Con rods

[DAVE BRADY]

I think that if BSA had not considered it a good idea surely they would have stopped ding it.  The operation to to drill these holes would have cost money so why do it if not necessary.  Do Carrillo rods have the hole?

Dave.

[Allan G]

I've just spent some time looking at Corillo rods but sadly none of them stated A65, however non of the rods I did see had the hole either. I think we have to remember that BSA had a lot of warranty repairs on these engines that I think they would try anything.

[DAVE BRADY]

Yes they did have a few reliability issues but these holes had been on all but the earliest twins and other makers did the same.  I think Norton had similar holes on some models so the belief that they were of some value seems to have been industry wide but sometimes one does it and the others follow just in case.
It would be interesting to see what difference the hole makes to the flow to left hand journal as well as the oiling of the left hand cylinder but how it could be measured I do not know.

Dave.

[bikerbob]

This thing about the oil hole in the left hand con rod has come up on variuos forums. As I understand it when the A65 was first introduced in 1962 it did not have the oil hole but BSA was recieving reports from dealers of seizures and partial seizures on the left hand cylinder so they started putting in the oil hole this had already been done on A7 and A10 engines for quite a number of years previously and was done to improve lubrication of the left hand cylinder. I have seen a copy on another forum of an instruction that was sent out to dealers intructing them that if a bike came in and had to be stripped right down for major work then the modification was to be carried out but they did not intruct dealers to carry this mod out on all bikes. So it is possible that some early bikes will not have this mod carried out. My own bike is a 1963 model but left the factory in October 1962 and has the mod done also my bike is still cmpletely standard and has the original pistons in the were fitted when it left the fctory.

[wardy]

Have a '71 Lightning and the drive side con rod definitely had 2 oil holes

[Allan G]

I've copied this from Mark Parker on Britbike.com; for those that don't know Mark's A65 is bored and stroked, it has his own modification off set 90mm norton crank and I believe B44 pistons, within A65 cases and mounted in a cagiva frame, this bike puts out more HP than any other twin of a similar capacity...

I've taken a rod from my motor when I first got it, (and it had done a lot of miles) and the rod was split exactly up the oil hole drilling to under the L/End which was only held by half the rod beam it definitely weakens the rod, I don't think they fail there usually but for some reason this one did. I think the rod was drilled so it had a little hole in each side and it was like a cutaway showing the drillings where it broke. Thats why I think the little grooves in the upper thrust faces would be a better option to get oil up the bore if you wanted more oil thrown that way. The BSA race rods which are the same as late uppers only with steel caps I put in it had no holes, I would use a rod with a hole or holes, but I wouldn't bother drilling a rod that didn't have it. They might have had that hose idea in mind Nert but the oil gets out past the bearing anyway and the system won't pressurize till oils filled the crank and i have good pressure building on the first couple of kicks if not the first kick when I start mine without the hole.

Incidentally I was looking through pics of my A65 from when it was first rebuilt (back when I knew nothing about these bikes and had someone do the work for me) the bike had a pre 70 rod in it and a post 70 rod (the late rods were about 17 grams heavier and shot peened) only when I was scanning old pics the other day I found out that what it had was two drive side rods so they both had the holes this would be similar to there being no holes, it was never a problem. New rods were fitted because the bike was getting some abuse and I wanted new rods to help strengthen the motor.

As I mentioned earlier the seizure problem was later cured when they changed to the 6CA points, the long dwell time (170 degrees if I remember rightly) was good for power but bad for points bounce it was this rogue spark from the points bouncing that was causing the seizure issues... it wasn't cured by drilling holes in the rod, they simply reverted to what the pre units had and worked on them, but pre units were fitted with magnetos and not points and they work differently. 

[DAVE BRADY]

Hi,

I think Mark Parker sums it up.  If your rods have holes use them and if they don't, do not drill them.
I would not set any great store in the fact that race rods do not have holes as race engines had to last a couple of races before being rebuilt and the minute reduction in strength was not worth the risk on a highly tuned and stressed engine.  Some race engines were built with 'wear' tolerances so that they would not seize and did not need much in the way of running in.
Only high mileage will determine if the holes are of any benefit but even then it will be influenced by riding style, oil changes etc.
It is interesting that although the hole could be a weakness 'little grooves in the upper thrust faces'  seem to be a good idea.  So the holes themselves may not be necessary but the effect they had was considered so resulting in 'little grooves'. 
Be careful making little grooves as they may weaken your con rod.

I remember stupidly fitting an oil pressure gauge on an A10 with a timing side bush.  When cold I could get nearly 40psi with several swings on the kick start.  Isn't flow is more important than pressure anyway?
After all the oil pressure warning light goes out at about 7psi.

Dave.

[Bess]

Hi,
   

Isn't flow is more important than pressure anyway?

I'm not convinced flow is more important than pressure on the A65 big end journal, it may be worth having a look at 'fluid bearing' principles. The rule of thumb is, most engines should be about 10 psi per every 1000 rpm, peaking around 55-65 psi.

Best wishes...

