Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65 timing side mods

hI TREV, looks like it is about .1 deep based on counting the thread pitches in the tapped hole . and i guess we know the diameter by how close it runs to the stud hole.
I think I will leave an extra .005"clearance from the bush end to the thrust washer.
I am going to try this on the firebird engine .
I can machine the thrust washer to eliminate the shims entirely.
If I do end up needing shims I certainly would NOT put them between the Thrust washer and the crankcase.
I will grind enough off the back of the crank gear to give the thrust washer some substance,
Probably make from H13.
Rob

So on the A70, the thrust washer and shims on the outside are sdjustable w/o disassembly and limits the cranks movement to the left instead of using the lip on the primary side roller bearing. Is the internal shim (like on a65's) still in there to limit movement to the right? I did not see it in the bulletin drawing.

Also of interst, Devimeade was being run by a former BSA guy and they were making 750's with bigger pistons where the BSA A70 does it with crank stroke. Was this a philosophical difference that started Devimead? The BSA A70 is now more like the old A10 but with high higher compression and a more torquy rather than revvy engine.

Mr Mike

Hi Alan- I have to go with what I have and what feel I can do.

To my mind, this looks like a half baked attempt by BSA to control the crank end float.

From Trevor's photos and description I believe the system is designed to work as follows:-
- a new recess is counter bored onto the outer side of the TS crankcase to allow for shims and a thrust bearing to be fitted
- a thrust bearing is fitted to the TS side of the crank behind the crank pinion.
- its not clear on the diagram but I assume there is a step in the TS crank to allow the thrust washer to be fitted tight against the crank pinion, otherwise tightening the TS pinion nut would lock the crank up against the cases
- the shims would be fitted between the TS bush and thrust washer to take up any end play

From an engineering principle I would have some concerns with this arrangement which are:-
- its not clear exactly what the shims bear up against on the crankcase. Its apparent that thrust washer secures the shim on one side but on the other side does the shim bear against the slim TS bush and/or the TS crankcase?
- I cant believe the shim would be designed to bear against an alloy crankcase which means it must have been designed to bear against the bush.
- Since the TS bush is so thin I would imagine the shim could easily become damaged and lead to an early source of failure
- I cannot see any evidence of a shim or thrust washer between the crank and crankcase on the inner side of the TS crankcase. It appears that the crank runs directly against the inner side of the TS bush or case, this may be OK though as I think there is a flange on the inner side of the TS bush.

Half baked, that much?
The crank bearing surface is also shorter to match the bush. The shims bear against the end of the main bush and case. If it was to bear only on the bush there would be no reason to make the counterbore larger than the bush O.D. The parts list does not say the thrust washer inside the case is deleted but that may be in the replacement parts list publication. Does anyone have 00-5722?
If the main bearing width was reduced by 0.1" the oil film thickness is reduced by 16% (SAE40, 180F, 50PSI, 0.0015 clearance, 2400lb load, 7000 RPM).
RGSROB - The step in the back of the crank pinion gear is 0.055" so you will not get much substance for the washer there. You might look at making a thin bronze washer held in the recess with split pins half intersecting the perimeter. Shorten the crank bearing surface to slightly more than the depth to the washer and to the diameter of the pinion shoulder. Make the thrust washer I.D. fit the shoulder and the O.D. clear the split pins. Shims can be put between either side of the thrust washer to set the end float.

The shimmed hardened washer was used on Ariel Sq fours from the mid thirties, for oil retention or side play, possibly both. You will loose some surface area as Mad says. You could shorten the pinion gear a little more than the A70 was, and cut into the bushing less.
The early ariels would suffer from low pressure when hot, but so did a lot of bikes back then even with end fed cranks with 2 rods to feed ..A larger version of Triumph plunger fed 2 mains and 4 rods.

You are still up against the small diameter of the actual bearing. To my way of thinking its better to run a heavy series needle roller, the bush probably has a higher load rating, but any comfort in that is taken away by it's practical working, and that's where the roller wins, simple to change, no line boring no crank grinding, end fed, and super long life for the bottom end. BSA should have fixed it properly, the race dept solved it with the combination bearing which Devimead then offered aftermarket. Devimead and others used A10 cranks and big bore kits to make the engines bigger. BSA then did 750 for the A70 only with an extra 1mm of stroke. Having run an A10 crank for a few years I expect an A70 could have been a nice motor.

