04-01-2020, 01:13 PM
I've only ever had 'spit and hope' engines and pretty much all of them have had over-bored standard oil pumps. Mostly done for me by Dave Dye; I've lost count of how many he's done for me. When warm, pressure at idle is normally around 5 - 6 psi, running it varies with revs, obviously, but around 15 psi at 5000rpm. The only exception to this was the engine in my Trials Car when first built in 2012. The pressure gauge is one that goes up to 60 psi (because I happened to have it available) and that never read less than 30 psi when running and 40 psi when revved. Same set up as normal and all a bit of a mystery. I recall putting a post about it on the old Friends Forum. The engine was run in as normal and its first event was the 2012 Welsh Trial. We did the 100 miles with no problem and our first two hills were at Smatcher. Cleaned both using 'plenty' of revs but when we set off for our next hills, a rattling noise indicated a failed big end.
Investigation proved that the oil jets had been home made by a previous owner of the crankcase and instead of a straight drilling, had been made to a venturi profile, internally, effectively restricting the flow through them and increasing the gauge pressure. The conclusion was that the pressure through the jets was too high causing the oil to 'bounce' at high revs when it hit the crank troughs rather than go where it was needed. A re-metalled big end and a pair of new oil jets solved the problem, the pressure on the gauge went back to normal, and in the subsequent 7 years it's been fine despite being revved to death many, many, times.
My point in all this that pressure isn't everything in a 'spit and hope' engine and, in excess, can be detrimental.
Steve
Investigation proved that the oil jets had been home made by a previous owner of the crankcase and instead of a straight drilling, had been made to a venturi profile, internally, effectively restricting the flow through them and increasing the gauge pressure. The conclusion was that the pressure through the jets was too high causing the oil to 'bounce' at high revs when it hit the crank troughs rather than go where it was needed. A re-metalled big end and a pair of new oil jets solved the problem, the pressure on the gauge went back to normal, and in the subsequent 7 years it's been fine despite being revved to death many, many, times.
My point in all this that pressure isn't everything in a 'spit and hope' engine and, in excess, can be detrimental.
Steve