What's the margin of safe spoke torque?

[SenseAmidMadness]

Specific question to anybody who's built up spoked wheels before.

I recently rebuilt the rear wheel on my 1980 CB750K with new spokes and nipples from CB750 Supply. I got it trued up, emailed Buchanan's Spokes, and they told me that the rear should be torqued to 60 to 65 inch-pounds. They also said the front should be 40 to 45 inch-pounds and I'm planning to tackle that next.

I bought a fancy Warp9 spoke torque wrench and set it to the correct 65 in-lb, and tightened up my rear wheel every 3rd spoke. My initial level of "true and tight", when I had trued the wheel and kept turning until I heard nice rings from all the spokes, was easily 1 or 2 full turns away from the correct torque spec. That worried me.
What's also got me worried now is just how untrue the wheel now is after the correct torque got applied to all the spokes. I had anti-seize compound on all the threads so they were all lubricated, but some were still harder to turn than others. Maybe poor quality spoke nipples; the kit I ordered was missing one of the inside spokes.

What I'm wondering is how close I need to have the spokes to their spec for safe riding without breaking spokes or ripping out the holes in the hub. I need to true the wheel again and I know all the spokes won't be the correct torque any more if I do that, because some will have to be loosened and others tightened.

I bought the torque wrench to give me an objective setting for all the spokes, but using it has just confused me more.

What's your opinion? Do I need to have them all very close to the torque spec, or could I have them safely be looser as long as all the spokes are reasonably close to each other?

 

[slmjim n Z1BEBE]

What is the torque spec in the FSM? 60 - 65 in. lbs. and 40 - 45 in. lbs. sounds high to us but, we're used to OEM mild steel spokes on Kawasaki Z1's. Torque spec on Z1 spokes is 22 - 26 in. lbs. in the FSM. That might be different for stainless spokes; we've never used them. We lube the underside of the head of the nipples where they contact the rim also.

There's an under-appreciated consideration of spoke torque in addition to thread stretch; the amount of force being applied to the holes and flanges of the hub. Too high torque on too many spokes can pull a piece of flange off the hub before any spoke threads strip. That was a problem on some vintage Triumph's & BSA's. Buchanon has most likely taken that into consideration on their recommendation, but it's still worth a mention.

We use a Fasst Co. adjustable spoke torque wrench with the only head we need for Z1's.
https://www.fasstco.com/products/spoke-torque-wrench
When we re-spoke a wheel, it usually requires 4 ~ 8 hrs. to true once all spokes are laced. We'd starve if we did it for a living.

Rims on a Z1 are centered laterally on the plane of the hub. Some other bike's rims are offset. That should be in the FSM also. We get lateral centering right first, then sneak up on the lowest correct torque a little at a time with lots of spins in the truing stand. We continue, making sure the rim remains centered, true & all spokes are somewhere in the range of torque as spec'd in the FSM.

Good Ridin'
slmjim & Z1BEBE

 

[SenseAmidMadness]

Thanks so much for your reply! I appreciate your input.

The FSM has no torque spec listed for the wheel spokes, which is why I emailed Buchanan's. My guess is that back in the late 70's, all motorcycle techs were so familiar with doing wheels up by feel that Honda didn't think it necessary to include the spoke torque spec.

What I'm wondering is: if I had tightened up the spokes by hand to, say, half of the recommended 60 inch-pound torque spec, would that pose a significant risk of breaking spokes on the rear wheel? I'm wondering if it would be better to skip the torque wrench for this particular bike if there's a nice wide margin for error on final torque.

 

[slmjim n Z1BEBE]

Surprised Mama Honda didn't spec spoke torque.

Found this:
http://forums.sohc4.net/index.php?topic=46857.0

The OP states "...1.9-2.2 ft. lb. for the front and 1.5-1.9 ft. lb.for the rear." We would never try to set torque that low using a ft. lb. wrench; it's far too close to the bottom of the scale to be accurate.

There's a couple other posts elsewhere on that forum that indicate the Clymer manual states 1.5 - 2.5 ft. lb.

A although the math is easy on this one, a conversion calculator indicates 2.0 ft. lb. = 24 in. lb.
https://www.thecalculatorsite.com/conversions/common/inch-pounds-foot-pounds.php

24 in. lb. is right in line with the KawasaKI Z1 FSM spoke spec. of 22 - 26 in. lb. using OEM mild steel, galvanized spokes. We suspect the spokes on your 750 are very close to the same gauge wire, if not the same, as those on a Z1. We can mic a Z1 spoke if you wish.

Good Ridin'
slmjim & Z1BEBE

 

[SenseAmidMadness]

If you could get the diameter of one of those spokes I'd definitely appreciate it.

Yeah, I just double-checked my genuine Honda service manual and it says nothing about spoke torque. Doesn't have procedures for spoke replacement or adjustment either, just a "measure wheel for runout" procedure.

Any guesses as to why Buchanan's recommended a spec over twice what is typical for other machines of the era?

I think the SOHC wheels are built just the same as these ones...maybe a minor update to the shapes of the hubs and bearing diameters but they're still aluminum-alloy hubs with radial flanges, plated-steel spokes, and plated-steel rims. I think the rim part was shared with earlier models too.

The parts fiche does list the wheel spokes as unique to 1979-1982 Hondas, and says the front spokes are "8X201" or "8X200.5". I'm guessing that's 8 gauge because it sure isn't 8mm.
Same story for the rears. 8x127 and 8x127.5 and not used on anything but CB750's and 650's for those four model years.

The good news is I haven't put the wheel on the bike yet, so I can un-torque the whole thing and use my spoke torque wrench to take it back up to a consistent 26 inch-pounds.

 

[slmjim n Z1BEBE]

Using a digital caliper. Our micrometer is... somewhere.

