Temperature differential, left cylinder to right cylinder.

kommando · 2026-08-01T08:41:58-0600

Fast Eddie said:
I understand pressure loss along a pipe as a concept (Box’s formula IIRC).

But in this case, the ID of the pipe (ie the central chamber) and the close proximity of the relevant holes, would mean an almost incalculable loss between the first and second hole I imagine.

We also have the added complexity of centrifugal force acting on the oil. Which, assuming neither hole is starved, would surely be equal on both holes?

I assume not, just because the friction losses are so very low does not negate the flow being lower on the drive side as the timing side has had its share already. That's why you need to model the whole system, its very complex and the hole position around the journal also comes into play. When one engine customer was presented with a model output that told him the crank big end journal hole was in the wrong position he ignored the recommendation, then the test engines started failing from worn big ends and he changed his tune. As you say the centrifugal also comes into play which we know will keep oil going to the big ends and produce an oil film even with the crank end seal gone as long as the crank end hole is flooded with oil so no air can get in.

Fast Eddie · 2026-08-01T08:43:57-0600

kommando said:
I assume not, just because the friction losses are so very low does not negate the flow being lower on the drive side as the timing side has had its share already. That's why you need to model the whole system, its very complex and the hole position around the journal also comes into play. When one engine customer was presented with a model output that told him the crank big end journal hole was in the wrong position he ignored the recommendation, then the test engines started failing from worn big ends and he changed his tune. As you say the centrifugal also comes into play which we know will keep oil going to the big ends and produce an oil film even with the crank end seal gone as long as the crank end hole is flooded with oil so no air can get in.

I think we see it differently.

So long as the pump can provide greater flow than both holes draw, and if there’s no loss between the two holes, I cannot see why the second hole would have either less flow or pressure.

I actually want you, or anyone, to tell me why I’m wrong, then we’d have an answer !

Skoti · 2026-08-01T09:49:31-0600

Maybe the oil return flow from the head through the barrel drilling on the right hand side aids cooling a little?

kommando · 2026-08-01T09:51:42-0600

Fast Eddie said:
So long as the pump can provide greater flow than both holes draw, and if there’s no loss between the two holes

But we don't know that and if you look at modern practice the oil pumps are gerotor type and are provide much greater volumes of oil per engine rpm. End of the day the definitive answer would come from a computer model of the crank, oil pump, OPRV profile, hole sizes. 15 years ago I could have asked for a couple of runs to see what it showed but that ship has sailed. Over the full 1000 to 7000 rpm range the answer would be different at different rpms.

Fast Eddie · 2026-08-01T10:04:15-0600

kommando said:
But we don't know that and if you look at modern practice the oil pumps are gerotor type and are provide much greater volumes of oil per engine rpm. End of the day the definitive answer would come from a computer model of the crank, oil pump, OPRV profile, hole sizes. 15 years ago I could have asked for a couple of runs to see what it showed but that ship has sailed. Over the full 1000 to 7000 rpm range the answer would be different at different rpms.

We don’t know that the Norton oil pump feeds more than the big end holes (wrapped in shells) take?

Fairy nuff. If that’s the case we got bigger problems !

kommando · 2026-08-01T10:34:21-0600

When problem solving and looking for a solution you assume nothing.

marinatlas · 2026-08-01T10:56:43-0600

SteveA said:
Yes, Copper head gasket. A 21 thou one from JSM. Same as I used with the iron barrels.

Definitely going to richen a little on the needle.

Hi Steve , about richen by the needle , I think you have the Victory book about Mikuni tuning where it is said you can add a 0.020 washer under the E-clip and thus making half a change (one notch is 1mm, one shim is only 0.5mm ) said also it should 0.25 OD , so a std 2 mm washer will do the trick with OD 5.5mm , Pierre

SteveA · 2026-08-01T10:58:46-0600

Triton Thrasher said:
If you’re raising the needle on the hotter side, you may well find that one notch is too big a change.

That is why I said put a spacer under the clip, half a notch. Also remember Mikunis have 5 slots on the needle, not the 3 that Amal uses..

SteveA · 2026-08-01T11:03:17-0600

velo54 said:
I'd swap sensors and gauges. Ignition timing probably has 2 separate pickup magnets, 180 degrees apart on the cam, so the timing from one cylinder compared to other on compression may be slightly different. Try swapping carbs left to right before changing mixture. Graham

You may need to study in more detail how those two coils work,
they are a single input trigger single to the electronics box. Both plugs fire every cycle.

SteveA · 2026-08-01T11:06:21-0600

Skoti said:
Maybe the oil return flow from the head through the barrel drilling on the right hand side aids cooling a little?

It might a little, though honestly I doubt it. In any case it would be a stretch for that to lower under plug cylinder head temp by 20C!

