connecting rod spit hole

I noticed the JS Carrillo rods do not have a spit hole drilled in them. It seems I could blank off the hole by swapping the shell bearings and achieve a higher oil pressure to the rods and rockers.

Can't do that with the shells I have for the JS long rods. Even if you could it wouldn't accomplish anything.

Schwany said:

Can't do that with the shells I have for the JS long rods. Even if you could it wouldn't accomplish anything.

Click to expand...

I think he means the stock rods with bleed hole.

OK, that being the case, I definitely would not do it with a Norton alloy rod. That may just be me though. Understood on the location on the hole on a Norton rod. The JS rod reference threw me.

Those are bright and shiny rods.

Schwany said:

OK, that being the case, I definitely would not do it with a Norton alloy rod. That may just be me though. Understood on the location on the hole on a Norton rod. The JS rod reference threw me.

Those are bright and shiny rods.

Click to expand...

Fully detailed (no power tools or mops) and seem to remember I went with the RGM shells and AN > bolts. < Even if they were of poor dimensions compared to the OEM bolts)
(RGM bolts in the picture)

Time Warp said:

Fully detailed (no power tools or mops) and seem to remember I went with the RGM shells and AN > bolts. < Even if they were of poor dimensions compared to the OEM bolts)
(RGM bolts in the picture)

Click to expand...

Impressive handywork!! Lot of satisfaction doing that kind of thing without power tools. I thought about doing it, but stuck aftermarket rods in my one Norton. I don't have the Brit bike fever as bad as most of you guys do.

From what I've read the bleed holes in the rods were put there because early on the Norton twin had a bad piston design that was subject to siezure so the holes were installed as a solution but it didn't work. So they changed the piston design to solve the problem and never bothered to change the holes. There is plenty of oil sloshing around in the sump and oil bleeding from the sides of the rods at the journal as it is.

Note that Triumphs etc don't have the bleed hole - its useless.

I spoke to Pete Lovell about this, he said he’d looked into it over the years and couldn’t find any real reason / benefit for those bleed holes.

However, he also reckoned that blanking them off gave no real benefit either!

I’m currently running two Norton’s sans holes FWIW.

The rod is orbiting the journal or maybe the journal is rotating inside the rod big end, which suggests the oil hole in the journal is a little like a rotary valve as it passes the hole in the bearing. Its not like there would be a jet for the full 360 degree's if the oil film takes the path of least resistance.

Jim Comstock would know., he probably put a camera in there.
Last post 2022, last sign in, April 2024.

Just rummaged in the old bits tin and found three of the shells i replaced when i had the crank out of Mitzi

Notice the middle shell and the worn patch around the bleed hole. Its gone through the top layer and has exposed the copper/bronze underlayer. Can't remember if it came from the drive side rod or the timing side rod. Probably the drive side rod as the oil supply to that journal has to get across the crank to feed it. The new shells went in with them blocking off the bleed hole, never liked them as they bleed off high pressure oil from the oil wedge just when it is needed most.

dobba99 said:

as they bleed off high pressure oil from the oil wedge just when it is needed most

Click to expand...

In addition you need the max bearing surface area on the top shell as the downward force from the combustion is applied to the top shell so it needs all the help you can give it.

kommando said:

In addition you need the max bearing surface area on the top shell as the downward force from the combustion is applied to the top shell so it needs all the help you can give it.

Click to expand...

I had never thought of that

The reduction in bearing area is tiny, not to mention the journal oil hole does not line up with the bearing hole until the rod is close to right angles with the throw (around 3:00 / 9:00) maximum torque.

No offence meant and it might be the lighting, but those shells look well beyond their use by date and look older than Methuselah.
The scores look like debris in the oil so the oil clearance might have increased.

Surely being a 360-crank combined with centrifugal force oil will feed the equally positioned journal oil holes.

Time Warp said:

The reduction in bearing area is tiny

Click to expand...

When I worked for a shell bearing maker the development dept had a program where you entered all the parameters for the crank/cod rods/oil pump including oil holes and their position and it predicted the oil film thickness at different revs and degrees of rotation and consequently the predicted life of the bearings. They then gave advice back to the engineers including repositioning of oil holes. One customer was warned his oil hole position on the crank conrod journal compromised the oil film thickness and would shorten the life of the con rod bearing but he refused to move the oil hole as it was just a program on a PC. So the development team ran some tests in the lab using the proposed customer hole position and the development engineers position. The results showed a catastrophic failure on the customer hole position and normal behaviour with the revised position. Presented with the results the hole was moved.

