Connecting rod bleed holes

1973x75

1973x75

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Nov 15, 2015
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Connecting rod bleed holes should be facing outwards. I just finished a rebuild, but I have them facing inwards. Can I leave it as is or do I need to open it up again? How critical is it? I’ve read that some rods (Carrillo?) don’t even have the holes.
 
No clue about critical, but the word OUTWARDS is all caps in my Hanyes manual. Could be important. Others will know all you need to know.

Correct no holes in the Carrillo rods at the big end. There is one at the little end.

Edit: I'm a big fan of not doing things over, but did recently, so I feel your pain. I'd probably tear it down again unless one of the members here that puts motors together day in day out says it's OK.
 
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Guessing the out-board facing holes are to ensure an intentional flow of oil to the main bearings… ??
 

Con rods oil jet holes...

Good, bad or irrelevant ... ?? I can see and argument for them being bad for oil pressure... I can see how it might be good for a timed 'squirt' of extra oil to cool pistons and lube bores... But I can also see how the same quantity of oil will exit the big ends as splash anyway, thus...
www.accessnorton.com www.accessnorton.com

Not a direct answer to your question but ..............
 
I suspect that if you leave it as is you'll be worried about it whenever you ride the bike. That'll take the fun out of it and it's all just for fun.
Is the engine completely assembled and back in the bike?

Glen
 
Rebuilt, ready to put back in the frame. Seems like some people find them completely unnecessary, which is encouraging. I’m leaning towards leaving t as is.
 
1973x75 said:
Rebuilt, ready to put back in the frame. Seems like some people find them completely unnecessary, which is encouraging. I’m leaning towards leaving t as is.
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Since it's not in the frame, I would fix it! However, you need new big-end nuts and if you used a composition head gasket, a new one. If you used gasket sealer on the base gasket, you'll probably need that as well.
 
Just what I wanted to hear. I spent the afternoon researching this, and came to the conclusion that its not worth swapping them back. Expert opinions think those bleed holes are redundant.
 
Just rebuilt a motor with the Carrillo rods and short pistons. Have not fitted this MK 111 engine yet to fire up. I ignored the rod shell up/down small oil hole fit as there are no holes in the rods applicable to position, for pressurized splash up to the O.E.M. underside of the pistons for cooling. The only holes visible were at the small end of the rods. . and of course the big end rod shells themselves. I'm thinking the Norton manual directions are not so Carrillo applicable . Correct me if wrong.
 
I was taught , on car engines that the oil hole or short side of piston pin " some pistons are offset by like 1.5 mm for quietness i think ,etc goes to the major thrust side . depending on bearing clearance oil ,comes out of the sides of the conrod .
 
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I don't think I'd worry about it
There used to be different opinions on BSA a series twin engines about which way the oil hole faced and I don't think it made a difference!!
 
baz said:
I don't think I'd worry about it
There used to be different opinions on BSA a series twin engines about which way the oil hole faced and I don't think it made a difference!!
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Thanks . Carrillo rods use Wiseco pistons that don't need underside squirt splashings , so I fitted the tiny shell holes facing downwards. I can't see any issue , that's why I didn't care up or down fit with the big end shells.
 
The squirt does not have enough volume to cool the bottom of the piston, its to oil the cylinder wall.

A piston cooling jet is fed 100% of the time and is usually in the block and pointing at the underside of the piston.



I had them in an Audi 5 cylinder engine I rebuilt.
 
Well, I’ve often thought that as part of oils job is to cool, wouldn’t it be better for these oil holes to aim to the centre of the barrel, which is hotter?

I don’t have an answer to my own question, but as pointed out by others, many after market rods don’t even have the holes, and they run fine.

I think it’s alway interesting to note that irrespective of holes or not, EXACTLY the same amount of oil passes past the shells and ends up as splash / mist. Which is what lubricates and cools the rest of the bottom end.

I had a long conversation with Pete Lovell about these holes and he had no strong opinions either way, having built many, many engines with and without, and not seen any differences in wear / life / etc.

So, if engines run well with the holes, and equally well without them, I can’t personally think of a practical down side to having them, but facing the opposite way.
 
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