I pulled the engine on the '94, nothing wrong with it, just making room for another.

I found a company called crankshaft specialist in my local area that I dropped a crank off that is being cut for .020" offsets in the rod journals. This is an idea that DP likes and I for one was paying attention. To complete the modifing I ordered another regrind cam from Delta. Homebrewed 18:1 anybody?

old school de-stroker crank, brilliant. Problem is, you only need .050 to lower the compression to 18:1 i thought and you will have a decreased total piston height minus .100. am i overlooking something?

coool idea, hope it wont snap it in half

I feel that way about any cast crank.

As far as .050" drop required, there were some offset wrist pin pistons on ebay (.020") that would get it most of the way there.

I feel that way about any cast crank.

As far as .050" drop required, there were some offset wrist pin pistons on ebay (.020") that would get it most of the way there.

what the hell is an offset wrist pin???? how does that work.

if ur heads are decked .010, that would make up for some of the extra offset.

Make a 15:1, then put a maxed out 4911 pump and an HX40 on there and run 45 PSI of boost, that would be interesting:rolleyes:

An offset wrist pin is usually .045 off center within the piston itself to allow a smoother running engine.That primarily is its purpose.

The offset is a custom option, and is done when drilling the wrist pin bore - sets the piston heighth in the cylinder to customer spec.

Some pistons get the crown flycut to lower compression ratio - some get deeper dish, or reshaped dish.

Both methods destroy the hi-temp anodizing in the crown area.

Offsetting the w\p bore raises or lowers - in this case - the entire piston, altering the c.r. without damaging the anodized crown.

Diesel pistons get much harder anodize to withstand the greater btu thruput created in turbo applications.

Big rig engines get cast-iron piston crowns to survive the heat and pressure.

I pulled the engine on the '94, nothing wrong with it, just making room for another.

I found a company called crankshaft specialist in my local area that I dropped a crank off that is being cut for .020" offsets in the rod journals. This is an idea that DP likes and I for one was paying attention. To complete the modifing I ordered another regrind cam from Delta. Homebrewed 18:1 anybody?

Can they nitride treat the crank? When was the last time somebody listened to me? Hmmm? Was it the ceramic muffler bearings or marine injectors will float your valves?

Need to balance the engine. A Must do on this deal.

When was the last time somebody listened to me?

Huh?

The crank guy swears he cannot really add material to a cast crank, another machinist said yes, but the work started at $300.

I have balanced all the rods/pistons to the lowest weight each time I reassembled starting with the caps and working toward the piston :)
Is there a way to balance the piston/rods to the crank weight?

marine injectors float the valves of 'course

Crank will need to spun balanced. I have used welded cast cranks in gas burners with no ill effects. Have no idea how they do it, but it's done in a lot of reman motors as normal routine. Probably sumerged arc welded. Need to check your pin height on each piston and match shortest piston to longest rod. Of course when installing crank check the deck height in all four corners to see if the block needs a little decking to square it up.

I was just looking at rod tools (dial and stand) in the northern auto parts catalog$45 USd. You buy one little thing and you get the catalog for life. I heat my home with them in the winter.

Take a flat plate and put two pins in it that the big end will fit over somewhat loose. Lay the rod on it with a wrist pin sticking up. Use a magnetic base dial indicator and indicate off the the pin. Rotate rod side to side to zero indicator. You now have a base measured rod. Check all the rest the same way with + or - in thousandths. Your not measuring the rod. Just finding the shortest to the tallest. Match the long rod to the short piston or in some cases to the shortest throw. All part of building a dam good engine. Some blocks you can put the tall rod combo on the lowest deck height. That way all the pistons will have the same exact deck height and all hopefully the same exact compression.

Pic (: )--o

Hot Rod O--{o]]

If it looks like I been there I have. Been der done dat.

If it looks like I been there I have. Been der done dat.


Yea, I have beer there too and drunk that, its all common stuff, nice and simple;)

Should be interesting...

On the crank, are you adding material to offset or turning down the crank to an undersize to acquire the offset, or both?

The pin bushing offset is another way to drop the c/r.

I'm confident you can do both and get to 18:1 no problem.

Question for GMCTD (since you're lurking round here)

You mentioned losing the Annodizing when modifying them, what the heck is the annodizing used on the pistons? If I recall correctly, a ceramic coating is applied to modifed pistons to protect them instead, isn't that just a good or better?