After that I never looked at an oil hole being a tiny item ever again.

Oil film thickness is king.

Time Warp said:

The reduction in bearing area is tiny, not to mention the journal oil hole does not line up with the bearing hole until the rod is close to right angles with the throw (around 3:00 / 9:00) maximum torque.

No offence meant and it might be the lighting, but those shells look well beyond their use by date and look older than Methuselah.
The scores look like debris in the oil so the oil clearance might have increased.

Surely being a 360-crank combined with centrifugal force oil will feed the equally positioned journal oil holes.

Click to expand...

Its not the fact that the journal hole aligns itself with the bleed hole twice each revolution which it does. Its that it is constantly bleeding off high pressure oil all the time the crank is revolving.

kommando said:

When I worked for a shell bearing maker the development dept had a program where you entered all the parameters for the crank/cod rods/oil pump including oil holes and their position and it predicted the oil film thickness at different revs and degrees of rotation and consequently the predicted life of the bearings. They then gave advice back to the engine including repositioning of oil holes. One customer was warned his oil hole position on the crank conrod journal compromised the oil film thickness and would shorten the life of the con rod bearing but he refused to move the oil hole as it was just a program on a PC. So the development team ran some tests in the lab using the proposed customer hole position and the development engineers position. The results showed a catastrophic failure on the customer hole position and normal behaviour with the revised position. Presented with the results the hole was moved.

After that I never looked at an oil hole being a tiny item ever again.

Oil film thickness is king.

Click to expand...

Interesting and you would be the one to answer on the subject based on your background.
#
#
Are we talking about that one worn shell and when did a Commando have high oil pressure.
That could be ignition, it could be excess oil in that cylinder, it could be old age and dirty oil. (It does have evidence of that plain to see) even acid etch from sitting, maybe even excessive idling at low rpms, high mileage etc.
What was the oil pump like, what was the actual across the board oil pressure.
What is the history of the engine.
I am certainly no expert, but where is the actual evidence considering the over 50000 Commando's built and it's not like folk are changing bearings on a regular basis if ever on a lot of bikes.


Did someone do a pressure test (Comstock) with both open and closed rod bleed hole, not to mention Post #8 by Fast Eddie which seems to suggest no difference.
I forget how I installed the RGM shells, probably in the aligned position but won't lose any sleep over it.

Whatever Norton did or didn't do, seems to work. At 17,000 miles my MK3 ,when I had it rebored to +20, my machine shop told be after I could have just honed to and used standard pistons. But at 17K I figured it would need the work. After 2 cam failures in the bike and lots of wear on the lobes and the 2nd time the cam and lifters. The crank still looks fine. So what ever Norton did and for what reasons is fine with me. My race bikes run for 1000s of miles and my MK2a has seen astronomical revs and it has seen more abuse than is believable. The strength of my Norton Engines is what makes me love them. The MK3 type cams just need to be replaced with a WEB Cam, and it's worth the performance gains.

Time Warp said:

Interesting and you would be the one to answer on the subject based on your background.
#
#
Are we talking about that one worn shell and when did a Commando have high oil pressure.
That could be ignition, it could be excess oil in that cylinder, it could be old age and dirty oil. (It does have evidence of that plain to see) even acid etch from sitting, maybe even excessive idling at low rpms, high mileage etc.
What was the oil pump like, what was the actual across the board oil pressure.
What is the history of the engine.
I am certainly no expert, but where is the actual evidence considering the over 50000 Commando's built and it's not like folk are changing bearings on a regular basis if ever on a lot of bikes.


Did someone do a pressure test (Comstock) with both open and closed rod bleed hole, not to mention Post #8 by Fast Eddie which seems to suggest no difference.
I forget how I installed the RGM shells, probably in the aligned position but won't lose any sleep over it.

View attachment 116860

Click to expand...

Oil pressure measured by a oil pressure gauge and the oil film thickness are in some ways completely unconnected. Of course for good oil film thickness you need a good supply of oil, the oil pressure is a good proxy for that but does not tell you what is happening in the gap between journal and bearing. There is a dam of oil created inside this space and its thickness must never get to zero, what effects that dam are many and the measured oil pressure will not tell you wants going on with oil film thickness, only that oil is present. You can currently only measure oil film thickness in a lab.

There are not stories of Norton twin engines eating their shell bearing but that still does not mean you could not make improvements.

1. The driveside shell bearings and the oil rings etc wear out faster than the timing side. My thoughts on a possible cure would be to reduce the size of the hole in the crank journal on the timing side in an effort to equalise the oil flow out of both crank journals. Other cure would be to increase the flow rate of the oil pump to increase oil flow from both holes.

