Boring Cylinders

VMacKenzie

VMacKenzie

New member
I was reading an old TDR magazine with an article on a Cummins (CMEP) plant tour where the author was able to view the engine building process (Issue 25 Page 66). When the block went through the machining process, a torque plate was bolted to the top in place of the head before cylinder boring took place, something commonly done with gas engines. I believe most here understand the purpose of this, but I got to wondering if this is ever done when guys do performance builds on their Cummins. I would think it would pay off on a diesel engine where cylinder pressures are so high and precision is key. Especially for those running 14mm studs and really torquing them down. . .certainly the block will distort differently than stock head bolts torqued to stock values.

Vaughn
 
My cylinders distorted .001" to .003" with the my plate on and torqued up with 14mm studs.

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Some say yes, some say no! I'm on the fence till I see my motor torn down and look at the wear patterns.

Jim
 
The head will only distort the top half of the cylinders where the studs are pulling on the block steel. Guess where the most critical ring seal is needed. I would agree it is getting picky but if I am going to build a motor I want it to last, and the 14s do pull a little harder and distort the block a little more. .002" increase in piston to cylinder clearnace helps keep things happy on a hard driven street truck also.

Scheids does it....
 
I'll agree with you on the .002 extra clearence, not as much longivity but it will sure help with it come to scuffing pistons.

3 inches thick on the plate......I think!

Jim
 
Jim Fulmer said:
I'll agree with you on the .002 extra clearence, not as much longivity but it will sure help with it come to scuffing pistons.

3 inches thick on the plate......I think!

Jim
Click to expand...

Solid 3 inch plate :eek:, its heavy , twice as stock head ?
 
boring

the machine shop that i used had a plate on the block and my girdle with the studs before they line bored the mains and for the cam journels and bored the cylinders so that everything was simulated as assembled.
 
Red Stroke said:
My cylinders distorted .001" to .003" with the my plate on and torqued up with 14mm studs.
Click to expand...

When speaking in terms of tight tolerances that is a lot of distortion.

Why would someone not want to use a torque plate if it was available when reboring? I wonder how often cylinder sealing decreases and blowby/oil usage increases when guys pull a head and reinstall it with studs. . . something that's done all the time.

Anyway thanks for answering my original question, I'd never heard mention of using a torque plate during rebuild operations but figured some were doing it.
 
So you guys are using a torque plate to put a stress on the block just like the head would do completely torqued down? That way when you bore it true it is tru with that stress instead of true without and then getting off when the head is put on and torqued?

Thats pretty cool. I wonder if I could weld two pieces of 1" plate together? lol jk
 
Muddin_dude06 said:
So you guys are using a torque plate to put a stress on the block just like the head would do completely torqued down? That way when you bore it true it is tru with that stress instead of true without and then getting off when the head is put on and torqued?
Click to expand...

Yes. Basically you are simulating the head being torqued down.

The Cummins block, while strong, does flex quite a bit.

This will promote ring seal etc.
 
One demo my teacher liked to do in high school shop class was to take an inside mic and square it up in a cylinder with enough tension to hold itself in place. Then he would squeeze the block with his bare hands, causing the block to distort enough for the mic to fall out.
 
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