English French German Italian Spanish

Brake m/c bore hone

Submitted by stan_thomas on Wed, 19/01/2022
Forums
Commando

Does anyone have experience of using a hone, such as this :https://www.pacehigh.co.uk/bc-style-flex-hone , to clean up the bore on a Commando front brake master cylinder (original)?

Any recommendations on abrasive type and grit?

 

Reason - corrosion from neglect has left some pitting in the cylinder bore and it seems to be leaking slightly (athough it works fine). If it was external, a polish with 1000-grit wet 'n dry followed by Solvol would clean it up nicely.

Submitted by steve_constable on Thu, 20/01/2022

Permalink

I have had good results by wrapping double sided sponge tape around a long drill bit until the diameter is just slightly larger than the bore and then sticking wet and dry to it. You can the turn it either manually or at slow speed with a drill.

 

Submitted by david_cooper on Thu, 20/01/2022

Permalink

There are small diameter conventional hones with stones. I considered a flexhone to improve a cast iron engine bore, but it's price and selection of grit size put me off. I'm sure they'd be good in a relatively busy workshop. But they are advertised to provide cross hatched plateau honed finish.  Is that what's needed for the master cylinder? I don't know.  RGM seem to sell a "universal" (i.e. not original) new master cylinder for not much more and possibly less than the price of a flexhone.

Submitted by dan_field on Thu, 20/01/2022

Permalink

I can’t speak for commando brakes, but all the hydraulics on my 1955 Ford were cleaned up with 1000 grit wet and dry around my little finger with WD40 as a lubricant - worked ok for them! Any slight increase in diameter was taken up with the seals. But I guess it depends how deep the damage is ?

dan

Stan, are you still looking to hone your master cylinder bore? I have a 5/8" Flex-Hone bought years ago to clean up a standard Commando master cylinder to use on a project. You can borrow it if you like.

I,ve just tried it on a scrap unit and it came out OK using WD40 as a lube. If the pits are too deep it won,t remove those but yours don,t sound too bad if it still works. Steve,s idea is one I,ve used on other things with success too.

 

Submitted by stan_thomas on Mon, 24/01/2022

Permalink

Thanks for the comments guys.

My master cylinder had signs of rust in it. When I took it apart the piston and spring were rusty and there was a bit of a depression in the cylinder wall roughly where the rear-most piston cup seal sits. I cleaned it up with scotchbrite on a rod in a drill and it didn't look too bad, although the marks were still there. Reassembled with new seals, the brake works fine. But after a while a trace of fluid forms around the dust boot. My guess would be that fluid is being left behind in the depression by the outer seal when the piston is pushed in and then ends up on the outside of the cylinder. Very small leak, doesn't noticeably affect the fluid level but it shouldn't be there. Since I re-used the piston after a thorough wire-brushing and polish with emery, it's always possible the leak is coming from the inside of the rear seal. Plan is to clean up the cylinder and rebuild with all new internal parts.

And thinking, oh-oh, I stripped my other master cylinders which all show very similar marks (3 Commando, 3 AP racing). So I don't know how much is corrosion and how much is wear. But I figure it'll take less than 0.001" to clean it up.

I had thought about fashioning something using emery to spin in a drill but then came across these Flex-hone tools which seem purpose made for the job and, since I have a few to do...

 

Neill - thanks for the offer. I will take you up on it. I'll try it on one of the pre-Mk3 master cylinders on the basis that, if it doesn't work out, it'll be a candidate for sleeving down to 13mm.

 


Norton Owners Club Website by 2Toucans