Crankshaft Bolts (2012)

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Been though this a decade ago with Zint at Lindskog's Balancing. What matters is the shaft area long enough not to put stress riser threads in the shear load zone. TC and I found that 850 studs are up to about anything the crankshaft cheeks can stand but does look cool to see APR fasteners in there. I had Peel's 750 crank drilled for interference fit for 850 size studs. I asked this fastener question in the Crank Prono post but not responses so hope yours gets informative attention. On her new crank I bypassed this for welding it with some access ports to clean sludge trap every decade or so.
 
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Stick with the factory (OEM) standard studs. Nothing to gain here. This is a solution hunting for a problem.

Besides, you are likely introducing an out of balance (rocking couple) condition when you go with bolts and nuts.

I thoroughly grenaded a Commando flywheel and the crankshaft studs were still in place.

If you are in the motor now and want to do something worthwhile, replace the cast iron flywheel with a steel one and maybe a lighter steel one; depends upon what you want to do.
 

lcrken

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I'd have to agree with Dances about using the standard studs, nuts, etc., although I'd go with the later design that used 3/8" studs, as opposed to the earlier 5/16" fasteners. Early cranks, up until '73 or so, used a combination of 5/16" bolts and studs, while later ones used 5/16" studs for all the fasteners. In 1975 they went to 3/8" studs all around, along with the other design changes to the crankshaft for the Mk3.

Having said that, I have to admit to using NAS nuts and bolts and AN studs on some race crankshafts. If you choose to do that, there are a couple things to keep in mind.

First, note that the top (closest to the flywheel edge) two fasteners (bolts in early Commandos, studs in later models) are a tighter fit than the other four fasteners. That's an intentional design detail from the factory. The tight fit of those two fasteners and the dowel pin are what locate the crankshaft halves to the flywheel very precisely. If you replace the fasteners, you want to be sure you still have that fit for the top two bolts/studs. It is pretty simple to keep that fit when converting the earlier crankshafts from 5/16" fasteners to 3/8" fasteners, which was a common racer mod back in the day. All we had to do was use a precision reamer to fit the top two bolts, after drilling them slightly undersize for 3/8". The other four fasteners could be simply drilled to size. This is a picture of a crank I did back in the late '70s showing the fasteners I used.



You'll note that the heads of the top two bolts, as well as the nuts, are reduced in size to fit the spot facing on the crankshaft halves. You'll also note that studs are still required for the two fasteners by the dowel, because you can't get bolts to clear the counterweights. Dances' comment about balance problems with using bolts instead of studs is well taken. I installed the bolts in a specific configuration, and then had the crankshaft balanced. As long as I kept track of the fastener conguration when disassembling and reassembling the crankshaft, the balance was undisturbed. If I were doing the same thing today, I'd probably just go with high strength studs and nuts instead. I used the 12-point NAS nuts and bolts because I was copying what Ron Wood and Axtell had done with Ron's crankshafts back before he had his one-piece crankshafts made. Besides, it looked really trick!

Ken
 

comnoz

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For high performance use I assemble the crank with the three stock locating bolts or two bolts and a dowel and then ream the remaining holes for 10mm ARP studs. After they are installed I remove the remaining stock bolts and ream them for the 10mm studs also. May be overkill but I have not been too happy with the new stock bolts I have seen lately. Jim
 

comnoz

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When I say I am not happy with new replacement bolts here is why.

This is an oem bolt from a factory crankshaft.



Here is a factory replacement bolt



Here is an ARP stud



I realize there is more to a bolt that it's hardness but an increase in hardness also generally indicates an increase in tensile strength. These numbers shown have not been corrected for curvature so the numbers are not as high as they would be if corrected but they are accurate for comparison. Jim
 

rvich

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OK, I'll bite. There are at least two holes that can't be reached for reaming while the crank is assembled. How do you get in there? Keebler elves?
 

comnoz

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Go ask Alice.

I make them oversize, that still leaves 5 bolts for locating. which is better than three. Jim
 

lcrken

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comnoz said:
For high performance use I assemble the crank with the three stock locating bolts or two bolts and a dowel and then ream the remaining holes for 10mm ARP studs. After they are installed I remove the remaining stock bolts and ream them for the 10mm studs also. May be overkill but I have not been too happy with the new stock bolts I have seen lately. Jim
Can't argue with ARP fasteners. They really know what they are doing, and their quality control is exceptional. I didn't realize that the OEM items had gone so far downhill in quality, but I guess it's not so surprising.

