The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: spyke on 28.06. 2009 21:08
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Hi chaps,
Firstly Im not trying to advise anybody or tell anybody anything, this is just a general observation for discussion!
Last night at a barby I met some old mates,we all used to own A10s and A65s in our late teens /early twenties.We all built our own engines,using a good local engineer to grind cranks and bore barrels.We all used to thrash the bikes and did lots of miles as we never had cars, none of our engines ever blew up! The timing side journel was always ground by the engineer to fit the proper lead bronze bush available easily then,which we used to press into the heated casing.
My point is -were we lucky , ignorant and on a budget?
-carefree with plenty of cranks,cases and rods in reserve?
Because two of us now have A10s again which we are building engines for, and after reading quite a few posts, it would seem that to even contemplate a rebuild without line reaming means guaranteed disaster! So,are we more enlightened now,or too precious (because parts are rarer and more expensive).
Im not a mechanic or engineer but have built many Norton,Harley,Ajs,twins and single engines and none have ended in mechanical disaster so is it the idiosyncracies of BSAs timing side that separates it from these others ,and should me and my mate get TL Engineering ,SRM,or suchlike to line ream our timing side to avoid tears!
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HI Spyke,
I think you have realy answered your own question *smile*
The original bushes were "lead" bronze,
Most of the pattern bushes available now are phosphor bronze which is harder
therefore it is more intolerent to misalignment!
The lead bronze bushes are very soft and the metal will "give" to accomodate minor misalignment
My ?0.02 opinion
Regards
John O R
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A funny thing about the original replacement bushes was that if you had the crank ground to specs the bushes once fitted to the crankcase seemed to have the correct clearance and no reaming or boring was necessary.
Trev.
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I was chatting to Derek at T&L, he will white metal a bush for about £60. And then there's Mike who makes them from LB1. Either way they do need line boring.
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Sorry,who is Mike who uses LB1?
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Hi there Spyke,
Going back to your original post I think your over the top statement is partly correct. These engines have been around for almost 60 years now and a lot of them are still going strong. Over that period of time probably hundreds of thousands of different people have worked on them. The thing is I do think we (and I include myself) tend to over complicate things a lot of the time.
There are other things that probably can be considered as well, for instance, back in the fifties and sixties if you needed a new part (like a timing side bush) you probably bought a BSA spare part, or if you needed pistons they would probably have been Hepolite which was of know quality unlike some of the absolute rubbish we have to contend with for spares these days.
The thing is as long as the basics are ok these things will go well and be reliable. It really doesnt matter if your timing is a degree or three out or if the valve clearances are not perfect etc. However having said that you do have to remember that we are now working on motors that are nearly sixty years old but when we were young they may have been only five or ten years old and like us age takes its toll. Things get damaged over the years and etc etc.
As long as the basics are right they are reliable and good fun to ride and you dont need to be a aeronautical engineer to put one together. We dont flog them like we used to so they get an easier life and modern oils are a lot better. Do the best you can with your bike and enjoy it.
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Yes, the original Vandervell bearings were more tolerant of misalignment since they were made of a soft lead/tin alloy (not bronze) but they were also much more tolerant of contamination in the oil. Nowadays, I think a lot of failures that blame the TS bearing are the result of contamination from crud in old oil tanks or junk coming out of sludge traps. Bronze is a different animal (lead bronze aka 932 or SAE660) as it is quite hard and will not embed contamination as white metal or the original lead alloy does. However, with return line filtration and proper setup, I think they can be as good or better than new. I used to align bore my bearings, now I use a piloted reamer and it works quite well.
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LB = Leaded Bronze ( Cu- Sn - Pb)
Originally they went from No 1 to 6.
It is an obsolete standard but still used by a lot of old timers.
LG = Leaded Gunmetals ( Cu-Sn-Zn-Pb)
Also numbered from 1 through to 10
Also an obsolete standard still in common use.
Also specified by percentages 85-5-5-5 ( 5% of each alloying element)
And yes we do tend to go a bit over the top.
This is due principally to the fact that we judge our bikes against modern machines and not as they would have been when they were new.
Tappets make a lot more noise than buckets running directly on the over head cams.
Breathers drop oil as compaired to modern PCV's burning crankcase fume.
Old fuels had a high ash content so you had to pull the engine apart to decoke regularly.
BSA recommended new big ends @ 30,000 miles, we expect them to do double that because modeern bikes will do 100,000 on a bottom end.