For those of you who have been following the ongoing crank snout failure concerns with PD blowers, you will recognize me as the guy who keeps stirring the pot. This is the Crank Tech II follow up to my original September 2011 thread. If you recall, in September 2011, I talked about the merits of using a crank stud instead of a crank bolt to hold the damper in place and showed how to do it.
Today I received the latest revision to my ongoing saga of snout improvement efforts as delivered by UPS. This generation of the fix involved re-doing the snout on the crank to remove all fillets, increase the snout diameters modify the rod journals (more on that in a different thread) preliminary polish and nitride hardening of the entire shaft and final polish.
I won't post the broken snout pics because I've long since worn those images out. Instead I'll show you what the modifications are and tell you why I did them. First lets start with a drawing of the original and modified snouts.
![Image]()
The basic design enhancement went through four revisions before it got to final machining. I had originally wanted to use a 1.530" diameter Chrysler snout and then spline the snout like a P-51 prop shaft. The 1.530" diameter required too much additional re-engineering of the cam drive and other snout driven paraphernalia so I backed off to a 1.400" diameter snout which turned out to still be quite large.
Another attribute I wanted to pursue was snout length. If you take a careful look at the stock damper, we have essentially 1" of press fit on the snout of the crank. A stock snout is 1.25" in diameter so we do not have even a whole diameter of press fit to help retain the damper. My original intent was to add 1.25" to the snout length and redesign the damper hub to take advantage of it. At the behest of my crank shop I later reduced that to 0.700" as you can see in design rev 1.1. I was still fighting an up hill battle on the stock forging so I relented and in design rev 1.2 I went back to a stock length snout. The crank really does need (for belt driven blowers) more snout length and more hub engagement but that is better handled in a billet solution.
The final design used a stock length but 1.400" diameter snout with the most generous full radius fillets the various compromises would allow me to use. The journal directly behind the the snout uses a 1.875" diameter up from the stock 1.528" OEM spec. This adds considerable strength to the front of the crank but precludes the possibility of using an OEM oil pump. For that matter the 1.400" snout diameter also pretty much throws out a nose mounted gerotor style oil pump. The oil pump needs to be external and either a dry sump or an external wet sump. I chose the external wet sump and I'll show how that all comes together in a build thread later.
The image below is a stock dimensioned snout on one of our forged cranks:
![Image]()
Notice the relative size of the front most snout journals compared to the #1 main. The shoulder just after the 1.25" nose on the crank is where the timing chain gear(s) are compressed against by the damper. This shoulder is essentially 0.125" on a side or the difference between the 1.25" snout and the 1.528" journal directly behind it. The OEM damper is held in place with a 12 MM bolt torqued to a preload of 10,000 to 12,000 lbs. Just going to a 9/16" stud will raise the preload to 24,000 to 26,000 lbs more than twice the clamp load and no tensile load on the snout - more on that later.
Below you can see the finished 1.400" snout on a stock forging:
![Image]()
Notice how the oil pump drive flats are gone and what was the oil pump drive journal is much closer to the size of #1 main. This journal increased in diameter from 1.528" to 1.875". I originally was going to us a 1.956" diameter but it created additional problems with the crank snout timing gear. The grayish color of the counterweights and the golden color of the journals is from the nitriding and also because I still need to wash the remaining nitriding residue off the crank and oil it.
With a larger snout diameter the lower crank sprocket needs to be modified to fit. I chose to use the billet steel Cloyes gear but I used two of them, bored them to 1.401" and modified them so they became two single gears with increased keyway engagement and identical in measurement so you did not have to pay attention to which one goes where sorts of complications during engine assembly. I also modified the gears much like TFS to allow independently changing the timing on each bank of cams. Here is a drawing of the yet in manufacturing gear(s).
![Image]()
These gears are made from two double row Cloyes gears by machining the rear gear off each and broaching the modified gear to provide up to 8Ëš of advance or retard. This will allow you to independently position each exhaust cam where you would like to have it with out all the usual angst that accompanies this process - and you can still use your stock upper gears on the two exhaust cams.
I had commented earlier that the snout stud relieves tensile load on the crank. The reason for this is the way the damper is held on the front of the crank. When you use a bolt, the bolt screws into the snout pulling the damper down until it bottoms out against the timing gear and the shoulder it has come to rest against. Continued torquing of the bolt applies increased preload to the damper by pulling the snout away from #1 main.
It is very similar to when we might stand over a 5 gallon bucket of paint and pull up on the paint bucket handle - our feet push down on the ground with an increased load equal to the weight of the paint bucket. Think of the ground as the crank timing gear and our feet as the OD of the crank damper pushing back on the timing gears. We are placing the crank snout under a tensile load equal to what we are using to hold the damper and gears on with. The narrowest point on the snout is the under cut where it begins stepping up to the oil pump drive journal. The tighter you clamp the damper and gears to the crank the greater the tensile load you place the snout under. At some point the combination of tensile load and torsional load to drive the blower breaks the snout.
By going to a stud, anchored behind the journal diameter changes, but down into the main or counterweight of the #1 main, you place everything on the snout in compression and remove the tensile load from the crank snout. The 9/16" stud solution provides more than double the preload (~24,000 pounds) of the stock 12MM bolt - with no tensile load applied to the snout. The 1.400" snout allows an upgrade to a 5/8" stud, without any loss of snout "wall thickness" and an increase to 30,000 or 33,000 thousand pounds of preload depending on stud material (8740/2000).