SteveA · 2026-08-01T11:16:32-0600

Fast Eddie said:
I think we see it differently.

So long as the pump can provide greater flow than both holes draw, and if there’s no loss between the two holes, I cannot see why the second hole would have either less flow or pressure.

I actually want you, or anyone, to tell me why I’m wrong, then we’d have an answer !

We might have to go back to flow and pressure. I agree you have to model it all, fluid dynamics don't always work as expected until you do.

Simplistically, my thoughts are that oil that has flowed out of the right big end doesn't get to flow out of the left big end! Centrifuge effect must be beneficial, but we would need to understand the dynamics of the oil inside the crank. It's coming in at an angle out of a small hole and it needs to fill the whole chamber before either pressure or centrifuge makes it flow out of the big end journals!

Model it!

Carl H · 2026-08-01T11:54:18-0600

Also, the head casting itself and finning on the head and variations in thicknesses as well as air flow to and around the head and cylinder could make a difference. Even valve seating and exhaust port shapes and exhaust pipe contact and carbon on the head and piston tops as well as on the exhaust ports, Which would be the source of a lot of the heat. A slight difference between compression ratio between the cylinders and other things involved with combustion. But the carbs are something that can be done to make a matched pair and a good way to improve performance and laps times.

kommando said:
When problem solving and looking for a solution you assume nothing.

With throwing in centrifugal affects; Does that mean the sludge trap or inner portion of the hollow crank doesn't stay totally filled and can be starved? ( When running the oil would thrown outwards) Or if a certain amount of air is always trapped that can vary. No matter what. I know the cranks drain down oil more or less amounts depending on the crank's position when stopped and how long and is replenished when started. Personally, I think there is always some air in the hollow center. It is kinda like air in the top of a soda bottle with nowhere to go. I have never had to regrind a crank or had excessive engine wear, so all systems seem to be working in semi- perfect harmony as is. Luckily.

kommando · 2026-08-01T12:20:52-0600

Carl H said:
With throwing in centrifugal affects; Does that mean the sludge trap or inner portion of the hollow crank doesn't stay totally filled and can be starved? ( When running the oil would thrown outwards) Or if a certain amount of air is always trapped that can vary. No matter what. I know the cranks drain down oil more or less amounts depending on the crank's position when stopped and how long and is replenished when started. Personally, I think there is always some air in the hollow center. It is kinda like air in the top of a soda bottle with nowhere to go. I have never had to regrind a crank or had excessive engine wear, so all systems seem to be working in semi- perfect harmony as is. Luckily.

My lathe only goes to 2000rpm and I am not about to spin a crank while feeding it oil to find out

. What you get as the oil thins out as the engine gets to temp and the clearances all grow as the parts expand is a drop in oil pressure. Norton use to advise owners not to fit an oil gauge as they knew the pressure would drop and with the old oils back in the day drop to zero under certain conditions. That could be a signal the flow of oil out of the pump was barely enough to match the oil exiting the crank so no pressure was seen but there was still flow. Oil film thickness between the bearing and the journal is the critical factor in bearing wear, this cannot be measured except in a lab so instead oil pressure is measured and its assumed if there is pressure there is flow enough to create good oil film thickness. That is why I run a 10/16W fully synthetic oil, oil filter and have no oil pressure gauge, that oil has the best chance of keeping a good oil film thickness even under marginal conditions.

This is the best resource for engine longevity.

Best Oils For the Norton Commando Oil Tests | Access Norton

Norton Commando oil tests by Jim Comstock with oil rankings, load capacity, total heat from friction, test graphs, raw data and comments.

www.accessnorton.com

For load factor read oil film thickness durability.

SteveA · 2026-08-01T14:03:08-0600

kommando said:
.........That is why I run a 10/16W fully synthetic oil, oil filter and have no oil pressure gauge, that oil has the best chance of keeping a good oil film thickness even under marginal conditions.

This is the best resource for engine longevity.

Best Oils For the Norton Commando Oil Tests | Access Norton

Norton Commando oil tests by Jim Comstock with oil rankings, load capacity, total heat from friction, test graphs, raw data and comments.

www.accessnorton.com

For load factor read oil film thickness durability.

I'll bet you don't! 10W60 maybe. I use Belray V Twin Fully Synthetic, which is a 10W50. It is the oil I can buy where I am located that is available and almost affordable here in France. I actually get it from a supplier in Germany. If I could get it I would use Royal Purple. Another oil I use in another bike with roller bottom end is Motul 7100 20W50 4T MA2, Unsurprisingly Motul is easy to get in France. Bruno Perlinski is an advocate of their 300V Competition oil.

Does it say anything in that thread about differential temperatures?

If I recall, the main tests themselves were not conducted in a suitably instrumented motor. Maybe I should take a look, but hell, its long!

