The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: mark on 14.04. 2010 22:46

Title: Conrod oil hole
Post by: mark on 14.04. 2010 22:46
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
Title: Re: Conrod oil hole
Post by: Josh Cox on 14.04. 2010 23:00
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.
Title: Re: Conrod oil hole
Post by: RichardL on 15.04. 2010 00:44
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. 
Title: Re: Conrod oil hole
Post by: mark on 15.04. 2010 00:57
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 
Title: Re: Conrod oil hole
Post by: Brian on 15.04. 2010 02:53
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.
Title: Re: Conrod oil hole
Post by: Josh Cox on 15.04. 2010 09:17
Well you guys can put it in your pipe and smoke it, I'm still putting a hole in each conrod...... *smile*
Title: Re: Conrod oil hole
Post by: muskrat on 15.04. 2010 10:26
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
Title: Re: Conrod oil hole
Post by: terryk on 15.04. 2010 10:41
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.
Title: Re: Conrod oil hole
Post by: Josh Cox on 15.04. 2010 10:44
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.
Title: Re: Conrod oil hole
Post by: MG on 15.04. 2010 10:54
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
Title: Re: Conrod oil hole
Post by: Josh Cox on 15.04. 2010 11:02
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 ?.
Title: Re: Conrod oil hole
Post by: MG on 15.04. 2010 11:08
Quote
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  *wave*).

Cheers, Markus
Title: Re: Conrod oil hole
Post by: MikeN on 15.04. 2010 13:54
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
Title: Re: Conrod oil hole
Post by: RichardL on 15.04. 2010 16:02
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
Title: Re: Conrod oil hole
Post by: Josh Cox on 15.04. 2010 22:47
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 ?.
Title: Re: Conrod oil hole
Post by: RichardL on 16.04. 2010 01:10
Josh,

I think I will stay waaay back from saying that having a hole in each rod is bad and will lead to engine failure. Frankly, I don't really know and I tend to agree with you that it is unlikely to cause a problem. But with me, there is always a "however." However, I am somewhat sure that having holes in both rods will not increase the amount of oil getting to the left side and having a hole only on the left side will increase oil to the right side (without decreasing oil to the left side). All of these volumetrics are, no doubt, very small in differences, but it is a little fun to torture the fluid dynmaics of it all (and at least three people here, who I know to know more than I about fluid dynamics, are probabaly about to tell me the level to which I am full of it).

Richard L.
Title: Re: Conrod oil hole
Post by: Brian on 16.04. 2010 04:20
In Munro's book of BSA twins he states that using a rod with the oil hole on the right journal will cause oil starvation on the left journal. Being BSA's technical manager at the time I think his advice is sound so anyone doing so does so at their peril.

He says that the oil hole in the left rod was introduced early in 1951 but doesnt say exactly why, just that it was done to promote oil flow to the left journal and also to aid with the lubrication of the left cylinder. Wether there had been some failures in the early engines is anybody's guess.
Title: Re: Conrod oil hole
Post by: Josh Cox on 16.04. 2010 07:27
Quote
In Munro's book of BSA twins he states that using a rod with the oil hole on the right journal will cause oil starvation on the left journal

That is exactly right if you have only one conrod with a hole and it is on the RH crank pin ( as mine was before rebuild ). But I believe you are missing the big picture.

If there is a no hole in the LH conrod, there will be no flow through the sludge trap and into the LH big end ( ergo oil starvation ), the oil hole through the LH conrod is there to promote oil flow through the sludge trap onto the lh big end and crank pin out onto the cylinder wall. If there was no oil hole, the only oil flow would be through the .001 crank pin / big end gap.

As there is no channel machined into either the crank pin, big end or conrod, oil will only flow through the hole when the conrod hole lines up with the crank pin / big end hole, i.e. at the top of the stroke (TDC).

When oil does flow through the hole, it lines the bore and keeps the cylinder cooler and the oil ring wet.

Doing this to both conrods is a good thing, remember in one 360 degree rotation of the crank, oil will only flow through the hole for approximately 5 degree (TDC- when the holes line up).
Title: Re: Conrod oil hole
Post by: Brian on 16.04. 2010 08:02
He states that the rod with the hole in it must be used on the left side only.

It is of course your choice if you decide to use rods on both sides with oil holes but BSA's technical manager advises against it.

