thook

hey all,
forgive please if this topic is already covered. i just didn't get anywhere with a forum search

i have a used mtb frame coming my way at some point. the head tube is 4.5" long and 1" diameter. my conundrum for the past several weeks has been trying to source a 1" steer tube to put an old marzocchi suspension fork on it when it does arrive. fyi, i have the fork, and currently it has a 1 1/8" steerer that bolts/clamps into the crown.

now, i've not had any luck sourcing the 1" tube at a price i'm willing to pay.....until today. the deal is it's a trade of identical fork crowns with a member on another forum. but, the kicker is his proposed crown has a steer tube of only 5 1/8" in length. ideally i'd need atleast 5 3/8" minimum with my "regular" stack headset. so, according to my measurements, 5 1/8" would only leave me enough thread just to get the top threaded bearing race on, but not the top lock nut. i do have a new short stack headset that might do the trick, but what about also simply cutting some of the head tube down to swing things even more to my advantage? i'm not concern with it throwing the geometry off as the frame is not suspension corrected, anyway. furthermore, the fork travel is only 60mm and shaving the head tube a tad (on the bottom end) couldn't hurt as far as geo is concerned. and, besides, i think a few mm's top and bottom would get me where it needs to be.

so, short of taking this to a frame builder ($$$!!), is there a good way for a rather tool skilled guy to do this at home with good shop tools? what tools would i need?

fyi, paint's not a concern as i may repaint, anyway.

thanks!

unterhausen

you can't cut off the top? I would not want to do this without access to a head tube facing tool. Getting it flat enough to have the headset work right is a very high level of skill. I think I have reasonable hand tool skills, and I suspect the headset would be sub-optimal if I did it. I think the first trick would be a way to mark it. You might be able to use the fork to do that, but I'm not sure how successful that would be.

Nessism

It could be cut down with a hacksaw but then it must be faced with a head tube facing tool. Of course that assumes you have enough head tube sticking up to make this happen.

unterhausen

I have a friend that never answers a technical question without pictures. Even if he knows what I'm talking about.

thook

i know what the head facing tool is. and, yeah, i was afraid i'd really need something like that to do this right. i was wondering maybe a flat file and gauging my work with a digital caliper around the circumference using the opposite/untouched facing to continually maintain evenness, if that makes sense. and, maybe just stick to trimming at the top of the head tube?
but, how hard is this tubing to hand file? i took a half round file to the underside of a unicrown fork to make a few mm's of tire clearance. i took off that "excess" under the crown you often see on the underside of the steerer. took about ten/fifteen minutes maybe

i have a picture of the frame in question in my email. i should be able to figure out how to get to the forum for illustration, but it'll have to wait until after work this evening

later. thanks for the replies!

unterhausen

filing is not likely to be difficult.

Andrew R Stewart 

I am not endorsing cutting down a HT (although I have done it, hence my not suggesting it). But facing a HT end without a facer is not too hard. A large flat sided file (could be a mill or half round, you pick) and a square with enough blade length are all you need. Cut down the HT end by about 2mm less then you want. File that end flat and square to the HT's length checking with the square held at least three different placements about the HT. One with the blade running down the HT at it's front, another with the blade running down the LH side as close to the TT and DT as possible and the last on the RH side. You will see that the blade isn't parallel to the HT surface and thus which portion of the HT face you need to file a bit more to square that portion up. Repeat all around the end. As you feel the end's squareness is achieved then run the file across the entire end's face with light and smooth strokes to best even the slight highs and lows. Do the other end of the HT.

I use my bench grinder to rough off the HT end as cutting a mm or 2 off with a hack saw can be an ticket to to a major saw slip and scratch.

This can get you very close with care and attention. The key is steady and focused filing with taking your time. Generally a few mms off the ends won't have the reamed ID depth become less then the headset cup's skirts are deep/long. I like to file a slight bevel/chamfer on the ID of the end to better allow the cups to slide in (especially if they're AL). Take care to check out any resulting fork crown/DT contacts as they get closer together.

