Hi yes, I know that's a pretty general question.
I'm a new owner, the bike has it's std tag on it
with 15K miles.
I'm dying to rip the barrel off of it soon and do some measuring and renewal as needed.
I've been doing a lot of reading abt the bike, especially thru this great forum.
I was maybe slightly dismayed to find the below.
do most of u find that statement true?

The M20 failed on its first submission to the War Office in 1936 (due to 'unacceptable engine wear') and only just passed the 10,000 mile suitability tests


Are we talking about a ring job and valve grinding every 10k or so
or other engine wear?
tnx Patrick

email (option): pwegelin@moog.com

Hi Patrick..That is only half the story...BSA did some work and resubmitted the bike in 37 when it passed all tests and was accepted for service..a later redesign further improved the design and incorporated some more 'modern' thinking.
The bottom end of an M20 if properly assembled and maintained is a 75,000 mile unit...I owned one that I bought from it's original owner that had not had the crankcases apart since new and had covered 104,000 miles.
Expect a top end overhaul around 50,000 with more frequent maintenance on the exhaust valve...Ian

email (option): ian@wright52.plus.com

If it's not smoking, dripping oil at an unacceptable rate, or making weird noises, leave it alone. (Remembering that normally it makes engine noises different and louder than those of a modern bike.)

Have you figured out the top speed yet?

email (option): jonny.rudge@verizon.net

Ha John,
haven't even drove it down the road yet as I don't have a helmet, insurance or NYS motorcycle license.
I did get it started last summer however and it did sound nice.
Barrel and head pretty rusty, so want to get it apart anyway for a clean-up and paint and measure things up.
patrick

email (option): pwegelin@moog.com

Good luck! That's how one of my rebuilds started more than 20 years ago and it's still not done. The frame has had a nice new coat of paint but resides in the basement. (Thankfully I have other M20s which are in running condition.)

email (option): jonny.rudge@verizon.net

AMEN! Unbidden 2 cents worth: DO NOT take it apart now if it is running well.

Just use a wire brush and a some hi-temp black paint on the top end if you want to spiff it up a bit. Content yourself with changing oils, lubrication, chain adjustment, wheels and tires.. After you have some miles on it, you can decide if it needs to come down.

email (option): teladelujo@msn.com

wow.

Hi Nick...my B33 did 78,000 after I restored it before I went into the crankcases again..and that wasn't for a mechanical failure but to do a 'cosmetic' rebuild.
I've owned numerous BSA singles over the last 35 years and have yet (touchwood) to have a big end or main bearing failure...Ian

email (option): ian@wright52.plus.com

that's music to my ears Ian as i have both a ZM21 i've just begun to build from swap meet scores and a ZB33 which i've pulled down for a freshen up after awakening it from a long rusty slumber in someones dark garage corner, i'm 23 and intend on using them both very frequently.

Hi Nick..I was 25 when I bought the B33 and now I'm 58...so I can vouch for the fact the bike is lasting better than I am.. ...Ian

email (option): ian@wright52.plus.com