First off I know this topic has been shuffled about quite a bit, however I do have a few questions about the con rod's little oil holes. Basically how effective are they.
1. I have 2 sets of con rods with no little oils. Should I use them as is or have a hole drilled in both, or one.
2. I have one set of con rods with one little hole. This set has the same part number as the two with out the hole.
3. I read on one thread here that the little hole on the left con rod faces the flywheel. Why is that? Seems to me squirting oil at the flywheel is redundant and aiming the oil at the bearing would be much better.
3. What are the consequences of putting the con rod with the little oil hole on the right side, oil hole facing the right. I just pulled a motor apart and this was how it was set up. The engine seized on the right side, but I highly doubt the seizure had anything to do with the oil hole.
4. I think if you had both rods with the little oil holes that faced toward the bearings you would improve the oiling of the bearings. Let me know what you guys think.
5. It also makes sense to me to have rods without any oils which would improve the strength of the rods. Oil is flying around in there anyway and how much improvement does the little hole give the engine.
If oil squirts at the piston underside it helps cool it and the rod, but a hole weakens it, there is enough oil throwing around for the D/S bearing, the T/S bush dumps enough oil under the right cyl that they put a little casting above it to stop all the oil going up the bore. I run rods with no holes and no ill effects. If you want oil up the bores you could file some little grooves in the top thrust faces of the rod to direct oil spilling from the rod bearings up, like on these titanium H**Da GP rods. I haven't done it myself so don't know if it effects oil pressure, but it might help oil flow.
I agree with Mark. The holes were likely to improve cylinder oiling. As the oil hole in the crank and the rod line up it is supposed to squirt a little splash of oil. How effective it is I dunno. My bike has holes on both sides of each rod. It was common practice in the period to do this on car engines. Don't see it today. I do not think it was to oil the DS bearing because it surely got enough from splash and those bearings do not need lots of oil to enjoy long life. How much do 2 stokes mains and rod bearings get?
I e-mailed SRM on this topic some years ago when I found two holes in each of my rods and they said that the racers and hot rodders did it to their bikes. BSA did it on the left side on the A65 and I believe some A-10 models. I don't know for sure. I do not know how much it weakens the rod but it surely doesn't make it stronger. I have had no rod trouble in about 8000 miles since rebuild, but I don't push the bike real hard.
The rod with the little goes on the left (D/S). In Bacon's book, he says the factory put it in because they had problems with the left piston seizing from not getting enough oil. The right, of course, gets plenty of oil from the timing bush which is why they have the flange on the T/S case above the crank. The hole makes little difference to the rod strength. The rod usually fails in tension from either the bolts or bottom cap breaking. The A70L had steel lower caps in place of the aluminum. If you put in a T/S roller like Mark has, I would put rods with little holes on both D/S and T/S rods since the T/S bearing no longer supplies oil for the right piston. These engines have minimal oiling already so you need to get the oil spread around to all the places that matter. Oil is flying around but running off centrifugally from the crank. For most of the revolution, that is not toward the cylinder. The rod holes are pointing at the cylinder most of the time.
Joined: Dec 2006 Posts: 51nisse
BritBike Forum member
BritBike Forum member
Joined: Dec 2006
I have holes in both my rods and have no problems at all with that. Decent oilpressure and everything. now I don't know what way they are pointing because I did't put i together myself, it was made by at workshop many years ago when they changed the timingside bearing
And I'm going to keep them when I dismantle the engine next time because I think that extra lubrication is a good thing inside the engine.
Richard: personaly regarding your point #3 I wouldnt put a rod with a hole on the RHS they dont need any help to lose oil pressure. Others have said its ok so cant say for sure.
With regard to the hole being to squirt oil OUT Ive always been under the impression that its not for that (as the hole in the crank and brg shell only line up with the hole in the rod for a couple of degrees per 360 degree rev) I was told yonks ago by a BSA mechanic (when such a thing existed) that the hole was to allow a drop or so of exta oil INTO the shell like under the force of the upward stroke of the piston.
Dont take that as definitive as many theorys exist about this issue.