Carl H · 2026-08-01T14:21:52-0600

kommando said:
My lathe only goes to 2000rpm and I am not about to spin a crank while feeding it oil to find out . What you get as the oil thins out as the engine gets to temp and the clearances all grow as the parts expand is a drop in oil pressure. Norton use to advise owners not to fit an oil gauge as they knew the pressure would drop and with the old oils back in the day drop to zero under certain conditions. That could be a signal the flow of oil out of the pump was barely enough to match the oil exiting the crank so no pressure was seen but there was still flow. Oil film thickness between the bearing and the journal is the critical factor in bearing wear, this cannot be measured except in a lab so instead oil pressure is measured and its assumed if there is pressure there is flow enough to create good oil film thickness. That is why I run a 10/16W fully synthetic oil, oil filter and have no oil pressure gauge, that oil has the best chance of keeping a good oil film thickness even under marginal conditions.

This is the best resource for engine longevity.

Best Oils For the Norton Commando Oil Tests | Access Norton

Norton Commando oil tests by Jim Comstock with oil rankings, load capacity, total heat from friction, test graphs, raw data and comments.

www.accessnorton.com

For load factor read oil film thickness durability.

I did try to make a simulated sludge trap and spin it in my lathe, but it was hard to pump the oil can fast enough to supply oil. But it was a try. Some of the things said years ago, I don't buy into as I haven't experienced 0 pressure or anywhere close to it. And I didn't get to see and tear down the Norton bikes that were going to 0. So to me it just folk lore. Kevin Cameron in one of his tech talks/ articles mentioned air going to the Babbit bearings is very bad as it blasts off the oil film.

A 1968 Commando that I ended up owning was a rolling basket case. when I rebuild the engine, I found it had no spring in the blow off valve, but the rods and crank looked ok and is still in the bike, But later on I found the ID's of the rocker arms were really rough as well as the shafts, so it showed the lack of pressure up top.

I can see how the Combat breather system can really inject debris in the oil and contaminate the whole oil system IF lots of unfiltered oil is being returned via the breather and the engine is shedding metal and aluminum and then kinda self-destructs. But under normal use I've never had problems with the Combat type bikes or pressure.

My experiences racing Nortons is quite different than the Nortons that were running in New England and came from elsewhere. We held the winning hand in many races, of course having some of the greatest racers in North America didn't hurt. But a great rider just needs a good bike and the magic happens. And my bikes filled their need for speed, reliably.

SteveA · 2026-08-01T14:32:53-0600

marinatlas said:
Hi Steve , about richen by the needle , I think you have the Victory book about Mikuni tuning where it is said you can add a 0.020 washer under the E-clip and thus making half a change (one notch is 1mm, one shim is only 0.5mm ) said also it should 0.25 OD , so a std 2 mm washer will do the trick with OD 5.5mm , Pierre

Yes, thanks, i have the manual, and some washers I bought years ago just for this job, just need to use them! Hope you are keeping well.

SteveA · 2026-08-01T14:41:28-0600

Carl H said:
I did try to make a simulated sludge trap and spin it in my lathe, but it was hard to pump the oil can fast enough to supply oil. But it was a try. Some of the things said years ago, I don't buy into as I haven't experienced 0 pressure or anywhere close to it. And I didn't get to see and tear down the Norton bikes that were going to 0. So to me it just folk lore. Kevin Cameron in one of his tech talks/ articles mentioned air going to the Babbit bearings is very bad as it blasts off the oil film.

A 1968 Commando that I ended up owning was a rolling basket case. when I rebuild the engine, I found it had no spring in the blow off valve, but the rods and crank looked ok and is still in the bike, But later on I found the ID's of the rocker arms were really rough as well as the shafts, so it showed the lack of pressure up top.

I can see how the Combat breather system can really inject debris in the oil and contaminate the whole oil system IF lots of unfiltered oil is being returned via the breather and the engine is shedding metal and aluminum and then kinda self-destructs. But under normal use I've never had problems with the Combat type bikes or pressure.

My experiences racing Nortons is quite different than the Nortons that were running in New England and came from elsewhere. We held the winning hand in many races, of course having some of the greatest racers in North America didn't hurt. But a great rider just needs a good bike and the magic happens. And my bikes filled their need for speed, reliably.

The zero pressure 'story' relates to Peter Williams and the IoM TT 'mountain mile' run at 7000rpm, and probably not the first lap, so that 1970s mineral oil would have been pretty much on it's last legs, so I doubt many of us could totally replicate the experiment. For my part, I use a pressure gauge as a test on initial start up of a rebuild, and then remove the gauge and put it back in my workshop. Of course it tells me nothing about what is getting to the left side of the crank!

We should also not that the works Norton team replaced the Norton pump with a high capacity external pump. Maybe Norman White could tell us if the left still ran hotter?

Temperature differential, left cylinder to right cylinder.

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