As with all modifications to old bikes be prepared to live with the consequences if it goes wrong.
Title: Re: Conrod oil hole
Post by: Josh Cox on 16.04. 2010 08:43
Well Brian , there it is in writing, when was this written ?.

First there was no oil hole,
Then there was oil hole, near side only,
Then in the A65, which by my calculations is virtually the same engine, both rods.

Other examples of evolution and the relationship between your bike and when it was made in the timeline, I believe in the early bikes for example, there was no oil to the top end ?.
Title: Re: Conrod oil hole
Post by: Brian on 16.04. 2010 09:07
The first edition of this book was 1955. I dont know if he was still the Tech manager at that time or not.

Its a book worth having if you can find one.

The very early A7 engines didnt have any oil feed to the rockers, then they put a oil feed to the exhaust only and finally to both. A friend has a totally original 48' model and it only had oil to the exhaust but my Star Twin (1950) has it to both so I guess somewhere around 49' they must have introduced the oil feed to both.

I cant remember what oil holes where in my A65 or A50 rods, it was too long ago. (memory's going!)
Title: Re: Conrod oil hole
Post by: 1660bob on 16.04. 2010 09:28
Josh-I think you misunderstand the purpose of the sludge trap. In your post, you talk of using oil mineral detergent to clean it out-I assume you mean with the engine running? NO! don`t do it-will mince your big ends. Its called a sludge TRAP for that very reason-it traps any sludge present in the oil that is being pumped through the crank and thus PREVENTS it (the sludge, not the oil)from passing through the shell/journal gap.Thus we should only get clean sludge free oil at the big end bearing surface.If you loosen all that crud (accumulated over years/1000`s miles) with detergent it will all be forced out through the b/e bearings and trash them in an instant.The only way to clean out a (BSA)sludge trap is to strip the motor and clean it  by hand.....
A little on how the sludge trap works will be useful: In the A10, the trap is a thin walled metal tube about 1/2"bore dia.It has a step up in that diameter at the "feed" end to about 3/4". There are two small holes halfway along the tube, these holes are where clean oil emerges on its way to the b/ends, and another single larger hole diametrically opposite the above pair (for the locating bolt).When the trap is correctly mounted in the crank, the two small  holes from which the oil emerges are positioned so they face inwards i.e. towards the crank centreline/axis.The principle of operation is : the trap is mounted in the centre of the hollow b/end journals in the crank.It is concentric to the big ends, but of course is not on the axis of the crank itself.Oil enters the sludge trap tube directly from the pump,at the larger diameter end,(the larger dia end matches the bore in the crank itself and prevents any oil sneaking past the trap and by-passing it, thus this fit in the crank here should be close).As the oil enters the trap it is subjected to high centrifugal forces due to the crank spinning, and is forced outwards, gathering along the back of the sludge trap wall, at the opposite side to the two small holes.Any sludge/debris in the oil is thus "pinned"  against the back wall of the trap tube,away from the two "exit" holes.The trap tube fills with oil,which is forced by sheer volume out of the two exit holes(against the centrifugal forces) into the crank journal leaving behind any crud "trapped"in the sludge trap..More later, Bob
Title: Re: Conrod oil hole
Post by: terryk on 17.04. 2010 10:47
The A7 longstrokes didnt have a conrod hole and they used the same type timing bush. Oil flows though the sludge trap and out the conrod bearings no problem as all other types of motorcycle and car engines that use this type of conrod bearing. The oil splashes up the cylinders on both sides and over all the internal moving parts.
Sludge traps are used on Triumphs etc as well. They are there to collect sludge. Oil flows through the sludge trap if there is a hole in the left rod or not.
I definitely would not have a hole on the right side conrod. This would reduce oil pressure to the left bearing just the same as if the timing bush has too much clearance it would reduce oil pressure to the bigends.

I recon but I could be wrong, that BSA with their new A7 and A10 design in 50/51 wanted to be sure that there weren't oil pressure problems to the left side and therefore introduced the oil hole. I haven't heard of left side oil starvation on the longstrokes but I'm no expert and I havent raced them as some others may have. I have quite a few longstroke engines and cranks and the left side doesnt seem to be a problem.

