My Pete rebuild

[Squish099]

Just remember.. The faster something spins the more critical balance is.. 2000 rpm max is a whole hell of a lot different then 8000.. And guys balancing to 0.05 gram are on big and small block ford/Chrysler/gm.. Parts are much smaller spun at much higher rpm. Usually the crank and is spun balance with Bob weights too so the crank counter weights match the assembly that's attached to them... Balancing rods and pistons do squat if crank ain't balanced too..

[Nostalgic]

(12-30-2021 )Squish099 Wrote:  Just remember.. The faster something spins the more critical balance is.. 2000 rpm max is a whole hell of a lot different then 8000.. And guys balancing to 0.05 gram are on big and small block ford/Chrysler/gm.. Parts are much smaller spun at much higher rpm. Usually the crank and is spun balance with Bob weights too so the crank counter weights match the assembly that's attached to them... Balancing rods and pistons do squat if crank ain't balanced too..

I realize it's a long way to 8k, but saying 2k max is a way too controlling statement lol. Bob weights aren't used to balance the crank like in a v engine. Inline 6 is a inherently balanced spinning triangle with 3 throws 120* apart, and stays that way as long as everything you bolt to it is balanced as well. Of course I'm betting on the hope that Cummins balanced the crank correctly lol.

[tree98]

Does the cummins factory even bother to weigh and match components when they build engines? Something tells me they just throw the parts in as they come down the line.

[Nostalgic]

They also push running the engine at 1200 rpm at high torque to save fuel and set new liners at .010". Benefit to pulling from the line that rods are more likely from the same batch as well, and wouldn't have as big of a weight spread.

I almost abandoned the saw cuts and went with new fractured rods, but at this point I'm just tired of returning stuff lol.

[Squish099]

(12-30-2021 )Nostalgic Wrote:  

(12-30-2021 )Squish099 Wrote:  Just remember.. The faster something spins the more critical balance is.. 2000 rpm max is a whole hell of a lot different then 8000.. And guys balancing to 0.05 gram are on big and small block ford/Chrysler/gm.. Parts are much smaller spun at much higher rpm. Usually the crank and is spun balance with Bob weights too so the crank counter weights match the assembly that's attached to them... Balancing rods and pistons do squat if crank ain't balanced too..

I realize it's a long way to 8k, but saying 2k max is a way too controlling statement lol. Bob weights aren't used to balance the crank like in a v engine. Inline 6 is a inherently balanced spinning triangle with 3 throws 120* apart, and stays that way as long as everything you bolt to it is balanced as well. Of course I'm betting on the hope that Cummins balanced the crank correctly lol.

Yes most I6 cranks are neutral balanced as far as firing harmonics. Your going through an awful lot to balance rotating mass. They do spin balance I6 cranks with Bob weights on performance built motors to get counter weights the same as piston/rod weight on that throw..

[Rawze]

(12-25-2021 )Nostalgic Wrote:  

(12-25-2021 )tree98 Wrote:  I don't remember seeing Rawze weigh all his parts when he did his rebuild. What am I missing?

I think Rawze reused his rods. I've never had a set of original assembled rods to use, they are not available new through Cummins, and buying RX's get you rebuilt rods that could have been manufactured over a 20+ year span.

The new block kit - the only way I could find to get a virgin block, comes with liners pre-installed, oil cooling nozzles & bolts, and dowels. The only advantage of buying a kit is that pistons would most likely all have the same date code and possibly vary a little less in weights. It would cost more because I would be buying new liners that I don't need.

And - I would still be faced with wide ranging rod weights.

Cummins is still producing new CM570's for export, but aside from snagging one of those on it's way out of the country, it's been pretty challenging to source all of the parts needed to make a brand new 14 year old model engine without going aftermarket.

well... at least if you precision balance it.. and get it right, then you could run it down the roads at its full 2700-RPM rating all day and not blink an eye about it. Of course, the bearing clearances for the rods/mains, would also need to be plasti-gauged too, (and all verified to be at 0.002" - 0.003") to ensure there is no variance in clearances, to help prevent any harmonics from setting in.

All the wrist pins bushings would have to be on the underside of the acceptance range too. Most already come this way from cummins when they are new if I remember right. matter of fact, the wrist pin bushing clearance it actually the absolute most precision, and critical measurement in the whole engine. The longevity of the engine depends on this very heavily, right along with raising of the liner heights above factory settings on an engine that has a lot of miles and is being rebuilt.

As far as machining some of the weight differences out of the rods, the outer shoulder (intake side) would be the best place for that. No way would you want to remove material form the center or any other part of it as it needs to hold up to 2,000 foot-lbs of torque without deflection otherwise.

just some random blabbering thought while enjoying my 3rd' beer, nothing more. I have never had to precision balance an engine myself, so its all just beer speculation.

[Nostalgic]

I only removed about 9 grams total from one fat bottom rod. I just removed a touch from the casting flash on the cap, but most towards the bottom on the beam's casting flash. Cummins is a little rough handed when they clean casting and had made a pretty deep gouging grind on one of the beams, so I only went deep enough to take most of the grind marks out.

Quality control from them seems to hinge on what kind of day the person doing final inspection is having. I see blem blocks for sale where Cummins rejected them for the front gear cover dowel holes being off center of the crank by .001" and just hope the inspector(s) doing the parts I ended up with were as thorough.

[Nostalgic]

(01-02-2022 )Rawze Wrote:  All the wrist pins bushings would have to be on the underside of the acceptance range too. Most already come this way from cummins when they are new if I remember right. matter of fact, the wrist pin bushing clearance it actually the absolute most precision, and critical measurement in the whole engine. The longevity of the engine depends on this very heavily, right along with raising of the liner heights above factory settings on an engine that has a lot of miles and is being rebuilt.

Like I mentioned earlier, 2 reman rod bushings were sloppy and out of round. One vertical measurement was @ 2.5032"

Not sure why the fractured rods have even tighter specs on the bushing but still use the same piston pins?

I didn't write them down as I checked the rods, but the 6 saw cut rods I'm using measure 2.5023-2.5026". All of which are looser than the 2.5017-2.5023" for fractured rods.



I checked some cores before I sent them in and they were mostly all worn in the vertical areas.

[Nostalgic]

In other news. My 3rd crankshaft came in today.
Refresher
#1 had the broken tone wheel
#2 - Remember how I said runout had a high spot? I decided to check a little more.


Cummins lists max runout criteria for reusing a crank. I'm ready to bet that just about nobody ever checks. In fact I'm just about certain of it. This includes Cummins lol. Either that, or I have had excellent luck in finding all of the junk...

Front oil seal runout .004" MAX .002"
Rear oil seal runout .002" MAX .0012"
#4 Main Journal .010" MAX .008"

According to Cummins, that NEW crank needs to be replaced. Cummins wanted it inspected by a certified tech. Same conclusion.

Today's crankshaft:


Front oil seal runout .002"
Rear .0018"
#4 journal .0035"

Little iffy on the front and rear oil seals, but went ahead to check the rest of the main journals...

Plotting journal runouts:



Passes by the skin of it's teeth with a .003" max allowable adjacent journal runout between 5 & 6.



I have a feeling that a 4th crank wouldn't be any better, but figured if anyone has ever actually checked a crank, this is the place to find out if these numbers are acceptable.