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

A65 bearing and rod issues have been discussed over and over on here, and other forums, on club nights, garages and sheds, rallies, and so on.
Blood has been drawn! This is clearly no trivial matter!

From what we've seen on a few high mileage engines with dropping oil pressures, one bearing shell on the drive side has started deteriorating.
A friend is working on one such engine just now.
Just as per Tridentman's recent post actually.
As discussions do, the thread wandered off a bit, but to re-cap:

Are the drilled rods really prone to breaking from the oil hole? These are the steel cap type.
Will a plugged oil hole lead to untold damage to the cylinder and/or main bearing? Many seem to have done this with no issues.
Does the very minimal pressure drop from when the bearing passes over the oilway affect lubrication very much at all?
Are new bearing shells from say SRM better wearing than the white metal originals?

The engine in question has an SRM oil pump and OPRV, and is sound in every way except for that single bearing shell and a very lightly scored journal, which may be ground.
It's a road bike, sensibly used and in good shape over all.
I'm thinking that I'd use the engine with no further mods than uprated bearings, except maybe for peening the oil hole in the rod shut.

What do you, the A65 experts say?

SR

on alloy you will do damage to the grain structure of the material by peening the hole closed bad bad idea imo

the bsa engineers seemed to think the hole was a good idea....so do i

ive seen a few broken rods but dont believe they had anything to do with the hole

if you are a mathematical fellow do a calculation of the cross sectional area of the rod at the hole part them calculate the area of the hole and figure out what % of the area has been removed by the hole its minuscule

"Will a plugged oil hole lead to untold damage to the cylinder and/or main bearing?"
no. Not at all.
my bike ran for years with the drive side rod oil hole plugged, it didnt break, and it still has the same mains. Bore wear did happen, but not because of this, no air filters was the reason. This on an end fed crank 750.
The std set up with the Timing side bush is a different matter, as the bush wears the drive side big end is the first to suffer.

Thanks for the input!

Ignoramus, IMHO peening might even be a good thing, rolling over the edge of the hole and inducing compression in that area.
But your concern is a viable one and will be taken into the discussion. The tiny reduction in cross section is of no consequence, I agree.
There are other ways to plug the hole too of course.

Gavin, you, along with Mark Parker and others have had the same experience, and the mileage to back it up too.
If it was my engine I don't think I'd bother though, in a sound but standard engine, that is.
I can't imagine the minuscule squirt lasting a tiny fraction of a second 2 times per revolution would have any impact on the hydrodynamic wedge in the bearing.
I don't have numbers but the oil inside the crank cavity creates a lot more pressure from centrifugal forces than you see on the oil pressure gauge.
That is unless the cavity is less than full, which would happen with a poor pump, leaking OPRV, and worst of all a sloppy main bearing. Different scenario.
Kommando says the original bearings were white metal and not what he'd have specified for a relatively high powered engine.
I'm thinking modern bearings may make a big difference.

My friend the engine builder has done most of the A65 plain mains around here. He's adamant that with a decent oil pump and OPRV (he favors SRM) a standard engine will run forever.
He makes and line-reams the bearings himself, as well as grinding the journals.
"Forever" in this context would mean well over 100.000 km I guess.

like all good analogies/metaphors it was simply to illustrate a point Allan ......not to be dissected , i am well aware of why the hole is there but maintain that the BSA engineers who knew more about the matter than you or I put it there for a reason........what i fail to see is why anyone would blank it off ...and yes i am aware that the early ones didnt have it.

You may have noticed that I actually removed the post before you had placed yours. My point however wasn’t to nit pick what you wrote, it wasn’t a good metaphor at all and read the wrong way would give someone the wrong idea, but I don’t think you got my point. Most importantly the oil hole is only there to help spray oil up the cylinder, it has little bearing on the oil flow across the journal.

