Con rods Oil Hole

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Colin R Campbell

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Hi Any one know why some rods have a oil hole and otheres don't Droped a rod the other day ( dont fit a oil pipe tap) new rod ( SH) has a hole Parts book doesnt show diferent numbers though Running in at the moment all seems OK But not many Commandos riders here in SA to swap info with
 
Colin R Campbell said:
Any one know why some rods have a oil hole and otheres don't
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Conrods with the bleed hole were introduced on the Atlas model from engine number 116372 in 1966 and approximately 10,000 engine units before the first Commando, so all standard Commando conrods should have the bleed hole.
 
The big end bleed hole is worthless and serves no purpose anymore - it was used when pistons were not designed correctly and there were seizures.
 
jseng1 said:
The big end bleed hole is worthless and serves no purpose anymore - it was used when pistons were not designed correctly and there were seizures.
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Let's hope so!!!!

My JS Motorsport Rods certainly don't have a bleed hole! Just kidding, Jim.

But seriously, I've been running various Carrillos with no bleed holes, quite spiritedly, for many years now, with no issues.
 
Jean got it right, 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. Races commonly block of the oil jets and hi end steel rods don't have them so its a non issue to keep or block them off but a bit more load tolerance if blocked off I'd think. There is way way way too little oil jet to have any cooling effect, takes like .6 L a min to make 100'F drop in temp on Norton size pistons and likely more being an air cooled engine. Manual says the oil jets go to outside of engine if that even matters in otherwise symmetric rods.
 
Is it possible some of that oil could find it's way onto the cam shaft and bearings ?

Just a thought.

Cash
 
The oil comes out through the sides of the bearing shells anyway, the hole just directs a small timed spurt up inside the piston, sticking plaster solution when the real solution was the correct piston.
 
ludwig said:
I often wondered , is someone here deliberately blocking these holes by turning the bearing shells around ?
I suppose it would have a positive effect on oil pressure ? ..
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Yes I normally switch the bearings. Jim
 
ludwig said:
comnoz said:
..Yes I normally switch the bearings. Jim
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Seems like a logical thing to do .
I allways found it strange to bleed off oil pressure right at the point where it matters most .
I have never seen this on any other engine ..
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good stuff guys
 
I have just dismantled a 1965 Triumph Bonneville and it has the same holes in the conrods as the Commandos.
 
I only asked about the cam as my high milage Mk3 ruined the left and lobes and cam bush, I found that the left hand rod had the shells swapped to block the squirt hole. Anyhow it's now squirting on both rods and I haven't noticed any pressure drop or anything untoward.

Cash
 
It was also fitted to B25 con-rods but not on the Triumph 500 (which used 2 B25 con-rods), all these conrods are alloy, on the steel con-rod engines eg C15,B40,B44 B50, pre unit BSA singles including Gold Stars etc there are no oil holes and no spate of seized pistons.
 
The oil hole, particularly on the drive side, promotes oil flow through the crank ( sludge trap ), no oil flow through crank = no oil to big ends.

My BSA's engine had the oil hole conrod on the timing side, the crank was completely blocked and the big end on the drive side was completely rooted.
 
Sounds like your BSA could have benefited from a good oil filter and some high detergent oil. Jim
 
Rod piston jets only needed if a piston pin oiling issues as not enough oil to cool. It pins get their fair share its a unless feature. Piston pin oiling has been assisted by a funnel hole on top or by drilling oil scrapper ring drain holes into it. You can put a rubber tip pump oil can on rod hole and see how nice pencil lead thick and straight a jet it produces to strike right at the pin seam so Norton got that feature right on for what its worth.

Cams once were pre-lubed by the valley it rested in but DS case lip got removed in later Cdo's so its gets its oil by crank sling and exhaust rocker drain past the lifter front bevels. I want to have Peel's cam drilled and pressure fed from the old breather cam hole. I wonder if JBWeld + pegs could create the oil valley bath again?
 
Thanks for the info guys I now have a confused 1971 Commando 1 rod with oil hole, one without Without on the timing side Lets hope it lasts No more Oil tap in line NOW ! Regards from a wet SA :)
 
Colin, It's easy enough to drill the other conrod so that you have a matched pair, simply use an old shell with the hole to locate your starting point and then drill slowly until you are through.
 
Comnoz,

Which is exactly what I did:

Con rods Oil Hole
 
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