Crankshaft Bolts (2012)

Someone should pester Sir Eddy on his 90' crank fasteners.

what is that? a studs or bolts, doesn't seems to go way through the flywheel i guess they have threads on the flywheel

i want to make a custom flywheel too.. ARP confirm that off the shelf 3/8" 12points bolt they have are 0.374" shank
is the NAS-626 or NAS-624 shank 0.375"?

OHhhh, good catch Martin I missed that detail. Must be as you say but will have to ask the details. Sir Eddy can only work a few hours and not a 'puter whiz so email brief but will talk shop in glee.

MARTIN.K said:

what is that? a studs or bolts, doesn't seems to go way through the flywheel i guess they have threads on the flywheel

i want to make a custom flywheel too.. ARP confirm that off the shelf 3/8" 12points bolt they have are 0.374" shank
is the NAS-626 or NAS-624 shank 0.375"?

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Almost all the common NAS, MS, and AN 3/8" bolts are .374" shanks. The usual limits for them in the mil specs is .3735" - .3745". There are some special mil-spec bolts for tighter fits, but I don't recall the details offhand.

Ken

I should mention that if you decide to use the NAS or MS "Superbolts" (NAS624, etc.) you have to use a washer under them that is beveled on the inside to clear the large radius between bolthead and shank. I suppose you could also just bevel the edge of the holes in the crank halves.

Ken

Zint @ Lindskog's and I found that there are no off the shelf super duper fasteners available with all the dimension distinctions ready to go. Counter sinking or contouring seats required for optimal configurations. Note how cosmoz did his ARP's recessed seats. A real shame if new stock 850 studs are inferior to what TC used in his engines over many seasons w/o ever opening up. He said 8000 intended shift point on his 150 hp engines but often over shot that with things happening so quick and harsh. it would be educational if anyone can report a crank failure that was fastener related to see what we might be risking w/o shopping outside Norton part numbers. After Peel's fastener saga a decade ago and seeing how nil issue sludge trap is, its was a no brainer to me to have it welded up with access ports to clear trap every couple decades or so.

Steve. If you look at the other pic of the flywheel,which is 4140, you will see the tapped holes that " Unbrako" super high tensile .3745" dia allen bolts that fit in .375 reamed crank holes. All bolts are exactly same length so when correct torque is known then the stretch method can be used for the hard to get too ones. The cranks positiveley position on the centre dowel and another one near the od of flywheel.With 3/4" of 4140 threads and a bit of loctite,those bolts are not going anywhere.
Sir Eddy.

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Only fasteners I measure are rod cap bolts and crank shaft fasteners and then only by stretch method while everything else is done like factory crew by pure feel.

There's some rules of thumb on bolt grade, length and dia and will ask Sir Eddy what is crank bolts were stretched too but i suspect it will land in the .0065-.007" range. Here's a fastener tech article I can just look as the pictures pretending to read.

http://sections.asme.org/wts/Flyers/FTI ... 090419.pdf

Ah, young weedhopper is learning. Gone are the days of "tighten as much as you can".

Good reference article there hobot. Good illustration of forces with and without lubrication and good discussion of design and specifications in elastic range.

Best to stick with OEM or EM recommended torques unfortunately they rarely specify whether they are lubricated or unlubricated.

Ken
the specs .3735-.3745, that mean using a .374 still can do right?
NAS or ARP 170.000psi yield strength for a try?

Hobot
from that picture i saw a thread on the crankshaft, am i seeing it right?
the very right corner hole.
so he is using a 3/8 allen bolts.. did he suggest a brand or anything?

Martin, turns out one of ole fart tough as dried leather Eddy has a crank for sale but don't know if fits you needs. Remember cam lobes and ignition triggers must be altered too. Here's latest update ...

Steve, Can't get back into Access to send messages.

Will know the stretch when I check the torqued up ones first;would guess .005-006.

