Hello All,
A long time since my last post as I have been doing my "down to the last nut & bolt" strip, full investigation, refurbish and rebuild(s) on my exceedingly smoky A10 SR/RGS engine.
After all of the investigations and part rebuilds to test theories (my own and those suggested by you guys, & why its taken a while) I have found a few definites on the reasons for the bad smoke issues especially when engine was hot.
Theory that the high flow SRM oil pump made things worse - proved.
Why? - pump delivering serious amounts of oil into badly worn big end shells and from them into the crank case, coupled with worn and scored bores / pistons where the excess oil was very effectively able to pass the rings into the combustion chambers.
Early phase 1 rebuild and new parts sorted the worn bores, pistons and rings without much improvement in smoking still due to volume of oil being pumped into the bottom end continuing to overcome the rings.
Just to add to the smoke, valve guides not badly worn but getting there, again the high flow pump doing a great job of pushing more oil than usual into the rocker shafts, it also finding its way into the chambers.
So, as I said in an earlier post, a 'perfect storm' of issues all contributing to create a brilliant A10 smoke generator. Causes confirmed via a series of part rebuilds to test our collective (yours and mine) theories.
What's been done ? - bores professionally re-lined back to standard and honed to match a set of new weight matched pistons, rings pins & clips, cylinders top face skimmed ready for crack tested and match skimmed head, spark plug threads worn so custom made brass inserts fitted along with new valve guides machined to match valves, which were fitted and re-ground at correct angle to achieve perfect seals, ports gas flowed and polished (not really necessary but hey, wth). Rockers & shafts checked, new rocker bolts, new RGS valve springs. Crankshaft sludge trap removed and cleaned out, new plugs, journals re-ground and match machined for new glacier big end shells, crank dynamic balance checked and adjusted, oil galleries cleaned out, new oil lines. SRM high strength rods checked, new big end bolts.
Cam and cam bushes checked, bushes replaced and line bored to match cam, cam followers replaced. New oil NRV spring & ball, oil PRV checked. Copper head gasket, copper rocker box gaskets, all new case gaskets etc, all oil seals replaced including crank end feed seal. This replacement definitely necessary as SRM confirm that it is normal for momentary pressure on this seal to potentially get up to 100psi before the SRM PRV inertia is overcome and it operates.
All engine casing stud and bolt holes checked for any distortion. Magneto advance unit refurbished and new springs fitted. Magneto cam ring found to be producing uneven spark timing between cylinders, fixing this problem proved to be a real pain so opted to fit a Thorspark electronic ignition system. What a revelation that is! Really easy to fit and set up. Spark timing between cylinders is now absolutely spot on. My Lucas magneto had been fully refurbished and apart from the uneven spark timing was working as it should but the Thorspark provides a really fat healthy spark even at gentle kick-over revs. So much easier to start the bike now and it runs a lot smoother. I have fitted it so that engine still looks like it has normal magneto ignition.
I have read a lot of the posts for and against electronic ignition and I am definitely not saying that the Magneto is no good cos' its fine, it works well on the road and has its advantages, just reporting that my first foray into electronic ignition on an A10 has been a real success and I now prefer it. At the end of the day its personal preference. I have managed to hide the Thorspark wires so you can't tell that they are there, plus get the engine kill button working as it would do on a magneto ignition, so the bike looks and operates as it should. (I can also revert to full magneto ignition really easily in the future if I ever decide to).
Carb jetting has been a challenge. Leaving the pilot and needle jets standard (25 and 106) and needle at position 2, I have tried different sized jets from 290 to 320, to 380 to 400 through to the 420 as stated in the manuals for this engine. Best jet so far is the 380, which is pretty spot on, that said, am going to try a 390 just to see if its just that bit better.
I also replaced the 19 tooth gearbox sprocket for a 20 tooth, which has had a dramatic effect on the road. Engine seems to pull better, cruise better, is less stressed and feels smoother. Possibly the 19 tooth was not the right size when used with my belt primary drive conversion.
(I changed to a 20 tooth on one of my A10's years ago and had a similar experience).
So, what turned out to be the main cause of the damage that caused the bad smoking and promoted all of this work?
Turns out that a previous refurbisher/owner had had the frame and some parts including the oil tank grit blast cleaned before repainting. You got it!, he didn't clean the oil tank out properly (or at all?) afterwards, which on running it for 2k miles very successfully wrecked the mains and most of the other sliding surfaces, plus seals etc. This confirmed by what I found in the crank sludge trap, the oil lines, the bottom of the oil tank, and inside the return oil side filter when I took it apart. If that filter hadn't been fitted I doubt that the engine would have lasted 200 miles let alone 2000.
Its been a challenging journey and I have learnt a heck of a lot going through it.
Result now; a fantastic, smooth running, non-smoking, smile provoking and very enjoyable BSA A10. Don't really mind if something else goes wrong, just gives me another opportunity to do some more fettling on this amazing machine.
Thanks all once again all for your; advice, theories, ideas, thoughts and support. If I can help any of you as a result of what I have learnt through this and previous experience, let me know.
BeezaDan.
