Engine Alignment

[RRoller123]

Question for those of you who have changed out engines in these cars:

Do you consider engine alignment variability on the mounts, or just overlook it? It would seem that most if not all of us overlook it, although the alignment along the longitudinal axis of the car would be of importance in helping elimination of vibration, off centerline torque forces, etc. Remember that old experiment in grade school, where one sits on a rotating chair and holds a spinning bicycle wheel? Those forces.

If alignment is considered, I wonder what would be a practical method of measuring the actual alignment along the longitudinal axis? The engine mounts, bolted hard onto the cross member, resolve the Pitch and Roll variability, but Yaw is still a variable when installing one of these engines.

Saying that the U Joints take out any misalignment is true, but that is not the point. The point is to make sure that the resultant rotational forces align along the longitudinal axis of the car.

Quite curious about this.

Pete

[18Fiatsandcounting]

Do you consider engine alignment variability on the mounts, or just overlook it?

Pete, I've always just overlooked it. Well, not exactly "overlooked" as I did think about this, but I didn't take any steps to address it. I've always put the engine and transmission back in, left the motor mount nuts loose for the time being, then secured the rear transmission mount. I rocked the engine back and forth as much as I could by hand, perhaps using a jack to lift the engine ever-so-slightly by the oilpan to let it find its "equilibrium", and then tightened the motor mounts.

-Bryan

[Odoyle]

+1 to Brian's assessment and procedure. When I put the engine + trans back in car I did have to readjust the alignment with the hoist, just to get things visually lined up.

[RRoller123]

That's what I figured, align it visually as best one can to the driveshaft support bearing, etc. I wonder what the forces actually are? There's a lot of mass spinning at say 5000 rpm in that engine and transmission. And although the torque arm is not that large, the speed and mass are pretty big, when one considers the effect that a low mass bicycle wheel spinning at very low rpm has, when sitting on that rotating chair.

Maybe swing/rotate the engine full Yaw one way, then back the other, and tighten it in what seems like the middle. This assumes that the mounting point geometry of the engine mount holes is correct. I suppose that is a reasonable assumption if the car hasn't been hit.

Curious. But not enough to run the calculations.

[18Fiatsandcounting]

I think a visual check is all that can hope for, and I think we have to assume that the engine mounts are where they should be.

I've bought a few spiders where the engine mounts were totally sheered in half, and the cars ran just fine. I only discovered that the mounts were broken when I raised the engine and the rubber part separated in two. On the other hand, given the state of some of these cars when I got them, engine mounts were low on my list of concerns...

-Bryan

[RRoller123]

I suppose doing it visually by the position of the back of the transmission would be best, as it is the farthest from the 2 mounting points, and most sensitive to Yaw.

So many curiosities, and now, so much time.

[18Fiatsandcounting]

So many curiosities, and now, so much time.

So I guess I shouldn't mention the potential of the front cylinders leaning out under heavy acceleration relative to the rear cylinders, due to the inertia of the fuel being sucked into the engine, and how one would (should) compensate for this?"

Ooops, too late... Sorry...

-Bryan

[dinghyguy]

Bryan,

Clearly you need to compensate for the thermal expansion of the exhaust side of the block relative to the intake side rotating the engine counterclockwise. That is why the exhaust is braced to the tranny, to compensate. Installing light aftermarket air cleaners also helps reduce the mass on the intake side to compensate. Look under common problems in your fiat manual for tolerances in Radians

cheers
dinghyguy (even later than Bryan)

[18Fiatsandcounting]

Clearly you need to compensate for the thermal expansion of the exhaust side of the block relative to the intake side rotating the engine counterclockwise. That is why the exhaust is braced to the tranny, to compensate. Installing light aftermarket air cleaners also helps reduce the mass on the intake side to compensate. Look under common problems in your fiat manual for tolerances in Radians

D'oh! I had forgotten this! I am so not worthy! Perhaps we should also compensate for the reduced gravitational attraction on the fuel when the car is high up on its springs (like cresting a hill, so gravity would be slightly less), or when the springs are fully compressed (such as bottoming out, when the car is closer to the ground)...

-Bryan

[18Fiatsandcounting]

Sorry, Pete (RRoller), Dinghyguy and I got carried away. You raised a good question in the original post, and I don't really have a good answer on this. Maybe someone else does.

-Bryan (He who never takes Fiats or himself too seriously, but cannot compete with Dinghyguy in the too small garage)

[RRoller123]

LOL, no offense taken, this is an actual thing, and we see it in motorcycles all the time. It is just more noticeable there because the mass is lower. And just to answer each of your concerns , it matters not as long as the engine is aligned along the longitudinal axis, then none of those nano-forces pushes the car to the side.

[RRoller123]

Here is a good study on the problem, written around diesel engines, but of course it applies to gas engines as well. Interesting engineering study on the topic.

http://mech-engineer.blogspot.com/2009/ ... nment.html

I think the rule they present about each end of drive shafts being the same angle off axis, if there is any, is the key one. (Figure 6) Any variance here is certain to induce vibration. Still not sure how the hell anyone would measure it though!

[RRoller123]

Clearly you need to compensate for the thermal expansion of the exhaust side of the block relative to the intake side rotating the engine counterclockwise. That is why the exhaust is braced to the tranny, to compensate. Installing light aftermarket air cleaners also helps reduce the mass on the intake side to compensate. Look under common problems in your fiat manual for tolerances in Radians

D'oh! I had forgotten this! I am so not worthy! Perhaps we should also compensate for the reduced gravitational attraction on the fuel when the car is high up on its springs (like cresting a hill, so gravity would be slightly less), or when the springs are fully compressed (such as bottoming out, when the car is closer to the ground)...

-Bryan

Apparently this is also a real thing with Caterpillar Diesel engine installations:

"5- Mounting
The engine and the driven equipment should be mounted so that any necessary shimming is applied to the driven equipment. The centerline of the engine crankshaft should be lower than the centerline of the driven equipment by approximately 0.0065 in (0.165mm) to allow for thermal expansion of the engine. The value 0.0065 in(0.165mm)allowed for thermal expansion is for the engine only. If it is anticipated that thermal expansion will also affect the driven equipment centerline to mounting plane distance, that value must be subtracted from the engine thermal expansion value in order to establish the total engine centerline to driven equipment centerline distance. When measuring this value, the TIR will be 0.013in plus the droop as estab lished in Step 1."

[tima01864]

I tink the pillow block would compendsate for any misalianment? The engine mounts on mine had sagged at least one inch off center and stayed that way indicating to me misalignment when bolted to the crossmember?

[RRoller123]

With misalignment in the prop shaft, the pillow block would induce vibration, not reduce it. Unless perfectly aligned with the prop shaft. There would be a natural harmonic frequency at which vibration would be noticed, and this is exactly what we see with older cars that have worn engine mounts. Unexplained drive line vibrations at certain speeds or rpms. Engine sags, and an angle is induced that mis-aligns the engine to the longitudinal axis, and strains the U-Joints, Guibo, Pillow Block, etc.

Yours was so worn that it was at least an inch off nominal! I bet that the car smooths out a great deal when the new ones go in!

Here is another interesting video on the topic. In this video, they refer to the droop caused by a bad engine mount as "Soft Foot". Makes sense, quite descriptive!

https://www.youtube.com/watch?v=iY5e9a_K7W8

I guess we could just go back to answering the same questions that have been both asked answered for decades, over and over. There is obvious great value in that, don't get me wrong, but I find this stuff quite interesting!