55tele

Crank preload bolt / cap on left side keeps coming loose.....Crank arms / BB are fine, no play.....is just that the damn cap keeps coming loose (I've tightened up snug once before about 100 miles ago) and there was some lube on it when I pulled it all the way out....

Is it acceptable to use some blue loctite to keep this bolt snug? I'd probably wipe both the axle thread and cap thread with some sort of cleaner, then use the blue stuff

I know I could run without it, but would rather have the bolt in place.....

Thanks

cxwrench

Well, since you haven't bothered to let us know what kind of crank you have...the answer is a solid 'who knows?'

Barry2 

As you pointed out.. you don't need to run the pre-load cap after you've tightened the crank bolts.
I'd avoid loctite on a plastic pre-load cap.

If it worries you, give it a wrap or two of plumbers teflon tape.


Barry

55tele

CX Wrench,

Thanks for the snarky comment. Since I did mention that it is a PRELOAD bolt/ cap, I would have thought you’d deduce it is a hollow axle crank...

Anyway , I’ve figured it out without your help

thanks

55tele

Thanks Barry2,

It's an aluminum bolt....I didn't measure the thread length, but pretty long...probably 15-20mm....

I used brake cleaner on the threads both on the axle and bolt.....applied blue loctite, ran it in and gave it an extra twist......I called Zinn in Colorado and they gave me the procedure.....

Thank you

cxwrench

You do know that there are more than 1 kind of hollow axle crank, right? You want help you need to provide details. Barry2 is incorrect, nearly every hollow axle that has a preload cap/screw needs to have that installed or the crank arm can work it's way off the axle...especially Shimano.

55tele

That's incorrect, this crank works just like a threadless headset......you use the bolt (set at about 1Nm or so) to pre-load the assembly; tighten the left crank arm with its fixing bolts to the axle (8-10Nm or so) and now I learn you need to snug up / and or loctite the preload bolt if you don't want it to spin out of the threads. But once the crank arms are set and torqued with their fixing bolts, the cap does not provide a structural function.

Perhaps I should have been more detailed about the crank. Perhaps you could be a little less sanctimonious......

cxwrench

I am most definitely not incorrect...ask me how I know. The cap backs up the pinch bolts. I've seen numerous Shimano left crank arms fall off because know-it-all home mechanics either broke the cap or lost it. This is not my first rodeo if ya know what I mean. The cap doesn't need LocTite, Shimano puts grease on the threads inside the crank axle. If it needed a thread locker they would spec it.

Moisture

My preload cap also loosens to the point where you can easily twist it off by hand. How it is being useful or keeping anything in place by that point?

Moisture

55tele

get past the snarky comments and conflicting opinions, and you'll learn a lot on here. Don't sweat it

cxwrench

I have installed hundreds if not a thousand or more Shimano Hollowtech cranks over the years. I have NEVER had a preload cap come off one that I installed. You are doing something wrong if yours loosens like that. The only thing that comes to mind is that you're not tightening the pinch bolts properly.

55tele

You are incorrect...the only function of the bolt is to preload the bearing...it does NOT act as some sort of safety "backing up the pinch bolts" unless the pinch bolts have not been torqued properly...

My bolt spun out twice....it won't now......

cxwrench

Shimano specifically calls out grease on the threads of the cap. Look it up. Shimano crank dealer manual If the pinch bolts were all that were needed to hold the crank arm on why did Shimano see the need to add the 'stopper plate' to the HT cranks? It wasn't there when the cranks first came out.

55tele

Well, you are correct about Shimano cranks, but my crank is not a Shimano.....The stopper plate on the Shimano crank arm is likely to be to prevent over and / or uneven tightening of the pinch bolts.

I apologize for not specifically stating the brand of my crank.

When I called my builder, he stated that the Driveline (my crank) pre-load bolts do in fact spin out and the remedy is to use blue loctite and run the bolt in and when it stops, give an extra twist to interfere with the crank, after the pinch bolts are torqued..

I'm all set....

cxwrench

Barry2 

If the retaining bolts on a Shimano crankset let go, that stupid plastic cap aint going to hold it on. That's what the thin metal retaining hook is for.

All the best


Barry

Koyote

From experience, I can confirm that cxwrench is entirely correct about this, as regards Shimano cranks.

Barry2 

With regards to Hollowtech II
Just what does a flimsy plastic cap achieve that a metal hook does not ?

55tele

Can you explain why, if Shimano directs to grease the crank axle thread and preload bolt, how, after the crank is set to the proper preload and the left arm is torqued down with the pinch bolts, that the preload bolt even has to be on the crank arm?

After the arm is set with the pinch bolts, what specific purpose does the bolt have?

I'm just curious...what is different about Shimano compared to other cranks?

I could see that if the pinch bolts are not torqued properly or if the arm to axle interface is compromised, so that the arm will not hold onto the axle even with the proper torque, the preload bolt might be THOUGHT to be a backup. But why would it be greased?

I would think Shimano advised to grease the preload bolt to ensure a smooth PRELOAD....

Enlighten me please....

cxwrench

The cap does 2 things, it is the preload adjuster and it backs up the pinch bolts. It's similar to but not the same as a threadless headset. You adjust preload w/ the cap. You then tighten (properly, by alternating) the pinch bolts. As you tighten the pinch bolts the axle is tightened around the preload cap. That's why it should never come loose. You don't tighten it very much when setting preload, definitely not enough to keep it in the axle w/o the pinch bolts. The stopper plate was added because people don't use torque wrenches and think 'tight enough' is enough.
55tele Do you have one? An old tele I mean? If so, very cool. I work in the bike business and find myself in touch w/ Shimano tech reps on a fairly regular basis. We chat about all sorts of things including how their stuff works...which is how I came to know about their crank design.

55tele

So, on the Shimano, is the left crank arm compressing around the head of the preload bolt when pinch bolts torqued? If so,I think I get it now....
The Shimano with the nylon bolt is held by the tension from torquing the pinch bolts....squeezing the nylon bolt...yes?

That is what is different......my aluminum bolt was a slightly loose fit even after torquing the arm down...probably to facilitate smooth preload....After torquing the pinch bolts, it depends on running the bolt in, thus the need for thread lock and / or an extra twist or interference fit to the arm...There is slight clearance between the bolt head and the arm hole, so the arm won’t hold my bolt....

Also my arm specs 8-10 Nm...less than the Shimano....

Yeah, I’m a guitar player....Telecasters are my main axe.....

cxwrench

Bingo...more or less. It compresses the axle around the preload cap.

Koyote

You’ve got a blackguard Tele?

55tele

No, I have several Suhr Telecasters, a Merle Haggard Custom Shop Tele and a Tele Custom Champagne Sparkle Tele...

Nothing vintage....

grizzly59

I love these threads