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May 8th, 2022
Thread Like Summary
Allan G, ChiefRider, Kev Ev
Total Likes: 5
Original Post (Thread Starter)
by Kev Ev
Kev Ev
I bought my first BSA in 1970. It was a C15 that a friend of my dad's was selling and was in bits. I paid £5 for it rode it on L plates, took my test on it and sold it for £15. After that I had a 1955 Royal Enfield 350 Bullet, a 1956 Triumph T100, a 1958 T120 Bonneville, which was the first bike I did a proper rebuild on and I spent a lot on the engine rebuild. I went on to own and ride a few Japanese sports bikes and a few modern Triumphs.

My current bike is a 1966 BSA A65 Lightning, which I bought in the mid 80's from a guy in Derby for £400. When I bought it, it was rideable but a bit of a mess. It had had a sidecar on it at some point and the frame was bent. The twin carb head had been replaced with a single carb head and the exhaust system was an aftermarket high rise system, similar to a Firebird. I spent about a year restoring the bike to it's original specification and as I had little experience of A65's and without the internet to help, I read a lot and employed the advice and services of SRM.

In the late 80's Steve McFarlane was still with them and I remember buying a brand new set of Devimead 650 cylinder barrels from him, which gave me nothing but grief for a long time. The start of that grief was when I first put the bike on the road. I had an oil leak which appeared to be coming through the cylinder barrel casting in the cam follower area. I contacted SRM and was passed on to Steve, who asked me to send them back and he would sort it out. At that time there was something going on at SRM and there seemed to be a clear divide between Steve and the rest of the crew. It was just before Steve parted company with SRM. Anyway I got the barrels back and once again tried to run the bike in. I kept getting the engine tightening up and at one point it locked the back wheel up on a sweeping right hander and resulted in a huge slide that I only just managed to recover from and luckily had a very wide grass verge to run off on. My experience riding speedway on my JAP 500 helped me out of that one, I'm sure. It could so easily have been disastrous.

All the time these 'partial seizures' were going on I was in contact with Steve McFarlane at SRM who insisted that the cause was 'my mixture must be too weak' and 'to get the carburation right'. I had fitted a twin carb head with pair of brand new Mk1 930 Concentrics on the bike and I was convinced I had them set up right, so after that near highside I stripped the barrels off and took them to a friend who worked for a local engineering company who were specialists in engine rebores and crank regrinds etc. He measured the bores on my barrels and there was just over a thou clearance on them, which was way too tight. I contacted SRM and was once again passed straight over to Steve McFarlane. I told him what I had found and he agreed to have a look at them. By now Steve had become more than aware that I was a qualified mechanical engineer, with a good amount of engine rebuilding knowledge on car and motorcycle engines. He confirmed the cylinder bore clearances were way too tight and honed them out. When they were returned to me I put everything back together and once again took the bike out on the road. Everything was fine after that and I went on to cover about 5000 miles trouble free. Once I had gained some confidence in the bike my first proper ride out on it was when I rode it from Hull to Knockhill, were a mate was racing his Norton in the Bob Mcintyre Classic. He had asked me to go along and be his mechanic for the weekend. The bike ran well, drew plenty of admirers and I entered it into a couple of shows, where it came away with trophies from both of them.

