has mine always vibrated like that, but I just never noticed it on the road?

 

[Mace]

I have spun many F motors to 3K and above. Pretty common actually.

Was the gear shifter vibrating as well?
(you were in neutral right??)

 

[ocdbeetle]

2800 is the sweet spot on my F......It really loves that on the highway.....although it only equals about 51 mph ....LOL............3k is ok too - just loud and seems like a tight rubber band......I could probably use some larger tires......

 

[MtnTrucker]

Just because it was vibrating above 2800 doesn't mean it's about to chunk a rod or anything unless you are also hearing bad knocking noises. It could be just a bad miss, could be timing, bad spark plug/wire or a carb issue. Check the easy stuff first.

 

[brider]

Yeah, I know they can rev happily to 3k and beyond, it's just the vibrating I'm wondering about.

Can anybody rev their F in the driveway up to 3k and report back? Smooth, or kind of vibrate-y?

 

[MoCoNative]

Mine is kind of vibratey, my 84 FJ-60 is kind of vibratey over 3, and if you run my T100 up to 4-5K it too is wound a little tight. Just a function of not having any load on the engine.

I would check plugs and such, give her a little tuneup, that will probably help with the vibration, sounds like it may have been a tad excessive in the vibration department for you to notice, may have a slight miss, especially since it has been sitting, could be old gas too.

 

[35inchoverdrive]

Are all your engine mounts in good shape? Otherwise, it's probably related to your 'stumbly' idle. Are your valves adjusted? How's the timing?

 

[pappy]

How old is the gas in the tank?

 

[brider]

All good suggestions!

The gas is 8-10 months "old", not really what I'd consider bad. I have NOT adjusted the valves in a long time, and I'm thinkin' that is contributing to it. But I also think the stock ignition (distributor and coil) is suspect, too.

But I've been ignoring a lot of these issues because the rig runs so well otherwise. Great vacuum, starts easily, etc. Just never revved it to 3k with no load before.

So I'll put this on the back burner for NOW, I've got a more pressing electrical issue, see my next topic...

 

[srgould41]

You might try a bottle of carb cleaner too. I bet there are lots of gum deposits in the jets and such. Gas does nasty things when sitting so long.

 

[mooker82]

I would think after reading your other post abou the electrical problems that you have something wrong with the fuel system or carb, since you said you smelled gas. Also gas sitting for 8 months is a long time unless a a fuel stabilizer was used.

 

[Weedhopper]

How old is the gas in the tank?

I was going to say that too. Drive it and get it nice and hot. It's been sleeping.

 

[65swb45]

F engine. 3k vibration.

FIRST things I would check would be the fan, fan bolts, fan spacer [if any] and the water pump. Where's that mushroom cloud emoticon?

If those all look good, chalk it up to poor balance in the motor. The first F motor I took into a machine shop HORRIFIED the owner! He said the difference between the lightest and heaviest connecting rod was 40 grams! It had a bad vibration by 2000 rpm.

Best

Mark A.

 

[brider]

F engine. 3k vibration.

FIRST things I would check would be the fan, fan bolts, fan spacer [if any] and the water pump. Where's that mushroom cloud emoticon?

If those all look good, chalk it up to poor balance in the motor. The first F motor I took into a machine shop HORRIFIED the owner! He said the difference between the lightest and heaviest connecting rod was 40 grams! It had a bad vibration by 2000 rpm.

Best

Mark A.

Funny you should mention the fan and water pump-the plot thickens! Sorry for not mentioning this history to you guys first!

Last year my big mod was swapping out the crank pulley/balancer for a 2-row (ended up being a 3-row, with the big A/C pulley) so I could install PS. Also swapped in a new WP with correct offset pulley. Fan is stock steel.

Kind of unsure how a WP swap and fan could cause imbalance, they're pretty much stock items and centered by installation as best they can be.

But the crank pulley-

I noticed a pronounced excess runout of the big A/C pulley, but there's NO WAY the balancer itself could be wobbling on the end of the crank. We all know how tight that keyed fit is.

Could the balancer itself (got it from a guy here on MUD) be defective? I think I know the answer to that...

 

[mooker82]

Funny you should mention the fan and water pump-the plot thickens! Sorry for not mentioning this history to you guys first!

Last year my big mod was swapping out the crank pulley/balancer for a 2-row (ended up being a 3-row, with the big A/C pulley) so I could install PS. Also swapped in a new WP with correct offset pulley. Fan is stock steel.

Kind of unsure how a WP swap and fan could cause imbalance, they're pretty much stock items and centered by installation as best they can be.

But the crank pulley-

I noticed a pronounced excess runout of the big A/C pulley, but there's NO WAY the balancer itself could be wobbling on the end of the crank. We all know how tight that keyed fit is.

Could the balancer itself (got it from a guy here on MUD) be defective? I think I know the answer to that...

Do yourself a favor and replace the metal fan. They have been known to basically explode.

 

[45Kevin]

Isn't the balancer balanced to a particular engine?

Although I have successfully changed balancers with no issues.