bsa girders

[douglas]

anyone know if pre-war girders on the big single models are any stronger than the wm20 versions which always seem to crack at the same points?i.e because they were throw away was the tubing of crappy quality?  douglas

[33d6]

Well Douglas, I wouldn't say that M20 forks are of crappy quality. It is some 65 years or more since they were made so having them start to suffer fatigue cracks after that time is pretty reasonable.
It could be one or two other things that are at issue here. Many M20 riders dont grease the forks often enough and more to the point they don't upgrade the original type of grease nipple for current style "hydraulic" nipples so they can't get the grease in where it's needed anyway. Anyone who still has the original style of grease nipple and tries to get grease in with one of those nasty little brass 'pom-pom' grease guns is working very hard to little effect. It might be how they did it originally but it doesn't work. Upgrade the grease nipples and use a modern  pressure grease gun. Of course a modern specialist grease or similar doesn't hurt either.
A well greased fork with a good working action resists cracking much better than one that has a stiffer action because the grease isn't getting right through.  
Upgrading is just a matter of screwing out the original 1/4"BSF nipples and screwing in new ones of the same size.
Finally, metal fatigue happens to all forks eventually. Earlier forks will have been on the road even longer and be even more tired. M20 forks are fine.
Cheers, Bob

[douglas]

dont be offended bob, i was only referring to the war models. most of the WM20's i,ve seen  have had a repair plus this bsa nut i know says it was common for them to crack!  douglas

[ojcdrc]

Douglas, I would suggest that you look at this a bit differently. As Bob suggests the condition of the forks very much depends on how they have been used and abused in the past. Many M20's were used for side car tugs often in extreme conditions which places severe loads on the forks. The fork tubes on your bike (from what little we could see in the photo) appeared to be okay. If they are why worry about it, there are still plenty of these bikes with original tubes on the road today. As far as the older BSA type girders I have seen just many of these with cracked or welded tubes as I have M20's and would suggest that they offer no real advantage.
I have a 37 500 BSA with the original fork tubes and its been going fine for the last fours. Hope this helps. Dave      

[33d6]

Don't worry Douglas. I'm not at all offended and it was the WD models I was referring to. I'm sure the majority of M20's on the road today are exWD beasties.
I would also agree with Dave that most have received a fair battering in their life. In my early riding days only desperate apprentices or students owned them (I had two) and we certainly never looked after them.
To my mind,  finding them still thumping along all over the world shows just how well BSA made them in the first place.
Cheers, Bob

[geoffus]

Bsa front forks went through a lot in the war years with mechanics who were not necessarily specialised in there upkeep providing the bike kept going no questions asked which is understandable in the circumstances the majority are probably almost as good as the day thay were made and unless you can see obvious cracks in the paint work and you realise that these are 60 odd years old I would assume you would use caution in putting these through hard times but on other side of the coin I still use forks from the twenties and find them ok    geoff