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PostPosted: Thu Feb 22, 2018 7:37 pm 
Dirt Disciple

Joined: Tue Feb 13, 2018 8:04 pm
Posts: 66
Location: Joymoney
Hi there,

I´m very new to the forum, although it helped me out a lot of times during the last years with the wealth of knowledge to be found here. I´m not new into old MTBs (in fact I remember them being "new") but only recently got my hands on one of my dream frames, a ´90 Merlin Mountain. It´s in ok shape, but does need some love. Hopefully some Merlin experts are able to help me out.

Firstly, it had a 26,9mm seat post mounted and is clearly a bit mushed around the clamping area :evil: . Thankfully no cracks to be found. My thinking is to ream out the top area of the seat tube to the correct 27,2mm diameter (it´s meaty up there) and do some careful filing to get the gaps straight again, and not just pry back the opening. Any better advice?

Second evidence of one of the previous owners being careless, the rear axle spacing as it sits now is at 132mm. So what would be the correct spacing, 130 or 135mm? I´m not going to try and realign, I just want to mount a hub with the correct width and otherwise leave it as is. As far as I can measure the stays appear to be symmetrical. Frame number is #29XX, indicating a 1990 frame (straight stays, rear canti brake).

And lastly, I measured the bottom steerer tube to be 29,9mm inner diameter. Does that mean it´s JIS standard? Weird as the original Ritchey fork has 26,4mm crown race diameter, indicating ISO. I have a matching crown race, but the bottom headsets cups I have on hand (Suntour XC Pro, Campa) measure 30,1- 30,2mm. That´s more interference and less fit than I like! My idea was to chuck a cup in the lathe and take it down to around 29,95mm. Again, any other advice is very welcome!

Cheers
Dr


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 Post subject: Re:
PostPosted: Thu Feb 22, 2018 8:09 pm 
Retro Guru
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Joined: Sun May 05, 2013 12:12 pm
Posts: 2069
Location: Bournemouth
Cool frames.
I can’t help on the seat tube or headset issue, but for the rear stays I have at least one bike (steel) which is set at 132, apparently so 130 or 135 will fit with only c.1mm movement of the stay each side. That would be about 1990 for the crossover of hub widths.
Not sure whether titanium would appreciate the slight movement so much?


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PostPosted: Thu Feb 22, 2018 8:44 pm 
Dirt Disciple

Joined: Tue Feb 13, 2018 8:04 pm
Posts: 66
Location: Joymoney
Thanks for the answer Mat, that´s a possibility I never thought of. Makes sense though, as you said 1mm either way may be within tolerances of the material.
Well the dropouts will have to move anyway if I don´t want to experiment with spacers. Perhaps I´m overthinking this "issue" ...


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PostPosted: Fri Feb 23, 2018 9:58 am 
retrobike rider / Gold Trader
retrobike rider / Gold Trader

Joined: Sat Jul 21, 2007 9:48 am
Posts: 7690
Location: Bristol
if you're really worried about the rear wheel it sounds like you have the tools and skills to tickle a 135mm hub down to 132mm.

The other two points, i'd ask a framebuilder. Believe Danson67 is the go-to guy around here


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PostPosted: Fri Feb 23, 2018 6:43 pm 
Dirt Disciple

Joined: Tue Feb 13, 2018 8:04 pm
Posts: 66
Location: Joymoney
Well I´m certainly known for wielding a certain rotary tool, but I´m relying on the help of friends with workshops for more involved work.
But thanks for the heads up regarding resident specialists, I PM´ed danson67. I also contacted Merlin directly for the axle spacing of the frame, maybe they can provide some info.

I also now have unearthed (or rather punched out) a little more info about the headset conundrum. I got the old upper bearing race out, which was still installed when I got the frame. I feared it would be seized, but it came out after only three rather mild blows on the extraction tool. The part that goes into the frame measures 30,25mm, so even bigger than the races I have. And after thoroughly cleaning the seats in the head tube the measurement there looks more like 30,0mm :roll: . It´s still a bit more difference than I´d like, but I think I can get away with a little polishing of the headset parts.

Attached a few pics of the seat tube area (sorry for the crappy phone pics). As with other ti frames there is a sleeve let in. It does not look like it´s aluminium, but also ti, welded on the top and machined down. That will make reaming a bit difficult. Before I cleaned it for the pic there were dirt deposits directly under the relief cut, indicating the seat post did not make contact with the inner wall downwards of the clamping surface.


