Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65 bearings yet again...

Too little end play will result in damage to the thrust washer (66 on with the correct crank), damage to the shoulder of the timing side main bearing that fits into the case (mostly on 62 - 65 engines), and can cause pinching of the rollers on roller bearing motors. On ball bearing motors, you get short bearing life, but chances are the TS will fail first.

Too much will cause knocking at low RPM. That is the crank banging back & forth inside the cases. IME, too much might cause issues, but not as many issues or as quickly as too little. The thrust washer has a hard life with too much since the crank bounces off of it.

The BSA spec is fine at .0015" - .003". Just take your time and make sure it is right and repeatable.

I'll be honest and say I don' have much experience with setting end float on A65's and I've only owned one which I bought and rebuilt over the last 10 years or so.

When I bought my 1968 A65 it was a pile of bits so I decided to rebuild it without spending a fortune, this meant I didn't go for and end fed crank, SRM oil pump or belt drive. Instead I was lucky to have a local motorcycle engineer (Tony Hartland) who was very experienced in fitting a new TS bearing, line boring it and assembling the bottom end with the crank cleaned, reground, new big end shells, roller DS bearing and correct shimming and later 1971 --> conrods without the oil hole. I added an SRM OPRV and checked the threads to ensure full engagement & no pressure loss, & added a small amount of thread sealer to ensure no loss.

I carefully rebuilt the alloy oil pump, repaired the gearbox & shimmed it, fitted a new triplex chain and new Sureflex clutch plates. A Norton type oil filter was fitted and the head reconditioned with new valves and guides.

So far after a few thousand miles all seems OK although I did have some problems with wet sumping. I have latterly fitted a later iron oil pump which has helped to resolve this.

My thinking is that the fundamental design is fine as long as an oil filter is fitted, the TS bush is Concentric with the drive side and the oil pump is in good order. The other issue not much discussed is the 4CA points system which reputedly caused a rouge spark on the drive side cylinder, so using a 6CA or EI setup is better in my opinion.

I've probably not been buggerig about with a65's as long as you, i didn't start till 1991 so i accept what you say about the oil pump thrust etc.
I have however seen drive side main ball races that have moved inwards in the cases and could come to no other logical conclusion. It may
be that either poor alignment or insufficient interference fit played a part but i still like to fit a ts thrust washer just in case.
I agree about the primary chain, most of the ones i've worked on they were never lined up properly, people loose the shins etc. Plus they are
nearly always too tight.

This is the end-feed setup on the A10/65 based thing i'm doing at the moment.
Nice and simple no welding, hollow oil pump stud etc.

https://i.imgur.com/bcVj5D4.jpg
https://i.imgur.com/hkSpFmH.jpg
https://i.imgur.com/ogbTDzI.jpg
https://i.imgur.com/yMc7D4V.jpg
https://i.imgur.com/XXkkFVU.jpg
https://i.imgur.com/wwn2mCO.jpg
https://i.imgur.com/d6uedlS.jpg

Just drill/continue the oil gallery into the lower part of the fixing hole and plug the inner end.

Sirs,

What I'm taking with me from this thread is as follows:

A standard A65 crankshaft system can work well, if set up to the blueprints.
Better still if fitted with an upgraded oil pump and OPRV.
Some prefer a ball bearing on the DS, but load capacity may be an issue on high torque engines.
Modern bearing shells wear better than the original VP white-metal ones. .
The DS timed squirt of oil isn't necessary and might induce a momentary break-down of the oil wedge inside the bearing.
Later rods with the steel cap are stronger than earlier all alloy version. Exotic variants may be even stronger, and some prefer steel.
There is some suspicion that the oil-way drilling in the rod is a stress raiser that can lead to breakage.
A Devimead bearing conversion, or variations of it, is favored by many. Necessitates an end feed conversion too.
An end feed conversion with a plain bearing on a hardened sleeve is possibly a great solution. Arnstein (and others?) has proved that it can work.
Thrust forces must be dealt with unless you use a ball bearing DS, or a compound TS. Arnstein use an outrigger bearing, but not viable for most people.
It's possible to convert to a metric DS roller bearing with thrust capacity on both directions, as on a late T140/TR7 TS. Some machining and/or grinding necessary.

What puzzles me is why so many stick an A10 crank, or even a Norton crank in there. One of the beauties of the A65 design IMHO is it's short stroke and stiff crank.
But that's just me, sorry.

SR

"What puzzles me is why so many stick an A10 crank, or even a Norton crank in there. One of the beauties of the A65 design IMHO is it's short stroke and stiff crank."

if you want more cubic capacity, big bore kits are sometimes unavailable, for long enough they were out of stock at SRM, now theres at least 3 sources, , then a D A10 crank is maybe easier to find.
Having tried both, i prefer the big bore to the long stroke. However , big bore plus long stroke gives 850 ish so theres that to consider. it probably depends on what the builder has lying around at the time.
I built my long stroke motor because I had good 1970 barrels that would overbore a wee bit and found a decent DA10 crank, big bore kits were not available at the time.
As for Norton cranks, never tried one , but the ability to rephase by staggering the big ends is an attractive feature.

NickL, You do know you can copy and paste your photos into the forum with imgur?

Quote
What puzzles me is why so many stick an A10 crank, or even a Norton crank in there. One of the beauties of the A65 design IMHO is it's short stroke and stiff crank.
But that's just me, sorry.


