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Crank Tech

52K views 113 replies 21 participants last post by  eschaider 
#1 ·
For those readers just coming to this thread, I have moved it from Allen's (Broke7) thread about broken timing chains because it was hijacking Allen's thread and I was the hijacker!

Ed


Keith, Scott and other interested folks,

I have attached several pictures of a crank modification I have recently done to correct some of the problem. The challenge we face with a larger bolt is the tug it places on the snout. When we tighten a bolt it clamps the damper and internals (gear, & timing wheel) to the front of the crank by exerting pressure on the components and squeezing them against a crank snout shoulder just in front of the oil pump drive journal. Essentially what the big bolt solution I used to use does is try to pull the snout straight forward off the crank.

I have come up with an interim solution that uses a stud that anchors in #1 main journal and sandwiches all the pieces without puling on the crank snout. I will do another post just on this technique in a week or so and include a second article on building your own dual disk clutch. For now here are some pictures of the parts and the process.

Here are the ARP parts needed:

Cosmetics Office supplies Wood Electric blue Auto part


This is the crank set up in a lathe ready to drill the stud hole:

Machine tool Gas Engineering Cylinder Toolroom


This is the tapping step while the crank is still in the lathe:

Machine tool Engineering Gas Toolroom Machine


And this is the finished crank:

Cylinder Machine tool Gas Auto part Engineering


When you have completed the modification the entire package of goodies on the front of the crank will get sandwiched between the nut and washer on the front of the crank and #1 main journal, making for a very tight and durable assembly. I've got to go back to my notes and check but if my memory is correct the torque on the 9/16 stud/nut package is about 165 or 170 ft/lbs and the clamp load on the package is more than double the stock clamp load - without any attempt to pull the crank snout off the crank.

I've got to see a vampire about a blood test right now so I'll get back with the other details when I return later today.
 
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#2 ·
I'm trying to get my head around the clamping physics in this.
The stud, being installed in the new threads inside the crank snout with zero torque during the installation, deform the snout
in a different way then having the threads screwing in under load?
So the stud/snout thread interface has more metal to metal contact to spread the load during the clamping phase, causing less distortion to the crank/snout interface. And the actual snout/thread interface is taking place at a different depth in the snout.
 
#3 ·
Drew,

The magic (if there is any) is in where the stud or bolt anchors to produce the clamping force. The OEM bolts all anchor in the crank snout before the oil pump journal. The stud goes all the way through the snout to the #1 main journal and sandwiches everything between the journal and the nut.

When you use a bolt that terminates in the snout it can produce similar levels of clamping force but it is doing so by placing the anchor point in the snout where it effectively tries to pull the snout off the front of the crank (at the juncture with the oil pump drive journal) as you tighten the snout bolt and raise the clamp load. The problem is the bolt anchoring point - it is forward of the register the timing gear(s) are being clamped against. By increasing the load applied by the snout bolt you are effectively trying to pull the snout off the front of the oil pump drive journal because the snout bolt anchors in the crank snout forward of and not behind that journal.

The stud approach goes even deeper into the crank past the oil pump drive journal and anchors in the #1 main journal producing a nice sandwiching effect with out placing any tensile load on the snout. If you have an aftermarket Kellog crank you can actually go back to and anchor in the front most counterweight of the crank. OEM Ford cranks use a cross drilled main style of oiling instead of the Kellog straight shot method. With a cross drilled main you can not get all the way back to the counterweight without obstructing part of the oil passage for #1 main.

It's easier to see than explain. I've got some drawings somewhere (if I can find them) from when I began the project. They illustrate the front of the crank. When you see the drawings, the lights go on quickly. I'll do a search and see if I can find an uncluttered one.

FWIW a grade 10.9 12mm bolt at 75 ft/lbs TQ produces less than 14,000 lbs of clamp force. An ARP 2000 9/16x18 stud at 170 ft/lbs TQ with a hardened steel washer, produces a little over 30,000 lbs of clamp force. This is a nice step up in the clamping department.



Found the drawing! Like they say a picture is worth a thousand words.

Rectangle Slope Font Parallel Symmetry


When you use a bolt instead of a stud the crank wants to break at the under cut fillet between the snout and the oil pump drive journal just behind the timing gears where it can do the greatest harm. This type of failure is very expensive because of all the damage it does to the heads, valves, guides and potentially cylinders especially if a valve breaks off and falls into the cylinder.
 
