Technical Thoughts on decreasing idle vibration?

So, I'm always one to poll many people to make a decision. One the one hand the idle is amazing, but on the practical side I'm shacking AC connections apart, throwing hood bolts and god only knows what else. Steering linkage? Here are two videos that I did of what my 1938 panel looks like at idle. This completely smooths out at about 1000 rpm. Most indications are this is the cam in the engine. The engine is basically hard mounted at the moment, so I've been considering the options to try and reduce some of this vibration. I compare it to riding a feisty stallion. Sometimes your in the mood for that, but there are times when something a little milder is called for. I also don't want to completely reduce the horsepower output. Would definitely appreciate some discussion.





Cheers,
One Shaking Panel

 

"The engine is basically hard mounted at the moment..."
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Could you explain that a little more?
No rubber at all at the stock locations?

 

Sure. No rubber. The person I bought it from said it was hard mounted, but I understand this to be a hard plastic/poly style mount after looking at it a little closer. All of the vibration of the motor is definitely transferred to the body. I'm wondering if anyone has ever contrasted these hard style mounts with more standard rubber ones. To be clear there I don't think there is much 'stock' in regards to the engine and mount. It's a custom frame and the mounts place the engine in somewhat of an inconvenient place in regards to oil changes. Oil filter and front tire suspension support are so close you can't even slip a standard oil filter wrench onto the oil filter, there just isn't enough clearance.

 

Thats your vibration.

 

I totally agree. HRP

 

Luckily, yes! Keep your eye on that headlight. It's shaking like crazy and so is the fender. I'm surprised I haven't lost the headlight. I have to tighten the fender bolts every time I drive it through the city. Make me feel better though and post a video of yours. Loctite is my friend, though it didn't hold the AC fittings.

 

Your video too please. If I wasn't dropping parts and shaking the side mirrors off I would be a little less concerned. I also keep loosening the power steering fittings to the point that I can't stop the leaks. I tighten one and then there is another one.

 

Simple, raise the idle rpm to 1050, you should be fine.

Mike

 

Sounds simple, except trying to hold this car back at a 1050 rpm idle is difficult. I have power assist brakes, but you still have to put a LOT of pressure on the brake to keep the car from moving from standstill at an rpm of 1050. I know, I'm asking for the world. I can be like that.

 

`Is there some reason you can't put rubber biscuits in?

 

I know they can sometimes cause clearance issues by lifting the engine, but I believe I could get some in. Questions is, has anyone compared the difference? I've had some local people say that it won't do that much. It is definitely one of the items I'm considering as a first step, though.

 

number one...Is your motor balanced????
and why did the previous builder hard mount it??
the video does not sound like a truck,sounds more like a threshing machine..

 

What Tim said ^^^^

 

You seem more inclined to accept the opinion of those who say "it won't make any/much difference" over those who recommend rubber mounts. Considering that rubber has been a standard component of engine and trans mounts for decades, and got considerably softer by design over the years, I tend to think the evidence is indisputable.

What I will agree with is, replacing your engine/trans mounts with factory style mounts as used on the era of your engine and trans will NOT solve ALL your vibration problems. I'll go further and say that a significant portion of your vibration issues, when in motion, are very likely suspension and body mount related. Cars of that era used minimal vibration isolation compared to vehicles designed in the succeeding decades. "NVH" .....Noise, Vibration and Harshness.....have been the focus of millions of dollars of engineering research in modern automobiles.

That doesn't make your problem hopeless, in my opinion, but I think it does mean you have to be willing to do those things that DO have a positive effect if you want a noticeable improvement.

Ray

 

You need a higher stall converter so you can raise the idle speed.

 

If your engine has enough guts to need to idle at 1000 rpm you will rip stock rubber mounts in half.

 

Never asked him, but I understand the rubber mount can absorb a little of the initial accelerating power of the motor. Don't know how much, to be honest, just something I read somewhere. So, I figured that was why.