Allan : "t I don’t think you got my point. Most importantly the oil hole is only there to help spray oil up the cylinder"

i know that is why it is there .......and no i didnt see you remove your post

But in the interests of clarity i have also amended my comment

one poster has a tag line "there are no bosses in technical discussions" ...........i do like that one

What year engine? Before I make any more comment, that would be good to know

This whole thing has come up before. Popular theory , which is what I believe, you can take with a tiny pinch of salt if you want , is that early motors suffered due to random sparks from the 4 CA breaker systems, , in an attempt to solve the overheat and sometimes terminal engine failure caused by the random sparks, BSA increased the oil flow through the crank with the hole to help with cooling, it wasnt till the 6CA plate came in that the problem was cured directly. The hole was maybe a solution to a problem that was really a bad spark thing.

Gavin : "BSA increased the oil flow through the crank with the hole to help with cooling, "

exactly the point i was trying to make earlier regarding oil FLOW, however since my comment wasn't widely appreciated i removed it in the interest of harmony

The main bearing does not need much oil as its rolling element, the cylinder probably does not need the oil but you can give it extra oil without the hole'





The oil film thickness is the critical factor inside a plain bearing, the pressure inside this oil film is many times greater than the oil pressure shown on a gauge but not easily measured. The oil pressure gauge is just confirming your clearances are correct to give the right amount of oil for the oil film in the plain bearing to stay in place and not fail resulting in metal to metal contact and rapid wearing of the plain bearing. So its a proxy reading not a direct reading of what you need to know. What is more worrying about the hole in the drive side top shell is its location at the exact point the pressure from combustion is highest and the oil film needs to stay in place, it reduces the area of the oil film at exactly the wrong point and just this alone says it needs eliminating.



Yes they are, never fit Whitemetal, but for a road bike the SRM are overkill and the overlay layer wears out quicker than the Al/Sn alternatives, but if you use the Al/Sn then you also need to fit an oil filter in the return oil line.

The steel capped rods i've seen had no oil holes.
My own original '72 a65 has no oil holes in the ds rod. (from the factory)

The normal reason for the drive side big end bearing giving up is lack of
oil due to worn ts bush, this is normally due to no oil filter being fitted or
infrequent changes.
I've built a few over the years with various configs, the oil holes didn't seem
to give problems, if you don't want the oil hole , fit a blind shell that side.

From about 1992-2014 there were only aluminium tin shells available new.
All the tri-metal types were old stock and hard to find. Al-tin are fine.

Thanks to all!

It's a late engine, I believe the engine # started with GD, which would make it a 70 I think? I haven't seen the bike and I can't say if has a proper filter fitted.
The rods are steel capped but with holes. I talked to my friend on the phone yesterday (it's a senior thing, actually talking on the phone) and he had peened the holes shut.
I'm used to Triumphs who never bothered with oil spray holes that I know of, and cylinder lubrication has never been a problem. The A65 system appears largely identical.
The shells will be supplied by Classic Motorcycles, the best parts source in Scandinavia. What brand they are, and whether oil holes or blind remains to be seen.
Fot it's sins, I haven't seen a tendency on a Triumph crank to wear one set of shells faster than the other, or much at all, even if people sneer at its archaic oil pump.
A65 bearings seems to wear faster on the DS, and they do so for a reason. Not knowing these engines that well, I still have opinions though and I believe A65s were let down by poor oil pumps, leaky OPRVs, and white metal shells.
The shells on this engine bore evidence of plastic deformation. Why this happens sooner on the DS is the question. Could it be due to the spray hole, or is it an oil distribution thing in the crank? This particular engine has SRM pumps and OPRV but wasn't born with them, so the damage to the shells may have started earlier.

My opinions and thoughts are based on my association with people suffering A65s for decades, and on what I've found in magazines and on forums.
I do therefore realize my opinions to be of little value in this context, but if I was to embark on a project, these things are what I'd concentrate on.
I believe the A65 to be a sound design, let down by a few sub-standard components.
A friend (yes I have more than one!) has got a genuine Lightning Clubman buried deep in his garage, I may want to help him with that...

PS. Clarification; the TS rod has no holes, while the DS one has two.
Inspected the bearings today, and the shells are of the VP variety. The TS pair looks good for more miles while the DS big end journal is worn 2 thou.
Both shells looked much like the one in Tridentman's post.
The main bushing is a little sloppy as well, though the journal appears to have stood up well. It will ground for roundness and a bushing made to suit.

