Oil pressure

[seattle##gs]

New motor. Old pump. I turned the rod bearings around so they blank off the spit hole in the rods. When cold the OP is at least 60. I rode it approx 2 miles and it settled down to 40. I realize the motor is not at operating temp yet but this is pretty good.

 

[DennisMo]

I am curious why you would cover up the spit hole.
I would think that the oil that goes up has two functions.
Firstly to work its way to lubricate and secondly to cool the pistons

 

[seattle##gs]

I was told the spit hole has no more function. It was used to solve an inferior piston design. I covered the hole to increase oil pressure to the rods and lifters and cam.

 

[robs ss]

I was told the spit hole has no more function. It was used to solve an inferior piston design. I covered the hole to increase oil pressure to the rods and lifters and cam.

The important lubrication to the cam is not pressure-fed. It is dribble-fed by oil returning from the head via the pair of chamfers on the front of the lifters. it dribbles onto the backward rotating lobes and into the contact patch of the lifter.
It goes without saying that the lifters are not pressure-fed.

 

[kommando]

The spit hole is at the wrong place, the bearings most heavily loaded position is exactly where the spit hole is.

 

[Andy Higham]

Was the spit hole for the same reason as BSA added spit hole? Piston failure due to timing scatter from the Lucas ATU ?

 

[SteveA]

JSM/Carrillo Norton rods don't have the hole.

Most modern race Norton motors have JSM/Carrillo rods.

Blanking the hole is not an issue.

But, when will you guys understand, oil flow is more important than oil pressure.....

Installing a new pump is worth more than blanking holes.

 

[kommando]

And oil film thickness in the bearing is the most important of all. Measuring oil pressure is a proxy measurement ie not a direct measure of oil film thickness, you assume good oil pressure gives good oil flow and consequently good oil film thickness. That's a lot of steps away from knowing what really matters is in its good zone.

 

[seattle##gs]

It seems to me that fresh oil gives the best oil film thickness and blocking the spit hole could only be a good thing though not mandatory. It did not wildly increase the pressure so what's the harm. It seems that the spit hole is an unnecessary bleed-off of oil.

 

[MexicoMike]

One night, during a serious bout with a bottle of rum I thought, "Tomorrow, for the first time I should check the oil pressure on my '73 Norton Commando." Fortunately, the next day I was sober and I've never been that drunk since.

 

[Fast Eddie]

I discussed the holes with Pete Lovell and even he didn’t have a preference, saying there seems good and bad reasons for both options !

Here’s my conclusion…

The flow via the big ends will be (within reason) the same with or without the holes as it is dictated largely by the pump.

Without holes, the oil will be forced to exit out of the sides of the big ends and be flung all around the crank cases.

This oil fling will do a good job of cooling the engine and lubricating everything in there.

If the flow remains close to the same, but with the holes blocked, it stands to reason that the pressure will be higher.

I therefore run without the holes in both my engines.

 

[Andy Higham]

As a slight but relevant diversion, some engine tuners spend nearly as long on "porting" the oilways as the cylinder head.
One VW aircooled tuner reckons he can increase oil pressure by 10-15% by flowing the oilways

 

[Grandad]

^^^ just curious ... any more info on these works done on VW engines ??

I'd have imagined that with less restriction in the oilways the oil pressure would be ultimately be less as the oil would be able to reach its exit point more easily - more flow and less pressure -

 

[Madnorton]

Many run with rods around the wrong way, holes blocked off or non-existent and all seem to run well. Increasing the oil pressure is pretty pointless once you get above certain pressure as the bearings will just utilise what they are being fed. 8-10psi / 1000rpm would be a good place to start. Not sure how flowing the oilways increases pressure, smooth oilways would improve flow characteristic but not pressure, if anything the more easy the flow the less pressure for a given pump output.

