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Engine mounts / engine twist

MaineShark

Well-known member
Joined
Sep 21, 2002
Messages
1,326
Location
Rockingham County, NH
Corvette
1979 L82, 1987 Buick Grand National
How much does the engine normall twist in its mounts, when you hammer the gas? How much is the most it ever twists, if things are working right?

How about if a mount breaks? And, are there mounts available which have safety stops, to limit motion if the primary mounting breaks?

Thanks,
Joe
 
Hi Joe,

I don't have the answer, that is, I don't know how much it's supposed to twist (or not). However, I'd also be very interested in hearing the answers to your question.

My (newly installed, rebuilt) engine twists sideways noticeably when I have the hood open and put the pedal to the metal. I've been wondering whether I should be worried about it or not.

The couple of local "experts" I've consulted seem divided on the issue: the guys who've worked mostly with just European and Japanese cars seem to find it ghastly that the engine would move even a millimeter, but the guys who (supposedly) know American cars told me it's perfectly normal.

Regards,
Arto
 
I snapped my motor mount on the left side on my 50th anniversary trip to bowling green (on the 69). Now the left sidepipe header is banging off the frame rail when I so much as breath on the throttle. It is terrible!

I have a new set of high performance poly rubber mounts waiting to go on in place of the GM mounts I had used. I will install these when I do the six speed trans.

Yes...they move around quite a bit.
 
engine mounts / engine twist

I broke the driver's side mount, rapping on my 76 while parked in my basement. I was showing a friend the difference between his 350 and mine, (his 350 early 90's, in a 74 SS Nova), when the support broke loose, I thought it was going to twist completely out of the car before I could get off of it. It would have hit the hood, had it been closed. I replaced it with the stock mount, I am sure the driver side is the one to go first, since it is the one with all the pressure on it. I will change all when the engine is replaced, not soon I hope... but I too will go the way of more HP!! I have very little twist with the mounts now.
 
i put poly heavy duty mounts in with my motor, hardly any movement. they have poly laminated between two steel plates and extra outter stops incase they become delaminated. i would say my motor rocks when blipping the throttle. the carb moves about 1/4". i don't know what it does under load, Brian
 
I had this problem in a former Street/Drag car that was running a small bock with about 400 HP. I put a turn buckle with ends bolted to the frame and the front of the block, inside hole, front of head , on the drivers side to eliminate the twisting. You don't put it tight just snug as engine is supose to move a little. I learned this from having a motor mount break in my old 62 vette. When it broke the engine dropped, the mechanical linkage stuck open and it was a very fast (read scary, curb to curb) ride until I shut the key off. The new poly mounts with the safety ears are suppose to eliminate this but I still would put on the turn buckle if I was drag racing the car. You can do the same with a small piece of chain but the turn buckle is more adjustable and if you use aluminum it can be polished.

Randy:w
 
Steel motor mounts

I had a 68 Camaro that I put a 427 in. The engine had tons of torque. I kept breaking the stock mounts, and a was getting tired of changing them out, so I installed steel motor mounts. That just about shook everything loose in the dash before I pulled the steel mounts out.

The only thing that really worked was I did something similar to what vette-dude described. Remember that this was in 1974, so there were no aftermarket mounts made from poly. I bought heavy duty truck engine mounts. I then welded a chain link to the frame and ran the chain up to the driver's side head and ran a bolt through the last link to the head to snug it down. (I came dangerously close to doing a BUBBA...no duct tape was invloved! ) I had a little slack in the chain, but not much so the motor could still move. When I really stomped on it, the car shook as if there was a solid link from the motor to the frame, but not nearly as bad as the steel motor mounts.

One interesting side effect from this is I noticed the driverside fender wanting to lift higher than before like in a small wheelie. I don't think the tire ever left the ground, but it was still cool!

Bill
 
Engine Torque & Motor Mounts

The amount of engine "flex" (twisting, as it's called here in this thread) depends on how much torque the engine produces & at what RPM. Under a "brake torquing" load, the engine can "flex" quite abit, especailly a high torquing motor. Continued brake torquing can weaken mounts quickly, just as it can if the car "hooks" up real good when "launching" from start & shifting through the gears (manual). That's why a true racer will have "Line-Lock" &/or a "Trans-Brake" to lessen the chance of breaking a mount. Also, as stated in this thread, you can do a number of things to lessen the chances of "ripping" the motor off the frame & outta the engine compartment. One is through solid mounts, & an engine flex plate can greatly help, but the ride can be terrible. What us "poor folk" (namely me) have done in the past is to use the heaviest mounts available & use a couple of short pieces of chain as a safety feature. the chains are slightly loose to allow for the motor to flex under torque & if a mount should break, the chain will act as a safety to prevent the motor from falling out of over flexing (the motor will only go so far before the chain will stop it),

Dave
 
Wow, lots of good info.

Let me be a bit more specific, on the flex/twist question:

I'm trying to determine how much play I need to allow, when connecting things from the motor (and attached accessories) to the chassis of the car. What's the most the motor will move, short of breaking a mount?

(I said "twist" because I'm actually more interested in the rotational motion, since the actual number of inches that any point moves is related to its distance from the center of rotation)

Joe
 
'69 and earlier factory mounts weren't "interlocking" and separated when they failed - the left side of the engine then pulled up, jamming the throttle linkage wide open. This resulted in the biggest safety recall in GM history, to install the cable-and-bracket restrictors on all Chevy V8's until the mounts were redesigned with the "interlock" feature. The currently-available GM and aftermarket interlocking mounts work just fine; they do require slight modification to the lower "V"-shields for the plug wires for clearance.
:beer
 
Joe - I would think that a nice combo here would be to purchase 'poly' mounts such as from "Energy Suspension"....Autozone has them right on the shelf, pretty affordable I thought...and look at attaching a chain tie-down mechanism on the drivers side to limit the travel of the engine "flex".

I have used this combo in my 70' Camaro SS that has a little fire breathing small block and I have had no problems. Oh...I went with the black chain so that no one would see it...didn't want to be too boastful you know:D
 
I have the poly mounts on my 73 from Energy Susp...theyre about $45 bucks each or so but not too bad.....awesome mount.......
 
energy susp. mounts here. Engien hardly moved, I broke the GM mounts, will never use those again.
 

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