SR

These engines were all designed before the computer software for modelling oil film thickness was written. Once it was written and all the crank/bearing parameters entered then you could see where the issues were going to be and change the parameters to get equal flows and pressure at both big end journals. Even without this software the evidence on all the twin engines (BSA.Norton and Triumph) show the driveside to have greater wear issues than the timing side. The solution is to first either move the hole in the shell to the lower shell or eliminate it completely plus changing the relative sizes of the hole in the big end crank journals so the flow of oil into both big ends was equal. That would then leave you with the initial start whereby the oil will always get to the timing side first, so the driveside is always going to suffer from this issue, maybe a 10/50 instead of a 20/50 would work here. I certainly use a 10/60 fully synthetic in my Commando engine, the magnetic drain plug on all the previous 20/50 dino oils furred up every oil change but since going to the 10/60 there is no fur at all, is that due to the synthetic oil or the quicker flow on cold starts or both ? .

Perhaps one of the other factors causing plastic deformation is the temperature of the bearings.
As well as lubrication the oil serves the function of cooling the bearing.
I have never measured temperatures in the two (timing side and drive side) big end bearings but because the oil travels first to the timing side first then the drive side I would have thought that the drive side bearing sees higher temperatures and that this could cause more plastic deformation/deterioration of the bearing material?
Would very much welcome Kommandos comments on this--he is a bearing expert---I am just a simple thick heat transfer guy.

For Whitemetal at least, being a soft and also low melting point material, then a lower oil flow will cause it to deform from higher heat, but that could be due to the oil film collapsing and heat being generated from metal to metal contact. The whitemetal is so soft and compliant the steel crank journal will be untouched so no clues such as a blued crank to show which one is the cause.

Thanks for the info John!

I occasionally copy and paste technical info from this and other forums for my own "Book of Knowledge" I keep. Just random tech information about mainly bikes that I have accumulated for years. Recently, I have only been infrequently saving anything.


But, with all of the bearing info that has been shared, it was time to expand the book.

Thanks again!

It would seem that many little design and manufacturing errors sometimes stacked up against the poor A65.
To recapitulate a few counter measures:
Journals ground to spec.
Correct bearings used, no white metal. Correct shimming and line reaming is a given,
Steel cap rods, or custom ones, sans the oil hole.
Enlarge the journal oil ways on the DS a safe amount.
A decent, and tested, oil pump, and OPRV.
Use a good 10/60 synthetic oil for safer cold starts.
Add a good return filter.

How does that sound kommando?

Let me add one thing maybe not discussed often enough; don't lug these engines. It's a killer.

SR

Most definitely don't lug an A65! it kills them. They like to rev.

If that is a true 70 engine, it "should" have the revised drilling for the drain oil at the OPRV. Early engines used an angle drilling into the sump, late engine were a straight shot to the suction line from the sump to the return side of the pump. The casting was revised on the late cases to make it possible.

The angle drilling cases were all over the place on separation between OPRV drain and the pressure side from the pump. I have seen cases that have had 2 or less threads to make a seal. That is a pretty critical area to have minimal seal.

Late cases are better. But, what are they using for a seal between the OPRV and the cases? it should e a very thin washer (1/32", 0.8mm) if I remember right. Some gasket sets & replacement seals for the OPRV are 1/8" (3mm) or so. Not good, as it raises the OPRV too high and the pressure side can bleed into the drain side.

I actually prefer to lightly chamfer the mouth of the OPRV cavity and run a thin O-ring as the seal. Just make sure it doesn't bottom out in the cavity

Good info and something I didn’t know. Does this thickness washer apply to all engines?

The best fix for an A65 is an end fed crank, ball located , no thrust issues , more oil to big ends. Les Mason knew a thing or two Wonderful . and before you say plain bushes are OK look at the size of a BMW plain bush R series and compare to BSA. The thread that precedes just adds fuel to the fire.
buying a Devimead in 1981 has convinced me, apart from the end feed mods its BSA crank, rods , cams, pistons and ile pimp, YMMV. theres a good bike in there just waiting to get out.

The fuel fitting for a Holley carb uses a thin metal washer, and fits the OPRV.