F & R Z1 spokes are slightly differently diameters.

Definitions:
Shoulder - thickest part of the spoke close to the hub, before it tapers.
Body - main body of the spoke between the shoulder & nipple.

F shoulder - 4.05mm
F body - 3.55mm

R shoulder - 4.55mm
R body - 3.55mm

Buchanan seems to specialize somewhat in stainless spokes. We've never used them. There may be a difference in torque values between stainless & mild steel. We can only assume they take into account radial tension on hub flanges.

You mention 650's. Perhaps spoke torque is available in a google search for 650's.

Good Ridin'
slmjim & Z1BEBE

 

[Loose Chain]

Having the spokes torqued the same amount doesn't mean the wheel will be true. It is a slow going process that takes patients and know-how. It is not just a matter of having a torque wrench. If you have the wheel laced then take it to someone that knows what they are doing to finish it.

 

[SenseAmidMadness]

If you have the wheel laced then take it to someone that knows what they are doing to finish it.

No. The whole point of me doing this and asking questions is so I can learn how to properly build up wheels. Taking it to someone else would defeat the purpose.

I also know that even torque doesn't automatically make a wheel true. Torque wrench gets applied to spokes *after* truing according to every guide I've read.

To slimjim -- thanks for your info. If I remember tomorrow I'll get some measurements off my new CB750 spokes for comparison.

 

[Loose Chain]

No. The whole point of me doing this and asking questions is so I can learn how to properly build up wheels. Taking it to someone else would defeat the purpose.

I mentioned taking it to someone to help in case you might be biting off more than you can chew. I know you want to learn, which is good but, sometimes people dive into things they really aren't prepared for. I have seen it too many times where people think that being a mechanic is easy and they end up causing unnecessary damage and huge costs to themselves. When a person is taking off their carburetors for the 5th or 6th time for example, maybe it is time to tell themselves they don't have what it takes. Many think that if they "Google it" or go on "Youtube", they too can be a mechanic. Carry on and good luck with your project.

 

[SenseAmidMadness]

Couple of fun new twists.

New spokes on the rear wheel:
4mm shoulder near the hub, 3.5mm the rest of the length.
So about a half-mil smaller than those Z1 spokes in both dimensions.

I did the "ping" test on my now-torqued rear wheel, and on the original 17 inch rear wheel that's still on the bike. Other than a couple "dead" spokes on the original wheel, the range of pitches were similar, with a slightly higher range for the 17 inch original wheel! Freaky.

Did Honda torque these wheels really high at the factory maybe? Buchanan's may have been simply copying Honda's homework.

 

[SenseAmidMadness]

I did quite a bit more digging and browsing forums and found a few encouraging things.

Guys who had lots of experience building wheels, back in the day, never used torque wrenches. They'd do the "ping" by ear test.
The impression I got from my reading says that the spokes being tight enough to ring, with the wheel true, means it's safe to ride on -- with the only risk being that if the spokes aren't as tight as recommended they may slowly loosen up with riding. I found plenty of people saying "ride a few hundred miles on your new wheels and then recheck spoke tightness as they will have loosened" including folks on the SOHC forums.

I also found a couple sites, including Fasst Co, saying that higher spoke torque than the typical 20-30 inch-pounds is safe, and that most wheels can go a whole lot tighter without damage. Their most popular torque wrench is fixed at 48 inch-pounds and they say that's a fine universal torque for dirt machines over 85cc; enough to stay tight but not enough to damage anything. One thread, and this was on a SOHC CB750 site, even quoted the same spec Buchanan's sent to me, which they had stated was for those SOHC spoked wheels.

All this basically leads to what I've concluded: the margin of safe tightness in building a wheel is pretty wide. The range between "the spoke doesn't ring" and "I ripped a spoke hole out of the hub" is much larger than I thought at first and spoked wheels can take plenty of force once the spokes are under enough tension to ring when struck.

I think Buchanan's, and Honda's factory wheels on my machine, lean heavily towards the "get it real tight and it will never back off" side of the tightness spectrum. That might explain why Honda didn't specify a torque spec *or* a repair/truing procedure for these wheels in the FSM. The expectation was, I'm guessing: these wheels should never loosen up enough to be dangerous.

Based on the "ping test" between my old and new wheels I think I'm going to loosen the wheel, re-lubricate all the nipple threads and the rim holes, and try again, this time truing it and more carefully tightening to a torque spec of 48 inch-pounds. I'll build the front to 36. Then in a few hundred miles I'm going to check again.

Pic is of the wheel when I finished it; gonna have to take the tire off again, but oh well. This has been a good learning experience.

 

[Loose Chain]

Don't over think it. If you have the wheel running true and all the spokes are tight, you are done. I have never used a torque wrench on a spoke wheel. I have done old British sports car wheels as well as bikes and it was all done by feel and never had a problem.

 

[SenseAmidMadness]

Several folks in my reading said the same thing. I just want to have a bit more of an objective reference for tightness of the spokes, if that makes sense.

I had no trouble building the wheel up and getting it nice and true until I introduced the torque wrench, so...maybe you're right. What really bothers me is I had both the lateral and axial runout down to .2mm or so and now it's a lot worse.

If I can't get this rear wheel both true and torqued with the wrench, then I'll stick to your advice and might even sell that torque wrench.

 

[Loose Chain]

You might be better off loosening everything off and starting over instead of "Chasing" it. It can be frustrating doing your first couple of wheels but it gets better.

 

[SenseAmidMadness]

You might be better off loosening everything off and starting over instead of "Chasing" it. It can be frustrating doing your first couple of wheels but it gets better.

That's the plan. Going to remove the tire and tube, loosen all the nipples completely, and start over, as annoying as it is.