Centering an engine on its mounts

[stephen low]

Seems such a harmless topic but have been battling the last couple of days to re-centre the windsor in Slowy on the engine mounts.

Had to replace my mounts after the F1 GP inspection way back when and ever since then the engine has sat further to the passenger side.

The movement was enough to have one of the exhaust flanges capable of rubbing on the chassis. There is bare metal attesting to this scraping happening.

This I think has also caused some further slight mis-alignment down the exhaust system. This mis-alignment has also pushed the twin pipes running under the diff / lower arm pivot to the driver's side enough to interfere and hit the lower arm under road shock.

Have been sufferings bangs and belts from the car on trips and want to fix all this.

So back to the engine mounts, is there a good way or a trick to get engine centralisation?

Know the mounts are correct, the same McKay part as originally used, but these have a slotted mount and wonder if I'd bolted the motor in high originally.

Or am I just not swearing enough at the beast lol!!!

Thoughts team??

[Tommy]

If the pad on the chassis is unchanged and the engine mounts are the same dimensions as the originals, I can only suggest one thing. Keep in mind that the change in position of the engine may be due to it being higher/lower, left/right, fore/aft, rotated along the axis of the car or some combination of all. Perhaps you could enlarge one or more mounting holes slightly to allow the engine to be shifted slightly. Keep in mind that a small change near the center of the engine can produce a much larger movement farther away at the end of the exhaust.

[stephen low]

Thanks Tommy

That both thoughts about enlarging the slot and the off-set translation affect to the rear had gone through the grey matter.

Hence why I think if I can better re-centralise the engine, the rear exhaust issue will also correct itself.

But the original mounts unmodified did have the engine central so am struggling to understand why and what has happened at the change over to the same but new mounts.

[eschaider]

Think about how much your engine offset is and then think about how much your pinion offset is.


Ed

[C5GTO]

Not sure what type mounts your Cobra has but I've heard of a situation where engine mounts were swapped side for side on a Cobra and it changed the engine position. You might want to look to see if both engine mounts have the same offset. If not, you might be able to swap them and have the engine re-centered.

[stephen low]

Thanks guys

Believe the mounts are symmetrical but will be fully removing to first check this and then try relocation via full refitting of engine mounts.

[eschaider]

Stephen,

You might want to take a step back before you begin your engine centering efforts and consider the following;

OEM rear axles use a pinion offset that differs by manufacturer and axle. Ford 9" rear ends use a 1 5/16" pinion offset from center, Ford 8.8" rear ends use a 9/16” offset from center and GM likes a ½" offset from center. The OEM manufacturers mount the engines in their chassis off center by the same amount the pinion is offset from the axle center.

If you use a stick axle the offset is baked in, so to speak. If you use an IRS center like the 8.8" T-Bird IRS, then you can easily center the pinion, although you will use different length left and right half shafts.

If you choose not to center your pinion you will need to offset the engine by an amount equal to the pinion offset for the rear axle you have chosen to use. If you do not then you will have your u-joints offset (and probably misaligned) in both the horizontal and vertical planes.

Most guys struggle with proper pinion angle positioning for just the vertical plane. If you center your engine without centering your pinion you will additionally be tasked with simultaneously aligning the pinion in the horizontal plane. The horizontal plane is every bit as demanding as the vertical plane because the transmission tail shaft mount is fixed and typically immovable.

My suggestion to you is determine your in car pinion offset (if any) and position your engine to match it. Alternatively, you can center your engine and cut your axle tubes to center the pinion in the chassis. If you go this route you might find you need to replace one axle tube to get the rear wheels where you want them.

Of course, you can ignore the horizontal plane alignment like some folks ignore the vertical plane alignment. The result is a driveshaft vibration that, depending upon the mismatch, varies from mild to impressive.



Ed

[xb-60]

Slowy, can you post a picture of the mounts so we know what they look like?
Cheers
Glen

[stephen low]

Ed

This is a refit from an existing set up, so very limited latitude, and frankly no need for this consideration, as 30,000 kms travel has proved the alignment is ok.

It is just a small wiggle in fit up needed, ala about 10mm extra clearance to the drivers side, that is the RHS of the car for us in Oz.

In fact I'm just trying to get the engine back to the location it was originally set up in anyway, for more clearance around the header flange that is rubbing on the PS against the chassis.

Glen

Can take a photo, if a more major strip down and refit this weekend doesn't achieve the expected result. But if you google Mckay part A1140 for a ford fairlane, you'll see they have a slotted chassis bolt location.

I might have to open up this slot to force the engine further away from the chassis, but think this effect will only achieve a limited change in location.

[stephen low]

Success over the weekend despite a 2 steps forward 3 back approach in what I'm correcting.

So fully removed both mounts, discovered they are symmetric offset matching, so doesn't matter which side they mount.

On refit I worked the problem side first (PS) to get maximum header clearance within the fitment limitations, loosely fitted up the DS side, then locked up the PS mount then the DS.

This resulted in about a 10mm clearance which is far more gap than I had, so I believe this will fix this strike issue.

But part of the work also involved replacement of a damaged sump. I wasn't sure if I could get the old sump out with the mounts on. I proved I couldn't so had to take the mounts off again.

However followed through on this work with the engine raised and managed to remove the old sump, clean up, re-gasket and fit up the replacement sump successfully.

Second attachment of the mounts in the same sequence got the same result as above, so happy boy all round.

Last part of my work is to fit up a sandwich plate to feed my oil cooler and 90 degree filter attachment fitting on the block and I'll have knocked off the major work I wanted to complete.

Then it'll be just the need to start refitting all the bits I'd taken off before a test run up and drive.