Motor Mount Questions

[JohnGunn]

Ever since I bought my 1994 Aspire about a year ago, I noticed that the car would buck rather severely when starting in 1st gear. Since I was able to avoid the bucking by careful use of the clutch and I had much more pressing problems with the car, I decided to put off doing anything about it.

The problem has gotten worse and I now want to address it. The clutch does not slip and I think the bucking comes from a rhythmic back and forth rotation of the engine on the motor mounts.

When I pry up on the motor mount brackets, the back one hardly moves at all. But, while using the same large screwdriver, the front mount is so easy to lift up that it appears to be bearing hardly any of the weight of the engine. I think this is where the movement is coming from. I can see that the front mount is not torn, though I suspect its firmness has been compromised by all the bucking. My feeling is that the engine would stabilize if more of its weight was resting on the front support.

Here is my first question:

My assumption is that when the engine is lowered into the engine bay it is supported at only three places, the three through bolts of the three motor mounts. Is that correct?

Next question:

Without the exhaust being connected to the catalytic converter, what is the relative percentage of weight supported by the front and back supports?

Question three:

When the down pipe is connected to the cat is it possible for the weight of the exhaust system to act as a lever to lift the front of the engine and cause all weight to be transferred to the back support?

Number four:

I've read about "normalizing" the mounts and the exhaust system by loosening all the attaching nuts and bolts and rocking the engine back and forth, slipping the clutch in first and reverse with the brakes on. Would this be an appropriate action for me to take?

I have never had a car that caused me to give any thought to its motor mounts, so all this is new to me. Any suggestions would be appreciated.

[walth]

it seems you have a bad mount.

1. yes, 3 bolts

2. I'd say... 40 right and like 30/30 trans?

3. the exhaust has like 10 rubber mounts that hold it up pretty tightly to the car. maybe if you undid all of them, yes it would act as a lever. probably not a good idea tho (jk)

4. no idea

[htchbck]

Here is my first question:

My assumption is that when the engine is lowered into the engine bay it is supported at only three places, the three through bolts of the three motor mounts. Is that correct?

Yes.

Next question:

Without the exhaust being connected to the catalytic converter, what is the relative percentage of weight supported by the front and back supports?

The same as it is with the exhaust connected.

Question three:

When the down pipe is connected to the cat is it possible for the weight of the exhaust system to act as a lever to lift the front of the engine and cause all weight to be transferred to the back support?

Don't do that.

Number four:

I've read about "normalizing" the mounts and the exhaust system by loosening all the attaching nuts and bolts and rocking the engine back and forth, slipping the clutch in first and reverse with the brakes on. Would this be an appropriate action for me to take?

Sure... if you're just that bored...

[georgeb]

The appropriate action for you to take would be to buy a new front mount.

[JohnGunn]

Overnight I thought of another question that may relate to this problem.

What is the function of the springs that are under the two nuts that attach the inlet pipe to the front of the catalytic converter? It appears to be part of a system that allows the exhaust system to be attached to the engine even when they do not perfectly line up. Is that correct?

Thanks for your assistance. I've seen these springs before, but never had to figure out what they were doing.

[htchbck]

They allow for flexing between the engine and exhaust. If you've ever seen one that has had the cat removed by a shop and a solid piece welded up instead of something that can flex, after a while, it will start to twist the downpipe. Like my old roommate's Aspire. Lol.

[walth]

there is a soft metal (I think) gasket that sits in the flange there. the springs maximize pressure on the sealing of the exhaust. Mine wasn't sealing too well (the springs may be tired) so I put like 4 washers under each spring to make it even better.

htchbck... yeah I thought it was a bit of an angle. I have aspire manifold ... festy downtube ... then cat back is aspire. the exhaust doesn't really like it. lol.

[htchbck]

You can get the braided type joint like the EGTs have at the parts store in a couple different diameters.

[JohnGunn]

98% Corrected

Normalizing the position of the engine on its mounts achieved a 98% improvement in the bucking that the engine used to do. Now there is only a slight hint of the old behavior which can easily be dealt with by the speed with which the clutch is allowed to engage.

For anyone with this problem I would suggest you try the following procedure before replacing any mounts.

The procedure allows the engine to adjust its weight on the mounts so that there will be no abnormal stress on them when the car is standing still on level ground.

This is accomplished by loosening all nuts and bolts, that attach the engine to the mounts and the catalytic converter, a turn or two (more on the catalytic converter nuts since they have springs that need more turns to be loosened enough) and then gently driving the car around for a while, being careful not to stress the position of the engine with any hard acceleration. At the end, before tightening the the nuts and bolts, move the car forward and backwards a couple of times using the clutch very softly.

There are 4 bolts and 12 nuts that are used in connecting the engine to other parts of the car.

1. Right engine mount bracket nuts (3).
2. Right engine mount through bolt nut (1).
3. Crossmember mounting bolts (4).
4. Front and rear mount nuts (2 each).
5. Front and rear engine mount through bolt nuts (1 each).
6. Catalytic converter input flange nuts (2).

