Vintage Dirt Bike Q & A

the small 3/4 inch bar thats part of the frame under the tank that holds the square box thingy on,seems to be cracked right through,is this a common fault or does it need to be properly welded back up?
excuse my terminology but i'm not really technically minded
also the fox air shox on the bike seem to be topping out as if theres no damping,when i try and adjust the bottom valve to 135psi it seems to transfer the pressure through to the top valve,when i then reduce the pressure in the top valve some oil comes out as well as the bottom valve reducing pressure,are the bladders needing replaced or have i just lost too much oil when i've been messing with them?the guy i've just bought the bike from said they were serviced recently,
also,it looks like it has an 83 cr480 front end on with the twin brake arm thingy,the brakes are non existant,is there a procedure to balance the arm or do i just replace cables/shoes?
the bike is white with a plain unpainted engine and a black frame,it has mugen stickers on ,was there such a thing as a mugen 250?and what did it look like compared to mine
thanks for taking the time to read this,any help or tips are appreciated
doug, from scotland

Doug,

I think it would be best to have the frame tab welded back on, but if you're like me and hate dragging the bike to the welder's, you might try epoxying the tab back on with JB Weld or its Scottish equivalent. As long as any frame ground wires are still in place, it should work fine (you might want to throw on a couple of tie-wraps for added strength).

It seems that Fox now makes mainly bicycle and ATV shocks, but here's an E-mail contact in case they can help:

atv@foxracingshox.com

Does your bike look like these?

http://www.acrmx.com/images/bikes/mugen250.jpg

http://ausvmx.ning.com/photo/mugen-me-2 ... ntext=user

I have the Yamaha equivalent of your front brake on my CR, and it's very powerful; if yours is weak, it's definitely out of adjustment and may have ruined the shoes. After replacing them, try this procedure (it might be a little different for your setup, but the concept is the same):

1) Lift front wheel off the ground
2) Screw adjuster rod fully in (rotate down on Yamaha setup)
3) Tighten front brake cable until primary shoe just rubs drum (one rub per wheel rotation)
4) Turn adjuster rod up until secondary shoe just rubs (two rubs per rotation), plus a little more
5) Tighten rod locknut, recheck for 2 rubs/rotation (if only one, repeat steps 4 & 5)
6) Adjust brake cable for normal operation

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

if it is this tube you have to weld it, otherwise the frame flexes too mutch and may break at an other place.
note the frame is made from chrom moly steel, this is important to chose the right weldingwire.
also check all enginemounts and the headstay are fastned right.

_________________
80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

http://ltthor.home.comcast.net/~ltthor/forsale.html
Parts and rebuilds for Fox Shox. Your bladders are probably toast.

_________________
Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

b-joe, nice work table

yes, at work there´s all you need to do with metal.

_________________
80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250