"There's the way it ought to be and there's the way it is" (Sgt Barnes)
The purpose of the hole is to enhance oil flow. If you take an empty garden hose, place your thumb over the end, and turn on the water, your thumb will stay dry. Let a little air out (like oil passing between a rod bearing and rod journal with .0015 clearance) and SLOWLY water will flow to your thumb. Take your thumb off the hose end (like the drilled con rod hole) and water will come much faster to the end of the hose, through the entire crank. The hole in the connecting rod is, after all, the end of the hose for the BSA A65 oil circuit.
This affect can be even greater if the engine was last shut down with the pistons up in the cylinder, meaning the rod journal is up and the sludge trap cavity can drain empty as well as the empty the crank drilling. Could take considerable time to fill the crank passages with oil after start up. It is a known fact the greatest percentage of all engine wear is during start up when lubrication is at its minimum. In theory, and practice, the journal does not ride on the bearing shell. The crank journal is suspended on a pressurized oil film suspending the hard steel journal from the soft babbitt bearing. Releasing your thumb from the hose is going to improve oil flow, and reduce the time for oil to get there and support the journal. No oil pressure, metal to metal. Thats engine wear.
A hole does not necessarily make a part weaker. On the contrary a hole of the proper size located properly (even a big hole) can actually make some parts stronger against predefined stress. So, unless some one tested this hole, we don't know. I have never heard of a BSA rod failing along the oil hole. Some where in an earlier post, lives a mechanical drawing showing the size and angle of the hole. If your gonna do it, do it like it says.
I've taken a rod from my motor when I first got it, (and it had done a lot of miles) and the rod was split exactly up the oil hole drilling to under the L/End which was only held by half the rod beam it definitely weakens the rod, I don't think they fail there usually but for some reason this one did. I think the rod was drilled so it had a little hole in each side and it was like a cutaway showing the drillings where it broke. Thats why I think the little grooves in the upper thrust faces would be a better option to get oil up the bore if you wanted more oil thrown that way. The BSA race rods which are the same as late uppers only with steel caps I put in it had no holes, I would use a rod with a hole or holes, but I wouldn't bother drilling a rod that didn't have it. They might have had that hose idea in mind Nert but the oil gets out past the bearing anyway and the system won't pressurize till oils filled the crank and i have good pressure building on the first couple of kicks if not the first kick when I start mine without the hole.
Mark I wouldn't drill the hole either. I like the notch idea better.
The hole promotes quicker flow of oil, not pressure. You may indeed have excellent pressure after the first kick. Just like the empty garden hose plugged with your thumb and the house valve on. (thats the thing with pressure, and hydraulics, etc. The pressure at the house is the same as the pressure in the 50 foot hose. But the hose is EMPTY.
Usually the a65l oil pressure reading is taken right at the pressure relief valve. No problem with pressure there, oil is usually held captive at the release valve cavity and its a short distance from the pump. Pressure would be almost instant. But no, or little oil flow to the drained crankshaft until it works its way through. A dead end will slow that oil flow to the needy parts far away from the pump.
(edited, added)Many a vertical mounted pressure sensor or even the inside of pressure gauges have never been touched by the fluid they are measuring the pressure of, as they are dead ended. Pressure is basically linear throughout the container. The media does not have to be present throughout the containment.
The beer in an unopened bottle is under pressure, yet the underside of the cap is untouched by the beer. Pop a hole in the cap, the beer flows out and wets the underside of the cap. Pour it in a glass and enjoy.
I am gonna quietly disagree with Nert (and others) on the oil flow. The little hole is only aligned a few degrees per revolution at which time the oil under pressure will flow and possibly squirt out this hole. It does not encourage more flow to the bearing as all the oil goes out the squirt hole. Once the hole is no longer lined up the oil will perhaps seep out the little hole just as is seeps out of the sides of the bearing with .0015 clearance. It does not increase flow to the bearing...just increases flow out the squirt hole right straight from the oil filled sludge trap. You garden hose example is a good one. Suppose you put two pin holes on opposite sides of end of a the garden hose. Let one side represent the normal flow that leaks out the edges os the bearing shell. The other hole is the squirt hole. When you uncover the squirt hole you will see a very slight pressure drop and less oil will momentarialy be going to the bearing hole. When you close off the squirt hole, the pressure returns to steady state. If the holes were say for example 1/4 inch in diameter, you would see a noticable drop in flow out of one hole when you uncover the other. Practically speaking this occurs very fast in an engine at say 3000 rpms where the hole is only lined up for perhaps 3 degrees out of 360 degrees. There is probably no measurable drop in pressure and whether it actually squirts or just dripples out I dunno for sure.