 

Ray, Thank you for your response. I actually don't have any issue when the car is in motion. She cruises smoothly once you get up to 1000 rpm. It's only below that rpm that she shakes. Someone else was asking if it was out of balance. If it was out of balance the vibration should get worse, bot disappear at speed. The truck really loves cruising right around 55. She'll do 75 without complaint, but as you say without much in the way of sound insulation the engine noise does start to increase a bit. As to believing one or the other, I'm trying to remain impartial. If someone told me they had a hard mounted motor with a similar idle and switched to rubber with a great improvement I'd certainly listen. Swade41 brings another point. Would a rubber mount survive the beating for very long?

 

maybe it is my computer but that thing sounds like it is running like crap.
did you ever put a vacuum gage on it? even when it revs it sounds like it is missing.

 

I agree that you probably need a higher stall converter.... something you could try is increasing the initial timing , then reset the curb idle ... if this smooths out the idle , then you'll have to limit the mech advance so your total timing is correct , but this might tame the rough idle a bit...
dave

 

AFA using rubber mounts , if you use a biscuit style mount w/a thru bolt , you won't be ripping anything apart..
dave

 

Heres another thing to look at other than needing proper engine and trans mounts .With putting a load on the engine the engine tends to lean from the torque ,with you bringing it up to 1050 it could be laying over [even w/solid mounts]enough to make the headers or anything else on the engine be relieved of touching the frame ,firewall,steering shaft and even the trans hump.gotta get it on a lift and throw a good eyeball on everything.

 

Sounds to me like it is badly out of tune.

If it smooths out with higher RPM it is not a balance issue. If it were out of balance it would get worse with higher RPM not better.

The engine is not firing smoothly at idle. Check compression and oil pressure to diagnose engine condition, 1 or more cylinders not firing correctly will throw it off. If it checks out ok then it is most likely a tuning issue.

Install rubber motor mounts and have the engine tuned by a good tuneup man. Since it is not stock you may need to find someone familiar with hot rod engines who can tune it from first principles without looking anything up in a book.

 

I have read a couple of story's of guys replacing the hard or urethane mounts with quality rubber and getting a lot less vibrations. I think also the biscuit mounts are not as good as the factory side mounts. I see you have a finished truck so I would do the rubber biscuits first before redoing the frame mounts. Also don't forget the tranny mount.

 

Have you checked the harmonic balancer and flywheel? Early and late motors took different weight balancer

 

Shelby Super Snakes and Dodge Hellcats use rubber mounts so I don't think you should worry about tearing them apart. What you have is a Hot Rod built by someone that bolted a lot of parts together without regard to being able to service it later.
The responders have given you all the fixes for the problem, it won't be easy or very cheap to fix them.

 

I'm not a ford expert, but isn't there 3 different weight combinations on those? You need the right crank, damper, flexplate combination.

And then there are 2 firing orders for small Fords? Is that right and how do you know what combination you have there?

We run SOLID mounted race engines and don't have those issues.
It's not a mount issue.


I see the problem now, A Delco Alternator on a Ford Engine. Culture Clash!!!

 

Hi Rusty,

I've actually had a hot rod engine builder retune it for me. I had him switch the tranny as well and take a good look under the whole thing. He managed to lower the idle without making the shaking any worse, but his diagnosis was the big cam causing all of that. She never puts out much in the way of vacuum, but I'm told it is what you would expect given the duration on the cam, about 230.

I greatly appreciate all of the discussion! At the end of the month I've got an appointment with another hot rod builder in Virginia to look at switching the engine mounts. I do tend to get lots of opinions before I make a decision.

Someone also mentioned missing, I would think this would also get worse at load. I admit I've not pulled ever plug. I just haven't had time, but when mechanics in the area have stood next to it no one mentioned it sounded as if it was missing. I also thought that this would get worse at speed as opposed to disappearing.

 

You need rubber motor mounts for sure and possibly a milder cam. Do you have the specs of the engine and cam? Ask the guy who tuned it what he suggests. I'm surprised you didn't ask his advice in the first place.

 

If, as you have said, someone told you it was cam related and you don't like it, change the cam!
For the record, I don't think it is the cam.