Leyland P76 Owners 2007

Technical

Why do engines always break mounts and lift the left side of the motor in "low" gear.

Emails taken froom the 215V8@yahoogroups.com

March 2007

-----Original Message-----

From: rinaldo181
I've pondered this myself.
I've seen the girdles that the HP boys sell and it's and entertaining thought that theses might be unnecessary contingent on the proper mounting of the engine itself.
If the issue is torsion then it also appears that the torsion is mainly applied to the drive line.
The engine is part of the drive line and the twisting or torsion is being applied to the engine block.
Consider this scenario as the expression :
Dropping the clutch off the line at the drag strip why is the left wheel always off the pavement first and what dynamics lift that side.
Where is the motor mount attached to the motor and how is that torsion affecting the or twisting the block.
Now Thinking about the earlier small block Chevy and their mounting config (4 point). It would be interesting to mount the engine at the rear (ridged mount maybe using a beefed up damper plate) of the block with a centre rubber mount in the front and the soft rubber mount on the trans.
During max torque situations (lowest gear) the engine would not be subjected to the twist that is normally applied to the side and through the length of the block.
I would be applied across the back of the block along the mounting parameters of the bell housing applying all the twist to the rear of the block and not "THROUGH" the block.
Remember the transfer of power "through" the block is enough to twist the frame and lift the front end and left side of the car.
Also remember the lower the gear in the transmission the more torque applied to the block i.e. the drive line twist.
I've tried to express this when the group gets off onto the subject (girdles etc) but I've never received and feed back.
My theory may be a straw-man but I thing the way these engines are mounted might have some relevance to the distortion / twisting phenomenon.
Does it take a degree to figure it out? The Almanac is the only paper that hangs on my wall, well there's the Hooter's babes, and a hub cap or two etc. Ya'll know what I mean.
Randy / Doc Holliday

Reply

By the way, the maximum torque generated by the engine does not change
depending what gear you are in.
The transmission simply trades off the amount of force generated for the distance travelled.
1st gear generates the maximum force but is doesn't travel very far per engine revolution.
High gear works the other way around...
Mike
San Diego

Reply

The "lower ratio" acts as a torque multiplier and does just that, it twists the frames violently especially when the inertia built in the engine is transferred to the output shaft when you drop the clutch.
This generates tremendous torque on the engine block where the mounts are located until all the inertia is expended.
If the transmission output shaft is 4 to 1 ratio (less the engine speed) then there is 4 times the torque (theoretically) being applied to the motor mounts, drive shaft etc vs when the transmission is in direct drive or high gear.
Why do engines always break and lift the left side of the motor in "low" gear.
Try holding on to a 1/2 hose reduction gear drill when you bind a bit vs a 1/2 horse direct drive drill.
The difference is wrist breaking.
That's why an engine will only typically bounce or raise in low gear.
The counter torque is being multiplied enough to break the motor mount or twist the engine out of its normal position.
Always happens off the line, typically.
BTW if you drop the clutch in reverse gear you would break the right side motor mount because the torque direction is reversed.
Randy
--- In 215V8@yahoogroups. com, "Mike Peissner"
Randy,
You are correct about the transmission being a multiplier but look closer at what I said. "...the maximum torque generated by the ENGINE..." that is before it goes through the "multiplier".
As for sidestepping the clutch, that exercise adds the energy stored in the flywheel, dampener and whirling crankshaft. Very powerful but it only lasts for a split-second. After that, you will accelerate based on the
output of the engine.
Mike

Reply

4 X 1 ratio 250 ft lbs = 1000 ft lbs torque.
Now for a "split second" all you have to do is "twist" the block from the external mounts and
you've thrown the alignment of the crank bore of the block out.
If it is 1000 ft lbs of torque just under the acceleration how much would it be dumping the clutch.
The line between the rear transmission mount and the side motor (toward the front of the engine) mount is being twisted or yanked and torsion.
There is no torsion being applied through the drive line including the crank till the clutch is dumped. You must look at the relationship of external forces being applied to THE BLOCK where the motor mount is bolted on the block toward the front of the engine and the mount on the transmission.
The linear proximity of the front and rear mount is actually twisting the block like wringing out a wash rag.
This would have the effect of throwing the line bore off and if only for a "split second" every time this happens eventually would self destruct the engine.
The trick is to have the mounts repositioned on the back of the engine (where the bell-housing meets the transmission) where there is no twisting going on "Through" the side axis of the block externally.
Meaning the energy is being placed at the rear of or at the point where the crank exits the block.
There was and old 4 point mounting on the Chevy's that excluded the mount on the rear of the transmission (there was rear transmission mount) I'm not saying this is the problem that cause the misalighnment of distortion of the line bore integrity. I'm saying there are tremendous pressures being exerted through those lines of mount points through those proximal linear mounting points. I'm asking if anybody has investigated the possibility the these forces being
generated externally through the block might not be part of the culprit. ie has anyone mounted the engine in the 4 point style as a trial to see if this would stop the distortion?
"There is a principle which is a bar against all information, which is proof against all arguments and which cannot fail to keep a man in everlasting ignorance-that principle is contempt prior to investigation. " or The proof is in the pudding.
Thanks
Randy
Last updated
Mar, 2007
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