Chainring Bolt/nut sizing for Bash Guard Install?
 

Hi everyone,

I'm installing a bash guard on a double chanring set, on my road bike, and I'm keeping both chainrings. So I'm adding the bashguard and spacer to the outer ring. The thickness of all the parts (both rings, spider, guard, spacer) is 14-14.5mm depending on how tight I squeeze the digital caliper.

My first thought was to buy a 14mm bolt and use the shorter nut that's on the CR. But then I wondered if that would leave threads grinding against the CR parts. So, maybe I need a 14mm nut, which seems to be a type of sleeve, so that all the CR parts are riding on it and not the bolt threads?

So my question is this: How long do the bolts need to be? How long do the nuts need to be? How much overlap is needed to securely hold the whole thing together?

(BTW I found some titanium bolts on eBay that have no threads for most of the bolt shaft, giving a nice surface to contact the CR parts. Any thoughts on these bolts?)

I've done quite a bit of research on this and have found no info. I apologize if it's been asked a million times, and I've just missed it.

Thank you,

James

There are 3 chainrings onto one set of bolts , made , the kit included 5 spacers & 5 sleeve bolts and nuts.

just like regular bolt sets for chainrings , but longer 3 chainnrings + 2 Spacers = the thickness of 5 chainrings

You should be able to find a set of chainring bolts intended for triple cranks with one 110 mm bolt circle. Suguino made cranks like this in the past and they used longer chain ring bolts to go through all three rings. A google search for "long chainring bolts" came up with a bunch of sources.

Most of the bolts I found on the 'net do not have actual sizes listed, and all the triple CR bolts look short. Also, many are without nuts.

So, again, what size bolt/nut do I need? Should the nut be as long as the bolt?

We don't know and even given the make and model of the crank and guard we won't know. Sandwich them together and measure the total thickness. No, the nuts don't have to be the same length as the bolts. You just need a bolt/nut set long enough to go through the total depth plus at least enough extra for the bolt to thread a minimum of it's diameter into the nut.

I found this on another site. Do people agree with it?

And so it's okay for the threads to make contact, and presumably get ground down, with the CR parts? Or doesn't the grinding happen? (I'm used to working on cars, so metal on metal isn't always a good idea).

Did you read what I posted immediately above? It says the same thing. What do you mean by "ground down"? This a a very straight forward use of a bolt and nut to fasten a bunch of parts together. Don't complicate it.

What some may be calling a 'triple bolt' is the ones that screw into the crank say the 74mm bolt circle on a 110-74 crank ..

That is why they dont include a Nut. the spacer can also be optional if the arm puts it in..

No grinding should happen chainrings are prevented from riding on the threads cuz they're resting on the shoulders of the crank arms. If you bash something with the bash guard it may contact threads of bolts but you don't use that area of threads anyway so no biggie.

Also if you get steel bolts they'll be harder than chainrings or bashguards

Thank you for the responses. But here why I'm getting confused:

What I have now, without the bashguard, the nut/sleeves are 10mm in diameter. The bolts are 8mm in diameter. And the holes in the CRs and spider are 10.1mm in diameter. The nut/sleeve (could also be called a bearing) sticks all the way through to the outside CR up to about 1mm short of the outer surface. Therefore all the hole surfaces are riding on the nut/sleeve.

If I use a longer bolt (about 6mm) without a corresponding longer nut/sleeve when I install the BG and spacer, there will be 2.1mm of open space between the bolt and the sides of the hole. That will allow play in the BG and it seems like it will slide around.

So, on is this not important on a bike? On a car, it would be. Or does it not matter with a BG?

Again, thanks for the comments.


Hillrider: Well this wouldn't be the first time I "complicated" something by over-thinking it! :)

On a normal chainring nut and bolt setup, the nut is long enough to engage all of the rings. The holes in the chainrings are sized for the nut. Otherwise the chainring may not be concentric.
Usually the nut just barely enters the outside ring/bash guard but of course cannot protrude or the bolt will not tighten down on the rings. The bolt should engage almost all of the threads of the nut and not protrude.

If the nuts are too long they can be ground down - I've done this when converting to single rings - for some reason it always seems hard to find the nuts and bolts for a 1X setup. Easy on a belt sander.

Bash guard doesn't require exact concentricity with spider or chainrings to do its job. A little sliding around won't matter.