Oil pressure

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seattle##gs

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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.
 
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
 
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.
 
seattle##gs said:
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.
Click to expand...
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.
 
Last edited:
Was the spit hole for the same reason as BSA added spit hole? Piston failure due to timing scatter from the Lucas ATU ?
 
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.
 
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.
 
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.
 
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.
 
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
 
^^^ 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 -
 
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.
 
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 oil old 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
Oil pressure

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 he same to with this one added modification.
Oil pressure
 
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 !!
 
Grandad said:
^^^ 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 -
Click to expand...
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
 

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