For added security after communicating with Jonn Magyor [Shrapnel Dodger] about 3 months ago about not using the stock cast crank halves. I am waiting for Gregg Blagus to finish building a 4130 billet crank.Gregg is well known and highly recommended.

He is also heat treating my original that runs +/- .001" and it will be for sale when it returns.The stroke is 59.6mm-with a 73mm bore is 499cc. That short stroke will give a safe piston speed of 11,000 rpm.Wiith 6mm valves;bsa followers;needle bearing rockers ;specially designed cam by Web Cam , and lighter springs than stock we will not put any overdue strain on camshaft,so do not anticipate any problems with the camchain drive as John Magyor had;if needed I can build a centre cam support.

The reason I showed my original bolt together crank was to see the feedback it received. It did get nortoneers attention.
Cheers. The Old Geezer. Ed. siredwardbs@canby.com

MARTIN.K said:

Ken
the specs .3735-.3745, that mean using a .374 still can do right?
NAS or ARP 170.000psi yield strength for a try?

Click to expand...

When I used NAS bolts, I was converting the crankshaft from the original 5/16" fasteners to 3/8" fasteners. Drilling the holes larger, and reaming to .375" size gave a good, tight, fit with the .374 bolts and studs. I don't know if the same bolts would give you a good fit in the MK3 crankshafts, which already have 3/8" fasteners.

MARTIN.K said:

Hobot
from that picture i saw a thread on the crankshaft, am i seeing it right?
the very right corner hole.
so he is using a 3/8 allen bolts.. did he suggest a brand or anything?

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He said he used Unbrako bolts. That's a common brand name, available from internet suppliers like MSC, Grainger, and McMasterCarr, and most other quality fastener suppliers here. Their alloy steel socket head cap screws are typically 190,000 psi tensile strength. However, the tolerance on their shank diameter is much larger than for the aerospace spec fasteners. For a 3/8" socket head fastener, they allow the shank to be .3678" to .375". It looks like Sir Eddy gets around that by using precision dowel pins to locate the crank halves on the flywheel. They are also not available in length increments of 1/16" like the aerospace fasteners are, so you would probably have to shorten them to suit the application. It looks like that is what Sir Eddy has done on his crankshaft. They should work fine, if done properly.

More info at http://unbrako.com/

It's fair to mention that Unbrako also makes fasteners for custom applications, and it's possible Sir Eddy has found some made to a tighter specification. Lots of interesting sorts of fasteners used to show up on the surplus markets, but most of that's dried up now that eveyone is worried about liability litigation.

Ken

for a 190.000psi that exceed ARP 3/8 off the shelf bolts tensile strength, but not 240.000 ARP custom option bolts.
but good enough for a off the shelf bolts.

http://www.ebay.com/itm/Socket-Head-Cap ... 2a178a4921

i think this is 3/8 inch bolts from UNBRAKO that can be use and order easily..

there is 16 option:
16 x (choice of): 3/4", 7/8", 1", 2 1/4", 3", 3 1/4", 3 1/2" or 4 1/2"

which one should i choose?
from the picture it's quite long so it can be cut to fit any kind application needed..

Hi Martin, not sure but but , isn't it better to fit UNF instead of those UNC, fine pitch seems better for that application....?

Has anyone actually had or heard of factory flywheel fasteners giving up before something else did first?
I had 3 crankshafts bent from either over rev stuck throttle way way beyond anything the tach could read or something else like rod cap bolt or piston parting give up first to lock up crank to bend it and ruin journals but factory fasteners were just fine and reusable. I collect failure stories and heard of a few cast iron flywheels exploding even at idle, so most though-effort should go into that most. If ya want a bit more toughness-tolerance in your parts and fasteners might consider the cryogenic tempering process. Cryogenic tempering is the only thing that worked to allow production of the Norton rotary crank as no metalurgy of crank or fasteners could handle the thermal distortion loads till they tried that and the rest is history. Here's a reference to translate or brush off like hobot lingo.

