Conrod oil hole

[mark]

I have a pair of conrods in excellent condition but they both have the oil hole. The manual states that only the left hand one should have it. What are the consequences of fitting both, or could one be blocked somehow.
Mark

[Josh Cox]

Hi Mark,

The oil hole ( as per the bacon book ), is there to promote oil flow through the crank, without the hole there would be very little oil flown ( if any ) through the crank and the sludge trap would be useless.

IMHO having both conrods spraying oil would be better, both cylinders being oiled, can not be a bad thing, next time my engine needs to be pulled down, I will drill out the RH conrod.

[RichardL]

Josh,

Having read every possibile book I could reference and all of the opinion on both sides here in the forum, my own opinion on this is that there should only be a hole in the left side rod and it should aim towrads the center of the engine. I am not of the group that believes the oil hole is there to spray oil on the left cylinder wall, though I will take no offense if others more sage than I and, perhaps, they are legion) say otherwise. According to my recollection, the oil will hit the crankshaft, not the cylinder wall, when the piston is at TDC. I believe what you said about promoting oil flow to the left rod journal is correct, but you don't want to depressurize more than necessary by opening a second hole. If it were mine, I would plug the hole in the right-side rod.

Richard L. 

[mark]

I am also of the opinion that the hole is there purely for the purpose of helping the oil flow to the left hand bearing and having one in the right hand side may lower the flow. I guess that I wanted to hear someone else say it  Any suggestions on how to block one of them. Peening over the end under the bearing shell is one option that comes to mind. If they made shells without the hole it wouldn't be an issue but I don't think that they exist.

Mark 

[Brian]

The hole is there only to promote oil flow and does not "spray" out. There is no reason not to use two left hand rods provided you either block the hole or find a set of shells without the hole. The hole in the left rod has to face inwards as stated.
If you do look for another rod be carefull as even though the rods all have the same numbers on them there are some differences in the castings and weight.

[Josh Cox]

Well you guys can put it in your pipe and smoke it, I'm still putting a hole in each conrod......

[muskrat]

OK what about putting the hole facing towards the drive side bearing for better lube ? I have done this for years with no ill side affects.
Wot you smoking Josh. Not flying but still high ?
Cheers

[terryk]

I have often wondered whether the hole needs to be there at all. There would be oil everywhere in the cases and cylinders anyway. Other engines dont need it and if the timing side main bush is the correct clearance and oil pump is good it should be fine.
After saying that, I still have over the years made sure the left conrod is right way round with the hole. But I would like to hear from someone that has run an A10 with no hole, does it make a difference or was BSA just a bit concerned about oil flow because of the timing bush idea.

[Josh Cox]

Terry, if there is no hole in the LH conrod, there will be no oil flow though the sludge trap ( inside the crank between the LH and RH crank pins ), which would block and the LH big end would get no oil.

When I pulled down my engine the conrod with the hole was on the RH side, the sludge trap was completely blocked, took long 6mm drill to get through, then blew out with an oxy.

It defies logic.

[MG]

I could imagine the intention of the hole facing inwards is to spill additional oil on the flywheel so that is flung up into the lhs cylinder. Just a theory put up for discussion.

Josh,
of course there is flow through the sludge trap, even if there is no hole. The oil is fed through the crankshaft (and therefore through the sludge trap) to the big end bearings. There it provides hydrodynamic lubrication for the bearings and escapes through the gap between crankshaft journal and bearing shell. That's why a sufficient flow rate is necessary to keep the lubricating film up (plus a certain amount of pressure to overcome centrifugal forces). The additional hole in the conrod imho just reduces the backpressure on the lhs by slightly increasing the volume flow rate and therefore balances the lhs and rhs big end oil pressure as the pressurized oil takes the way of least resistance (just like myself   ).
The sludge trap gets blocked from years of operation and lack of maintenance, so sludge's building up in there (which is the purpose of it, requiring periodical cleaning).