Or, you can use two half main bushes inserted from each side of the case, add a couple of dowel pins to keep it from rotating and narrow the pinion gear slightly for the thrust washer. I have never seen the pinion gear wear out. It would most likely need to be reamed in place for fit.

Trevor,
I had my SRM roller/ball timing side conversion done 20 years ago. It's still going strong after 50,000 miles only the quill end feed has been replaced, this is the same type of bearing that Devimead used.
With regards to the A70 combination why doesn't any one ask the owner of Burton Bike Bits, he rebuilt an A70 a few years ago and was published in Classic Bike. The A70 was specifically built for racing in America and I'm sure that some of our racing American friends would have had some say as to how they would like the engine to be improved.
I had my conversion done because I didn't want to keep redoing the bottom end and having talked to a number of side car racers, during the 70's, most of them had it done as a matter of course. This allowed them to race for the full season without having to worry about the bottom end or having to dismantle it. The standard bottom end is good enough as long as it's put together properly and the oil is filtered using a car type filter. Ensure the oil pump is in excellent condition and don't thrash the engine too much.
These bikes are getting older by the day, don't expect miracles, but they are meant to be ridden.....

Enjoy them.

Keith.

an earlier poster made mention of the fact that most car engines use plin mains to feed the crank. The big difference is that the mains on the cars are double shouldered solidly locating the crank. The final A70 solution goes along way to emulating the standard auto motive bearing characteristics as far as a guaranteed location and minimal end float.
Yes I would love to put an SRM type combination bearing in and come up with an end feed.However, I want to give the standard set up the best chance of suceeding first. The input from the group is a huge help to achieving this.

The solid flanged main bearings were replaced by plain main with 2 loose thrustwashers with one on each side on the car engines in the UK in the 70's. As 90% of cars in UK are stick shift this worked but the US with 90% automatics stayed with the solid flange main as the auto box pushed the crank more than a stick shift.

Not sure that is the issue with the A65 as the gearbox is not directly on the end of the crank pressing it in and out as the clutch pedal is pressed.

You maybe right, I worked for the company that supplied the bearings for the Zetec engine and it was the UK version they added a series of ramps in the thrustwasher to act as oil collection points which supports what you say. The old brain cells are not what they were.

The biggest problem with BSA's is that the cases are split vertically. This makes controlling thrust in both directions difficult at best not to mention problems with oil leaks. With horizontally split cases (like cars and other motorcyces) installing the thrust washers can be done and measured before final assembly. Some engines have flanged thrust surfaces as part of the main bearing and generally are fitted in one particular main bearing. Others have two half moon thrust washers installed on both sides of the main to control axial thrust. Both styles do the same thing...contol endplay but is not easy to do on a vertically split case. This is particularly important as Kommando says in manual transmission cars as the action of the clutch pushs the crank forward. If the thrust surface is worn out you can see movement of the crank pulley when some depresses the clutch. While our BSA's don't have to deal with the action of the clutch on the crank, controlling endplay is still important and BSA knew this. That's why they originally started with a ball bearing so the crank does not move laterally. When they went to the roller on the primary side they should have installed a ball on the timing side and been done with it. Triumph did it and BSA owned them since the early fifties. BSA has only to blame themselves.
That's why I went back to a ball bearing instead of a roller on my motor.

RSGROB...let us know how you figure out the endplay for that rare A70 you have.
Mr Mike

Yes, many car engines (low rpm, low stress engines) relied on plain bushings for main crank bearings.
Show me one which was stupid enough to rely only on the oil passing through one bush, on one end of the crank for the lubrication of the entire crank.

