Milling for compression

-
RustyRatRod said:
It does not change valve train geometry one iota, but you might need shorter pushrods.
Click to expand...
I don't understand why you say this, Rusty. It would definitely change the angle at which the pushrods operate; that should be obvious. However, I am not saying it would change the pushrod angle too much for proper operation.
 
Bill Crowell said:
I don't understand why you say this, Rusty. It would definitely change the angle at which the pushrods operate; that should be obvious. However, I am not saying it would change the pushrod angle too much for proper operation.
Click to expand...
LOL!! Then the valvtrain geometry must be f**kin' DESTROYED on the originally designed 170 slanty, since the deck height is OVER 1.6" SHORTER than the 225, the pushrods
are nearly perfectly straight-on in every direction on a slanty. Please don't post uninformed speculations, You're doing the OP a disservice, this is how people end up chasing
mice in their heads.............................
 
Killer6 said:
LOL!! Then the valvtrain geometry must be f**kin' DESTROYED on the originally designed 170 slanty, since the deck height is OVER 1.6" SHORTER than the 225, the pushrods
are nearly perfectly straight-on in every direction on a slanty. Please don't post uninformed speculations, You're doing the OP a disservice, this is how people end up chasing
mice in their heads.............................
Click to expand...
OK, your point is well taken. Sorry.
 
With the pistons that far down in the cyl, I'm thinking you got a set of the "low compression" pistons, I have seen advertised, online. Measure the distance from the top of the piston to the pin hole, and post it. I have the numbers out in the shop.
PS: The slant six can take milling the head .100 and the block .100, without problems, some have gone even more. There is no way a slant will have quench issues, with a flat top piston, unless the piston comes out the top of the block.
 
Charrlie_S said:
With the pistons that far down in the cyl, I'm thinking you got a set of the "low compression" pistons, I have seen advertised, online. Measure the distance from the top of the piston to the pin hole, and post it. I have the numbers out in the shop.
PS: The slant six can take milling the head .100 and the block .100, without problems, some have gone even more. There is no way a slant will have quench issues, with a flat top piston, unless the piston comes out the top of the block.
Click to expand...

Thank you all for the info! Will post some measurements when I get back to the garage. It would seem that if milling the block .100 and the head .100 is fine, then I should be safe to do 0.050 on the head to get my numbers to where I'd like them.
 
If You're going to run any kind of real cam lift, You will definitely want shorter pushrods, and You will want to make sure the head bolts will not bottom before coming up to
torque. Grade 8 washers will handle that........
 
Killer6 said:
If You're going to run any kind of real cam lift, You will definitely want shorter pushrods, and You will want to make sure the head bolts will not bottom before coming up to
torque. Grade 8 washers will handle that........
Click to expand...

Agree about the head bolt, and washers. Disagree about the pushrods. Every thing else staying the same, except for the cam, you might need longer pushrods, with a big cam. The nose of a cam stays at the same hight from the center of the "stick". To gain lift the base circle gets smaller, which locates the lifter lower.
When cutting the deck and/or head, then shorter pushrods might be needed. As with anything else MEASURE,MEASURE,MEASURE.

One of my engines, has .125 cut from the head, and has a .520 lift cam, and uses stock length pushrods. The head mill, and smaller base circle of the cam, cancel each other out.
 
I know nothing about the /6 but I am a machinist....If you mill .1 off the block and .1 off the head you would then remove .2 off the threads of the head bolts, clean last thread and deburr completely. The questions is: Will there still be enough threaded portion left on the head bolt so that the shank does not bottom out into the block?? Most head bolts have some extra threads beyond what is needed to properly torque (there is a reason for the extra threads), if you are familiar with "thread theory" you'll know that you need a certain number of threads beyond those in the block to prevent premature failure.

treblig (Treblog)
 
If losing .100 of thread engagement causes the head bolt to fail Mopar did a really poor job the their R&D of the slant 6.
 
roccodart440 said:
If losing .100 of thread engagement causes the head bolt to fail Mopar did a really poor job the their R&D of the slant 6.
Click to expand...
.1" of thread engagement is not lost. I wasn't even talking about losing any thread engagement. What I wrote was that the OP would have to remove .2" off the bolt threads so they don't bottom out "if" he removes .1" off the block and .1" off the heads. If you take .2 (total) off the heads/block then the head bolts should be .2" too long. The other point that I was making is that you have to be sure that there are at least 2/3 threads left unused (above the block). Thread theory (taken from "engineerdog" website) states:


""Bolts actually stretch very slightly when force is applied, which causes the loading on each thread to be different. Because of this stretch, when you apply a tensile load on a threaded fastener the first thread at the point of connection sees the highest percentage of the load. The load on each successive thread decreases from there, as seen in the table below.

Additional threads beyond the sixth will not further distribute the load and will not make the connection any stronger.

6-threads-at-most.jpg
""


This is the reason that all head bolts have about 3 or more threads still visible (if you could see through the head) once they are properly torqued. If you only have "one" thread showing above the block surface then that one thread ends up taking 100 percent of the load. This would be a point of potential failure since the shank (un-threaded portion of the bolt) is stronger than the threaded portion). As you can see from the chart above, the few threads that are left above the block as like a spring to absorb load (torque).
I was trying to warn the OP that if he removes .2" off the bolts he should try and ensure that there are at least 3/4 threads still left protruding once the head is torqued.

I'm not making this stuff up.

Treblig
 
That is why I use hardened washers, approx the thickness of the amount milled off, under the head of the bolt. Keeps approx the same thread engagement.
 
As I said, a Grade 8 washer is all that is needed IF one were to find that the bolts would bottom, in My case there was plenty of room left with roughly .125" removed total.
I surely wouldn't be grinding/shortening/dressing perfectly good bolts. As Charrlie_S said, MEASURE, MEASURE, MEASURE, I take nothing for granted when building anything.
I post things such as pushrod length as things to look for because they are, not that they will absolutely be needed, but very well may be. Again, in My particular case, My
Crane chrome-moly pushrods needed shortened with the 276/.490" Purple Shaft I used and the above milling combo. At max-lift the adjuster cups were just touching the
rockers, but keep in mind, I believe the Crane cups were "deeper" than the OE cups. LOL!!! JINX!!!! Doggone-it Charrlie!!!
 
Washers = check. Will get.

Piston measurements:
Top of piston to top of wristpin hole = 1.3"
 
Love the new signature. lol

Treblig said:
I know nothing about the /6 but I am a machinist....If you mill .1 off the block and .1 off the head you would then remove .2 off the threads of the head bolts, clean last thread and deburr completely. The questions is: Will there still be enough threaded portion left on the head bolt so that the shank does not bottom out into the block?? Most head bolts have some extra threads beyond what is needed to properly torque (there is a reason for the extra threads), if you are familiar with "thread theory" you'll know that you need a certain number of threads beyond those in the block to prevent premature failure.

treblig (Treblog)
Click to expand...
 
Charrlie_S said:
Close enough. I got 1.304
Just as a comparison, I checked a TRW forged piston at 1.315
Click to expand...

So sounds like stock piston, not low compression or anything special. Guess my block is just extra thick. Gonna go forward with the plan and bring everything to the machinist.

Thanks so much for your help - will keep posted!
 
You must log in or register to reply here.
-

Back
Top