ZHANG Shusong(Xi'an Institute of Technology)ZHOU Shulan;TONG Ailian(Nei Monggol Research Institute of Metallic Materials,Baotou)
A study of toughening effectiveness and mechanism owing to the improvingof mierostructure morphology has been made with the high strength steel28Cr2MoV as an object.It was found that the impact toughness α_K and fracture toughness K_(ie)were improved remarkably in all tempering temperatture region.The improve-ment of toughness at high temperature tempering is mainly due to the spe-cial effects acted by the carbide particles not thoroughly dissolved in rapidaustenizing process.The solute riched vinicites beside residual carbide serveas nucleation position in austenizing process,refine the austenite grain.The-se residual carbides also serve as dislocation multiplication resource in sheartransformation under coolig precess and achieve high dense dislocation inquenching structure.The dislocation provides a lot of nucleus to facilitate,thecarbide precipitating finely,dispersedly and thoroughly at tempering process,and therefore the toughness of the steel at high temrerature tempering isimproved significantly under the same strength.

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MARTIN.K said:

for a 190.000psi that exceed ARP 3/8 off the shelf bolts tensile strength, but not 240.000 ARP custom option bolts.
but good enough for a off the shelf bolts.

http://www.ebay.com/itm/Socket-Head-Cap ... 2a178a4921

i think this is 3/8 inch bolts from UNBRAKO that can be use and order easily..

there is 16 option:
16 x (choice of): 3/4", 7/8", 1", 2 1/4", 3", 3 1/4", 3 1/2" or 4 1/2"

which one should i choose?
from the picture it's quite long so it can be cut to fit any kind application needed..

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As marinatlas said, but maybe more forcefully, you don't want to use the coarse thread fasteners in your ebay link. You want to use 3/8-24 fine thread fasteners for this application (or maybe 10 mm if you want to go metric). If you want to use the Unbrako brand, they should be readily available from any on-line industrial supply source.

You can get them from Grainger

http://www.grainger.com/Grainger/socket ... sst=subset

or MSC

http://www1.mscdirect.com/eCommerce/Nav ... ndizedOk=N

or McMasterCarr

http://www.mcmaster.com/#socket-head-cap-screws/=jf3sj1

Another quality maker of socket head cap screws is Holo-Krome, which some of these suppliers also carry.

You also want to be careful about shortening longer bolts. You need to make sure that you are relying on the shank portion of the fastener for shear strength, not the threaded portion. That means making sure the shank portion is long enough to extend through both the crankshaft ends and the flywheel. One of the benfits of using aerospace fasteners is that they are available in 1/16" increments of length, which allows you to pick a length that has the correct shank length.

Ken

http://www.ebay.com/itm/12-pcs-MS21250- ... 92&vxp=mtr

i saw this, i try to look on the spec for this bolt but google can't help me.. anyone know this bolts tensile strength?

That ad has the word 'nickel' in it which I presume means plated. Hydrogen embrittlement is the enemy of high tensile bolts under tension.

what about Cadmium plated steel? are they bad under tension too?

http://www.ebay.com/itm/3-8-12-point-Bo ... eb&vxp=mtr

i bought unbrako 3/8" for fitment test they stated 190.000psi tensile strength.. but still looking for something else that is better, most of the aviation parts seller on ebay don't know what the bolts are used for..

MARTIN.K said:

http://www.ebay.com/itm/12-pcs-MS21250-06020-12-Point-Bolt-3-8-24x1-25-Nickel-/150619540882?pt=Motors_Aviation_Parts_Gear&hash=item23119fcd92&vxp=mtr

i saw this, i try to look on the spec for this bolt but google can't help me.. anyone know this bolts tensile strength?

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Their auction listing says 180 - 200 KSI. My listing for MS 21250 says 180 KSI. And I wouldn't worry about hydrogen embrittlement. These are Military Standard bolts so would have been properly treated after plating, if required. I don't know if "diffused nickel plating" requires heating for hydrogen embrittlement protection after plating, but if it does, the mil=spec will require it.

Ken