J

Not to get too off topic, but I was just thinking of the time a mechinist "cleaned" a set of pistons for me and glassbeaded all the anadizing off the crown. :(

Picked up the crank today. The crankshaft specialist said maybe 1.8 thousandths drop would be possible and I asked him to go as far as he could. The crank was marked 3.784. That means with a .010" over headgasket I'm already passed 18.5:1 without drilling anything, but don't you just know I'm going to hog on those pre cups a little.

I'm just waiting for a set of main bearings and the Delta regrind cam and ARP headstuds to put it together.

There exists several types of anodizing - oxidation protection and impact\scuff protection are the two most common, ranging from soft to hard

NASA developed a harder denser form for use on the edges of surfaces exposed to re-entry heat, also resistant to impact damage.

Composed of jillions of tiny, ceramic-like beads, it is super heat-conductive across the surface, but insulative below the surface, preventing hot-spots by conducting and quickly radiating the heat across the entire surface

It is used on high-quality aluminum Diesel pistons - resulting in very high prices.

Any machining to the crown removes the hard-anodized surface, which requires either re-anodizing process, very expensive, or flashing a thin ceramic coating onto the bared aluminum, not expensive.

Anodize is chemically part of the aluminum surface - ceramic coating is.....coated on.

And, imo, nowhere near as protective for turbo use.

Cutting the piston crown also removes material designed to survive Diesel service temperatures and pressures, where offsetting the wrist pin reduces piston heighth in the cylinder without losing any designed-in strength

Cheaper replacement pistons use the less expensive form of hard-anodizing normally used for scuff-resistant service.

Note - most quality heat sinks use the same standard hard-anodize coating, which is somewhat thermally insulative.

The anodizing prevents thermal conduction, so in high-wattage application the sink usually will have the anodized surface milled off where the transistor\diode\ic is to be mounted.

Personally,
I've seen too many 6.5L pistons with cracks across the crown with the ceramic coat still in place to think that cutting into the crown would be an option.

Research the "why" of the crack, and you will know, fer sure.............

Well, screw it - I'll tell ya..................

Each piston is very close-fitted into each cylinder which aids heat conduction into the cylinder walls and water jacket.

This can be done because the fuel, a light oil, is injected as the piston nears TDC - engine oil lubricating the piston\cylinder wall is not washed away, as in a gasser.

Unfortunately, any excess heat can quiclky result in scuffing - greatly excess heat results in the piston binding in the cylinder.

Combustion pressure and low-rpm torque is great enough to keep the rod moving when this happens, with the result that the rod attempts to remove the wrist-pin thru the bottom of the piston skirt on the down-stroke, or shove it thru the piston crown on the up-stroke.

Voila - crack city.

I've seen the scars the compression rings leave TDC. Heat makes the diesel work but overheating will kill it.

So cracking is not limited to high boost pressure, but actually to do more with the internal heat issue within the cylinder itself, eh?

well put, GMCTD

Thanks for the explanation GMCTD!

J

With less heat and pressure being generated at 18:1 at idle or under the full boost of a holset, the pistons should not crack as fast or as often

kn - can you re-post that 21:1 vs 18:1 cyl pressure chart that you did awhile back?

CR CR
psig psia 21.3 18

0.3 15 319.5 270
1.3 16 340.8 288
2.3 17 362.1 306
3.3 18 383.4 324
4.3 19 404.7 342
5.3 20 426 360
6.3 21 447.3 378
7.3 22 468.6 396
8.3 23 489.9 414
9.3 24 511.2 432
10.3 25 532.5 450
11.3 26 553.8 468
12.3 27 575.1 486
13.3 28 596.4 504
14.3 29 617.7 522
15.3 30 639 540
16.3 31 660.3 558
17.3 32 681.6 576
18.3 33 702.9 594
19.3 34 724.2 612
20.3 35 745.5 630
21.3 36 766.8 648
22.3 37 788.1 666

Ok, thanks QM.

First - if you look at 10.3psi Boost, you'll note cyl press is 532psi at 21:1cr

Compare that to cyl press at 15.5psi Boost with 18:1cr - 532 vs 540, very close right?

50% more Boost for the same cyl pressure has gotta do some good, right?

And, it does - check the cyl pressure with 21:1cr and 15psi Boost - engine has to work harder to push the pistons up against that higher pressure.

Increased pumping effort = reduced power.

While those are static pressures, compare any of those to the 3000psi combustion pressure in the cylinder when the engine is puttin' out - Boost pressure ain't what kills the 6.5.

Increased Boost can reduce EGT's - how?

And what does kill the 6.5?

tbc............

And what does kill the 6.5?


A heavy right foot?

A heavy right foot?

Great.. I'm screwed then :ro)

The short block is ready to go...