Cheers, Markus

[Josh Cox]

Hi Markus,

The average big end clearance is what, .001 ?, not much oil is going through a .001 gap at 60 odd PSI. I think the hole is more important that many think, remember if the oil pressure is below the required pressure to open the pressure valve, exactly what will be receiving oil ? ( cam in its oil bath, rockers from the return line and the big ends and drive side bearing from the conrod oil..... a bit of leakage from the timing side bush ).

My theory on fixing the sludge trap blocking is to use OMD, Oil Mineral Detergant, LH drilled conrod ( and RH for me next time ) and a good oil filter, the sludge trap should be spotlessly clean ?.

Has anyone restored and engine that was run on multi-grade OMD ( with or without filter ) ?, how many miles and how was the sludge trap, bores and internals of the cases ?.

[MG]

The average big end clearance is what, .001 ?, not much oil is going through a .001 gap at 60 odd PSI.

Right, that's what keeps oil pressure and hydrodynamic lubrication up at low flow rates (low rpm/idle).

I agree that the hole makes sense, otherwise the BSA engineers wouldn't have bothered to change the design, but I'm not sure if it is a good idea to fit it on both sides.
Oil is fed to the big ends through the timing side bush, this being the first point to reduce the oil pressure, the second one being the rhs big end. The residual oil pressure has to be sufficient to enable proper lubrication of the lhs big end. Therefore I think they incorporated the hole on the lhs to increase flow to this point, which is farthest from the feed pump, reducing the pressure on the rhs bearing and improving lubrication on the lhs.
If you increase the flow rate on the rhs big end, you automatically reduce the residual oil pressure and therefore the feed rate to the lhs bearing. Although, with an oil pump in good nick, I would consider this discussion academic.

Yet I don't see the need for additional oil flow on the rhs? Even if the relief valve is closed, the camshaft gets the oil draining from the rockerbox (coming from the return line), flinging it up to the cylinders, and the timing side bush is the first bearing to get oil from the pump anyway.


Unfortunately I don't have enough long-time experience to give an answer to your sludge trap question, but I would also think that with a good oil filter and modern oils (which are designed to keep particles in suspension to deposit them in the filter), sludge build-up should be almost zero.
I'm sure someone will be able to tell us (Trev  ).

Cheers, Markus

[MikeN]

Any suggestions on how to block one of them. Peening over the end under the bearing shell is one option that comes to mind. If they made shells without the hole it wouldn't be an issue but I don't think that they exist.

Mark 

Mark.in reply to your question. If I was going to plug a hole in a con rod i think i would tap a thread and screw in a grub screw if you are so equipped. I dont remember what dia the hole is now on the BSA rods but if its say 1/16" dia then you could tap it  M2 or 8BA . You would only need a few turns , say 3-4mm depth. Obtain or make a suitable screw and saw off the head. make a small saw cut for a screwdriver slot . Wind in with some loctite and its done. I would tap from the bearing end of the rod outwards.
  Another way would be to find a suitable dia peice of wire and form a head by peening with a hammer ,or turn up a pc of aluminium to fit with a small csk head if you have access to a lathe.lightly csk the inside of the rod and insert with a retaininng loctite. file or scrape flush.
 i dont think I would try peening over the hole. With soft alloy rods you may distort the (half) bore of the rod.
Mike

[RichardL]

Please see the attached link for info on the hole diameter. As you can see, we have been around and around on this topic. Followed enough, you would learn that MAP rods do not include a hole in either, because they didn't think it was necessary. I didn't buy that and ended up drilling a hole in my left MAP rod. So far, so good, about 1275 miles.

Richard L.

http://www.a7a10.net/forum/index.php/topic,1499.msg10279.html#msg10279

[Josh Cox]

Markus,

The port on the oil pump is what, 5-6 mm diameter ?, one single hole in a conrod is 1mm ?, I believe there is plenty of oil to feed both big ends with holes through conrods, and T/S bush.

I do not think the pressure will be considerably reduced by a small increase in volume flow due to the extra conrod hole.

There are many thing we can do to make these bikes more reliable, I believe this can not hurt.

On the link Richard L provided, there was mention by Trev that both of the A65 conrods were drilled ?.