[DAVE BRADY]

To a large extent the pressure is a measure of the resistance to the flow generated by the pump.  Too much resistance and there is reduced flow, especially if the pump is a bit tired and cannot keep a good flow against the resistance  The cooling effect of the oil on the bearing surface is reduced, the oil may get too hot and become less protective.  So there is a balance to be established but unless an oil pressure  gauge is fitted there is no way of knowing what oil pressure is being maintained.  We all look in to the oil tank to check to see if the oil is returning and therefore flowing and on an A65 the only thing to say if there is a problem with the oil pressure is the light which goes off/on at 7psi.  A big advantage of the end feed conversion is that all the flow goes to the big ends.
There was an article in a MCN or another publication some years ago in which Triumph ran a twin with no or very low oil pressure for the equivalent of several thousands of miles.  When the engine was stripped and examined there was no more wear than would have been expected for that mileage.  Probably not an exact replication of those miles on the road but a good indicator that the flow was more significant than pressure.
I will try to find the article.
Also, I may fit a pressure gauge to my high mileage A65 to see what pressure it is running at.

Dave.   

[Allan G]

I agree with dave on the flow over pressure, you see some people using 60wt oils to get the pressure up in hot climates but your limiting how much fresh oil can flow and not only lubricate but also cool the bearings (shells).

Another thing to think of is the 7psi light switch, it's use is to tell you if the ignition is on or not, if there's no oil in the tank and anything before the switch then it's helpful there too but should your shells start melting because of not enough oil or a blockage causing back pressure (which wouldn't switch the light on) then as the shells start breaking up and the aluminium coating starts to mush it will block the journals, any oil there would cause more pressure but no flow to the journal.

Another use for the oil light is to tell you when your shiny stainless oil pressure release valve has stuck open 

[Bess]

Hi Dave,
             That answers the question, are holes in the con rod important? I guess with holes the oil pressure will fall and the flow will increase, two holes even better.

If you are fitting a gauge this might be worth a read. If you get the pressure right the designed engine tolerances will allow the correct flow, I might be the only one but I will be keeping my bike's pressure up:

Best wishes...

[DAVE BRADY]

Hi,

I think all I will be doing is fitting the oil pressure gauge.  In fact I did this today and bearing in mind that this  engine has done over 100,000 miles without the bottom end being disturbed, the pressure came up to about 40psi just on the kickstart and once running it topped out at about 55psi as the release valve operated.  I did not get the oil up to full running temperature and it was fresh oil but I did keep it running with a bit of revving for about 10 mins. and the pressure at tick over was still about 40psi.  If I get a chance I will try to go out for a run next week and see what happens.
With this mileage the big ends must be well run in and allowing a lot of flow.  One day I will strip this engine down to see what it is like inside but I reckon it is good for a few more miles yet.

Dave.   

[Bess]

Hi,

I have gauges on my bikes and so does my son. I too checked the pressure not the other tests outlined on that sheet, never had the need. I posted it as it is the only reference I have to oil specification and pressure. The specification in the workshop manual being 50 psi at 3000 rpm when warm, but 12 different oils are specified.

His oil pressure was in specification mine wasn't. Luckily we fitted gauges as the flow into the oil tank looked fine but 5 miles out, my oil pressure dropped considerably. I once thought it's the flow you want. But remembering 'fluid bearing' principles from my apprenticeship days dismissed it. I fitted a new SRM pump, the pressure went 15 to 30 psi. I fitted SRM PRV increasing to 35 psi. Changed the pressure gauge its now at 50 psi in all circumstances. I think a proportion of the oil, when hot, was passing the oil pump teeth and circulating in the pump, worn pump. I am happy the pressure is now to the designers' specification, on a newly built engine if the pressure is correct the flow must be correct. To me, if the pressure is low the flow could be low and there's an issue such as no oil, tank/sump filters blocked, badly worn oil pump etc. as outlined in the workshop manual. Or more importantly, the pressure is low because the main bush is worn, end feed conversion seals leaking etc.

As for the oil pressure switch my thinking is, it is set at 5-7 psi as at idle say 850 rpm the pressure could be a minimum of 8.5 psi (10 psi per 1000 rpm) no warning. On a worn engine, possibly of no oil, worn pump or filters blocked etc. then the pressure could be below the switch's set point giving a visual warning. I don't believe it's safe that an oil pump delivering pressure slightly above the switch set point say, 10 psi at 3000 + rpm is okay.

That's why I'm not convinced flow is more important than pressure, I am up to being persuaded otherwise though.

[Allan G]

Just wait until that stainless Oprv Gauls and sticks on you. Checked 3 now on different bikes and each one was buggered.

[Bess]

Hi Allan,
             Galling, I did hear of issues with the cheaper end of the market so bought into SRM. I tried to make the original OPRV work correctly but being sold the incorrect spring and not convinced the existing threads were sealing between the galleries, gave up. It would be interesting to compare failures of the original OPRV design against the SRM solution as the original had its failings.

To help I have a filter in the return line to give it every chance to continue working correctly and fitting the pressure gauge gives me immediate indication of any issues. I feel I can't do much more in the oil line to mitigate the risk.

You've had some bad luck with galling, out of interest how many bikes have you checked to find 3 with issues?

Best wishes...