To Drill or not to Drill

My new Cafe'd bike has been converted to belt drive, in it's primary, which is running dry (without oil). The Seller advised me to drill quite substantial breather holes (around the size of an Oz 50c piece) along the lower edge of he primary case, to facilitate cooling in my tropical climate. Does this sound right? Is it an essential mod? Or do I have alternatives less radical than drilling into an original Norton part, where it's most vulnerable to picking up road grime & moisture?

my clutch used to run very very hot until i drilled the inner and outer case and i'm in the UK so i would definately drill ,,,,,,,,,,,,,baz

dont forget you will need a seal on the clutch centre nut to keep the gearbox oil migrating into the chain case

I have a BNR belt and clutch in my 74. I run it closed up as it would be standard. My worry was
ingress of dust. Im a street rider, rarely flog it. Im in NYS so not especially hot nor do I ride when
it is over 90 or so.
Asked Bob about this and he said:

"It's not necessary to vent the std cover, there is less heat from the belt
than the chain and unless you slip the clutch more than normal, it should be
quite ok."

I've been running a Hayward belt in a closed dry case on a Triumph for years and nothing has got hot.

Hi Old Scratcher.
If you were to drill, you could perhaps find a way to retain a sheet of 20 or 50 micron stainless steel mesh in or across the hole to permit air flow without particle ingress. The mesh is used to strain honey, etc.
Ta.

Why not just leave out the two filer screws and the timing scale access screw? Don't take it out in the rain

There are screens the same size as the inspection plugs, no drilling, just screw in.

I have run a dry belt primary for the past 17 years with no venting, all inspection caps in place.

It gets hot here in the desert southwest USA. Drill if you want something to do, not because it is necessary.

give it a try and see if it runs hot or not make sure you have it adjusted right ,,,,,,,,,,,,,baz

Drilling can make it look cool, but it doesn't help the belt at all. Jim

needing said:

Hi Old Scratcher.
If you were to drill, you could perhaps find a way to retain a sheet of 20 or 50 micron stainless steel mesh in or across the hole to permit air flow without particle ingress. The mesh is used to strain honey, etc.
Ta.

Click to expand...

Treacle is very good for making a non-toothed belt grip.

just do what ever pleases you and the conditions expected as cooling does not matter a whitworth even if it does run cooler all the designers, manfactures, vendors and famous installers know all the items are fine enclosed as hard as your engine can strain them. Love all the various tastes in the vent patterns. I liked the Hover Vacuum Cleaner art deco of the full face cover so did Peels by opening the front of inner case, with stone screen and filer filter pad behind that with the exit vent a bottom rear bend of inner case where I thought there might be some lower pressure to help draw the front blast out and also let water out from heavy rain and creeping water crossings. Normal versions tend to remind me of crop circles which are fascinating. i tend to crash on THE Gravel for too many reasons and through pasture grass full of bugs and pollen and seed grains so messes more than civilized paths. One little pensivenessness I learned the hard way about belt drives strengths coming apart away from home, they can take holes through the flats ya can run a pencil or knife through but only takes a fine grit layer polishing away the edges to simply unravel. That made me add grit-dust filter material as after thot.

It's your bike, you do what you want.
Beltdrives vary on heat. My RGM seems to swell a bit so I keep the belt on the slack side. As long as it is tight enough to not jump teeth on the drive sprocket, all is good. But too tight could be catastrophic.

Yeah man Pete nothing says made in Britain like art deco crop circles...

Enclosed for me ,no need to vent and let IN dirt. RGM ,love it.

Thanks for the replies everyone. The usual interesting cross section of opinions I'm coming to expect from this place. For the record, I DON'T want to drill holes into anything made by Norton, over 40 years ago. I would drill holes if it was absolutely necessary for the cool running of the bike. But from the reports from those who live in a climate as hot as I do, I don't think it is necessary. & if it was I'd consider returning the bike to it's original chain drive, as I don't like doing any mod that can't be reversed, as that compromises originality too much IMO

Shoot I live with a split brain annoyance so to ease my conflictiveness I*d keep the nicest cover intact and crave up another with crop circles to switch as mood strikes. Just nil concern about heat issue on belt or alternator as the enclosed oil bath likely gets hotter than enclosed dry belt d/t oil helping carry crankcase combustion heat all over. Comnoz noted cooler TS case with lower oil level drain.

I just cut a 50mm length out of the primary cover gasket , then you can put that where you like, ie at the bottom , or right at the back on the largest radius of the cover.
Some use perforated stainless steel mesh pressed into the inspection cover holes.
Being in New Zealand , we do have extremes of weather.
Regards Mike

THE ughlest way to me is just leaving the plugs out like they just fell off. Gap in rubber oil ring is cleaver concealed way that solves everything easy, cool.