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Discussion Starter · #1 ·
Hi there,

just about to embark on an engine rebuild. My bike is an XL125 (mid 70s) and it has a CB125S (early 70s) engine.

After a mammoth clean-up operation I've removed 20 years of crap from every part and found that luckily most of them have survived.

visit my blog for pics

www.matthewsimkins.co.uk/XL125blog

The main casualties were the bolts and my question is what size are the crank case bolts? They look like M6 and I'm guessing that Japanese bikes would be metric. Also I'm not sure whether there would be different thread sizes etc.

I'm also looking for the same kind of info for the countersunk bolts that hold the centrifugal oil filter cap on.

Any bolt info would be appreciated.

Cheers.


P.S the other casualty was the piston, some fun pics of a completely destroyed piston (and luckily an unharmed cylinder) to come :p
 

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The Angry Pasty Muncher
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6,170 Posts
Hi there,

just about to embark on an engine rebuild. My bike is an XL125 (mid 70s) and it has a CB125S (early 70s) engine.

After a mammoth clean-up operation I've removed 20 years of crap from every part and found that luckily most of them have survived.

visit my blog for pics

www.matthewsimkins.co.uk/XL125blog

The main casualties were the bolts and my question is what size are the crank case bolts? They look like M6 and I'm guessing that Japanese bikes would be metric. Also I'm not sure whether there would be different thread sizes etc.

I'm also looking for the same kind of info for the countersunk bolts that hold the centrifugal oil filter cap on.

Any bolt info would be appreciated.

Cheers.


P.S the other casualty was the piston, some fun pics of a completely destroyed piston (and luckily an unharmed cylinder) to come :p
Easiest way would be to measure them, most will be M6x1 or M5x0.8 or M8x1.25mm possibly M8x1mm chances are these will be the thread pitches you will have you can get them in all lengths and cap head (allen key) or countersunk

try WWW.FWB.CO.UK

we use them at work they sell everything you need and will be available in stainless, high tensile, zinc plated anything you want really and will cost you pence each
 

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Discussion Starter · #3 ·
Cheers Jason

I wasn't sure to start with as they didn't seem to hit 5mm and 6mm exactly.

No harm in buying some cheap bolts though and I'm sure I'll find that the 'Ms' will fit.
 

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As a rough guide a bolt has a head 4mm bigger.
A 6 mm bolt will need a 10 mm spanner.
 

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Ridden for years
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You could just try and see if the threads sit inside another bolt. you know, hold them next to each other and see if the pitch sits neatly between another known bolt's pitch.
 

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Discussion Starter · #7 ·
The thread pitches seem to match standard metric equivalents. I never knew there was so much to bolts!

Got a box of spares on its way from David Silver soon. looking forward to cracking on with the rebuild.
 

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Red Blooded Biker
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That engine in bits reminds me of when I used to work on my CB125S back in the '70s. I went through two cams & two cylinder heads due to oil starvation, a gearlever return spring & a 2nd gear. The engines on the 125 were pretty basic, but it taught me how to work on engines & how to do things for myself & not to bother with dealers/bike shops.

As far as the nuts & bolts are concerned, they're mostly standard metric stuff. The VJMC magazine has a bloke who makes unusually sized screws & bolts for those who want absolute authenticity, but I went the stainless steel Allen bolt route with many of my early Hondas because of the cheesey material that were standard back in those days.
 

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Discussion Starter · #9 ·
yeah standard m6 bolts are working fine. Nice to have the allen key head, only 3 of the originals survived impact driving.

I've ordered more for the clutch cover too even tho they were all fine.
 
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