longstroke engine

[vagabond]

I have been offered a long stoke engine suposedly for a rigid A7. I am getting confused with reading the threads. is the rigid longstroke different from the plunger longstroke or is it the same animal.
Thanks Dave

[Brian]

Hi Dave, it can get a bit confusing.

Basically there are two types of A7 engine, the earlier commonly know as "longstroke" and the later shortstroke. The longstroke was used up until 1950. In 49' and 50' it could be fitted in either a rigid or plunger frame.

The shortstroke motor was introduced for 51' and was available in a plunger or rigid frame. As far as I know 53' was the last year it was used in a rigid frame.

What you need to do is get the engine number from the engine you have been offered, once you know what year it is from then you can work out which frame it could be used in if you want to build an original specification bike.

[vagabond]

Hi BRIAN
THANKS FOR YOUR INPUT. I would like to build an original spec bike allthough they wont be matching numbers. I am aiming for a 48 long stoke rigid with interchangable hubs and bolt on gearbox. (unless someone can donate a frame and and engine with close to matching numbers)
DO YOU BY ANY CHANCE KNOW WHEN THE GEARBOXES CHANGE FROM FIXED TO ADJUSTABLE,
at what frame number did they chang over hubs etc
IS THERE A LIST SOMEWHERE AS TO WHAT CHANGES TOOK PLACE AT WHAT ENGINE/FRAME NUMBERS.

[Brian]

Dave all the rigid and plunger models have the bolt on gearbox. The seperate gearbox was introduced with the swingarm models. Any bolt on type gearbox will bolt to the back of any of that type of engine. There are some subtle differences in the bolt on type box but they are all interchangeable.

If you want to build a 48' you need a rigid "onepiece" frame. When they introduced the plungers in 49' the frame design was changed to a bolt together construction.

I am fairly sure a 48' has the interchangeable wheels. As far as exactly what changes took place when is very hard to work out. Export models had subtle differences to home models and which country they were exported to also made differences.

I dont want to sound pessemistic but if you only have a engine then its going to be hard work to find the rest. Maybe search for a basket case would be a better option.

[vagabond]

Thanks Brian
I think they changed from interchangeable hubs early 49
Upto now i have located a longstroke engine in bits and a gearbox.
Road runner says he has some engine spares for me. but still no rigid frame and hubs. i may have to look for a basket case or move my goal posts toward an early 49-52 longstroke plunger model'
Anyone got an early plunger frame or basket case?

[terryk]

Yes the 1948 had interchangeable wheels the 1949 introduced the different front hub. You will be hard pressed to find rigid A7 parts I would look more along the lines of a plunger A7 longstroke.
What country are you in?

[vagabond]

I am now thinking along the lines of an early lonstroke plunger as there dont seem to be many rigid frames about.
I am in the uk. SHEFFIELD)

[beezermacc]

I have quite a bit of experience with longstroke engines and, to be honest, I don't think they're very good, which is probably why they redisgned them after only a couple of years. The cams and cam followers are very prone to wear as they don't have an oil bath; on most longstroke engines I've stripped they are totally kna****ed. The cam followers are so small the contact heads are like knitting needles! The engines often overheat due to the rapid piston speed and steel rods. If you're planning on doing serious riding rather than just 'showing' you could be frustrated by frequent mechanical problems.

[bikerjohndavies]

Hi Vagabond, I think a number of other forum members may join me to disagree about the comment that long stroke engines are not very good but I do agree they are very prone to cam / cam follower wear. I know that a fellow owner has had Gary Bowden of Bowden Auto Engineering of Patchway, Bristol constructed an oil bath for the cams on his long stroke engines to solve this wear. Also, a modern material cam which Newman Cams can produce is also a great help. He cut a new 67-695 cam for me and hardened the NOS cam followers I had to match and charged me less than Draganfly wanted for a reprofiled cam.

[fido]

My '48 rigid has been extremely reliable and I have never had it apart. The valve clearances do not need frequent adjustment so I don't think cam or follower wear is excessive.

[LJ.]

I can also chime in on how good the early longstroke A7 is... Lovely little bike, easy starter, sounds really nice, smooth ride etc etc. It has got me worried though about wear and tear. I'm wondering if the gearing is too high? My motor seems to race and would benefit from a 42 tooth rear sprocket. Maybe this was the problem with engines wearing so quickly??


Edit: Good to see you with us again Fido and I notice your now in Hungary... Have you still got your A7? is it with you at the new address? I have a pal hoping to move your way soon sometime nearer his retirement. Keep in touch! 

[beezermacc]

What I love about these forums is the debate about this, that or the other. I bow to those who have utterly reliable A7 longstrokes. I wonder why, as they are so reliable, they were completely redesigned after only a couple of years. I also wonder why some owners go to the trouble of retro fitting an oil bath for the camshaft. I don't remember BSA being keen to waste their time redesigning perfectly good engines, quite the opposite actually. Their staid attitude to development eventually led to their downfall. As with any old BSA engine if they get abused (e.g. thrashed and run with cr4ppy oil) they will eventually wear out. If they get pampered they will last for yonks. To qualify my previous remarks I respectfully suggest that the later A7/10 design will stand a bit more abuse. We can all find anecdotal stories to  support our arguments. For instance I only know of one other A7 longstroke in regular (though not very regular to be honest) use which was completely rebuilt with a stellite reprofiled cam and new cam followers. On the other hand I know of four blokes who did 2650 miles on A10's recently and never got the spanners out at all! And, by the way, three of them were absolutely standard engines, not SRM specials. These are anecdotes and prove nothing. Maybe somebody on the forum is sufficiently well connected with the BSA technical department or design shop to tell us definitively why BSA scrapped the longstroke design. Wait a minute....I'm having a deja vu moment.... we had such a talk from a respected BSA designer at our club a few moinths ago and he described the longstroke engine as 'absolutely dreadful' ....but maybe he was wrong! (or not?)

[LJ.]

I fully agree with what you say about the love of these forums and the ability to debate, thank you for your posting, especially your first post on this thread, (reply #7) and for pointing out why you are critical about the long stroke engine. This now makes me especially more aware of what might possibly go wrong with this early design, as I have never had one of these engines apart.

[Brian]

As the owner of a longstroke (1950 Star twin) and until very recently a shortstroke (1951 A7) I think beezermacc's comments are fair.

The longstroke did suffer from camshaft wear and this is backed up by the fact you simply cannot find seconhand ones that are useable. Having said that, with modern oil that is changed regularly I can see no reason why they would not do decent mileage trouble free.

The shortstroke I had was a little rocket. If you rode it "normally" it wasnt anything special but if you flogged it, or rode it "like you stole it" it was a rocket. It was faster than a A10 up to about 50 mph.

They are both good bikes and like all things have good and bad points. If you want to do just normal riding around the countryside and join in on rallies etc a longstroke will serve you well. On the other hand if you want to do higher mileages and tend to ride a bit harder than normal then I would go for the shortstroke.

I sold my 51' A7 but if a shortstroke Star Twin was to come available I would buy it if I could.

[vagabond]

As you will all probably have noticed I have now found a 1950 plunger frame.
But there is very little else. I need the footrests, stands, rear wheel, tank, guards and brackets,
And so it begins. I must be mad.
any donations greatfully received.
Cheers Dave