The old quest for power, i'm afraid.
The SRM 750 kit made a great engine but on the track it just wasn't fast enough.
The 850/900 kit needed a longer stroke crank, the norton ones were available
for reasonable money, are strong and as Gavin said, they could be offset by
making different flywheels. I had one up at 920cc at one time but the 80x89
motor was the sweetest one i ran with a 76 deg offset.
I wouldn't bother for the road nowadays though. Not that keen anymore.

Well I did say it sort of tongue in cheek. I do know the reasons, but a shorter stroke means a stiffer crank and higher revs. I like that.
Norton de-stroked (possibly not even a word?) their incredibly long stroke twin from 89mm to a semi-long 80,4mm to gain stiffness, reliability and ultimately power.
BSA did well with their 650 to cut stroke a full 10mm to 74, which I feel Triumph should have done too when they went to unit construction.
Both the A65 and the T120 started out right but later got bigger valves and ports, too large for their size, so going bigger suited them well.
Going bang quite frequently with it, but what the hell.

But who am I to even talk about this stuff? Here's the truth, I really admire you guys who do or did all this, and envy your skills and determination!

SR

Why is this thread being censored / edited so much ? OK there's clearly been a difference of opinions but surely nothing significant in the scheme of things, if this is the way this forum is heading then I'll be checking out, including my subscription. Come on chaps stop being so sensitive we're discussing old bikes for f##ks sake, there's always someone who knows more than you do, live with it, when its true learn from it.

We are (or should be) all mature adults on this board so for Chr*sts sake lets live and let live.
No need from what I have seen for any censoring of comments.
We are all old enough and strong enough and ugly enough to give and take a few strong words.
If you are not then you are in the wrong place.
Restricting freedom of expression is what started Germany on the wrong road in 1933.

Triumph Acclaim!! (Seig Heil)

You are right Stein about shorter stroke BSA motor having all these advantages you wrote about, but it has also one disadvantage - annoying vibration making you tire quickly somehow more annoying and more difficult to stand than Triumph.
I used very heavy handlebar weights to cure it ( in reality the vibes stayed there but frequency changed more to my liking ) so I felt better and started riding faster.
Result was broken brackets and higher oil consumption.:)
I sold my BSA without those weights and tried it a few times without them, after 200 km I was really tired.
Switched to Trident, which I like very much ( other than annoying oil leaks ).

Well put Kev, and thanks to Tridenman too.
For my sins I haven't been banned yet but this may get me there.
Arnstein is still banned, I just checked his profile. If Gill didn't ban him, Morgan must have. It makes me queasy.
I won't sit still and let it happen without speaking up, as I see no reason, not on this thread anyway. Words and caustic remarks were passed, but nothing worse than most men would take.

Lift the ban, this is no medieval church.

SR

Back on track!
A65 vibrations are well known, and very real! However, I can't see how the stiff crank would create more vibration, the reason must be found elsewhere I believe,
For comparison, when Triumph introduced their T140 based short stroke 650 (76x71.5) everyone who tried it commented on its very smooth low vibration engine.
The TSS got a stiffer crank to cope with the increased power and it reduced vibrations markedly.
But then perceived vibrations depends on the whole system, the frame and attachment points, and maybe some ancillaries.
So who knows. I guess A65 owners will have tried a bunch of different solutions, like altering the balance factor and/or dynamic balancing.
But would they have vibrated less with a longer stroke or a weaker crank?
Interesting stuff.
After I went Triple back in 93 I haven't looked back! :-) I had a BSA A75 which I traded in for a new Daytona 900 which I still have, and 7 years ago I got my stubby fingers on a 72 Trident.
It's the only old Brit Bike i take for longer rides these days, its ride quality and speed belies its age, it's brilliant! And it's oil tight... for now!

SR

Not to diverge too much from the thread but the source of the vibration is mass centres flailing around offset from their spin axis and other masses translating without equivalent opposite motion. This along with the timing bearing could be addressed by recasting the case for a metric ball bearing on the timing side, metric roller bearing on the drive side and plain bearing support plate between the case halves for the 90 degree offset three bearing crank. The wide centre plain bearing would supply the rods with oil.
Keep the quaint pushrods, roller chain primary and camplate shift direct drive gearbox.

If you ride a 750 kitted version of the engine the vibes are reduced considerably.
The tall pistons with their weight high above the pin is a main contributor, even
if you just cut a standard barrel down and run t140 or a70 pistons it reduces the vibes.

Ask anyone with a 750 kitted a65, they'll all say the same, it makes a big difference.

It's what AJS/Matchless did, minus the 90 degree crank. It did work well too, once they had their crank manufacturing sorted.
But it cost money. Cheaper the Triumph way, so people could afford them.
Not the pinnacle of crankshaft designs, it worked well enough to keep us interested, nearly 5 decades after BSA seized production...

SR

Very interesting. I rode a Devimead kitted A65 LC once, but decades later I can't recall how it felt. Can't have been too bad then...?
I just learned about the tall A65 pistons. I've seen them often enough but never studied them. The T140 piston is quite a bit shorter overall but also from the wrist pin and up.
The T120 piston is even shorter from the pin, and much lighter than either.
I've often thought that the top heavy piston contributed to the T140 piston noise from cold, and its higher weight must contribute to increased vibrations.

Btw, part of the questions about pistons I had in an earlier post was if the T140 pistons were derived from the A70 project, as the rods were.

SR