 

[Schwany]

I never tried blocking the oil holes when using stock rods, but my oil pressure numbers are exactly the same with the JSM rods and the same old oil pump. Might depend a little on where the oil pressure is being measured as well.

I port the dribble holes in the valve spring pockets to theoretically get more dribble oil on the cam and tappets sooner. Gotta be good for at least .00025HP.

Intake side example

Pre-Commando head. Also fill the pocket between the two valve spring pockets on the older head with epoxy. The epoxy has not broken apart and caused a doom and gloom disaster.

I have a Commando head I've done the same to with this one added modification.

 

[Grandad]

I can see the benefits of non pressure fed ( drainage ) flows - not thought of that aspect - any attempt to " focus " flow directly onto cams etc has to be good.

Like the pink " bum " ... Lol !!

 

[Andy Higham]

^^^ just curious ... any more info on these works done on VW engines ??

I'd have imagined that with less restriction in the oilways the oil pressure would be ultimately be less as the oil would be able to reach its exit point more easily - more flow and less pressure -

The idea is that the oil can flow along the oilways, and build up pressure against the shells. With restrictive oilways, the pressure can be higher at the pump / oprv than at the shells

 

[Torontonian]

Flip the shells over nowadays .

 

[SteveA]

................Not sure how flowing the oilways increases pressure, smooth oilways would improve flow characteristic but not pressure, if anything the more easy the flow the less pressure for a given pump output.

I'm sure it doesn't increase pressure, I think it does increase flow. I have done a little work around the oil feed to the pump on the basis inflow is good. That won't affect pressure either.

Some of my understanding on pressure and flow goes back to the '80s when I was involved with a software simulation model of an aircraft hydraulic system. We had long debates with aircraft systems designers and users (pilots!) about the effects seen on system gauges when different pumps and valves were operated! Somehow these people never see the same thing! Sometimes they wanted to force our model to do what they 'thought' they saw. And often we were able to prove they were wrong! And sometimes we were able to identify that they had given us bad data, for example the length of a hydraulic pipe installation was different to the designed pipe length!

I'm past even thinking about fluid dynamics, but generally, if you increase flow, say by opening a valve, you reduce pressure.

 

[Madnorton]

I'm sure it doesn't increase pressure, I think it does increase flow. I have done a little work around the oil feed to the pump on the basis inflow is good. That won't affect pressure either.

Some of my understanding on pressure and flow goes back to the '80s when I was involved with a software simulation model of an aircraft hydraulic system. We had long debates with aircraft systems designers and users (pilots!) about the effects seen on system gauges when different pumps and valves were operated! Somehow these people never see the same thing! Sometimes they wanted to force our model to do what they 'thought' they saw. And often we were able to prove they were wrong! And sometimes we were able to identify that they had given us bad data, for example the length of a hydraulic pipe installation was different to the designed pipe length!

I'm past even thinking about fluid dynamics, but generally, if you increase flow, say by opening a valve, you reduce pressure.

Yep, resistance increases pressure, otherwise a hydraulic system would not need a PRV or sensors to start/stop the pump - shut all the valves on a hydraulic systema and see what happens. If the pump is of adequate spec then it makes no difference as to what the wall of the oilway is finished like as the resistance given by the bearing shells can be considered a constant. Providing the pump is suitable for the system it makes no difference if the oilways are smooth or not smooth. I would predict only a marginal difference with smooth oilways as it may lead to the system draining quicker in the event of a system failure where the pump could not maintain pressure.
I once had BAE boffins tell me and my bosses I was wrong on something I recorded on a UV recorder on a submarine - the UV trace did not lie. Their theory saying I was wrong only worked in one perfect scenario which would be impossible to obtain. Their biggest brains arrived to watch me face plant due to the huge cost of testing my theory, the submarine sailed for a few and the condition was replicated to their amazement. This lead to changes in software of the system they designed.
Many years working on sea water systems, hydraulics, pneumatics and fluidic control panels, hydraulics I liked, HP air not so much.