I have also over the years pulled A10 engines apart that didnt have the oil hole in the left conrod or it was blocked. I cant comment if the hole makes a difference though. It usually was the same old reasons that you strip an engine it was blowin smoke but maybe previous owner had given it a quick re-ring and valve job and didnt do the bottom end. You would think if it had a total rebuild then the person doing the engine would see in the manual about the oil hole. If it had a total rebuild and not used a conrod with the hole then it doesnt make a difference whether the left rod has a hole or not. If its been running that way till the rings wear out or guides depending which one is the cause of the smoke then obviously there is enough oil getting to the left side because that would be after several years. 

Another issue Im thinking about is making a trough for the cam on the longstroke engines like the later design models. These longstroke cams always seemed to be worn badly. The latter design crankcases have a cam trough so I think some sort of one would be benificial to reduce cam and follower wear. I do have a few ideas to make a cam trough. Whats your thoughts?
Title: Re: Conrod oil hole
Post by: trevinoz on 17.04. 2010 22:53
Just my thoughts on this subject.
It seems that the hole was provided after the "new" engine configuration had been in service for a while and either problems had come to light or Bert Hopwood had a revelation and decided that oil flow to the LH journal had to be enhanced.
Surely the oil pressure at both journals will be the same with the hole acting as a relief valve for the chamber.
Providing a hole in the RH rod shouldn't affect the LH rod. Two holes in the chamber will tend to lower the pressure but the pump should supply enough volume to overcome this.
In the late A65, both rods were drilled but by then the pump had a wider gearset thus higher output volume.
I have seen many engines which were worn badly on the LH side or thrown the rod on that side, but this was caused by the sludge trap being blocked.
I feel that it doesn't matter whether one or both rods are drilled, it is essential that the trap is clear and the oil pump is in good nick.

Terry,
           Regarding the long stroke engine cam and follower wear, have you considered having the bits nitrided?
Triumph did just that to stop premature wear on the exhaust cam.
They even eliminated the oil feed to this area. It seems to have worked OK.   

   Trev.
Title: Re: Conrod oil hole
Post by: terryk on 18.04. 2010 14:05
Gday Trev, yes thats what I will do with the worn cams and followers that I have when I get them reconditioned. I do have one really good longstroke cam and a new set of followers that I want to use on the 48 so I thought a trough of some sort would give them a longer life.
Title: Re: Conrod oil hole
Post by: Josh Cox on 19.04. 2010 06:39
Thanks for your input Trev.

Sorry to keep banging on about it, I think it very important to remember that the oil hole/s only line up with the crank pin holes for a very small part of a 360 degree rotation of the crank ( i.e. 5 degrees or there abouts ), so I do not believe any one part could be adversely effected by the RH conrod having a hole.

If it was a serious concern for you, make the LH oil hole bigger than the RH.

Where's Olev, that guys usually got an opinion on most things...... *smile*
Title: Re: Conrod oil hole
Post by: A10Boy on 27.04. 2010 12:51
Quote
Sorry to keep banging on about it, I think it very important to remember that the oil hole/s only line up with the crank pin holes for a very small part of a 360 degree rotation of the crank ( i.e. 5 degrees or there abouts ), so I do not believe any one part could be adversely effected by the RH conrod having a hole.

Sorry Josh, but I have to disagree.

The position of the hole is irrellevant as there is a film of oil under pressure between the crankpin and bearing surface and oil is being fed in there under pressure through 360 degrees rotation, so oil flow through the hole will be more or less constant. Also, there are two holes on the crank, [from memory], each perpendicular to the axis of the crank throw, therefore, the holes will only line up about 87 degress before and 87 degrees after TDC.

Simple laws of physics dictate that if you introduce a hole [or vent] into a pressurised area, you reduce the pressure within that area. It might slightly increase the flow, but it will reduce the pressure, as you are helping the pressure escape. If you make the LH bigger than the RH hole, you will reduce the pressure even further. As terry points out, other MC and car engines using plain bearings didnt have holes fitted and BSA engines dont need them either, apart from oiling the cylinder above. The BSA hole is so small to be insignificant.

Any fluid under pressure finds the easiest path to escape. Therefore oil being pumped into the crankshaft via the TS bush would escape by the easiest route before a more difficult route, this would lead to say 60% of the oil going out via the RH big end, and say 40% escaping via the LH big end. It is this imballance which caused starvation to the LH cylinder and piston. This is what BSA tried to correct by introducing the hole in the LH conrod.

I think its best to leave the set up as STD.

Sorry, I know most of that had been said before.