Give 'em 3' of rope...

["Graydon D. Stuckey" <graydon@apollo.gmi.edu>]

On Wed, 2 Oct 1996, Bob D'Amato wrote:

> 
> Well I have a couple of issues on this one, but most of all:
> 	A) Graydon has NEVER been wrong

Hahahahahaha, ROTFL!!!

> OK, rope, I personally would not do that because an average person with a 
> breaker bar or torque wrench can produce more torque than the engine can. 
> Dont beleive me? Put your manual tranny in gear, stomp on the brakes, and 
> have someone tighten that nut. You wont get very far without slipping 
> your clutch. Now if you can exert more pressure than the engine can, what 
> are you doing to the rods or the bearings, or even the head and bolts? 

Bob,  suppose your engine is rated for 150 ft-lb.  That means that the 
force on the piston has to be enough to produce about 30 ft-lb (approx - 
I am not going into a p****** match over this) AT THE CRANK.  Due to 
losses in the piston, rod, bearing, cams, etc, the energy at the 
combustion chamber is probably roughly 4 times what actually gets out the 
crank.  If we assume the 4X number to be close, then you've actually got 
120 "ft-lb" at teh piston.  I _think_ this is still a little bit low, but 
even if we leave it there, you are right, the 400 ft-lb (is that really 
the spec on that bolt?) is still a little more than twice the 
average operating stress in the piston.  However, the peaks in the piston 
can be 5 - 10 times higher than the average at the peak of combustion, 
and these are akin to shock loads.  Since the breaker bar on the crank 
pulley is a very gentle, smooth load, I think that it is still less 
dangerous to the head/piston/bearings/etc.

> The other reason is what if a small peice of the rope were to get behind 
> one of the open valves, and as you push your piston up....(You get the 
> picture)

	A small piece of nylon rope will loose every time compared to a
hard steel valve.  Besides, the way you end up feeding the rope in there,
the rope will be pushed up onto the bottom of the vaves.  Highly unlikely
to get under the valves.  If you are really worried about that, then make
sure you are on the compression stroke so that the valves are closed. 
Also a piece of nylon rope will burn up VERY quickly under combustion
temperatures. 

> Also... Even if it is the same amount of cylinder pressure you are 
> exerting as when the cylinder normally fires, it doesnt mean its the same 
> thing. The rope will not give even pressure to the head and walls like 
> normal combustion. You will have 'pressure hot spots'.

I don't think so because the rope compresses into a big ball that nearly 
fills the entire combustion chamber.   I think you get pretty even 
coverage over the top of the piston.

> (Give it a running start). You should easily exert the required 225 
> lb/ft. Besides, it wont loosen, thats the way the engine normally turns. 
> (Refer to letter A above)

Aha!  Is the spec 225 ft-lb?  Then I really see no trouble with the rope 
idea.

Later, ---------------------------------------------------------- 
Graydon D. Stuckey 	'85 Mazda RX7 GS, no toys 
graydon@apollo.gmi.edu 	'86 Audi 5000 CS Turbo Quattro, has toys
Flint, Michigan USA	'89 Thunderbird SC, lotsa toys