#5 ·
Ed, your right, the pic explains it quite well.

But does anyone know why Ford undercut the fillet at the snout/crank interface.
That seems to be the last place you would want a decrease in cross section.
I remember looking at a Kellogg aftermarket crank and was impressed at how nicely they rounded all the stress risers
and polished and shot peened their cranks. I think that alone would make it worth stepping up to Kellogg or Scat crank.
Even though you have to make sure that you get the correct rod and main bearing shells to accommodate the fully rounded fillet.
And have you seen any of the billet cranks. Real works of art but a ton of money.
 
#6 · (Edited)
The answer is actually a two part answer Drew. The first part is that is the way (with a few exceptions) Detroit OEMs have always built their cranks. The second part is why. The answer to the why question goes something like this, when you finish a crank with full radius fillets the cost is deceptively high. To maintain the radius within the design specs the crank grinding wheel requires more frequent dressing - much more frequent. The cost associated with this is viewed by the bean counters as being unacceptably high.

Remember in Coletti's book he commented that the Manley rods were several times more expensive than a block. According to Coletti, Ford paid $56 for a single gold plated (Manley) rod and in the book he says, "...two of these rods cost more than a whole [Terminator] block." The incessant drive to control cost in Detroit's manufacturing phase frequently demands compromises. The Manleys got through because of approaching deadlines and a lack of credible alternatives. The cranks were lucky but not as lucky.

Kellogg who has been the source of untold high end, high performance cranks in Detroit OEM circles for decades, was an easy fix for crank durability that more or less still fit inside the bean counter's envelope of acceptable pricing. Part of the ability to meet target costing was the use of undercut instead of full radius fillets. The cranks still had the center counterweights which many production cranks lack - again for costing considerations. The crank material was the now famous micro alloy that mimics a lot of 4340 characteristics. The finished product however still had the undercut fillets.

When you buy an aftermarket Kellogg you still get undercut fillets but you do get a better oiling system than the OEM Ford specified cross drilled mains. The undercut fillets on either crank are a real problem for Terminator engines and the undercut between the snout and the oil pump drive journal is Public Enemy #1. That is not only where we break the cranks it is the worst possible place to fail because it separates the timing chains from the crank killing the valvetrain.

The crank snout stud is an interim fix for the snout problem and, while it really isn't as much of a fix as it is an improvement (because I think it will potentially still fail) I don't have the time yet to produce the real fix. The "real" fix involves increasing the snout diameter, modifying the snout journal lengths to work with a new splined lower gear, trigger wheel and damper. The finished crank will have a snout that resembles the drive snout (albeit different dimensions) on the P-51 engine in the pic below.

Gas Auto part Machine Metal Event


This new crank will obviously be a billet effort. It will use a new dual lower timing gear that is independently indexable for each cylinder bank within less than 1˚(crankshaft). There will be full radius fillets used everywhere on the crank and the material will be one of the super alloys for ultimate strength. I have a an initial proof damper design completed and manufactured along with a lower blower pulley drive that is secured by both fit and six 10MM fasteners. The lower blower pulley drive has been designed with provisions for an external wet sump (or dry sump if you prefer) auxiliary drive.

At first a billet seemed like overkill but the further I got into my project the more it screamed for a custom crank. I will probably get to the crank in the early spring. As I do I will post up pics so you can see more of it. In a few weeks (more or less) I'll do a write up on the studded OEM temporary fix.

Ed

p.s. The billet is currently planned to use a 5/8" ARP 2000 stud in the snout, that will anchor in the #1 counterweight and provide right at ~40,000 lbs of preload when you torque it down to 235/240 ft/lbs. Rememebr the stock 12MM grade 10.9 bolt is 14,000 lbs (or less) preload at its torque spec.
 
#7 ·
Thanks Ed!
I really enjoy getting the inside history on why and how cost cutting at the development level has turned out a good, but could have been great, product.
Are any of the forged aftermarket cranks fully rounded, or is the only way to get rid of that stress point at the snout to have a custom billet crank made.

