The 2000 L67 Motor Mount Mod - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-10-2004, 12:29 AM   #1
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Default The 2000 L67 Motor Mount Mod

Well, I've ordered the parts I need to complete this relatively simple modification.

After some careful analysis of the structure, suspension, subframe and the 3 other engine mounts, I truly believe that no real harm can happen. If anything, it will be safer by not relying on the oil filled internal shock absorber from failing and coming apart. This new mount will isolate the vibration well enough.....vibration will not be transmitted through the stock rubber subframe bushings....in fact the subframe will be taking some of the torque so there should be a significant improvement in reaction forces. Most importantly a lot less engine rock with subsequent flexing of intake, exhaust, hoses and wiring.

That stock rubber isolator is huge and must weight 5 lbs. It measures 3 5/8" f/f but it is easily compressed by hand and if you grab the bolt studs on either end you can bend one, the piston shock absorber end. When the engine is resting on the mount it compressed about 1/4" at rest. The motor is balanced with supports very well. One on each side, one and the rear and the big one up front that is the damper in this classic engineering example of a mass, spring, damper system. This system is used in our cars to give them that "you can't feel it shifting" comfort and cushion the torque transfer during abrupt changes in thrust in either direction.
The braking forces are dampened by the subframe bushings, so they will be more than adequate to withstand the acceleration forces.



The mounting bracket for the engine that attaches to the front mount is massive cast steel that weighs almost 4 lbs as well. I'm not going to change that one, it'* a very good strong design.
I am going to make up a spacer disc out of aluminum structural bar stock 3" diameter, following the basic outline that rround gave me. Kudos to Rod.
On either end will sandwich a 3/4" urethane waffer.
Keep you posted but work is busy so I won't be doing much until the weekend.
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Old 02-10-2004, 01:51 AM   #2
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I pressed down on mine yesterday to see if I could compress it, squash. The jelly roll has got to go. your going to replace the mount too? That is a big chunk of iron, how are you going to lighten it?
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Old 02-11-2004, 02:10 AM   #3
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Sorry you must have misunderstood. I am not going to replace the iron mount, just the blubber damper.
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Old 02-11-2004, 07:40 PM   #4
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thanks 2000 Silver Bullet for taking the picture.
i forgot how big and ugly that thing was.
ROD
p.*. don't forget a pic of your new mount.
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Old 02-13-2004, 12:29 AM   #5
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Just a test fit while I'm waiting for the fabrication of an aluminum spacer to fit between the twin 3/4" urethane isolators.
Was able to reuse the original locknut with the new bolt. The bolt cost me $10. at the hardware store and I used high strength washers.


The motor is still propped up on blocks, so the nut isn't tight.
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Old 02-13-2004, 09:26 PM   #6
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Made the aluminum center today at work, 3"round 2 5/8" high with a 17/32" center hole. I ordered the urathane bushings from redwood plastics, hope to have them next week.
SilverBullet, are going with 2 nut top and bottom or just using a nylock nut?
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Old 02-13-2004, 10:17 PM   #7
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Your center aluminum wafer should only be 1 1/2" high if you are using two 3/4" urethane cushions on either end. That includes using a 1/8" washer on top and bottom.
I used an M12 metric bolt so was able to reuse the original all metal locknut, so I saved the nylock nut. Make sure you use a 180 mm long bolt. There will be plenty of room for double nutting if you wish.
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Old 02-14-2004, 10:28 PM   #8
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Got the car off the jack stands with the mount tightened up.
Tryed rocking the car back and forth with it in park and the hood open.
No noticeable engine movement. No mushy rocking motion.
It'* rock solid.

I just may have to make a Bonzai run tonight with my open headers......
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Old 02-14-2004, 11:03 PM   #9
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Quote:
Originally Posted by 2000SilverBullet
Got the car off the jack stands with the mount tightened up.
Tryed rocking the car back and forth with it in park and the hood open.
No noticeable engine movement. No mushy rocking motion.
It'* rock solid.

I just may have to make a Bonzai run tonight with my open headers......
Go for it buddy, its not really as loud as you think, and with out the back preasure you cant really step in to it so no worries with the neighbors.
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Old 02-15-2004, 12:58 AM   #10
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Get some vids of that!!! I wanna hear.
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