incorrect torque spec for caliper hex bolts in Haynes?

[marp68]

So, I stripped one of the two caliper hexa bolts when mounting the two caliper halves together.

Haynes said 43-73 ft.-lb (6-10) mkg. Even though it sounded suspicously high I started working my way up and finally stripped one bolt and hole.Are these torque spec really correct for this thin bolt? For the bigger two bridge bolts Haynes spec 53.5-68 ft.-lb (7.5-9.5 mkg).

Anyone has the correct torque spec for the whole brake systems. I don't trust my Haynes no more.

And would helicoil make it strong enough to retighten hard enough? Or are this caliper wasted?

 

[grizld1]

Back in the day Yamaha printed a number of wrong conversions in their service literature, which Haynes and Clymer copied faithfully (another example: 44 ftlbs. specified for the 8 mm. fork damper rod bolts; the correct conversion is 14 ftlbs). The metric specs are reliable; when in doubt, do your own conversion!

 

[theDQG]

Back in the day Yamaha printed a number of wrong conversions in their service literature, which Haynes and Clymer copied faithfully (another example: 44 ftlbs. specified for the 8 mm. fork damper rod bolts; the correct conversion is 14 ftlbs). The metric specs are reliable; when in doubt, do your own conversion!

Mind elaborating, please?

 

[marp68]

Since I had my doubts on those figure but went ahead, I'm more than angry (and ashamed) with myself right now.

Would helicoil be a suitable repair for this mounting?

grizld1, since the ftlbs in this case corresponds with the mkg and neither of them is right, do you perhaps have the correct torque spec for the caliper halves mounting? Or what would you recommend?

 

[gggGary]

Sorry Marp yet another "educational expense". IMHO no helicoils on brake calipers. No torque wrench (or spec) is a substitute for common sense. You know that now but I sure get tired of seeing parts ruined............. You see an odd spec do a little checking to see if it's real or a typo. There are a few high torque apps on the XS and elsewhere GOOD manuals make a point of stating yes this is a high torque bolt etc.

 

[gggGary]

That was from Yamaha and the 10 X higher torque one paragraph to the next seems rather suspicious doesn't it? I don't think in metric, so these have little meaning to me.....

 

[grizld1]

DQG, and there are conversion calculators all over the net if you don't know the factors. Use one; Google is your friend.

Marp, if the conversion is correct, I'd have trusted the specs too. I don't know why a helicoil wouldn't work. Maybe gggGary or 2M will weigh in with torque and repair recommendations.

Edit: Dang you're fast, Gary!

 

[grizld1]

60 kg-cm is 4.34 footpounds; that sounds light, but Gary pegged the error ; Haynes misprinted mkg for kg-cm, giving a spec 10 times too heavy.

 

[5twins]

That old type caliper is held together with 4 fasteners, two larger and two smaller ones. That's why two torque values are given, one for the big bolts and one for the little ones. No matter, they're both wrong and too high. If I run across a given torque value that just seems wrong, I go with the standard for that bolt size. If it's threading into alloy, I might even use a bit less than the standard.

 

[gggGary]

Standard torque specs any great deviation from these should be viewed with suspicion. Note this and my previous pic are from the FACTORY manual.

 

[marp68]

Thanks for the input. I don't know why I didn't stopped and checked. Normally I'm very careful with everything, since not being a experienced mechanic. Suppose the small intuition bells I heard somewhere ringing in my head wasn't loud enough this time.

Anyway, just have to bite the bullet. Seems to be different opinions about the helicoil, and I have great respect for the knowledge of these two gentlemen. Is it not the two bridge bolts that really keep the halves together and the two hex bolts that keep it tight enough to get the o-ring to seal properly? Wouldn't this mean that there is less pressure on the hex bolts? And since I only ruined one of the holes, a helicoil could be used?

Or would it be possible and better to make a larger threaded hole, say M10? Or would that get to near the fluid hole?

The only remaining option is then to get another caliper. Not so easy to do in Sweden. One can buy it complete with piston and pads from Heidentuning or XS650shop and have it shipped.

 

[gggGary]

I will fully admit to not looking over an early caliper to refresh my memory. For the small bolt if there is room I would go with an oversize bolt as much preferred to a helicoil.

 

[5twins]

Upon further study, I think the original given torque value may be correct. The error was in the conversion. 100 kg-cm = 1 kg-m, not 10. That would be 7.3 ft/lbs, not 73. 7.3 ft/lbs is right for an M6 bolt. I don't doubt it would strip trying to put 73 ft/lbs to it. I would try a Helicoil. What have you got to lose?

 

[grizld1]

Darn, you guys are fast!

Marp, trust Gary on this. And of course you're right, 5twins, 1 m = 100 cm, not 10--oops! But Haynes still misprinted kgm for cm-kg. The worst of the mess is that the same errors are repeated in printing after printing.

 

[gggGary]

What's up with the the write up KG-CM, table M-KG. reversed order AND a 2 decimal point unit change in the same service book. Guess those Japanese/english manual translators weren't techies....

 

[marp68]

So, I will take the caliper to the fine work mechanic on Monday. This have to be drilled carefully and straight and I don't have the right tools for that. Any more thoughts on making room for an M10 bolt? The caliper is down in the cellar now, so I will take a look tomorrow to see if there may be some room for a bigger bolt. Won't look pretty though, but safety first...

Thanks for the torque spec. Must have had a temporary blackout. A great example of stupidity. And extemely frustrating after carefully cleaning the brake system, installing new pistons etc and about to rebuild everything.

 

[weaselbeak]

I wouldn't worry about a helicoil. If possible I'd just tap it up a size larger.

 

[TwoManyXS1Bs]

If space is critical, there's also the 'in-between' UNC and UNF options.

8mm = 0.315"
3/8" = 0.375" (9.5mm)
10mm = 0.394"

A 3/8"-16 UNC thread would be like a M9.5 x 1.5mm (tap drill size = 0.312", about 8mm)
A 3/8"-24 UNF thread would be like a M9.5 x 1.0mm (tap drill size = 0.332", about 8.5mm)

 

[Oddjob]

I too am curious as to why a Helicoil wouldn't work in this application...

 

[grizld1]

Marp68, 9 mm. isn't an extremely common size, but the bolts and taps aren't hard to find off the hardware store shelf even here in the Southern Illinois backwoods; can't be much of of a challenge to locate in Europe. It's enough of a step up to provide plenty of thread depth.