And that RR aircraft engine is absolutely fantastic. I always love looking at them. Too bad they would create too much nose weight in our cars.
 
#8 ·
Thanks Ed!
I really enjoy getting the inside history on why and how cost cutting at the development level has turned out a good, but could have been great, product.
Are any of the forged aftermarket cranks fully rounded, or is the only way to get rid of that stress point at the snout to have a custom billet crank made.

And that RR aircraft engine is absolutely fantastic. I always love looking at them. Too bad they would create too much nose weight in our cars.
Sadly the forged aftermarket crank manufacturers are currently sourcing their inventory from Kellogg. As a result they all have the undercut fillets which (along with some other considerations) is what drove me to the billet alternative. The easiest test to see if they are really manufacturing the crank themselves is to ask for it to be finished with full radius fillets everywhere. The moment you ask for that the manufacturer starts to back down. The most amazing part of this is that all of their other forged racing cranks (which they actually make) will come with full radius fillets as a standard feature. Only their least expensive entry level products may not have full radius fillets - which begs the question why would you use undercut fillets on a high end crank like a Cobra?

Today no one makes a forging for our engines that has full radius fillets. The undercut fillets are a significant part of the problem but snout diameter is also a bad boy. A 1.25" diameter snout with undercut fillets on a engine with a crank driven blower, like ours, is an accident looking for a place to happen. The reason Ford went to the front support for the crank on the Terminators, I suspect, was that it was cheaper (cost again) than a new crank design for a limited production vehicle with an engine approaching its end of life. Our crank snouts were designed for normally aspirated engines at the very beginning of the ModMotor's life cycle more than a decade before Terminators saw the light of day. The engine is (especially with big blowers and high boost) asking for a more robust drive system than you need for the n/a version of the engine.

I understand the thrill from the Merlin, they really wind my spring up also. Whoever thought of the Merlin name for them hit the nail right on the head, because they certainly are magic! As old as they are, they employ a lot of design decisions that are amazingly applicable today.



p.s. Now with a little more tire pressure and some magnesium components ... maybe?!!!
 
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#9 ·
I really enjoy getting the inside history on why and how cost cutting at the development level has turned out a good, but could have been great, product.
Oh you don't know the half of it... I swear that old fart could give you the inside story on almost ANYTHING in the automotive world, especially Chrysler engines :rofl2:

Good stuff Ed... those pics look familiar for some reason. What would be nice would be to see some pics of the "old skewl toy" that lies in pieces in your garage :imao:

Shannon
 
#11 · (Edited)
Rd, I am going to bring a spare crank over to a friend's dad. He is a metallurgical engineer at McDonnell Douglas.
I want to get his opinion on Tig welding in the undercut, machining and polishing it down, and re heat treating the crank.
Then aerospace shot peening it. Should be doable unless the heat of welding compromises the snout interface strength.
But then when you ad up all the costs involved how close does it get to your billet crank?
 
#16 ·
I think you can do this Drew. Without access to the facilities necessary to do it, I suspect it might be cost prohibitive. I am not familiar enough with the C38 MicroAlloy I believe they use in the crank to know how it will respond. You're Dad's friend will be or at least will be able to get access to the information. As you discover more about it please share it with the rest of us.
 
#18 ·
That is one fine looking crankshaft Micah. Bryant makes some very nice pieces. If it is not too much trouble could you take a couple of photos of the the counterweight cheek/rod journal intersection so readers can see the full radius fillets that Bryant uses there. While you are at it, it would also be helpful if you could take a picture of the snout for the same reason.

Great looking piece. If you aren't already, you will be glad you made the investment.

Good luck on your build.

Ed
 
#19 ·
The undercut on the snout was the main reason I went with a billet crank. I run a cog driven procharger and I wanted the crank to be as robust as possible to prevent any possible issues down the road. I'm also going to design a crank support to work with it as well to give it that much more strength. I went with a Scat Pro Billet crank made from EN30B, nitrided, gun drilled mains tapered counter weights etc. It's a night and day difference when looking at it compared to one of the Kellogg cranks, hopefully I won't have to worry about it at all.

Do you think that there is any benefit to running the stud setup like you have on a billet crank? If so, I can always pull the crank back out of the engine and get this done since the motor hasn't been started yet. Of course I would have to have it all balanced again I'm sure which means that it would all have to come back apart.
 
