Chinertown
Chinese Carbon MTB => 29er => Topic started by: SVChucko on December 21, 2021, 11:57:21 PM
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At long last, the FM10 frame I ordered in mid-September arrived at my Silicon Valley home, just in time for the holidays! Merry Christmas to me!
The box was in pretty good shape considering it had been in transit for 3 months.
I went over the frame with a fine tooth comb once I got it unpacked. There was some minor cosmetic damage to the pre-installed upper headset bearing race - but as I will explain later, that won't matter. Some minor paint chipping around one of the rear end pivot bolts, and the rough end of the bottom bracket tube, were about the only things I could complain about.
I was disappointed that there aren't any strings strung through the cable holes. That'll make things tricky when I put it together.
Here are some pictures to get it started.
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First order of business was taking out the shipping strut and installing a Manitou Mara shock in its place. The trunnion end fit snugly, as it should; but the rocker end was too tight to fit the mounting hardware, so I took one side of the rocker off for a look.
First good sign: all the bolts had a threadlocking compound applied, and were TIGHT.
The rocker and trunnion ride on 19 x 10 x 5mm bearings, sealed on both sides. This is the common 6800 size. Bearings are pressed into the frame and rocker such that bolt torque holds them in on one side, and a ridge in the bore holds them in on the other.
There appear to be some tooling marks on the inside of the trunnion mount, where they won't be seen once the bike is assembled.
More pics...
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I did a little test fitting of some of the parts I've acquired for this bike. The bore for the bottom bracket is undersize... yeah, it's a press-fit BB, but it's undersize enough that I'm a little nervous about pressing it in like that. I may take some sandpaper or a bottle-brush hone to it.
The bike came with the outer races for the headset bearings already pressed in. I'd bought a ZTTO headset for this bike, so I checked to see whether the bearings would fit in the races. Lower race - looks good. Upper race - the diameter is right, but the race is too shallow, and the bearing would be sticking up through the top tube. So that's one thing I'm going to have to fix. Any good tips on removing a headset race from a carbon frame?
And as luck would have it, that's the race with the minor cosmetic damage from shipping. So as I hinted in the first post, the cosmetic damage won't matter at all.
I took out the rear axle shipping brace and installed the real axle. First "oops" on this new frame: my Allen wrench wasn't fully seated when I torqued the derailleur hanger bolt, and I messed up the bolt head. Fortunately the damage is minor, and with a little care, I managed to get it up to proper torque. Also fortunately, I ordered a spare hanger some months ago!
I measured the width between the rear dropouts at about 146mm. This is a Boost frame, so that's a bit snug, but I'm sure it can be "persuaded" to fit the 148mm hub.
One more picture of the messed up bolt head, and that's it for today.
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Lots of progress tonight. I tapped out the factory-installed upper headset race without incident, and pressed in the race that came with my ZTTO headset. I installed a Cane Creek Helm II fork, temporarily using a 70mm stem and an old Titec Pluto riser bar. The stem may stay, but I will definitely need a wider bar.
I got a set of take-off SRAM Code RSC take-offs for a good price off eBay, from a bike dealer in SoCal. I mounted the calipers, but the rear caliper bolts are too long for this frame. I need to find shorter bolts. I already had brake rotors (203mm front, 180mm rear). When I tried to install the front rotor, 2 of the 6 bolt holes in the Goldix GDX 370 front hub stripped before I could get them up to torque! I've complained to the vendor. We'll see how that works out. The rear hub didn't have that problem, fortunately. But now I need to replace the front hub and rebuild the wheel.
I mounted the ZTTO 11-speed cassette and Sensah derailleur and shifter. Routing the shifter cable housing and the rear brake hose was a hassle, but nowhere near as bad as I'd feared. I won't cut either to length until I have a handlebar.
I took an old seatpost and measured the insertion depth. I came up with 160mm (this is the 17.5" frame). Looks like my best bet is a OneUp Dropper V2 150mm. I may not be able to use all the travel, but I can shim it down to 140mm. That's more travel than I can get with any other post in this frame.
After months of staring at a pile of parts, it's starting to look like a bike! Still a long ways to go, though. I have to buy and install some cockpit parts (bar, saddle, dropper post, pedals) and a chain, and rebuild the front wheel, before it'll be rideable.
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Not a lot to show, but progress has been made. The Hope hub, an SQLab 30X bar, a pair of Ergon grips, and a OneUp dropper post are now in my hands. I finished rebuilding the front wheel just a few minutes ago.
The bearings in the suspension are all standard industry sizes. The trunnion bearings, the rocker pivot, and the rocker-to-seatstay bearings (that's 6 total) are all 10mm ID x 19mm OD x 5mm wide. The industry part number is 6800-2RS. The 2 swing arm bearings are 15x28x7mm, industry #6902-2RS. (The -2RS stands for "2 rubber seals".)