At this point, all things being equal, I would not do this to a stock crank again. Instead I would build a billet crank with the same modifications and importantly the longer snout. The costs get close enough and the literally clean sheet of paper approach you can take with a billet make it a far more attractive solution - not to mention the dramatically better steels available and substantial increase in component strength.
Today I received the latest revision to my ongoing saga of snout improvement efforts as delivered by UPS. This generation of the fix involved re-doing the snout on the crank to remove all fillets, increase the snout diameters modify the rod journals (more on that in a different thread) preliminary polish and nitride hardening of the entire shaft and final polish.
I won't post the broken snout pics because I've long since worn those images out. Instead I'll show you what the modifications are and tell you why I did them. First lets start with a drawing of the original and modified snouts.
The basic design enhancement went through four revisions before it got to final machining. I had originally wanted to use a 1.530" diameter Chrysler snout and then spline the snout like a P-51 prop shaft. The 1.530" diameter required too much additional re-engineering of the cam drive and other snout driven paraphernalia so I backed off to a 1.400" diameter snout which turned out to still be quite large.
Another attribute I wanted to pursue was snout length. If you take a careful look at the stock damper, we have essentially 1" of press fit on the snout of the crank. A stock snout is 1.25" in diameter so we do not have even a whole diameter of press fit to help retain the damper. My original intent was to add 1.25" to the snout length and redesign the damper hub to take advantage of it. At the behest of my crank shop I later reduced that to 0.700" as you can see in design rev 1.1. I was still fighting an up hill battle on the stock forging so I relented and in design rev 1.2 I went back to a stock length snout. The crank really does need (for belt driven blowers) more snout length and more hub engagement but that is better handled in a billet solution.
The final design used a stock length but 1.400" diameter snout with the most generous full radius fillets the various compromises would allow me to use. The journal directly behind the the snout uses a 1.875" diameter up from the stock 1.528" OEM spec. This adds considerable strength to the front of the crank but precludes the possibility of using an OEM oil pump. For that matter the 1.400" snout diameter also pretty much throws out a nose mounted gerotor style oil pump. The oil pump needs to be external and either a dry sump or an external wet sump. I chose the external wet sump and I'll show how that all comes together in a build thread later.
The image below is a stock dimensioned snout on one of our forged cranks:
Notice the relative size of the front most snout journals compared to the #1 main. The shoulder just after the 1.25" nose on the crank is where the timing chain gear(s) are compressed against by the damper. This shoulder is essentially 0.125" on a side or the difference between the 1.25" snout and the 1.528" journal directly behind it. The OEM damper is held in place with a 12 MM bolt torqued to a preload of 10,000 to 12,000 lbs. Just going to a 9/16" stud will raise the preload to 24,000 to 26,000 lbs more than twice the clamp load and no tensile load on the snout - more on that later.
Below you can see the finished 1.400" snout on a stock forging:
Notice how the oil pump drive flats are gone and what was the oil pump drive journal is much closer to the size of #1 main. This journal increased in diameter from 1.528" to 1.875". I originally was going to us a 1.956" diameter but it created additional problems with the crank snout timing gear. The grayish color of the counterweights and the golden color of the journals is from the nitriding and also because I still need to wash the remaining nitriding residue off the crank and oil it.
With a larger snout diameter the lower crank sprocket needs to be modified to fit. I chose to use the billet steel Cloyes gear but I used two of them, bored them to 1.401" and modified them so they became two single gears with increased keyway engagement and identical in measurement so you did not have to pay attention to which one goes where sorts of complications during engine assembly. I also modified the gears much like TFS to allow independently changing the timing on each bank of cams. Here is a drawing of the yet in manufacturing gear(s).
These gears are made from two double row Cloyes gears by machining the rear gear off each and broaching the modified gear to provide up to 8Ëš of advance or retard. This will allow you to independently position each exhaust cam where you would like to have it with out all the usual angst that accompanies this process - and you can still use your stock upper gears on the two exhaust cams.
I had commented earlier that the snout stud relieves tensile load on the crank. The reason for this is the way the damper is held on the front of the crank. When you use a bolt, the bolt screws into the snout pulling the damper down until it bottoms out against the timing gear and the shoulder it has come to rest against. Continued torquing of the bolt applies increased preload to the damper by pulling the snout away from #1 main.
It is very similar to when we might stand over a 5 gallon bucket of paint and pull up on the paint bucket handle - our feet push down on the ground with an increased load equal to the weight of the paint bucket. Think of the ground as the crank timing gear and our feet as the OD of the crank damper pushing back on the timing gears. We are placing the crank snout under a tensile load equal to what we are using to hold the damper and gears on with. The narrowest point on the snout is the under cut where it begins stepping up to the oil pump drive journal. The tighter you clamp the damper and gears to the crank the greater the tensile load you place the snout under. At some point the combination of tensile load and torsional load to drive the blower breaks the snout.
By going to a stud, anchored behind the journal diameter changes, but down into the main or counterweight of the #1 main, you place everything on the snout in compression and remove the tensile load from the crank snout. The 9/16" stud solution provides more than double the preload (~24,000 pounds) of the stock 12MM bolt - with no tensile load applied to the snout. The 1.400" snout allows an upgrade to a 5/8" stud, without any loss of snout "wall thickness" and an increase to 30,000 or 33,000 thousand pounds of preload depending on stud material (8740/2000).
At this point, all things being equal, I would not do this to a stock crank again. Instead I would build a billet crank with the same modifications and importantly the longer snout. The costs get close enough and the literally clean sheet of paper approach you can take with a billet make it a far more attractive solution - not to mention the dramatically better steels available and substantial increase in component strength.