I did one time sketch out the crank and the hole in the rod thru 360 degrees and it did in fact aim towards the general direction of the cylinder walls when the holes were lined up. I also researched this some in repair manuals of engines during this period and they actully show pictures of the oil squirting onto the cylinder walls. Of course these are illustrator's representation of what the engineers claim happens. Personally I think that it is likely only marginally more effective at oiling the cylinders than the general splash and mist of oil generated by the the crank rotation. I do not think that these rod holes are a common practice in todays engines most of which run 55-60 psi at 2000 rpms and 25-30 psi at idle...something most BSA's did not.
As far as the strengthening or weakening the rod, I dunno. I suspect if it strengthed the rod you see all rods with holes in them. I suspect it weakens the rod but only very minimally. BSA was likely looking for answers to left rod failures at the time. I feel like the rod failures were due to marginal cylinder lubication and imminent seizing to the point the rods were near failure. The rod holes together with later improved oil pumps were directed at fixing these problems.
Nert....like they say just when you think youve heard it all. I can see where you are going with your garden hose analogy. But still recon the bearing rod interface never realy empyts out (unless bike has been sitting for ages) due to "boundry lubrication" the sludge trap proably does empty more depending on where in the cycle it sits.
"There's the way it ought to be and there's the way it is" (Sgt Barnes)
I can argue my point, i can argue in favor of your point. I see it all, question it all, and am open to all. I never close my mind.
Amazing, we can sit here and hypothesis, theorize, engineer, guess, second guess, speculate, develop, have foresight, and evaluate hindsight. Makes you wonder. Is a good engine good by design, or accident? OR Is a bad engine bad by design, or accident?
Yep Nert: Armchair expertise sure is good. What realy got me thinking about your hose analogy is that I have an oil pressure gauge hooked up with a peice of that clear hard plastic tube which is way too long. Due to lazyness i never did get around to cutting it to the right lenght and just kind of coiled it up with some zip ties(about 18" extra lenght, it used to be in a V8) and when I fire up the bike it instantly reads 60psi but the clear tube never fills with oil.
The concept which amuses me is wondering if there was a "retro design improvement seminar" conviened in which say the 10 most vociferous forum members had to redesign some A65 parts AND had to agree on any design changes we might design a washer in 6 mounths ...its all good....I know i would hold out for electro-polished stainless, all we would need to agree on would be the diameter, grade, thickness,manufacturung method, surface finish, tolerances, ID clearance and chamfer sizes.
"There's the way it ought to be and there's the way it is" (Sgt Barnes)
We are not all gonna agree on every point, but I have personally benefitted greatly from this site for the engines I have rebuilt. That's a kudo for you Morgan. That's what is so good about this website. I never had a shop repair manual or a parts catague until I found where to buy them. I rebuilt a couple of BSA's before the internet and although the ran ok they were not altogether right. When you get everything right they run pretty darn good and are pretty reliable...so I for one am thankful for all the input I have benefitted from that is posted on this site...even the info I don't completely agree with.
We are not all gonna agree on every point, but I have personally benefitted greatly from this site for the engines I have rebuilt. That's a kudo for you Morgan. That's what is so good about this website. I never had a shop repair manual or a parts catague until I found where to buy them. I rebuilt a couple of BSA's before the internet and although the ran ok they were not altogether right. When you get everything right they run pretty darn good and are pretty reliable...so I for one am thankful for all the input I have benefitted from that is posted on this site...even the info I don't completely agree with. Mr Mike
I have to agree with that Mr Mike..... and I am very thankful for the wealth of information and the various debates that ensue. There is so much valuable imputs on every subject needed to keep these BSA's running and running well. I am glad we don't all agree.... it seems to bring more info to light!