The bearing locations all have room for wider bearings, but you'll probably need longer bolts. The 6800-2RS can be replaced with a 3800-2RS. This is a 10x19x7mm double row angular contact bearing which should withstand a substantial radial load. This bearing is not all that common, but it is available and not outrageously expensive. Real World Cycling (a.k.a. EnduroForkSeals dot com) has a 3800 bearing which is 8mm wide. As far as I can tell that is not a standard size - I think they advertise it as a replacement for a specific Trek model.
The first photo shows the rocker pivot bearing - note the excess threadlocker compound that flaked off.
I unscrewed several of the suspension bolts to get a better look at them. (This may have been a mistake.) The bolts are all aluminum. Given my recent experience with Chinese threads in aluminum, that makes me a little nervous. They all had threadlocker on them when I removed them.
The rocker pivot and the rocker-to-seatstay bolts are the same size. The bolts are 10mm x 1.5 pitch, with a small 14mm diameter x 2mm high shoulder under the 19mm diameter head. The length under the shoulder is 19mm, of which only the last 11 mm are threaded. The bearing rides on the unthreaded shank, and on the shoulder. The second photo shows the rocker bolt removed from the first photo.
The shock trunnion bolts are also 10mm diameter, but with the standard trunnion 1mm pitch (which is considered extra fine). The bolts also have a 19mm head and a 14x2mm shoulder, and 15mm under head length, of which the last 10mm are threaded. I cross-threaded this bolt trying to get it back in, which is why I said it may have been a mistake to take it all apart. I finally got it back in straight. I think it'll be OK. But I'm already looking for a replacement. The 3rd photo shows the trunnion bolt before I cross-threaded it.
The swing arm bearings ride on an axle which extends through the front triangle. There's a bolt on the right end of the axle, it's a serious shoulder bolt. Threads are 12mm x 1.25mm pitch, 18mm long. The shoulder on which the ID of the bearing rides is 15mm diameter by 7mm long. There's a second shoulder, looks to be 19x1mm, directly under the 28mm diameter head. See the 4th photo.
I hope to find time tomorrow to run the seatpost cable in the frame and install the post itself. Once that's in place, i can install the bottom bracket and crank, trim the cables and brake hoses, and go looking for a saddle and a chain.
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More progress... no pics today, sorry.
I finally got the last bit I needed to finish the build: helicopter tape (ISC Surface Guard OG-HD) for protecting the downtube, chainstay, and various other parts which could get bits of dirt, sand, and rock thrown at them.. Frankly I did a fairly ugly job of putting it on the frame, but then I was the kid who always had glue fingerprints on the models I built. Anyway, the frame is protected, and I can always redo the tape later.
Once that was done, I re-routed the shifter cable and rear brake hose in some windshield washer tubing I had laying around, to reduce cable rattles. Then I routed the cable for the OneUp dropper seatpost.
Now that all the internal cables were routed, I could install the bottom bracket. This took a few tries, as the bearings on both sides of the frame kept getting cocked. I did a little bit of sanding on the inside of the bores, on the side that was getting hung up, and eventually everything went together. Then I installed the crankset, which took a couple tries as well before I figured out which side the spacer goes on, and which spacer my setup needed. Once I got that sorted, I installed a pair of Shimano PD-ME700 pedals.
The seatpost went in, and an Ergon saddle went on top of the post. Last thing I did before calling it a day was cutting the shift cable housing to length.
There's probably a day's worth of work left before I can think about riding it. The brake hoses need to be shortened and the brakes bled; dropper post lever installed; install a chain and set up the derailleur and shifter; get the bar, saddle, and controls where I want them, and go over all the bolts with a torque wrench a couple more times. Then there will be pictures. And riding.
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I finally set up the cockpit yesterday. It was no surprise that I had to shim the OneUp dropper post. The FM10 design has a shallow seat tube, and at the full 150mm extension, the saddle was just a tad too high. But I picked the OneUp because it had the shortest insertion depth at 150mm, and because they claimed you could adjust the travel in a couple of minutes without tools. They weren't lying. I only needed to shorten it by 10mm - one set of shims - so I still have plenty of room to drop the saddle in the rough stuff. I set up the handlebar angle and the controls much like my old bike.
I was a little disappointed to see that the saddle-to-bar distance was actually shorter than my old bike. I had a bike fit done last summer, and the fitter thought the bar was too close on the old bike. OTOH, the old bike was designed around a 100mm stem. The new bike has a 70mm stem at present, which I thought would be too long. The grips on the 16° SQLabs 30X bar are in line with the steerer. I might try moving the saddle back on its rails.
It's a gorgeous day here in Silicon Valley today, so I took the new bike to a popular local preserve for a shakedown ride. And had a blast!