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PostPosted: Thu Mar 01, 2018 2:43 pm 
retrobike rider
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
Posts: 2309
Location: A wretched hive of scum and villainy...
Looks like the top section of your seat tube is probably a welded in machined extension, rather than a welded internal sleeve.
Something like this:
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The joining weld could be hidden by the TT and SS welds.

There is plenty of material to ream it out (2.275mm wall on a 1 1/4" OD seat tube), as long as precautions are taken not to eat away or fold in the RH side of the relief slot while reaming. This means that it is unlikely to initiate a crack if it does need bending back out. On the other hand, a lot of force would be needed to overcome the yield strength, and it needs to be very well controlled, or the corner could easily get ripped off.
Probably better to try the post fit first.

If you take a seat bolt (probably M6 cap head), run it through the threaded LH half of the seat bolt fitting, insert a piece of thin sheet metal in the cut relief slot and tighten the bolt a little further, pushing against the sheet metal. This should gently open up the top diameter of the seat tube enough to insert the correct size post (27.2mm?), without taking it past the correct size.

As long as the seat post fit is OK and doesn't need work, remove the reversed seat clamp bolt and re-fit through the correct RH side. Tighten to correct torque, probably around 8-10Nm.

Ride the frame and use it as normal for a few weeks, keeping an eye on the area, then remove the seat post and look again at the fit of the top of the seat tube. It should have relaxed back to fit a bit. If not, then some more reaming or re-forming work may be needed.
Cross that bridge if you come to it...

All the best,


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 Post subject: Re:
PostPosted: Fri Mar 02, 2018 8:03 pm 
Dirt Disciple

Joined: Tue Feb 13, 2018 8:04 pm
Posts: 66
Location: Joymoney
Thank you Dan for your recommendations. Glad to hear that the wall thickness would be sufficient for reaming.
Unfortunately there are no threads in the welded seat binder, it´s just for a through bolt. But it gives me confidence that it can be bent back without doing further damage.

Meanwhile I contacted an old family friend, who is a retired safety engineer for nuclear reactors and quite experienced with Ti tubing. He had no concerns about bending Ti 3Al 2.5V alloy. Turning a conical mandrel to insert into the pinched seat tube was his immediate suggestion. It sounded as if this would be the method "per the book". I´ll be at his place in a couple of weeks.

Thanks again for taking your time to respond and watch this space for the next post "mandrel stuck in seat post- advice needed" :?


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 Post subject: Re: Re:
PostPosted: Fri Mar 02, 2018 8:10 pm 
Dirt Disciple

Joined: Tue Feb 13, 2018 8:04 pm
Posts: 66
Location: Joymoney
MatBH5 wrote:
Cool frames.
I can’t help on the seat tube or headset issue, but for the rear stays I have at least one bike (steel) which is set at 132, apparently so 130 or 135 will fit with only c.1mm movement of the stay each side. That would be about 1990 for the crossover of hub widths.
Not sure whether titanium would appreciate the slight movement so much?


It seems like you were right, I´ve found this old sale thread, where the advertised frame was also 132(,5)mm.

viewtopic.php?t=94872

That hopefully means the frame is not damaged in this regard :D


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 Post subject: Re:
PostPosted: Fri Mar 02, 2018 8:46 pm 
.o.T.M Triple Crown Winner
.o.T.M Triple Crown Winner
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Joined: Sun Dec 31, 2006 12:59 pm
Posts: 3462
Location: Sunny South of France
Merlin used generaly 27.2 seatpost but sometimes, because the owner tightened too much the seatbolt, the diameter becomes smaller. When Isee your pictures, it's what happened to yours.
But there's a solution : take a tube around 25mm dialeter. Put it in the seat tube and turn with big movements front and rear and right and left: the idea is to open the diameter. When it's Ok, the two screw cylinders will be aligned .
I did that on my 2 Merlin Frames :D


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PostPosted: Fri Mar 02, 2018 9:52 pm 
Dirt Disciple

Joined: Tue Feb 13, 2018 8:04 pm
Posts: 66
Location: Joymoney
Yes the frame came with a 26.8mm post mounted :evil:

If I had to open it up just a little I probably would have a go myself, but it is quite a bit deformed. I´ll have the specialist look it over, I´m not in a hurry.


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