engine bolt and swing arm bolt material?

mAd mOrdigan

mAd mOrdigan

Been Around the Block
I posted this in another forum that was cb750 specific but maybe I'll try here

so in trying to get some rearsets fabbed up, I realized I need longer engine hangar bolts and a longer swing arm pivot bolt. i normally go to the hardware store and get some all thread but it dawned on me while staring at the swingarm that I need one made of pretty hefty material for the swingarm bolt in order for me to not die from the swingarm falling off if the bolt snaps. this may be obvious to some but what's the stock bolt made of? can I just buy high strength steel all thread such as this provided it's the same diameter and I can cut it down to my liking?

http://www.mcmaster.com/#standard-threaded-rods/=ydxip7

or does anyone have a better idea?
 
I found a longer swing arm bolt at an auto suspension garage. It was all thread but was hardened. Better than soft hardware store steel. It is 9/16" but fits nicely in the swing arm. Are you sure you need longer engine mount? Usually the stock pegs are mounted there so in my case I actually had to cut it down once I removed the stock pegs.


Yeah Son!
 
Certainly you can buy strong enough all-thread. The problem is that the swing arm needs the correct diameter to align the spacers/bushings/bearings correctly with the frame. If you can in fact get the major thread diameter to match your situation, than it should work fine, if not exactly engineered very elegantly. The only other concern is that all-thread is inherently inferior as the continuous thread makes a crack-prone stress riser at the base of every thread. The stock bolt is smooth at the critical locations and is much more reliable. Surely you can find an alternative solution to mount your pegs.
 
There are enough machinists and fabricators here that I'm sure someone could make you a proper part.
 
in this case yeah I need a longer swingarm bolt or cut. portion of my frame to get the rearset brackets to work. I was told a cb750F 77/78 had a longer bolt.. problem is I hardly see spare parts off those years F models
 
Sorry I didn't get back to you. Was at the Indy GP all weekend, and driving all day yesterday.

What'd you need? I have a couple dozen orders to get caught up on from the weekend, but I could get it in this week.
 
mAd mOrdigan said:
in this case yeah I need a longer swingarm bolt or cut. portion of my frame to get the rearset brackets to work. I was told a cb750F 77/78 had a longer bolt.. problem is I hardly see spare parts off those years F models
Click to expand...

i have a set that SHOULD be for F model. What length do you need?
 
The engine bolt is normally grade 8 or 9, swing arm pivot is almost certainly grade 9 or 10
Shear strength is probably around 55 tons.
Haven't done any research or testing since early 70's though
 
Do you have actual dimensions? I may have something at work that'll do the trick. No promises but I'll look.
 
Best guess is Grade 10. If you want a custom rod turned, ask for 4140 steel. Harder than regular steel, more wear resistant, and more corrosion resistant. You could always go with custom sized chrome (Induction hardened) bar which is very hard. You'll pay for it to be threaded and a head put on it, but it'll last forever.
 
it doesnt need to be nor are any of the stock vintage jap stuff any tougher than cold rolled,they all cut and machine easily
grade 10 would huge overkill and totally uneccasary
the exeption would be like a vintage husky mx bike some of them used a scary small diameter swinger axle 10mm and 12mm and you can bet they are good heat treated swedish steel
 
Most 'vintage' Japanese bikes only use 10 or 12mm dia swing arm bolts, some, larger diameter ones, are known to break pretty easy (eg XS650, but I'm pretty sure that’s because they are severely overtightened?)
 
I am damn sure and almost positive the ones from Japan are made from melted down Ford, Chevy, Oldsmobile, Buick and Dodge cars and trucks :o
 
As XB mentioned, stock bolts are not particularly hard or strong or large diameter.

If you are considering getting a custom swingarm bolt made, you may want to think about going up a couple of sizes and hollow it out for more strength and less weight.

For example I recently fitted a larger diameter RF900 swingarm bolt into a GT750. Had to ream out one side to size and drill and retap the other side so the bolt tightened into the frame.
 
This: is how I handled fitment on a CB to FZ swinger swap, had to skim off a few thousandths on the stock chunk and cut the FZ, drill an plug weld as a unit... Worked perfect, but added a few OZ's
30de0351f576258bb040a6ac25fb5e51.jpg
3ae52c2d5f1988fb227e3a4690f60412.jpg
a4cde40930f821785fc2f31f75d24f07.jpg



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