Only a couple of minor issues came up during the shakedown ride. The seatpost creaks pretty badly in the frame. The headset developed a little bit of play, no surprise, and no big deal. Some of the helicopter tape I put on the chainstay had come loose and was buzzing against the tire. And (oops) I put the rear tire on backwards. ::) I wish I could blame the bike for my (lack of) fitness, but I didn't really notice the weight of the fatter tires.
The ZTTO 11 speed cassette, Sensah CRX shifter and derailleur, and low-end SRAM 12-speed chain combination worked great. I had no issues with shifting. We'll see how that changes as it wears. No issues today with the Goldix rear hub either, thankfully. I'm still leery after the rotor bolt threads stripped in the front hub, and after all the reports of Chinese star ratchets breaking down much sooner than expected. The 16° bar seems to suit my hands. The Ergon saddle seems kind of firm, but then I haven't done much riding lately, and I know I won't notice it after a few weeks.
Overall it rides a lot like my 2007 vintage 26er. This is both good (no major adjustments to riding style) and bad (expecting the spouse to say "You spent $$$$ for a bike that rides just like the old one?!)" ;D It did seem a little easier to control on downhills.
I'll want to go over everything with a fine toothed comb before taking it for another ride. And I'll cut down the steerer tube by about 20mm. I'd left it long just in case, but the Cane Creek Helm II fork seems to work fine.
I may build a set of 29" wheels and trade off to see if the extra width of the 27.5" tires makes up for the lower bottom bracket. The trails I rode today had been groomed recently, so there wasn't a lot of rough stuff to provoke pedal strikes.
Pictures attached as promised. I went with a stealth matte black theme because I'm lazy, and I suck at painting. ;D (I was the kid who always had glue thumbprints on any model kit I built.)
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I was wondering what size headset you ordered and if you like the Zitto headset?
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I got the ZTTO ZS44/56, it's the correct size for this frame. I thought the quality was decent when I installed it. I only have 2 rides on the bike, so it's too soon to tell how it holds up.
I need to replace the rear thru-axle before I'll ride it again. On the 2nd ride last weekend, I did a few small jumps, and heard a small 'crack' when I landed one of them. I suspected the rear thru axle. When I got home and got the axle out, it was intact. But when I went to put it back in, it wouldn't take full torque. The head kept turning, but I checked the other end and it wasn't turning. It couldn't turn, because the threads had bottomed out.
The factory axle appears to be carbon composite. I was concerned that it wouldn't hold up (I'm about 220 lb/100kg), so I ordered a 175mm aluminum axle from another AliExpress vendor, along with some spacers to dial in the exact length. This was before I discovered the bottoming issue. I won't ride the bike again until I get the new axle in.
If you're buying an FM10, do NOT buy the factory rear axle.
The original rear thru axle is 12mm diameter by 173mm long, with a 1.5mm thread pitch and 15mm long threads. Clearly 173mm is too long if it bottomed out. 171-172mm should be ideal. It works out that 171mm w/ 1.5mm thread pitch is a Shimano E-Thru standard - for a 142mm hub - so there should be no shortage of options on the market.
The threads it screws into are about 14.5mm deep, so the axle should have at least 15mm of thread length to be safe. Unfortunately that means the Wolf Tooth 172mm thru axle, with 13mm of thread, won't work. [edit] It looks like the MRP Race axle will work - they don't have the thread length on their site, but a close look at a product picture shows more than 10 threads. I just ordered one.
I still have to go looking for the source of that 'crack' when I landed the jump. I haven't done a close inspection of the frame yet. Maybe later today.
The other issue I had on that ride was that the Goldix freehub slipped noticeably on a couple of occasions. I took it apart, and cleaned up the star ratchet to look for signs of damage. I didn't see anything obvious. It might just be that the too-long axle left a gap just big enough to allow the ratchet to slip. That's another reason I'm looking forward to putting in a correctly sized axle.
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Confirmed, the MRP Race axle, 172mm long, 1.5mm thread pitch, is a perfect fit in the FM10. It doesn't bottom out when torqued to spec (10 n-m).
Looking forward to taking this bad boy for another ride tomorrow or the next day.
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Nice build.
My frame came with all parts upgraded. Bolt for non trunnion shocks was solid steel. Rear axle was Aluminium (don't remember if 7070 or 7075. It is printed on the axle.) and the seat stay has a new pocket that works with 200x55mm shocks. (Ordered from Amazon)
What is the chainline for this frame? 52mm or 55mm?
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My frame came with all parts upgraded. Bolt for non trunnion shocks was solid steel. Rear axle was Aluminium (don't remember if 7070 or 7075. It is printed on the axle.) and the seat stay has a new pocket that works with 200x55mm shocks. (Ordered from Amazon)
What is the chainline for this frame? 52mm or 55mm?
