Jakedatc

What type of stem cap is this. i need a new one for my CX bike since the hex hole is a bit stripped out from previous owner. It screws onto a larger bolt rather than having the normal bolt through the middle of it

HillRider

What you show is not a "stem cap", it is an expander plug used in place of a starnut in carbon steerer tubes.

The proper stem cap for that type of expander plug has a cylindrical downward lug that is internally threaded and screws on over the external threads outside of the (damaged) hex bolt.

BTW, I hope your stem doesn't really extend that far above the top of the steerer tube when in use. The steerer is well below the stem's top clamp bolt and isn't supported nearly well enough. The gap should only be 2 or 3 mm.

Jakedatc

so i should search for an expander plug cap?

and yea, the thread that pic came from the guy had his plug in the wrong spot and was causing a larger gap.

markjenn

FYI, if the picture shows the stem in its seated position, it appears to me that the steerer is cut too short or you have too many spacers below the stem. I believe the spec is that the steerer is supposed to sit a max of a few mm below the top of the stem. (Just re-read that this is a photo from another bike, so yours is probably Okay.)

- Mark

Jakedatc

NOT my picture... only pic i could find of that type of screw thing

Edit: also the screw/bolt part isn't damaged. the hex hole in the cap is a bit messed up and i'd like a new one. would rather not get a whole plug setup since it is set perfect and i don't want to mess with it.

Andrew R Stewart 

I have not seen the top cap that fits this type of plug available separate of the plug, excepting loose/used parts in a spares box at your LBS. But I haven't had to really find this out. I suspect that you'll be getting a complete plug. Andy.

Jakedatc

AHh they seem to be cheap though, the bolt size should be standard right?

https://www.ebay.com/itm/FSA-Compress...-/331692837779

fietsbob

Metric system is a standard, the Foot and its fractional divisions is another standard..

But those expansion plugs are of several designs, created by different companies [FSA being just 1]

wanting a share of the market sales for that piece for many bikes..

(Just a guess, since I never got into Carbon forks)
that could be the missing part, in your picture, the aluminum cap using the larger external thread of the expander..

the hex cap screw , my mechanical supposition, is what expands the expansion plug into the carbon tube.




...

wschruba

That's probably one that will fit? Nobody will know until you remove your stem and measure the steerer tube--there are a handful of manufacturers who use 1 1/4 tapers at the top.

Jakedatc

Well at 9 bucks i'll go for it and re-do the whole thing if the cap part doesn't play with the existing one.

bike is Salsa chili con crosso.. seems to have a normal 1 1/8 stem on it. Cap that is on there now was a pain to get back on when i flipped my stem so i'll wait until after my race this weekend to fiddle with it.

revcp 

Looks like it might be FSA. But, yeah, a new expander plug with cap is cheap.

HillRider

Yes, I've seen that type by both FSA and Look and I agree finding the mating top cap as a separate part is unlikely.

Other types of expanders do use a center bolt and a top cap design that works like one for a starnut. Buy an entire expander.

Jakedatc

top cap i have now is Reynolds.. the link i posted shows the whole expander so if it doesn't match then at least i can do the whole thing

and yea, my road bike has a carbon steerer too and has the normal type.

Andrew R Stewart 

A couple of points


First is never describe a bike part as "normal" (as in "normal type"). In today's age this means less and less. What you are doing is assuming the other guy has the same frame of reference as you do. Especially if you're special ordering or can't touch and feel the part before paying for it this assumption can bite back.


Second is that there are two basic designs of plugs that are removable. One uses the bolt that goes through the cap to both pull the cap down (or pull the steerer up) as well as provide the expanding force for the plug portion. I don't like this type as the plug/expanding portion can just slide up in the steerer causing it to bottom out on the cap's underside. No headset bearing preloading results. One more example of having one part do two things. The other type has the plug have it's own center piece which threads into a bottom cone and when tightened the expanding shoes (as in drum brake like) grin the steerer ID. Then the cap is either bolted into this fixed in position plug with either a separate bolt or the before mentioned boss with internal threads. This type is far easier to set and use. Andy

HillRider

The first expander design you mention, the one piece with a center bolt that both expands the plug and sets the headset preload, can slip if not fitted properly. The Profile Design version has a stiff spring under the top cap surrounding the bolt to tension the expander to lock it in place as the bolt is tightened and generally works well enough. It is important to be sure the plug body and steerer interior are free of grease and oil or it will indeed slip.

Jakedatc

OK, I finally got around to trying to put the new expander plug in. The issue I have is that the cap part does not have a very wide tube to help push out against the stem. Why would they have a 1 1/8th expander and only like 3/4" cap that goes onto it? The plug part covers the bottom bolt of the stem but the top stem can be pushed in much more

Took my own pictures this time to not confuse people..

Old cap on right with this metal tape on it, apparently to fill in more of the gap, new on left that leaves a huge gap


only a 3mm gap from the steerer to top of the spacer