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Dexta Oil pressure relief valve

PostPosted: Sun May 27, 2018 3:44 pm
by Nick
Hi guys, I have finally got round to looking at my dexta's extremely high oil pressure (80psi on crank speed).

For those of you who don't know : The engine has been completely re-built (about two years ago) and whilst examining the original oil pump, I found some cracks around the top two fixing holes, so I ordered a new pump (from the land of nearly right :curse: :curse: ). I fitted the new pump and the engine ran very nicely but it has very high oil pressure, I guess with everything being new and tight as it should be with a newly built engine. However I had read that the relief valve should be set to 60 psi, so naturally I assumed the new oil pump was faulty so I had another sent out free of charge.

Two years later I have finally got round to replacing the pump, so I have taken it out, and before putting the other new one in I wanted to check that it would work. So I have taken all three relief valve assemblies apart and found that the plunger in the old original pump is 1.6mm shorter than the newer ones, plus the spring in the old original pump is a coil shorter than the newer ones and the old spring is not as tough to compress as the newer ones.

So obviously the reason my oil pressure is high is because the plunger is longer on the newer one and therefore it takes more pressure to let oil by, plus the spring is tougher to compress and takes even more pressure to let oil by.

Do I put the old relief valve assembly in a new pump?
Do I shorten a new plunger and try that?
Has anyone ever come accross this before?
And why don't things made these days work properly, it really annoys me! Surely they should be tested before being sent out and sold?! :curse: :curse:

Re: Dexta Oil pressure relief valve

PostPosted: Sun May 27, 2018 3:46 pm
by Nick
Oh yeah forgot to say, I am going to rig up some sort of pressure tester before I put anything back in the tractor, what would anyone suggest I set the relief valve to?

Re: Dexta Oil pressure relief valve

PostPosted: Mon May 28, 2018 8:25 pm
by Nick
Well, I rigged up a test station today, just by turning the pump over by hand I had 80 psi - not good!

I ended up cutting a spring to make it shorter (guessed how much) and ended up with the pump relief valve tripping at around 50 psi, which I am quite happy with!