To make it possible to tighten the nuts and bolts to the correct torque, I chose to clean all threads involved. I first used an 18 inch long 1/2 inch breaker bar to loosen all nuts and bolts. Several required a couple days of PB Blaster treatment, so take your time.

Once all were broken loose. I removed all nuts and the four crossmember bolts (Caution: remove and work on only one crossmember bolt at a time. Otherwise the engine will drop down. Three are enough to hold it in place while working on the forth.), cleaned the threads with a wire brush and applied anti seize compound.

Doing this made a dramatic improvement, say 95%. The other 3% improvement came when I removed and replaced the down pipe while trying to drop my oil pan, proving that the exhaust system can place stress on the engine.

You'll probably have to use jack stands to get to the rear mount, and I removed the air filter box to ease access to the right mount through bolt.

It took some time, but the pay off was well worth it.

Good luck.

[htchbck]

Normalizing the position of the engine on its mounts achieved a 98% improvement in the bucking that the engine used to do.

I am curious to know the scientific method by which you deduced the 95% and 3% improvement, respectively? I have never been able to achieve that level of accuracy. Usually I end up with an estimate of percentage with an error of +/-5%. I would like to better measure my improvements in the future, do you have an suggestions for improving my improvisations of improvement?

BTW, if your exhaust system is placing strain on the engine... something is wrong.

[Christ]

The exhaust actually does partially restrict engine movement. Pretty obvious when you have a solid mounted exhaust, because you can actually feel it in the car. It does have enough stiffness with the OE rubber mounts to cause the engine to jack sideways slightly if the right side mount is bad, the twisting action misaligns the axles under load, often causing vibration.

Generally, if it's gotten to this point, you'd just replace all the engine/trans mounts.

"Normalizing" is something I've never bothered with, because the only time it seems like it would apply is after things have gone off kilter to begin with.

[Bert]

If the motor mounts are really in bad shape, or you regularly hot-rod the car, I would imagine the exhaust connections at either the manifold or the cat are going to break continually. I would love to find correct-diameter and short braided flex pipe to address this since fractured pipes and leaking joints are a routine annoyance for me.

[nitrofarm]

If the motor mounts are really in bad shape, or you regularly hot-rod the car, I would imagine the exhaust connections at either the manifold or the cat are going to break continually. I would love to find correct-diameter and short braided flex pipe to address this since fractured pipes and leaking joints are a routine annoyance for me.

Pics seven & eight show an adapter I made for a 1.75" flex pipe. I just used a piece of roll bar tubing that I had laying around it fit perefect. Flex pipe was $18.00on eBay shipped. I dont like the Doughnut/slipe joint connections.

http://www.fordfestiva.com/forums/showthread.php?t=39776

http://www.ebay.com/itm/160642224483?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

[nitrofarm]

Normalizing the position of the engine on its mounts achieved a 98% improvement in the bucking that the engine used to do. Now there is only a slight hint of the old behavior which can easily be dealt with by the speed with which the clutch is allowed to engage.

John the best way to do this is with a engine hoist.Loosen ALL attach points,but don't remove the nuts.(Having all the weight of the eng/trans on the hoist) The goal is to get the motor/trans "Squared up" in relationship with chassis. The engine mount on the RH side gives lots of room for this. Once the engine is where you want it.Lower it back down.And start by tightening these 3 nuts first.
I'm glad you where able to get rid of your "Noise" but I have a sneaky suspicion its going to come back with a vengeance. Start saving for a couple new trans mounts. If they are as old as the car,they are very old.The rubber just gets old & weak after many years.This gets worse if they get oil soaked. The back square one gets oil soaked the worse.(But maybe your car didnt have any oil leaks) The just get saggy like an old Hag. Good Luck & Happy Holidays.

[JohnGunn]

do you have an suggestions for improving my improvisations of improvement?

This has little to do with science, and it goes without saying that there is a healthy margin of error in the estimates given here. But, since you seem interested, here is the basis of my approach.

I start with a knowledge, from repeated experience, of the magnitude of the problem. In this case the motor would violently jump around, causing the whole car to act like a bucking horse. That was a very reliable and consistent effect, which over time I could well remember.

If I did something to try and improve the problem and it did not change anything, I would call that 0% improvement. If what I did made the problem disappear, I would call that 100% improvement. If my actions resulted in the bucking motion of the car to be about half as bad as it had been, I would call that 50% improvement.

My first efforts at normalizing the stresses on the engine while not a 100% improvement were very close to it. I could still feel the start of a slight jumping depending on how fast I released the clutch pedal. I gave that a number close to 100%, 95%.

That would have been my final estimate, except that afterwards I had to remove and replace the exhaust down pipe in the process of getting my oil pan off. I wasn't expecting any effect on the amount of movement my engine experienced in moving the car in 1st gear. But when I got it back together and drove it, I noticed a small but significant improvement. It was still not 100%, but more that half way of the distance between 95% and 100%. Thus the figure 98%.

BTW, if your exhaust system is placing strain on the engine... something is wrong.

Agreed. And what I did in trying to normalize forces on the engine went a long way toward correcting that something.