2. I use undrilled shells in both top and bottom positions.

3. Use an oil with the best oil film thickness capability, this will be a fully synthetic oil and one from the list already on the site.

4. For racing engines use the Trimetallic plated copper bronze shells, road can use the bimetallic aluminium/tin with no reduction in bearing life.

5. Fit a filter in the return line.

kommando said:

Oil pressure measured by a oil pressure gauge and the oil film thickness are in some ways completely unconnected.

Click to expand...

Very true.

If you have an oil pressure gauge on your Commando, you can see this in action. Hot day, idling at a red light and your gauge may show 0-6 psi but your engine does not self-destruct. It actually takes very little pressure to keep the oil flowing and the big-end shells lubed.

I first learned something about this with the water pressure to my house. When I first moved in, I complained to the water company that the pressure was too low. The tech showed me that the pressure at the street and at my kitchen sink was identical and just fine. He then had a look around and found the water filter I didn't know about. I changed the filter, and the "pressure" was then just fine - especially in the shower, it's about how much water moves, not the pressure.

I never fully understood the difference in pressure and flow until I got into sand blasting. A little "pancake" compressor that can produce 150psi is almost worthless for blasting because they can only supply about 2cfm (cubit feet per minute) of air. The more air that moves is the more media that moves. Minimum for decent sandblasting results is about 10cfm and any pressure over about 50psi just turns the media into powder.

Time Warp said:

Interesting and you would be the one to answer on the subject based on your background.
#
#
Are we talking about that one worn shell and when did a Commando have high oil pressure.
That could be ignition, it could be excess oil in that cylinder, it could be old age and dirty oil. (It does have evidence of that plain to see) even acid etch from sitting, maybe even excessive idling at low rpms, high mileage etc.
What was the oil pump like, what was the actual across the board oil pressure.
What is the history of the engine.
I am certainly no expert, but where is the actual evidence considering the over 50000 Commando's built and it's not like folk are changing bearings on a regular basis if ever on a lot of bikes.


Did someone do a pressure test (Comstock) with both open and closed rod bleed hole, not to mention Post #8 by Fast Eddie which seems to suggest no difference.
I forget how I installed the RGM shells, probably in the aligned position but won't lose any sleep over it.

Click to expand...

The reason those old shells look like they do is because they have been exposed to air after they were removed and the surface has corroded (think of a sheet of lead, scrape a new shiney surface on it, leave it for a few years, nearly ten in this case and then look at it, it won't be shiney then!)
Pressure fed plain bearings, or even oil ring fed plain bearings (oil at zero pressure entering the bearing) develop what is called the oil wedge, this wedge of oil is created by the revolving action of the shaft, drawing the oil around with it until the shaft is supported and held away from the bearing shell itself. This wedge pressure can get to very high levels.
I worked with steam turbines and the like for many years. The shafts on these machines have bearings that can weight more than a ton. The biggest ones i dealt with were pressure fed oil through 100mm diameter pipes at around 7 Bar pressure. As you can imagine each bearing had pressure gauges etc and was monitored with vibration detectors and the like. One of the daily checks was to see what the wedge pressure was on each bearing. This pressure was tapped off the bottom bearing (actually the jacking oil connection, I'll come to jacking oil later) It was quite usual to see the wedge pressure to be over a 100 Bar. So that is a gain in pressure of at least 93 Bar solely by the action of the shaft revolving and drawing the oil around it.
Jacking oil is what is used to enable the shaft to be turned when doing maintainance and when the shaft is on barring (really big stuff like this doesn't like being stationary, if the system is shut down, say when the steam boiler has a leak, the shaft has to be kept turning so it doesn't hog, bend in other words)
Measuring the oil wedge pressure in our Norton big ends is highly improbable (i won't say impossible, someone might prove me wrong!) but it is a lot greater than the oil pumps outlet pressure.
I'm with Kommando on the drive side big end wearing faster, but it is because of the large hole in the flywheel and the fact that the crank cheek faces are not sealed. You have a large void in the middle of the crank, you pump oil into this void and swing this void around at few thousand revs which increases its pressure, then expect the oil to climb up into the driveside crank cheek and lubricate the driveside big end.
When i stripped the crank there was evidence of the oil in the void leaking out between the crank cheeks and the flywheel, ergo the drive side journal has a worse oil supply than the timing side.
When i rebuilt the crank i blued and scraped the high spots off the crank cheeks and flywheel and after assembly used a thin wicking grade of loctite to help seal the void.