850 conrod oil hole- necessary?

Is it necessary to have this hole open, or can I close it off with the bottom shell in the upper position? Or leave it open and let the oil spray on the inside instead of toward the outside of the cylinders. Thinking of flipping the rods around to see if can minimize piston tilt at TDC .
Doug

You can switch the rod shells and do away with the hole. Jim

An old bodge back in the day wasto swap top and bottom shells over to blank the hole over motor with low oil pressure or one that used to much oil because of worn bores or oil rings.
Carrillo steel rods have no oil hole but are intended for racing where mileage is lower an stripping the motor to inspect an replace parts happens more often than a road engine.
If this is related to your problem of rod not being parallel on crank then if it was my motor i would leave holes open an use a top quality oil in hope that it would help reduce as much friction as possible to extend life of motor before another costly rebuild. As (understandably) am guessing you are thinking of running motor as is and at least getting some mileage out of it before yet more money goes on machining crank etc to try and fix the issues it has.

Have you had the crank apart? Just clutching at straws with regards to your piston till problem but if some dirt or tiny dent etc on mating faces on reassembly went unnoticed then issue maybe crank not the rods.
Try rods in all possible combinations of assembly on crank ie swap left to right an holes facings inward and outward. But obviously not swapping caps just complete rod.
After each trail assembly check rod measurements at TDC and BDC as you have done in first place which showed up the problem.
If despite swapping rods the measurements do not changed then the crank is the problem.

Early in Commando production they were having piston seizure problems that was 1st thought to be lack of piston pin oiling so the rod hole squirter was tried w/o help and later found issue d/t bad batch of pistons but never corrected the rod hole. I've pumped oil through hole to see a pencil lead thick solid stream hit the piston pin seam toward engine center but only squirts twice a revolution and does nothing good for engine lube or cooling but does tend to bleed off oil wedge pressure so the wiser racers and others flip the bearing shells to occlude it. Carrilo will make the holes if asked but its like the newly wed husband asking why bride was cutting the ends off a ham to cook and told ask her mother, who said they didn't have big enough pan back then.

Early in Commando production they were having piston seizure problems that was 1st thought to be lack of piston pin oiling so the rod hole squirter was tried w/o help and later found issue d/t bad batch of pistons but never corrected the rod hole

Click to expand...

You have got this from BSA in the mid 60's it was they that added the hole to cure driveside piston seizures and only later did they find out it was due to rogue sparks caused by the 4CA points cam profile which was the true cause, they did not drop the oil hole. Triumph did not add the oil hole but had the same rogue spark, Norton con-rods have oil holes before the Commando for unknown reasons too and they may be related to the 4CA or maybe not, depends on when they were introduced.

I've seen references to the bad piston batch before Combats so see if you can find that but the holles are not desirable in Commandos. Don't know who produced Norton rods in house or outside source. What may be worth while is notching rod big end rim so the expelled oil is focused to spary continuously at bottom of piston for cooling. Kohler engines have 3 notches to spray pistons, cam-valves and governor gizmo overhead.

I would not just arbitrarily block off the squirt holes. They may do some good as far as longevity. I don't know of any studies done either way.

That being said 2 of my street Commandos have Carrillos with no hole.
One of them is my injected bike which has a drilled cam which might lube the pistons a bit. Jim

i''ve looked pretty deep and wide a long time on oil aimed at pistons to grantee the ONLY thing the Norton hole do is add extra heat to oil for undetectable amounts taken out of pistons. Some experimenters with constant oil jets found out the hard way unless really massive amounts of oil sprayed on scale of whole engine supply it can fry oil then smoke oil then flash combust it. If the pins needed this oil then the hard wrung racers would of noticed long ago. Best thing to be said for Norton holes is at least don't do much harm as only exposed 2 instants per revolution. Btw Atlas rods were not holely. 6 start oil pumps allowed experimental oil holes.

Posted by mark_zenor at August 09. 2014

Hmmm, just want to add that I believe the conrod oil hole was added to address a perceived problem of lack of oil on the cylinder wall. When actually it was a early batch of pistons were bad and caused siezures but Norton thought it was piston pin source so made oil jets aimed twice a turn to strike at the piston pin seam.

The NOC at http://www.nortonownersclub.org/support ... do/conrods describes this feature, and details the issue of the pump speed.

Click to expand...

J.B. Nicholson - Modern Motorcycle Mechanics

750 cc Con Rods:- In 1966 when the oil pump speed was increased and other lubrication modifications were introduced on the 750 and 650 motors a 1/16" diameter spray hole through the rod big end was provided to give additional piston and cylinder lubrication. These rods should be installed with the oil spray hole to the outside of the engine, i.e. away from the flywheel on each side. This rod big end spray hole is not recommended on the 1965 and earlier motors with the slower speed oil pump and if a later rod is being fitted to one of the earlier motors the spray hole can be simply peened shut from the outside.

Click to expand...