Con-rod oiling holes

[A10Boy]

and this turns out to also be the crankshaft position when the oil hole lines up with the bearing feed hole in the crankshaft

It isnt actually, the big end oil holes are at 90 degrees to the throw of the crank so the oil holes line up just past half way up the up stroke and just before half way down the down stroke.

[MikeN]

It turns out that the flywheel is no good at getting oil on the cylinder walls bacause the spray comes off the flywheel at a tangent and with the large OD of the flywheel, very little, if any gets in the bores. 

What makes you say that oil comes off the flywheel at a tangent? I would of thought centrifugal force would fling it off the flywheel radially.
MN

All particles leaving a round, rotating object depart at a tangent...that's physics.  Ever watch rain water coming off a tire without a mudguard?  F1 cars or bicyles in the rain?

If you want to see a particle leaving a rotating object watch this. Its funny and a good example of physics in action
http://www.youtube.com/watch?v=iRasoZMirRc&feature=player_embedded
Mike

[bsa-bill]

I read an article that was a history of the A7/A10 development, it stated they had trouble with the drive side cylinder overheating and modified the left hand rod by adding the much mentioned/maligned hole ( that's maligned not misaligned).
OK all I need now is to locate the said history - see the credibility of it and be recognised as the Smart **** that  know I am

Oh if it was that easy, I can't remember where I read it, and have trolled search engines in vain.
So it is I believe up to all of us to do whatever we think is correct, I  follow BSAs thinking whatever it was and stick to the "hole fires at the cylinder wall theory.
It is one of those subjects that if ever solved would diminish our enjoyment of our hobby, leave us with a little less to discuss - up there with the meaning of life and the oil thread, if someone discovered beyond doubt the best oil for us to use in our A's what would be left to discover

PS It's 47 in case it had escaped your notice

[beezalex]

It isnt actually, the big end oil holes are at 90 degrees to the throw of the crank so the oil holes line up just past half way up the up stroke and just before half way down the down stroke.

Damn...you're right...I really stepped in that one....so squirting at the flywheel again, we are.

[RichardL]

As for the "equalization of flow" thing...the sludge trap basically forms a reservoir at static pressure that supplies the big end bearings.  I don't see how there can be any difference in pressure between the two journals unless the trap is plugged.  All adding a significant hole anywhere in the system does is lower the overall pressure...thus REDUCING the flow from the journals.

If one looks at ductwork and piping design, one will notice that after one or more tap-offs of air or liquid, respectively, the engineers will reduce the cross-section of the duct or pipe to maintain pressure at the more distant tap-offs. Now, does that really explain why reducing pressure at the far end of the sludge trap via the infamaous hole will promote greater flow to the left side journal? Hmmm, I'm still dancing around that one.

Richard L.

[MG]

Gents, you got me thinking about the whole flow rate issue. This is the physical explanation I can come up with:


Watch out guys, switching on smart idiot mode now!


Bernoulli tells us: p + rho/2 * C^2 = const., where p is pressure, rho is the fluid's viscosity (which we assume being constant) and C is the fluid's velocity.
As both big ends are exposed to the same surrounding pressure p inside the crankcase, you can derive from Bernoulli's principle, that the fluid's velocity must be the same at both big ends, regardless of their cross-sectional area. We are neglecting line loss here, as the sludge trap is not very long this should be insignificant enough.

The volumetric flow Q is defined as
Q = A * C.
C is the same for both big ends, like stated before.
So with an increase in the cross-sectional area A, the flow rate MUST increase as well.

So YES, the with the drilling oil flow to the lhs big end WILL increase.


In case the oil pump is not able to cope with the higher flow rate (at low rpm for instance), this will lead to a reduction of volumetric flow at the rhs big end due to the principle of continuity accordingly:

Q_oil_pump = Q_big_end1 + Q_big_end2

***smart idiot mode off***


Jeez, now I really need a cold Goesser to clear my mind...  


Cheers!

[MG]

To make that a bit more ostensive:

As for the "equalization of flow" thing...the sludge trap basically forms a reservoir at static pressure that supplies the big end bearings.

Now let's use a plastic cup to act as the sludge trap. Punch two holes of the same diameter into the bottom and close them off with your finger. Fill the cup with water. What you have now is a "reservoir of (hydro)static pressure". This is the same situation as with the crankshaft, with two openings ending up in an area of constant and alike pressure (atmospheric pressure here).
Take your finger off the hole and watch the flow from the holes.
Now make one hole significantly larger than the other one and repeat the procedure.
You can also count the seconds it takes until the cup is empty in both cases and you will see the increase in the overall flow rate when increasing the cross-sectional area of one opening.
(Q_cup=Q_hole1+Q_hole2)

Contrary to the flow rate of the oil pump at constant rpm, Q_cup is variable here.


Looks like the Goesser slowly is doing it's job...  

[beezalex]

Yes, but the extra flow through the orifice doesn't help the bearing at all.  The hole might as well be on the side of the sludge trap...none of that oil enters the journal.

[RichardL]

After so much pallaber, I need to correct myself and re-evaluate my thinking. On my merry little brain ride, I kept envisioning an end-feed tube as the reservoir. Nay, nay, foolish self, the reservoir is limited, I believe, to the circumferential area around the sludge trap (for cranks with sludge traps) Therefore, there is no "tap-off" as I was saying.

