proper installation on 390 motor mounts

[Caddyrag67]

How do the motor mounts mount to the block side on a 390? do they go on the front side or right behind the front side mounting bosses? In other words does the metal portion of the motor mount mount on the front side of the engine mounting boss or behind the front engine mounting boss? I've looked all over the Internet for a photo of how they're mounted but cannot find anything hopefully one of you can give me some insight.

[Roger Zimmermann]

Do you still have the '58 car? The motor mounts are installed exactly the same way.

[Caddyrag67]

i do but the 365 was pulled out a while ago getting built so i dont have that to go off of...

[Roger Zimmermann]

Unfortunately for you, I restored 3 similar Cadillacs, but I never took pictures from the motor mounts. However, this is a topic which is coming from time to time. By searching in that forum, you may find the needed explanation. I just remember one side is installed after and the other side in front of the boss.

[Jason Edge]

Not sure if it is the same on 65 and later 429's since motor mounts changes and mounting ears changes due to 1964 to 1965 frame change, but for the 1963 390 and 1964 429 the RH passenger side goes on the front of the engine mount tabs and LH driver side goes behind the engine mount tabs as seen below:

[Skwerly62]

Brendon, I will check my 60 today and let you know. All indications are it has never been pulled.

Chris

[Caddyrag67]

thank you will be standing by

[Jay Friedman]

Not sure if it is the same on 65 and later 429's since motor mounts changes and mounting ears changes due to 1964 to 1965 frame change, but for the 1963 390 and 1964 429 the RH passenger side goes on the front of the engine mount tabs and LH driver side goes behind the engine mount tabs as seen below:

I don't know if my '49's 331 motor mount set up is relevant to a 390, but it is the same.  The left mount is behind the tabs on the block and the right mount is in front. 

I wonder if this difference has something to do with the 2 banks of cylinders being slightly offset from one another, with the the left bank (odd-numbered) cylinders slightly in front of the right bank (even-numbered) cylinders.  This is because the left side connecting rods are attached to each journal of the crankshaft in front of the right side connecting rods.

[59-in-pieces]

Brendan,
Here are some pics from the front of a 390 CID Cad block - 1959 or 1960.
They must be offset in order to mount into the frame - both can't be forward nor both behind the flanges.
Not my best effort in taking the pics, but hope they help - click on pic and it gets bigger and blurrier.
Have fun,
Steve B.

[Caddyrag67]

so i got some new motor mounts on the friends 390 and it still is sitting extremly low. you cant even install a belt without pulling the pulley off. this was the whole reason we put new mounts on because we thought the old ones were blown out causing the sag, but thats not the case. what is the cause of this or is this normal? he has a 59 390 in a 57 deville which i know was originally a 365 but it should be the same mounting points? 

[Caddyrag67]

thank you 59-in-pieces.  that cleared that issue up. on the issue with the sag

[Roger Zimmermann]

Do you have the correct mounts? It's not logical that you have to remove the pulley to install a belt. Or do you have the wrong pulley?

[Caddyrag67]

mounts are for a 59 which is same p/n as tge one for the 58 and the pulley is the original off the 59

[J. Gomez]

mounts are for a 59 which is same p/n as tge one for the 58 and the pulley is the original off the 59

Brendan,

The clearance between the frame and pulley would be about ½” at least that is my current measurement on my ’56 365. I would guess the same or similar would be applicable on the later models.

The engine tilts down a bit at the rear once it is mate with the transmission, on my 365 I have about 25 degrees downward angle (did not trust my memory so I just checked) not sure if the later 390s would have the same angle. 

If both old and new MM have the same thickness +/- age and wear and tear on the old, you should be fine. One item, have you check the rear MM on the transmission cross member?

Both are key to keep the correct position on both engine and transmission. The small downward tilt allows for the extra gap between the frame and pulley. Just a thought. 

Good luck..!

[Caddyrag67]

transmission mount was changed too. does anyone know if the crank pulley for a/c cars is the same diameter from 365 to 390?

[Skwerly62]

My apologies for the lateness. Skipped my mind with life gettin in the way!
The pass side goes forward and the drivers side goes aft of the block ears on my 60.

[J. Gomez]

transmission mount was changed too. does anyone know if the crank pulley for a/c cars is the same diameter from 365 to 390?

Brendan,

The MPL shows different part # across each year, my '56 triple pulley measures about 6 1/2" not sure what would others would be.   

Good luck..!

[Carl Schreiber]

All -

Can anyone provide the diameter / thread size / length of the 3 motor mount bolts?  Working on a 57...

Thx!  C

[DeLoreanDMC81]

Just came across this post. I also bought new motor mounts because there was no way to remove the pulley belt, the crankshaft pulley was way too close to the frame. After installing new motor mounts, the crankshaft pulley is still the same distance from the frame. I’m quite annoyed. Because there is absolutely no way to change the belt, there is no room to slide it off.

James