Wednesday, March 28, 2007


HyMDT Cruzbike Folder (Update#2)

I learned a great deal during my experimentation period with the hybridization of the Downtube and the Kona MTB. I like the idea of a 20 inch wheel in the back and if a frame with a disk brake mount is used there is not a compatibility problem. I am looking at a small chrome-moly diamond frame. I didn't get a chance to experiment with a seat post suspension, but the lack of a rear suspension is not really an issue for a paved or gravel road machine. With a weight distribution of 50/50 the front suspension takes more of the load than a conventional hard tail, and it is possible to put some weight on the arms when riding on rough surfaces as well as shifting more weight to your butt by leaning forward a bit, transferring even move weight to the front suspension. A hard tail is a hard tail whether you have the pedals in front of you or below you the way it seemed to me although I didn't try steps I jumped curbs without much problem.

For the record I have rebuilt the Downtube after replaceomg the original NECO Bottom Bracket. I replaced the BB bracket with a Shimano UN54 - 107mm sealed unit which is the same as UN52 as far as I could tell. It is a nice fit for chainline etc. with the Bulletproof 110mm BCD double. I am using just the inside ring (34T) but there is room for a chainring on the outside. 110mm BCD chainrings are available in just about any size you may want. The Bulletproof cranks are not the lightest but they make a nice running system with the SA8 rear hub.

There are several things about the NECO BB that I really don't care for.

1) the splines are shallow and slightly oversized thus hard on removal tools, and the threads were dry so removing the BB to grease the exterior threads is something that must be done when the bicycle is new, otherwise the frame may be damaged when it must be removed with extreme force because the bearing are shot.

2) the lock ring, the same thing used on a cup and cone set up, is necessary to set the bearings but is there a cone is on the sealed end? Maybe, but I couldn't tell by looking, the thing is sealed, kinda. (added 30Mar07) Well I did figure out how this thing works, I took out the seal gave the axle a sharp rap with a hammer while the drive side was still n the frame and the adjustable cup was removed. It came out quite easily.

The bearing has a retainer which could be removed and replaced with all ball bearings. The BB could be serviced without removing the right side. In fact, that is the way it should be done. I will have to say that after I figured it out this is a better deal than I thought a couple of days ago. The things you discover by playing.

It is all guess work where it should be set such is the case with the cup and cone but .... Like I said long ago--replace the BB with a sealed unit. Basically do it when the new bike is being checked over by the LBS and forget it for years. Even a moderately priced Sealed BB will last a long time. I guess I still stand by this advice, but if you do you own work the original BB is okay.


I also replaced the stem with a 7 degree 130mm stem to fit me and reduce the globby looking adjustable unit that is fine if several people are using the bicycle but that is not the case here. Besides I still have the adjustable unit in the parts cache.

I took the cassette head set assembly that I had installed for the Manitou fork off the Downtube and reinstalled the stock head bearing assembly.

I am going to put a moisture seal in place now as the stock head set assembly does not even have a gasket to protect the bearings.

I will detail that in a day or two. It can be done for pennies and it keeps the bearing clean and dry--remember it is the dust and grit that destroys the effectiveness of the grease and wears out the bearings.
Prevention is the best maintenance.

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Thanks for the BB info. My cup (left hand in your pic) has only 9 rather than 11 balls, so maybe there are variants on that Neco BB?
I took out the right side to be sure the threads are ok, but didn't tap out the bearing.
The lockring was way overtight & got a little damaged removing it, but the BB itself came out ok with the Shimano tool.
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