Richard, You hit the nail on the head. The debates and differences of opinion are what cause us do investigate further, study the problem, and ask a lot of questions, grill the machinist, and double check everything. Most of us don't do this for a living...it is just a hobby, but it is quite satisfying to pull up amongst other bikers, many of whom have their oil changed at a shop, and know that your put every last part of your bike back together.
1. Early A65's used rods with no oil holes. The oil hole was a running change made, I think, during the 1965 model year. IMO, all of the early rods are questionable. The late shot peened rods are much better
2. See above, the drilled rod had a different final part number but was made from the same forging. The number you see is the forging number.
3. The factory specified facing the flywheel like the A10. Some US BSA dealers said it should face the DS. I have taken unmolested engines apart that face the DS & face the flywheel. The late engines have dual oil holes....
IME, early engines with no oil hole in the LH rod generally have failed DS bearings & scuffed LH pistons. From the failed bearings I have seen, it appears to be lack of lubrication. The engine may have oil flying around, the DS bearing may not actually require that much oil, but DS bearing is fairly well buried on these engines. The oil hole seems to help increase oil supply to the LH side.
But, A65's tend to run a fair amount of side clearance on the rods, more than is typical or recommended design practice. This in itself should promote adequate oil flow in the bottom end.
4. You can put the rod with oil hole on the RH side, but why? An engine with the oil hole on the LH side works. IMO, you will achieve better oil flow through the crank with the small pressure drop on the LH side the hole will introduce.
5. The "oiling" of the bearings is a function of the flow of oil into the bearing/journal area from the pump and the state of the hydrodynamic wedge formed from the viscosity of the oil and rotation the crank.
The journal bearing goes from boundary lubrication at rest/low speeds which is merely the existing film of oil (VERY thin) to hydrodynamic wedge as speed increases. The bearing actually rides on the hydrodynamic wedge during operation. Oil needs to be supplied in adequate volume and pressure to cool and cleanse the hydrodynamic wedge. If you have sufficient oil flow and pressure coming into the journal bearing, excess oil is forced out of the wedge. The most flow at the rod oil hole will occur when the hydrodynamic wedge passes under the oil hole. This momentary drop in pressure at the wedge will require adequate flow of oil back into the journal bearing system to replenish the oil lost in the hydrodynamic wedge. Hence the "pressure drop" promoting oil flow through the crankshaft.
6. IME, I have seen few if any signs the oil hole causes failure of the rod. Though I know of a few people (Mark Parker being one) who have. B25's & some Tr*umph 500cc twins (basically the same rod) have had failures through the oil hole.
Most A65 rod failures tend to be the early rods. Even piston siezure can cause the rod to fail. Again, the best A65 rods are the late shot peened rods. Or spend the money for aftermarket rods. There are some really good rods available now - Ridgecrest & MAP are 2 examples.
The rod bolts are also questionable in some A65's. I have seen enough failed rods that originated with the rod bolt to believe the rod bolt is marginal. IMO, too many stress risers in the design of the rod bolt.
Wow, What a thread.... Thanks for all the information. I think Rich B answered my questions best, so I am going to run a single oil holed left rod in this build. I have in my rod stash the no oil rods and the twin oil holed rods. Suffice to say I will shot peen the and drill the early rods. My only question is where can I get better rod bolts. Thanks to everyone's response. Richard.
'where can I get better rod bolts.' In a set of new aftermarket rods, they really are not that dear, by the time you spend money on old rods I would think a new stronger set would be a better investment. cost about as much as two tyres. I've done it bought some used Commando rods spent a lot of time polishing them so there were no marks on them, they looked great and then took out the T/side case.
I wouldn't waste my time with doing anything with early rods. There are enough late rods around to use if you must have BSA rods. If you have a set of late rods with dual oil holes, they are already shot peened. I would use the late rods and use your early rods as a paperweight. Or throw them at the neighbor's dog.
Like Mark said, the price is not bad on aftermarket rods.
Through this rebuild, don't forget to install a late oil pump (68 on) and an SRM OPRV. Your early pump should join the early rods in whatever method you choose for their demise