The feed holes in the sludge trap are equidistant from their respective rod journals. So, it is reaonable to assume that, without the ding-dang hole, the journals should get the same amount of oil. OMG! Now what?

Maybe the hole came into being before the sludge trap and the "tap-off" logic applied.  Then, the hole could have  lingered on past its need, but we seem to have statistical evidence of more heat failures on the left in sludge-trap bikes (Oh, that's going to be the name of my bike "The Sludge Trap Express", or maybe not).   

Sooooo, if the flywheel can't really spray the cylindar wall, maybe the purpose is just to promote more droplets/mist floating around in the crankcase for better lubrication of both cyclinders . That would help explain a hole in each rod for the A65.

To the extent that I have forgotten any part of this discussion that took place in a past life of my own, please forgive.

Oh, hear me Oija Board! Conjur the spirits of Mr. Hopwood and Mr. Pike to answer our  questions and put us out of our misery!

Richard L.

[MG]

Oh, hear me Oija Board! Conjur the spirits of Mr. Hopwood and Mr. Pike to answer our  questions and put us out of our misery!

Amen! 


Hadn't the A65 oil pump been of greater capacity in order to supply two drilled rods?

[groily]

But don't SRM often install their own (presumably higher-capacity) oil pump along with their rods with no holes at all? Or would that only be with the end-feed conversion?
It's all Greek to me . . .
So glad Markus I'm not the only person here who struggles regularly with AMC year-on-year oiling mods - other whole forums exist for the unravelling of those arcane mysteries and to keep us from mis-matching parts with terminal consequences. At least no issues over holes in rods, and equal oil distribution to both big end journals via the centre main bearing . . . .
Sounds so perfick - but weirdly enough BSA twins seem to work for rather longer between radical surgery despite their timing-side centric way of shoving the slime around.
What did Triumph have, on their plain bush engines? Did Mr Turner feel the need for an 'ole on the far end? If, that is, his piston pump actually had the oomph to get the oil that far anyway after all the exertion of pushing out the tit on the tell-tale plunger?

[beezalex]

A65's didn't start with larger oil pumps...only the later ones got bigger capacity...but they need it: Higher RPM (Bearing oil consumption goes up) and larger bearings I think are the major reason.  BTW, SRM A65 oil pumps are the same capacity as the later model stock pumps.

[MG]

So glad Markus I'm not the only person here who struggles regularly with AMC year-on-year oiling mods

Well, if you haven't got enough problems, you gotta go out and buy some.  

Some of the decisions the AMC engineers made are absolutely unintelligible to me, like omitting the pressure release valve in some years. I mean, we all know about the oil-tightness of our old girls, even when oil pressure does not exceed levels of 150 psi.
I'm rebuilding the engine with '59 crankcases and updated these to the latest specs (retro-fitted the release valve, drilling through the inlet camshaft tunnel to oil the lhs cylinder, etc.)

Actually I have incorporated everything that makes sense to me, time will tell how good my decisions were...


Recently I read somewhere (can't remember where unfortunately) that Bert Hopwood had designed his A7/A10 engine within only 10 days, including making all necessary drawings for manufacturing.
Incredible achievement, regarding how well it performed and for how long a time this concept did proove it's quality.

Hats off to Mr. Hopwood!  

Markus

[Stu55Flash]

Hi not stripped my engine yet, so don't know from first hand but not mentioned on here so far:


Service sheet 202 says that on models after ZA10-4712 for A10 and A7 from AA7-101 the crankcase is modified to supply oil to the camshaft trough and directed to the cylinder walls from here.

Also in the Haynes manual on page 26 its says that after 1951 the left hand con rod of all engines has a special drilling and it is therefore not possible to interchange the con rods. If they are interchanged the left hand big end bearing will be insufficiently lubricated.

So is there possibly an issue with pressure at the left hand big end if oil pressure is lost on the right hand side. To test this is there any difference between the left and right journals when measured?

Great discussion thread!

Stu

[MikeN]

So glad Markus I'm not the only person here who struggles regularly with AMC year-on-year oiling mods

Recently I read somewhere (can't remember where unfortunately) that Bert Hopwood had designed his A7/A10 engine within only 10 days, including making all necessary drawings for manufacturing.
Incredible achievement, regarding how well it performed and for how long a time this concept did proove it's quality.

Hats off to Mr. Hopwood!  

Markus

Markus,
  The above isnt quite correct,
 Im looking at the transcript of an interview between a journalist from "the motorcyle" magazine and BSA's Mr H Hopwood,Chief designer (Motor Cycles). he says that he was "in" on the design of the BSA Vertical twins but it was Mr H Perkins, Assistant Chief Designer who laid down the A7 engine and it was, in Mr hopwoods words, "Mr Perkins baby".
With support coming from Mr, D W Munro of the Technical department.
  They discuss the original A7 and although there is no mention of the con-rod hole ( I dont think the early ones had them. the rods were made from nickel steel), it does mention that the oil pump passes 126.6 pints per hour and the return pump passes 177 pph at 5000 rpm which may be of interest.
MN