1970 Lightning big end replacement

[PeterR]

Hi Dave, yes the other circlips seem fine.  As you sugested the previous rebuild included new Hepolite .020" pistons and rings, so either a manufacturing fault with the ring groove or the circlip was not correctly fitted.  We'll never know now..
I do appreciate your interest, so getting bak to the big end failure I am anxious to make sure that whatever caused the problem does not occur again.  Given that both bearings have failed and it is likely to have been a lack or oil, can you you assist with the best procedure to check that the oil pathways are working properly, is it possible to check the operation of the pump (should I disassemble it?) and so on.  Just in case it was petrol contamination I will overhaul the petrol taps as well.
Thanks again.

[DAVE BRADY]

Hi,

I would suggest getting everything very clean and really make sure that all the oil ways are clean.  Use brake cleaner or carb cleaner  in the oil ways and, if you have one, a good blast with an air line.  Do this a few times just to make sure.  The cleaner should be getting blown out as clear as it was sprayed in.
If the pump is rotating it will pump oil but if worn internally it will not be efficient.  It can be stripped and checked for scoring but in reality if it is badly worn it will be best to replace it. It should also be flat across the joint face.  Post some photos of what you find. The oil pressure relief valve could also be suspect.  Again any scoring would, in my opinion, mean replacement but a new spring should restore its function.  Once you have made sure that every thing is clean and working it is down to good parts and careful assembly.  Get a torque wrench and use the settings in the BSA workshop manual.
There are some good videos on you tube.
When buying parts get the best you can find - you will pay more but get a more reliable engine.  Keep the bearing surfaces nice and oily during assembly but not the threads  of the big end bolts - they should be dry for correct torquing.  Once you have the rods assembled on the crank, oil can be pumped through with an oil can so you can see that it is getting through.  Use the oil can to check all the oil ways in the crankcase from inlet from the tank through the oil pump oil ways and the pressure relief valve.
If you are not replacing the timing side bush make sure that oil is easily getting to it - when checking the pump oil ways ,oil should come through the bush.
Apart from all this cleaning and checking it is down to careful assembly and proper running in.

Dave.

[PeterR]

Hi everyone, the rebuild of my 1970 A65 is proceeding slowly, following its big end failure (amongst other problems).  The post mortem has revealed an intriguing earlier mod(?) of the conrods.  The drive side conrod has a small hole at the top which I assume was mean for some measure of oil lubrication but it has been infilled where it meets the crankpin.  The timing side has no such provision.  Does anyone know whether this was a standard detail, a modification later removed or whatever?
Thanks for any suggestions.

[Spaceman]

The hole in the LH conrod was put there to throw oil out to help lubricate the LH piston - the RH piston was considered to get enough lubrication from oil thrown out by the timing side bush. Some people say the conrod hole is not really needed (a BSA bodge?) but, apart from weakening the conrod, it doesn't do any harm. If the hole is there and is blocked up, it would be worth opening it up again provided you don't damage the conrod in any way in doing this.

[PeterR]

Thank you Spaceman, more evidence of how BSA used its expertise to prolong a the life of an engine design that had reached its use by date.  The mod to the mod looks like it was done professionally so I think I will leave it as it is.  The Big end failure was I think caused by a more generic quantity/quality of oil problem so will do my best to address this problem.

[Spaceman]

The only thing that comes to mind as to why someone would block the conrod oil hole is if a previous owner thought it might result in lowering the oil pressure to the LH big-end bearing and decided to eliminate this concern. Given the oil pressure will naturally be lower for the LH bearing there was/is something in this concern?

[Bess]

Hi,
    Service sheet has the explanation and the hole should be pointed inboard, the later rod had two holes, one pointing inboard the other pointing outboard.

Best wishes...

[PeterR]

Wow Bess, what an awesome piece of detective work!  Mystery solved, so thanks so much.

[ChrisG]

The general school of thought is that the hole was there to throw oil up into the bore, but I read recently that whilst it may have achieved that, it was there to help with the 'flow' of oil to the LH conrod, as the feed into the crankshaft is on the far right, the oil will favour the RH conrod first leaving lower flow to the LH one. The hole gives an escape which will help improve the flow. Thinking about it, that makes good sense to me.

[Spaceman]

The hole in the conrod will definitely increase the oil flow rate to the LH big-end bearing but, unfortunately, most of the extra oil will end up escaping out of the hole, albeit lubricating the LH cylinder in the process. The escaping oil will tend to reduce the oil pressure inside the LH big-end bearing and this could then end up reducing the effectiveness of the lubrication there. This was possibly the reason the oil hole was blocked off in the A65 in question with less LH cylinder lubrication traded off against better LH big-end lubrication.

[Bess]

Hi,
    The con rod hole only lines up momentarily with the crank twice a revolution, I'm not convinced the oil pressure will reduce to any degree to worry about.

Best wishes.

[PeterR]

Hi everyone, I am on the home run with the rebuild, and the crankcases are back together along with the barrels and pistons.  My question is at which stage in the reassembly should I put the engine back into the frame.  I recall when I was doing the strip down the clearances between the rocker box studs and the top frame tube were very tight.  On the other hand, it will be easier to manoeuvre the engine into the frame when it is lighter and fit the head, rocker box, primary drive etc later?
Thanks in advance for any suggestions.

[Gup holland]

This is the moment for me, less weight. Rest later stage.

[DAVE BRADY]

Hi,

I always fit the pistons and cylinders after fitting in the frame. If I have taken the gear cluster etc. out I leave them until the cases are in the frame.
As I have as bike lift, I find this easier as the working height is great for the top end and if needed a stool is handy fire the lower bits.

Dave.