Lets look at how the stock shystem might work , oil at pressure enters the timing side bearing, BSA provided a shelf on the crank side to prevent oil from this bearing spraying up the t/s of the the bore wall, no need for oil cooling to the bore here it would seem .

The crank is spinning at start up in a sump full of oil , throwing oil everywhere, .the cam bushes rely on this , and they dont wear out , significantly so that works OK.

oil in the crank centre passage that has made it past the timing side bush leak , goes to the timing side big end, some squirts out, whats left goes to the drive side, if theres a hole in the shell that lines up with the rod the oil pressure wedge has gone ,

at operational speeds there will be a general thick emulsion or miasma of combustion gases and oil concentrated on the timing side which gets 2/3 of the oil pumps output, 1/3 from the bush, 1/3 from the timing side big end , possibly why the drive side inlet cam is the first wear.

While all this sturm and drang is goin on the oil pump is doing its best to empty the sump, once it does , less oil is thrown around , the lack of oil scraper on the whipping flywheel encourages spray to the cams,
cool oil to the TS bush gets sliced by the crank spinning round then fed and warmed again before meeting the drive side big end.
Its only a wee oil pump. Look at any other oil pump from a bike bigger than a 500.
The moral of the story is , if you dont have a 4ca breaker plate fit your drive side big end shells so the hole is covered and live on, if you do have a 4ca plate it wont matter , your engine is going to fail soon , one way or another ( and, get an end fed crank , if you want to live happily ever after).

Edit, this is probably the third or forth i I have typed this sort of pro end feed prose, I cant stop myself, all the other end feed guys will be reading this and thinking smugly ,
yeah,
then all the timing side bush guys are goin
naw,
thats not strictly adequate, well neither is the stock bush set up, its pish. Yeah fit a filter , its still pish, try finding an original steel backed bush, maybe fit some " bronze". euch find a 10 dan machinist to hit that 0.0015 sweet spot. Sure every back yard cheap do it upper can do that.
re edit, this not aimed at you Stein, Im sure your guy goes up to eleven. just ranting.

Can't agree with a lot of your thoughts Gavin, the pump is not much smaller than a norton's.
There are hundreds of a65' +a50's out there that have standard bushes fitted.
Where the failing was mainly was no oil filter plus the majority of the bikes were sold in the 'states
where they were a cheap toy so little maintenance was done. Ball and roller races are ok with that
bush arrangements are not.
Whilst the end feed setup is a better idea many people don't like the use of a needle roller instead of
a proper roller bearing. I am not a fan of the use of the combination type bearing used by the main
converter of these motors. The actual load capability of the steel housed bush is greater than the needle race.
A lot of people don't like the idea of running a thin walled needle race in aluminium and say a steel sleeve should
be used. I'm not knocking it but the *** conversion is not the be all and end all of engineering in many people's
opinion. No circlip on the feed seal for instance. It was designed by Mr Mason as a compromise, BSA would
not change the casting to accommodate a ball or roller race.
The end feed setup is often used as compensation for people's inability to do the original job correctly.
I've done several over the years, indeed i have one on my bench at the moment with an end-fed A10 crank fitted
the main reasons i end fed/needle converted this one is that the customer was convinced it was better and the crank
main journal was stuffed anyway. I still don't use the combination needle race though.
The pump on a 650 triumph for instance is the same as it's 500 brother and the 750. Over the years they expanded
and if they were in production now they would probably have a deeper timing cover to accommodate the
2 inch bore piston pump further upgrades would require......
Dave Madigan came up with the best a65 oil pump solution i've ever seen but no-one was interested.
Much better than a reproduced identical aluminium gear pump.

I still say, put together properly with a good oil filter and standard bush these motors are good for over 50k miles.
That's all you could expect from any of it's cousins without a fairly major overhaul.

Good to hear ya Nick,
"The end feed setup is often used as compensation for people's inability to do the original job correctly."

Thats exactly where I fit in, some guy in a shed trying to keep his bike running. . Hard works no easy, and easy works hard to find.

I looked an an XR750 stlylee HD oil pimp the other day for a Buelll , it was like comparing a Hare to a Rabbits heart HD to BSA
the hD was twice as wide , twice as high. it cost two arms and a leg. add a zero to SRMS pump.