#20 ·
The undercut on the snout was the main reason I went with a billet crank. I run a cog driven procharger and I wanted the crank to be as robust as possible to prevent any possible issues down the road. I'm also going to design a crank support to work with it as well to give it that much more strength. I went with a Scat Pro Billet crank made from EN30B, nitrided, gun drilled mains tapered counter weights etc. It's a night and day difference when looking at it compared to one of the Kellogg cranks, hopefully I won't have to worry about it at all.

Do you think that there is any benefit to running the stud setup like you have on a billet crank? If so, I can always pull the crank back out of the engine and get this done since the motor hasn't been started yet. Of course I would have to have it all balanced again I'm sure which means that it would all have to come back apart.
SCAT makes some great cranks and is among the oldest of the manufacturers out there Jim. The EN30B steel is one of three or four steels that produce really tough cranks. It is one rugged, resilient steel. I understand your affection for the crank support, billet crank not withstanding. Until you put one of these super cranks next to a Kellogg it's hard to really appreciate just how much better a billet is. The OEM undercut on the snout is a real show stopper for me also and the reason I finally embarked on the billet solution.

Whether an individual decides to go billet or Kellogg the stud is a good thing to do. Even on a billet, if you can take a tensile load off the snout and leave only a torsional load for driving the front end accessories and blower it is to your advantage. On a crank like your SCAT I believe you will have what is called straight shot oiling to the rods. Straight shot is a single drilling from main to rod journal without cross drilling the main. Straight shot oiling is much preferred today over the cross drilled method the OEM crank uses.

Because you are most probably straight shot you have the benefit of going all the way back to the #1 counterweight - unless you had SCAT rifle drill the mains. If the mains are rifle drilled then you can only go back to #1 main with the stud. The big deal about the stud is it takes away a tensile loading from the crank snout that does nothing positive and a lot of things negative. The stud also lets you really clamp down the entire snout assembly so you can get away from a lot of the fretting and work all those parts like to do as they move around ever so slightly on the crank snout in service.

If you want to do the stud let me know and I will dig out the ARP part numbers for you so you don't have to do an Easter egg search for the components. For everyone else that is reading this as soon as I find those part numbers again, I will publish for everyone.

FWIW the stud does not require rebalancing the crank. All mass removal is symmetric about the crank centerline and therefore does not affect balance. Almost forgot this point from your post; to do the stud you will have to remove the crank from the engine. It is a virtual impossibility to machine it (especially EN30B) in the block. It has to be done in a lathe in a machine shop.

Can't wait to see you car finished Jim - it should be an animal.

Ed
 
#22 ·
Thanks for the reply Ed. I'll look more into the stud when I get a chance to get home again (in another few months). I can pull the crank no problem, as the motor is just sitting in the car, I can pull it out and put it on a stand in no time. The crank does have straight shot oiling and chamfered oiling holes, it's also gun drilled and has the Pro Comp lightweight counter weight design. I also had it double keyed, although I don't envision needing to use the double keys since the balancer is an interference type press fit. The crank was a bit pricey, but so were all the other parts I used and I didn't want to run the risk of busting the crank at the factory undercut and destroying all the other parts in the process. I consider it to be a sort of insurance I guess. I sold a few parts to help offset the cost, so at the end of the day it wasn't too bad I guess.
 
#23 ·
subscribing - any updates here ?

I have a 4V 5.0 stroker running an overdrive balancer and a YSI blower on a single keyway - it's apart about to be freshened -
 
#26 ·
subscribing - any updates here ?

I have a 4V 5.0 stroker running an overdrive balancer and a YSI blower on a single keyway - it's apart about to be freshened -
Hang tight Mark (is that correct?). There will be some intermediate updates that will provide a pretty good fix - not as good as a billet but pretty good. I'll need a couple of more weeks before I have the first prototypes ready to show.

Ed
 
#29 ·
I have heard the F8 Bearcat would would turn circles around an F4U Corsair. The Mustang could out-climb the Zero which was the first American plane to be able to do so. Changed the tides of the war.
 