Ken
 
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From the pictures Jim was so kind to provide I see that the first item is a bolt, the second and third items are studs. I would not expect a bolt and a stud to have the exact same hardness as their applications may be a bit different. Would be interesting to see a factory bolt compared to an OEM replacement bolt and to see a factory stud compared to an OEM replacement stud. No doubt the ARP's are likely tougher than the factory or OEM. If you can get ARP's to drop in with little to no trouble then why not?

From my experience, the most important thing is getting the components properly assembled and properly torqued.

Not too long ago a major "Yahoo" on this list spouted off about how you are supposed to get these crank nuts and bolts as tight as you can lean into it with a wrench - well that is flat out foolishness.

These fastener applications, like most, are designed to be in the elastic range of the bolt/stud material. If you think that tightening them up closer to or into yield is good, what do think happens to the bolt once it goes under dynamic loading and is further loaded?

Anyway, just my opinion here but unless you are really going to stress this under race type conditions, stick with OEM bolts and studs and proper assembly and torquing as it is a non-issue.
 
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Here's Peel example of factory and upgraded steel smaller OD lighter one. That alone relieves some of the fastener strain. We might speak with Anover's to order up a batch of APR fasteners made to order. The magic marker black out is where to remove mass if wanting to lighten it even more.



BTW I notice some nut have threads relieved on one side and flush to the flat on the other. I reasoned the relieve side goes against the nut seat, yes no?
 

comnoz

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Dances with Shrapnel said:
From the pictures Jim was so kind to provide I see that the first item is a bolt, the second and third items are studs. I would not expect a bolt and a stud to have the exact same hardness as their applications may be a bit different. Would be interesting to see a factory bolt compared to an OEM replacement bolt and to see a factory stud compared to an OEM replacement stud. No doubt the ARP's are likely tougher than the factory or OEM. If you can get ARP's to drop in with little to no trouble then why not?

From my experience, the most important thing is getting the components properly assembled and properly torqued.

Not too long ago a major "Yahoo" on this list spouted off about how you are supposed to get these crank nuts and bolts as tight as you can lean into it with a wrench - well that is flat out foolishness.

These fastener applications, like most, are designed to be in the elastic range of the bolt/stud material. If you think that tightening them up closer to or into yield is good, what do think happens to the bolt once it goes under dynamic loading and is further loaded?

Anyway, just my opinion here but unless you are really going to stress this under race type conditions, stick with OEM bolts and studs and proper assembly and torquing as it is a non-issue.

The bolts and the studs test the same. Jim
 
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So if I understand this correctly, the factory studs and bolts test the same for hardness and the OEM studs and bolts test the same for hardness but are softer than factory (studs and bolts) and ARP or hardest.

Correct?
 

comnoz

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First off I want to say that I am in no way putting down Andover for the crankshaft bolts being provided. It is simply a matter of economics. The original bolts were heat treated high tensile bolts and studs. They were built to a spec and were ordered in large numbers.

Heat treated special bolts in the numbers needed to supply the Nortons today would be extremely expensive. What is being provided today are simply machined from stock bolts. They are obviously adequate for the majority of users of these bikes as I haven't heard of a bunch of loose crank bolts that would be the result of bolts that were stressed beyond their limit.

For racing engines I would look beyond what is being supplied as factory replacements. Jim
 
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Jim, i decide to go with ARP.. can you share the ARP part number for the stud you used?

i contact ARP about the bolts last night they say for a 3/8" bolt they have the shank will be .374 not .375 this also won't matter right?
 

comnoz

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Martin,
I don't know if the .374 bolts would be a snug fit in the locating holes, I have never tried them. I will have to do some looking for the 10mm ARP numbers I use. Jim
 
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Martin,
These guys are a great source for NAS hardware. They can supply exactly what you need including the correct grip length so that nothing is riding on the threads. They have one of the best catalogs ever. Fastener porn. :shock:

http://www.coastfab.com/hardware.html
 
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Thanks for posting that link rpatton, another great reason that I love this site. Cj
 
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Hi, should be nice if someone could sort out the specs of the studs/bolts we need for our crank ,from that catalogue, so newbies could ordered them , without hesitations or misunderstandings........I had to admit , i was a bit lost when serching in it!!
 
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marinatlas said:
Hi, should be nice if someone could sort out the specs of the studs/bolts we need for our crank ,from that catalogue, so newbies could ordered them , without hesitations or misunderstandings........I had to admit , i was a bit lost when serching in it!!
http://www.google.com/url?sa=t&rct=j&q= ... PQ&cad=rja

This is a good primer on ordering bolts. You might have a hard time getting replacements for the studs. The stock parts might be ok on the crank, but the cradle bolts could use an upgrade, oversized.
 
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