Theres a bit more info on the A70 differences on the Burton Bike Bits website Here

which sounds like the Moto Guzzi setup. the entire crank lubricated through one front bearing.
my LMII is regularly revved to plus 8000 rpm (track days) and has just done 204.301 km.

the difference is the oil-pump.

regards A

DavidP sez:

"Show me one which was stupid enough to rely only on the oil passing through one bush, on one end of the crank for the lubrication of the entire crank."

Yep..stupid alright, exactly in the pattern Edward Turner set for the Brit industry when he designed the original Speed Twin the same way........

That was different. The bush in the Triumph timing cover wasn't a main bearing and didn't appear to suffer from load or wear.

It would work if the bearings were strong enough and there was enough oil. It's when engineers skimp a bit on everything, there's nothing in reserve. Once the main bush wears a little, the timing side big end appears to get much less oil.

nonesense,most engines are fed thro the mains and many have been in the past includung triumphs, this whole thead is nonesense,theres nowt wrong with the standard set up if done right,iv rebuilt an a70 and really didnt understand why they changed it ,all they did was lose bearing area on an engine that needed more and why after altering all those parts why didnt they just chuck a ball in and end feed it?

I do not see how this can be nonsense . It has added significantly to my body of knowledge on the subject and obviously shared a lot of excellent ideas.
To say the standard set up is fine is definitely head in the sand .Although this does kind of depend how you use and maintain it.
The reason I bought this up was to see if I can do some minor mods to a standard A65 that would minimise some of the issues.
I cannot afford to send my engine to SRM , the shipping from Canada would be more than the conversion.
Somebody in the states was doing the conversion- All I have seen on these was major problems. As a result I believe they no longer offer this.

Rob sez:

"The reason I bought this up was to see if I can do some minor mods to a standard A65 that would minimise some of the issues."

Somehow through all of this thread, not even sure which vintage bottom end you are building....

I agree with wak on the bearing, IMO, the TS bearing is too small, it should be at least 1/4" wider & bigger in diamenter. The oil pump is marginal, especially at sustained high RPM. The OPRV and drain from the OPRV can be an issue (depending on vintage).

And yet with todays oils and a filter, there are lots of A65's that seem to rack up lots of miles. For all the bottom end threads you find on the internet, reality is, very few people actually lunch a bottom end.....

Main bearing, not much you can do for the size. If you use a 2 piece bearing, make [email protected] sure the bearing has a dowel pin to prevent the bearing from rotating or sliding in the housing when running. Both are bad things. IMO, the sliding of the bearing within the housing is where the myth of endplay cutting off the oil flow originated. I have seen early motors with the bearing out of position from sliding and the oil holes cut off. The big ends were trashed.....

Use as late of an oil pump you can find or spend the big dollars for an SRM pump. The SRM is the same capacity of the late BSA pumps. D or DD BSA pumps are pretty decent pumps and not uncommon either. Make sure the currently available crap aftermarket oil pump gasket fits the engine. Most don't and require TLC to make fit.

Run a return line oil filter.

Run a BSA or SRM piston type OPRV. IMO, the SRM OPRV has bettter fit/finish than the BSA OPRV. Use as thin of a gasket possible or chamfer the case and run an o-ring as the seal.

OPRV drain - through at least early 69, the OPRV drain was an angle drilling to the sump. Depending on the casting & machining fixture set up, the angle drilling can range from really good for the engine to really bad. At a minimum, you need 2 full threads between the oil in cavity at the base of the cavity. I apply a thin sealant to the case threads below the drain hole when there are only 2 threads available for a seal. Late cases have a straight OPRV drain that goes to the suction side of the return pump.

Just a little care in these areas does wonders for the reliability of a unit twin. And most of it takes time, not cubic dollars.

Rich B plus fit non whitemetal big end bearings which should never see the inside of an A65, there are plenty of Al/sn and Cu/Pb bearings around including Clevite manufactured bearings commissioned by SRM.

rgsrob, so i take it youve had a bottom end fail due to end float ?

Wak, I don't know if anyone would ever know if end float was the root cause of failure.Especially as thjey sort through the pieces.
I just know that excessive endfloat cannot be good and i am going to try my best to eliminate it.
I am also going to incorporate as many other good ideas that came to light via this string which apparently is of no use to you.