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Milling Aluminum Block Deck Surface
https://slantsix.org/forum/viewtopic.php?t=31557		 Page 1 of 1
Author:  Dusty Desks [ Tue Oct 07, 2008 7:37 pm ]
Post subject:  Milling Aluminum Block Deck Surface
Is it possible to take a 225 aluminum block which is unusable because the deck surface is too far degraded to be repairable and mill it 1.00 inches, and install a 170 crankshaft and rods to make a 170 aluminum engine? Besides salvaging a rare block, it seems such an engine would be more reliable because the shorter iron cylinder (which is supported at the bottom) would be considerably stouter, and this along with the lower power level considerably reduces the microscopic sideways movement of the iron cylinder relative to the head and gasket (all dissimilar metals) during engine operation due to piston side forces against the cylinder wall which causes the problem, what physical chemists call "fretting corrosion".
Author:  Joshie225 [ Tue Oct 07, 2008 8:06 pm ]
Post subject: 
I'd considered the same thing, but where do the head bolts or studs go? If there were enough meat left in the block you could drill and tap it deeper, but I don't know if it's possible.

A 170 block is about 9.10" deck height which makes it 1.6" shorter than a 198/225 give or take a little. The Mopar Performance/Direct Connection books are wrong.
Author:  Dart270 [ Wed Oct 08, 2008 6:04 am ]
Post subject: 
I have also thought of this. Josh is right the head bolts have nothing under them after about 1.2" down. You would need to devise a whole new way of fastening the head on.

However, it does look like you could mill 0.100" and still have enough bolt engagement. Doc?

Lou
Author:  Doc [ Wed Oct 08, 2008 10:54 am ]
Post subject: 
If you have been following the "Buster" engine thread, you saw how I fixed my latest, badly corroded Alm block.
http://www.slantsix.org/forum/viewtopic ... 3&start=30

For minor pitting, sand blasting and then epoxy works well.

You can mill .100 off the alm block's deck but the rear edge has a top lip that starts getting thin. "Back-filling" along that edge with epoxy is a good way to make sure it holds a seal.

And no... you can not machine any RG (225) block into a shorter 170 (G) block, cast iron or aluminum. You will run out of head bolt hole boss material. You could swap-in a 198 crank and con rods to make an aluminum block 198.

With that said... what if I carefully cut the top off an aluminum block, just below the bolt holes, just the aluminum block's perimeter... leave the cast-in iron liners "sticking out" the top by an inch & a half. Now, mill down the block's perimeter the needed amount and then re-attach the top deck... then machine down the protruding cylinder liners to match. :shock: :roll:
DD
Author:  62 alum [ Thu Oct 09, 2008 9:48 am ]
Post subject:  198 crank
With the 198 crank do I need the 198 rods or the 225 rods to lower the pistons in the cylinders to be able to mill the alum blk for the right compression.
Author:  Doc [ Thu Oct 09, 2008 10:31 am ]
Post subject: 
A true 198 will need a 198 crank and con rods.
A "long rod" 225 will need a 225 crank, 198 con rods and shorter 2.2 type pistons.

The only time I use 225 con rods is when building stroked crank SL6 engines. (4.440 stroke)
DD
Author:  Dusty Desks [ Fri Oct 10, 2008 3:46 pm ]
Post subject: 
Maybe it would be possible to install a 198 crankshaft with 225 rods, and then mill the block down just enough to maintain a good compression ratio of at least 8:1. Only about 0.3 inches or so would need to be milled off. The crankshaft would need to be rebalanced, and custom-length valve-train pushrods fabricated. Some 170 aluminum engines were made during development, and I heard that one or two even might have made it out into the world. I wonder how they did that. Did they have some way of using the die-cast design, or were all the aluminum 170 engines sand cast?
Author:  Doc [ Fri Oct 10, 2008 4:22 pm ]
Post subject: 
The prototype aluminum block 170s were said to be sand casted units.
DD
Author:  Dusty Desks [ Tue Oct 14, 2008 7:15 pm ]
Post subject: 
Here are some calculations regarding the possibility of building a 198 cu. in. aluminum slant six while in the process of fixing a badly degraded block deck surface:

(C.R. = compression ratio)

stock 170 engine / 1.82 rod ratio / 8.5:1 C.R.
stock 198 engine / 1.92 rod ratio / 8.4:1 C.R.
stock 225 engine / 1.62 rod ratio / 8.4:1 C.R.

198 cu.in. engine built with 198 crank, 225 rods, RG block:
1.84 rod ratio / 5.6:1 compression ratio

In the configuration described immediately above, if the aluminum block were milled 0.306 inches, the compression ratio would be 8.4:1, same as stock.

The head can always be milled .100 to lessen the amount needed to be taken off the block deck, and Doctor Dodge says the aluminum block can also take .100 milled off. So, recalculating the compression ratio assuming this gives 7.1:1 C.R.

Next, a compression ratio of 8.0:1 is assumed, and a calculation done to figure how much the block has to be milled to yield this figure. A C.R. of 8.0:1 is realistic and practical for use with modern regular gasoline, and many stock slant sixes may have actually been built at the factory with a C.R. closely approximating this, although Chrysler never changed the 8.4 figure listed in their official printed literature. For an 8.0:1 compression ratio, it calculates out as 0.178 inches needing to be milled off the block, coupled with .100 off the head. Whether an aluminum block will take this amount, or preferably the full .206 inches, would have to be determined by closely measuring an actual block. Either way, I doubt that this small amount less of cylinder head bolt thread engagement would matter, since I expect there is a large safety factor in this area.
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