I am now currently in the process of doing a second full rebuild on the bike and putting a few things right that I wasn't completely happy with the first time round. I intend to fit the Devimead 750 kit that I bought from SRM in the early 90's and have sent my bottom end, con-rods and pistons to SRM for a complete overhaul and crankshaft dynamic balancing. They are also supplying me with one of their oil pump kits, a new camshaft, a new high strength Moly pushrod set (I have a set of new cam followers) and a new OPR valve. Along with all the seals, gaskets, con rod bolts etc. the total bottom end bill is going to be around 2K. On top of that I bought another cylinder head which SRM have overhauled, fitting new larger inlet valves and opening up the porting and gas flowing it to suit the 750 kit. That work cost me just over £700 but it means that I have the original 650 barrels, cylinder head and 30mm carbs. I was originally intending to fit Mikuni carbs and I rang SRM a while ago and spoke to Geoff Dewhurst. At the time they only had 30mm Mikunis in stock and I I asked him if they could get me a pair of 32mm Mikunis. His reply was 'why do you want to fit Mikuni's?' I replied that I was under the impression that SRM recommended them. He then went on to tell me that the new Amal Premier Mk1 Concentrics were a better option. That was ok with me, as I like the Mk1 Concentrics. I personally think they are the best looking carb on the A65 engine and they fit well with the original air filters. I've never had a problem with setting them up and they have alway been reliable in my experience.

Allan G has offered me some good advice with his thoughts on what I should be doing with the engine and it has got me thinking about the ignition system and the camshaft.

I would appreciate the thoughts and experiences from other A65 owners on these subjects as I would like to fit the best ignition system and camshaft, Bearing in mind the amount of money I am piling into the engine, it would be daft to cut corners.

Thanks, Kev E
Liked Replies
by Adam M.
Adam M.
My opinion about it goes with PRT, if you really want to improve your engine install new rods and a stock cam is very good.
I don't understand why refurbishing of lower end cost so much if only new oil pump, bearings, rod bolts and gaskets are involved, but know nothing about British prices.
All this enlarging of ports and bigger valves to me is a folly, in English circumstances with narrow winding roads you need more torque down low to ride effectively. With my A65 i dreamed about bigger 750 block, until I bought small port head and found torque I never had before. Not only that, but engine started revving much better and accelerated it seemed endlessly. I realized back then my bike is much faster than me and stopped dreaming about more power, just concentrated on brakes to make them better.
It was a right move, better brakes and solid suspension allowed me to ride faster and safer, so this is my advice about A65 BSA, based on 10 years of ownership and wrenching.
2 members like this
by Allan G
Allan G
Another word of advice, forget their stainless oprv, I’ve had/seen 3 of them stick. LF Harris is making them now, It’d be worth fitting one of theirs. Look up KBH motorcycles on eBay. They’re about £35

The pump is a decent bit of kit and has become a feature on the engine builds list. When I do them. Their chrome-moly pushrods are decent also and this is what I am using at present.
1 member likes this
by NickL
NickL
The standard t120/t140 oil pressure relief valve is fine. (50psi)

Uprating that valve on an end fed motor is asking for the seal to invert
With cold oil the standard valve cant relieve enough pressure on a
standard motor so when only supplying a pair of big ends it's way over.
The higher capacity pump will also add to the problem.
The american approach of 'fit the biggest' is not always the correct way to go.
Think about the steps you've taken.
End fed motor so now no main bush. (30%+ extra capacity from the pump)
New oil pump with larger gears than original '66 one. (15-20% extra capacity from the pump)
75psi oil relief valve. (which can only relieve completely at 50-60 C upwards)

To compensate i'd be running 5-30 oil. or even lighter. Don't rev the bike when cold either.

The late a65 rods were shot peened which was a good stress relief method.
I f i were spend this amount of money on a bloody old a65 i'd stick new steel ones in it
they aren't any more expensive than alloy ones and will last longer. The 750 kit is a good move
they run better smoother and pokier with them. There are some decent pistons around for them
now too (E+V Engineering) rather than the old GPM ones. If you are changing the cam, the SRM
race one is not a wild cam and is tractable with more mid and top, it also doesn't rattle like a tin
of nails. With the 750 kit the p'rods are shorter so be aware if going to fancy ones.
Years ago i had a 750 jumbo kit that was porous at the rear of the pushrod tunnel and try as i
might i couldn't cure it.
Sensible mods like mushroom headed tappets are good, Hyde t120 ones are good.but may need
shortening. Spend time on the gearbox, the pain of the A65. A 7 plate clutch conversion is also good.

Just my 2c.
1 member likes this
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