This is pretty much what I do when building a frame, during the end steps, to reduce the cutting time on my facer. Andy

thook

'bout the hacksaw...i was never thinking of going in that direction. without a real miter, it's butchery at best, ime. i was thinking more in terms of an attachment i might be able to use on my drill press, but if a simple flat file would do the trick then that seems the easiest to control though it will take elbow grease. i can do that

now, why would you not suggest doing it? there's no incentive in messing up the frame, and if the proposed steer tube isn't going to work, i can live with that. i'll just keep looking. there again, i simply have to find my calipers to see if this short stack headset will do the trick. i've just misplaced them. in the meantime, i figured it would't hurt to ask about trimming the headtube to satisfy my overly active imagination

unterhausen

I would definitely suggest trying the short stack first

Andrew R Stewart 

Various reasons I don't suggest it. You can screw up and really badly scratch the frame from the saw/file. You might not have the patience/skills to get the HS bearings parallel to each other (the goal of facing), If the frame were a lugged one and having stamped (not cast) lugs you can open up a cavity in the crotch of the joint. If the headset cup skirts are long or you cut off too much the skirt might bottom out before the cup was seated. Because if you're the original owner any warranties will be voided. And because of the general philosophy in the repair business of not going to non reversible results if at all possible. I'm sure others could add their reasons.

Try the low stack height headset. Depending on the OEM VS the possible replacement HS you might gain as much as 7mm, on paper. If this isn't enough let us know. Andy

thook

@unterhausen.....thank you. yes, i will. you just wouldn't believe how difficult it is to find a steer tube for this fork. well, maybe you would.

oh, since we're on the subject, i have wondered if i couldn't just use a regular steer tube....one otherwise meant for brazing into a regular fork....and shimming it to fit in the crown. again, the steer tube clamps in. if this would work, then those tubes are cheap (nova cycles, etc) and i could get the exact length i want. i wouldn't mind having a few cm's of spacers to be able to get a regular quill in the mix with the bars nice and high

Andrew R Stewart 

The issue with shims is that poorly applied they can substantially reduce the crown's ability to clamp the steerer. You have twice the amount of pinching down to tighten the crown clamp. One is that of the steerer inside the shim, the other is the shim's OD in the crown. As there's no suspenders (as in belt and...) with a fork I would be very careful on how I made sure the crown/steerer were secured as well as how the crown's future fatigue/stress life is dealt with. (Belt and suspenders" as in every frame tube, but the steerer/crown, is joined at both ends. So a joint failure on a stay or main tube still has the other end to carry the loads for at least a little while. But the crown/blades are only connected to the rest of the bike via one joint at the steerer's base) Andy

thook

thanks, andy.

it's a tig welded trek 850 antelope from the early 90's, so not lugs to screw up. and, i'm not the original owner and for sure there's no warranty to void, anymore. now, judging by the photos, the headtube has atleast 1cm of extension before the top tube and down tube joints. think it safe shaving some length off the ht would still allow the races to seat properly? i understand what you're saying by that, btw....though it hadn't even occurred to me before your mention of the issue

otoh, if a steer tube/shim idea would work (ie...nova cycles), i will blow this shaving business off entirely. heck, might just do it, anyway. i've sent three messages to the guy with the steer tube and i've not heard back from him. he's actively posting on the forum, so i would guess he knows i've messaged him. whatever, though

thook

i see. hence some fork designs (older rst forks, etc) using a cir-clip to secure. yeah, there's no provision for that on this fork. so, i can see where tolerances would be a must. i don't like the idea of the steer tube/shim slipping about. scratch that, then

Andrew R Stewart 

I tend to write my replies to also serve other readers, hence my broad range of reasons.
Do the math after measuring headset cup skirt lengths and the frame's HT reaming depths. This is only to avoid the need for a reaming/facing job from a shop/builder. This is what you're trying to avoid after all, I believe. Andy

Andrew R Stewart 

A slipping steerer in crown might not be the biggest potential negative Andy

thook

what? like broken body parts....maybe?

Andrew R Stewart 

The suspension fork crowns, that I have seen, that use a pinch bolt method to secure the steerer are made of Al. So if a crack were to develop from the clamp being over pinched one would want to know that ASAP. because cracks in Al tend to grow in size far quicker the with steel or Ti. Like I said without a second end of the blades being attached to the steerer when that first end fails it's not good. Sudden loss of steering and perhaps at the same time the vertical support that the fork provides to your body plus your speed equals ouch. Andy

thook

well, that would suck, too!

heard back from the guy this morning finally. "oh, no. i'm sorry. the fork sold already". umph :/

i'll just have to wait for something else to turn up. probably for the best, but atleast i know now this is an option. although an extreme one ideally avoided

thanks for your time, gentlemen!