#32 ·
The F8F bearcat was faster then a F4U Corsair but the Corsair was the first US Fighter to exceed 400mph but the Bearcat was to late for the war. It was actually on ships on their way to the Pacific when Japan surrendered The Mustang was used less then the Navy fighters in the Pacific and the Corsair and Mustang could out climb a zero depending on speed entering the climb(initial climb). The F4U and the F6F Hellcat that came before it used BNZ tactics, Boom N Zoom, to dive down on a enemy plane make a pass and use there overwhelming speed to pull away for another attack. The F4U was much more able to do what the pilot wanted because it held a 50 mph speed advantage over the F6F depending on altitude.

I could write this whole forum full of dissimilar aircraft comparisons but Ill stop there. lol
 
#31 ·
While on topic, for years during Sun-N-Fun we would fly up to Jimmy Leewards Air Ranch in Ocala and join the picnic with the warbirds from the show.
Usually a dozen P-51's, occasional F4U or FG, P-40, AD Skyraider, and a ton of one left flying WWII aircraft.
Pretty cool times, but now that's all gone now that Jimmy Leeward passed. Great guy.
 
#34 ·
Ahhh, I see we have drawn out a lot of ex and current military and just plain aircraft enthusiasts with this one.

I'm overseas right now for a friend's daughter's wedding. Depending on internet access and quality I'll try to post responses but will get to everyone when I get back in a week.

Thanks for all the enthusiasm and shared knowledge.

Ed
 
#41 ·
Taiwan for the wedding of a friend's daughter. Trust me it is more fun back home.

BTW have any of you ever noticed at weddings all the women are grinning ear to ear and all the men, save one, are straight faced. The only guy smiling is the groom - he still hasn't figured it out yet.

Ed
 
#37 ·
Thanks to Administrator MF/Ken I am finally able to view the details starting on the first post of the thread , I think this is a great idea , I'm thinking the shank of the stud will add some rigidity to the crank snout also. Did you end up with much or any clearance between the stud shank and the crankshaft ? also after drilling did you ream to your final inside diameter ? Right on the money or slight interference would be perfect! What are you machining as far as keyway slots for the balancer/pulley drive ? You probably need to modify a balancer installer also, right ? Great tech !

Have a blast at the wedding !
 
#39 ·
Thanks guys ! nice mofasta build , although I am running a different balancer , this tech works for me ! My lethal Lincoln is going to love this !
 
#42 · (Edited)
Mark,

I think you mean the reluctor. Both the reluctor and the lower timing gear will need to be opened up to 1.4" in diameter with the keyways deepened also. Not real tough but not a walk in the park either.

Here is some more info on the crank mod and why in another thread clic here => Crank Mod Info

Ed
 
#44 ·
Apologies Mark, the eyes are tired and the fingers are too. Didn't mean to click the edit button on your post.

The short answers is no because the snout is bigger at 1.4 inches. If you use one of the cinch lock type centers that have a mandrel held in place by the snout bolt with a locking mechanism for locating the degree wheel on the mandrel then you are good to go.

Ed
 
#46 · (Edited)
Ricky,

I accidentally started this post as an edit to your post above Ricky, apologies for mis-mousing the edit post button.

Virtually all forged ModMotor cranks available from anyone today are OEM Ford units made by Kellogg for Ford. In fact if you look at the crank cheek between #1 main and #1/#5 rod journal you will see the Ford Logo forged right into the crank.

The crank shops that try to tell you it is their own custom forging are both BS 'ing you and don't deserve your business. When the cranks are in fact Kellogg forgings they quickly gets to a commodity status and like tomatoes at the supermarket you want to buy the cheapest tomatoes that are the same size (stroke). I would go shopping for a good used crank and don't forget manual trans Mach I's got the same crankshaft.

BTW although the crank material is advertised by the aftermarket crowd as 4340 it is not! It is a modified C38 micro alloy that is similar to but not 4340. Additionally the cranks are very soft inside. The OEM hardening process is paper thin. When I went through the modification process on the Kellogg shaft in my recent post on crank snout fixes click here =>Crank Snout Fix we had to nitride the entire crank before I was willing to use it in my engine.

