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M49 advice please!


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Here is one type of M49 rear hub. I just measured the liner of this one as 144mm OD. Nominal ID is 140mm. I am planning plan to machine this one out to either no grooves or a maximum of 142mm ID with some grooves remaining. 

There is another type of M49 rear hub fitted to early build M49s that I will post up a photo of later if you think it is helpful. This earlier hub has a liner with the same nominal ID (140mm) but has a much bigger OD (147mm)

IMAG5367.jpg

IMAG5368.jpg

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7 hours ago, feetupfun said:

Here is one type of M49 rear hub. I just measured the liner of this one as 144mm OD. Nominal ID is 140mm. I am planning plan to machine this one out to either no grooves or a maximum of 142mm ID with some grooves remaining. 

There is another type of M49 rear hub fitted to early build M49s that I will post up a photo of later if you think it is helpful. This earlier hub has a liner with the same nominal ID (140mm) but has a much bigger OD (147mm)

IMAG5367.jpg

IMAG5368.jpg

That’s interesting David is there much visual difference between the hubs

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Just spoke to in motion, apparently the brake surface was just chromed in the factory. Mine has obviously had a cast iron sleeve fitted in the past and that is almost worn through to the aluminium! Looks like I'm going to have to bore it out and re line the hub, I'll repair the bearing diameter at the same time. It'll keep me off the streets! I'll let you guys know how it goes....

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As I understand it, if your hub is 2-piece with a removable spoke flange, as in the pics. from feetupfun , then it's the old style "heavyweight" item. This would have an iron brake drum which was actually cast-in as an integral part of the hub, and brake shoe linings 40mm. wide..

Hardchrome lining is a feature of the later one-piece "lightweight" hubs with brake linings 25mm. in width. 

Remember, blueflag - a picture speaks a thousand words.........?

Edited by lorenzo
Additional info.
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On ‎25‎/‎02‎/‎2018 at 6:17 PM, mrb505 said:

That’s interesting David is there much visual difference between the hubs

Yes the earlier one has a narrower brake drum contact surface, the smaller spoke flange is part of the hub casting and the fins on the drum are machined not cast

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Been too busy the last couple of days to make any progress, I'm hoping to try and get the hub bored later on. Another question, I know I'll probably get flayed alive for suggesting it but I've found some cast pipe in a scrap bin, it would only need a lick on the o/d and bore to be spot on for size. It's not cast iron, it's a nickel chrome alloy steel, basically stainless. I'm happy to try it out, thoughts guys? (The only cast iron I have is a huge chunk and it seems a waste)

Edited by blueflag
Grammar
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40 minutes ago, blueflag said:

Been too busy the last couple of days to make any progress, I'm hoping to try and get the hub bored later on. Another question, I know I'll probably get flayed alive for suggesting it but I've found some cast pipe in a scrap bin, it would only need a lick on the o/d and bore to be spot on for size. It's not cast iron, it's a nickel chrome alloy steel, basically stainless. I'm happy to try it out, thoughts guys? (The only cast iron I have is a huge chunk and it seems a waste)

Some alloy steels have a low coefficient of friction so be careful. Mild steel or cast iron are the go for brake drums

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Well, just finished machining the drum, it is indeed a cast - in liner. I've taken it out to the nominal diameter of the aluminium, I'm guessing 144 ish mm. Just got to sleeve the bearing diameter while it's set up and sort out a mild steel sleeve for the drum.

Slowly getting there!

20180228_180316.jpg

Edited by blueflag
Missing photo.
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Trying to find time to make and fit a new drum. Hopefully it'll be done this week. 

My mate has suggested going hydraulic on the rear, if I can find a suitable slave cylinder I'll have a bash. If I go ahead in the future I'll make a complete new brake plate to save ruining an original Bultaco part. ?

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6 hours ago, blueflag said:

Trying to find time to make and fit a new drum. Hopefully it'll be done this week. 

My mate has suggested going hydraulic on the rear, if I can find a suitable slave cylinder I'll have a bash. If I go ahead in the future I'll make a complete new brake plate to save ruining an original Bultaco part. ?

Best read the trials regs, rod or cable for brake operation in classic classes.

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