Project CRF300L: old tubes and dirt bike rims

Project 300L Index Page
See also: Tubeless conversions

After less than 20 miles I’ve already got myself a rear flat, luckily at home. At some point I was going to remove the stock IRCs, seal the rear rim for tubeless tyres and fit some proper tyres for the ride to Morocco. May as well do that job now. While I’m here, allow me to give my usual shout-out for Motion Pro Bead Breakers, an alternative to standing on or otherwise levering the tyre bead to achieve the same result.

I spun the wheel on my exciting new stand you just read about but couldn’t see any nails or similar. I did wonder if I pinched the tube a couple of weeks back, but if I did, it only gave out now.
Pulling the tube out I was shocked to see a huge gouged hole like a mouse had got in there. Maybe I did it just now removing the tyre, but can’t say it was a struggle. Who knows, but I also noticed how the folded rubber tube cracked like it was ancient. Then I clocked a date stamp from November 2014. Yikes, nearly 9 years old! Well I suppose I should be impressed that a: Michelin date-stamp their tubes (can’t say I’ve ever noticed this feature before) and, b: that this tube lasted nearly nine years without a repair (assuming it had any use in that time)! Obviously the tube isn’t worth repairing. Good thing I noticed now. I just picked up some old Mich tubes from 2017 and they are nowhere near that far gone (nor do they have that date stamp). Could it even be a fake Mich tube?

Cracked rubber; not a good look.
No MT stamp
No lip so unsuited to DIY tubeless sealing ;-(

When it comes to sealing the rear rim, I was also bummed to see the stock Excel J 18 2.5 rim has no safety lip, in which case I can forget about doing a TL conversion. That’s odd as, like I’ve mentioned over the years, I recall actually grinding the safety lip off a rear DID rim on my tubed XT600 way back in 1985 to make desert tube repairs easier. I assumed such safety rims had become defaults on all spoke/tube rim as they help a tyre stay on the rim when it loses pressure.

This means I’ll have to lace a new lipped MT rim onto the hub to get TL – a couple of weeks and a couple of hundred quid. And while I’m at it I may as well get professional CWC Airtight sealing (left; as on my Himalayan) instead of my labour intensive DIY efforts, as on the Africa Twin. Or I could just live with inner tubes. On a travel bike (as opposed to a weekend trail bike) not sure I can go back to all that potential aggro and added toolage.

I also noticed there’s no cush drive on the 300L. It makes me think this is a dirt bike rim from Honda’s MX bikes. A part number check would reveal all – maybe later or you can do it for me.
Cush drives add weight and expense and absorb a little power, but reduce drivetrain lash to the transmission including the chain.

The thing is, at 28hp and however few torques, a 300L hasn’t got enough grunt to strain the components that much, so I can live with no cush. Apparently my old XR650L was the same but I never even noticed. A mate who’s currently importing one has, and dug up various rubber-insert sprockets (left) to reduce the lash from the much torquier 650 thumper. And in fact the 250L I had years ago didn’t have cush.

So net result of today’s puncture:

  • it pays to verify you inner tube’s age (if you can) as well as old tyres (all have date indexes). Or just get new tubes.
  • If I want a tubeless rear I’m going to have to get a new wheel built up on an MT rim, in which case I may as well have a proper sealing job done like CWC Airtight™.
  • OMG there is no cush drive ;-0
  • Is it time to consider mousses? A light slow bike like a 300L is suited to them, but afaik they come rated at no more than 15psi which to me is on the low side for road riding, even at only 60mph.

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