The axle is probably 7075, that's the more common alloy.
Chainline is 52mm, standard Boost width. The ZRACE Dub crankset has worked well to date. I may swap out the 32T chainring for a smaller one. There are lots of short steep stretches on the trails here.
I had the bike on the stand yesterday. The shifter cable seemed to have stretched a bit. While adjusting the cable, I noticed some shifting issues that suggested a bent derailleur hanger. I got out the hanger gauge, and sure enough, it was bent - not much, but it doesn't take much with 11 cogs! I bent it back and everything was fine again.
As mentioned earlier, I felt like the medium frame isn't quite long enough for me. To get a little more cockpit room, I swapped out the SQLab 30X bar for a Salsa Bend Deluxe, 740mm long with a 17° bend. The Salsa bar bends forward before it bends back.
I rode my favorite trail yesterday for the first time with this bike. I was slow up the hills, but that's not the bike's fault! The Salsa bar felt good. I had a minor pedal strike (actually crank strike) at a step-up to a bridge yesterday, first one so far. I haven't got the rear shock figured out quite yet. I think it needs more pressure to support my fat @$$.
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I got sick of the pedal strikes with 27.5+ and went with a cheap set of Giant 29" wheels. Made such a difference to the bike it's not funny.
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I haven't done a lot of MTBing this summer, unfortunately, so I don't have much in the way of updates. The last time I rode the FM10 was in late June!
The seatpost creak was due to the post bottoming out in the seat tube. I raised the post a couple mm, and now the creak is gone. I'm really happy with the OneUp dropper post so far.
The trunnion bolt I cross-threaded won't come up to full torque now. Entirely my fault that it got cross-threaded. I posted a message to Seraph on Aliexpress late this afternoon (California time), got a quick reply (as in minutes!), and I have ordered a replacement. I don't feel safe riding the bike in this condition, so I'll dust off the old 26er for the next couple of rides, until the new bolt shows up.
While I was fooling around with the shock, I noticed it wouldn't pivot very far on the trunnion bearings. The problem was excess resin on the inside of the trunnion mount. I used a file to grind it down, and the shock now has a pretty good range of motion, though still stiffer than I'd like.
I'll put together a set of 29" wheels this winter, after I pay off some bills.
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Another update, sadly without putting many more miles on the bike. Work and chores have gotten in the way.
Seraph was quick to send a replacement shock trunnion bolt. It came with a spare pivot bolt as well. Not bad for US$10 plus state sales tax shipped.
I've ordered the parts for the 29" wheels. I went with Koozer 490 Pro hubs (steel axle in the rear hub) and Dairsbike 34mm internal width rims. The hubs are here, the rims haven't shipped yet. I also ordered another 11-50 11 speed cassette from ZTTO, along with 203mm and 180mm brake rotors, just so I can swap wheelsets without hassle.
Another concern: The binder bolt holding the shock to the rocker arm doesn't reach all the way through. It measures about 7mm too short. This explains the funky wear pattern on the bolt - it's bending under load. Worse, the Allen bolt that threads into it is only 10mm long, so that means there were only about 3mm of thread holding everything together.
I ordered 68mm replacements from Delt. That's a little long, but better too long than too short. The bolt should go completely through the assembly. I'll need to put a washer under one end, fortunately washers are cheap.
So far that means the rear through-axle and the shock-to-rocker-arm bolt supplied by Seraph were inadequate. The thru-axle wasn't part of the frame deal, but the shock bolt was. I wonder what will be the next issue to come up?
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The new binder bolt for the lower shock mount arrived Friday, and I just now installed it.
The first photo is the "before". Note the big gap between the end of the bolt and the surface of the flip chip.
The second photo is the "after". The 68mm bolt is a perfect fit; it's nearly but not quite flush with the flip chip.
The third photo shows the difference between the original bolt and the replacement. The circles indicate areas of visible wear on the bolt surface. The wear mark on the left lines up with where the rocker meets the shock mount bushing. The middle mark is near the eye of the shock. The mark on the right is where the bushing meets the rocker arm on the other side.
You can also see how few threads were holding the bolt in place!
The 29" rims have arrived from Dairsbike, along with brake rotors and an 11-50 11-speed SL cassette from ZTTO. I've ordered spokes from WheelBuildingParts dot com, an L.A. area vendor. they had the best price on Sapim Race 2.0/1.8/2.0 spokes. As soon as the spokes arrive, the wheel building can begin.
For the gram geeks, the Dairsbike rims claimed 460g, and the one I weighed is 457g. Koozer claims 170g front, 320g rear for the XM490pro hubs; I got 186g and 329g respectively. The ZTTO cassette claims 590g, and my scale says 579g, including the zip tie holding it together for shipping. I didn't bother weighing the brake rotors.
Next purchase for the FM10 will be tires.