While you are looking at that post look at the "stock" crank picture. It is actually an aftermarket crank advertised as the usual double throw down ultra blitz racing crank. Take a close look at the cheek of the crank between #1 main and the #1 rod journal. It has a Ford Logo forged into the crank at manufacture. This is a Kellogg crank at a premium price that a major vendor is parading around as a custom forging. The crank even has the under cut fillets right from Kellogg that Ford specs on these cranks. Aftermarket crank shops always use full radius filets on their own manufacture cranks - it's stronger.

The crank your link points to is advertised as having full radius fillets on the rods and mains. If it does it is truly a custom ground forging. Whether or not it is real 4340 or micro alloy requires additional investigation. The easy way to determine if it really does have full radius fillets is to request close up pics of the rods and mains. The full radius fillets will become immediately visible. Ask for a photo with the cheek between #1 main and #1 rod journal visible so you can look for the Ford Logo in the forging. If you do not see the Ford Logo ask if the crank is a Chinese forging. Even with full radius fillets (if it has them) you still have a crank with a tender snout.

If you want to use an OEM crank and don't mind doing a little work, you can use a Coyote crank. FRPP sells them for about $225-$250! Spend a little money at a crank shop to finish the crank for our mod motors and you will be lots of dollars ahead of the game with a mini stroker that will bring you to about 289 cubic inches - how cool is that? Remember though you still have a crank with a tender snout.

As you already know from reading the snout fix post, if it were me again I would just go to a billet crank from the get go. It is unquestionably the best solution and with hard ModMotor parts like cranks all but non existent today and when you do find them they can be so-so, the billet crank solution makes a lot of sense.

Ed
 
#47 ·
Great info once again ed. I can't thank you enough. Does the coyote crank offer any benefits other than 8 cubes? A 289 would be cool. My dad would get a kick out of that! What mode are required to put it in a teksid? Are the 5.0 stroker (3.75 stroke) cranks made well?
 
#48 · (Edited)
Ricky,

The 5.0 cranks are the same Kellog forging the 4.6 uses except ground with small block Chevy rod journal sizes (not a bad idea) at a stroke of 3.75 or 3.8 I can't remember which and all else the same. One of the two strokes is aftermarket and one is Saleen. This is the same crank Ford used in the Saleens. It will give you 297 cubic inches with a std bore. Ford claimed 302 for the magic of the number.

I tend to shy away from the strokers because of how far they pull the edge of the wrist pin below the bottom of the bore at BDC. The flip side of that coin is there are a lot of Saleens and stroked mod motors using the crank - successfully. Personal preferance in the end probably.

The Coyote crank is a bit longer in the snout than a 4.6. It is also worth while checking into rear flange dimensions. Ford mounted the crank position sensor wheel on the back of the Coyote crank between the crank and the flywheel. I don't know if they changed the thickness of the rear flange for the reluctor wheel or not. If they did you can run a Coyote reluctor wheel back there. If they didn't you just bolt up the flywheel and either way you are ready to go.

The front of the crank is a little longer than our mod motor crank to accommodate the TiVCT hardware. The crank grinder would have to bring the stop for the lower crank gear back to the same dimension as a 4.6 crank. The incremental increase in snout length will do you good in terms of locating the damper and preventing movement of the damper.

FWIW the Coyote oil pump is a higher volume pump than the Cobra pump to take care of the TiVCT hardware's appetite for oil. If you use this pump your oil pressure will go up and you ought to look into a higher volume pan.

Ed

<Begin Edit>

Clarification

The 5.0L Coyote crank does not use Chevy journals for the rods. Ford's Saleen crank does. The after market '5.0L' cranks for mod motors, available as either 3.750 or 3.800 stroke, also use small block Chevy rod journals. Both the Saleen and the aftermarket 5L stroker cranks use a 5.850 long rod. Some Eagle crank strokers use a 5.950 long rod. Eagle Specialty Products 5.950 rod is, I believe, unique to them. A standard bore block with a 3.75 stroke crank displaces 297.3 cubic inches and a 3.800 stroke displaces 301.2 cubic inches.

<End Edit>
 
#55 ·
Cory,

Usually your crank shop has nitriding facilities available to him. It is better to do it through a crank shop because when they come back from the nitriding process they require a clean up and final polishing. The appearance of the crank right out of the nitriding process is a dull grey everywhere including the journals. The crank shop cleans the crank and then polishes the journals so it looks and works like a crank again.

Ed
 
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