18 replies to this topic

[andyt]

Since rebuilding my 998 A+ engine i've put about 500 miles on it, it had the ball type pressure relief valve fitted by me when i rebuilt the engine thinking that it was better than the original bullet type. The engine has oil pressure on the gauge of 75 psi and this never really changed weather the engine was cold, hot, idling or reving over 2000rpm.

Having read many of the threads on the forum about the use of the ball type today i changed the oil and also switched back to the bullet and its original spring, now the pressure is 75 psi when idling and 95 psi when revving over 1500 rpm.

Have I done the right thing by changing as the pressure seams pretty high whilst driving now, should I change it back?

[mini13]

that does sound a bit odd, and definatly needs looking at.

 

did you change the spring when going from the ball tot he cup? as normaklly the ball gives more pressure.

 

also pull the cup and check for marks on the side,

[Cooperman]

Are the pressure quoted when the engine is hot or when initially started?

 

If it is 75 psi at start from cold, then that is not unusual. When running normally at working temperature the ideal pressures are in the region of 50 psi at 3000 rpm and 65 psi at 4000 rpm and above with a new engine. 90+ psi is fairly common with 20w50 oil and cold start. It normally soon falls back when fully warmed.

 

Run it in carefully, then see what you have when fully hot.

 

If it stays too high when fully warm fit a slightly weaker spring, but I doubt that will be necessary.

 

The plunger-type valve is much better than a ball-type.

[russo]

When changing from ball to bullet type relief valve, each one has its own spring as the ball is thicker than the inside if the bullet, so hence putting more tension on the spring resulting in a higher oil pressure.

[andyt]

The oil pressure with the ball and its own spring was 75 psi weather the engine was hot or cold and i had cut a coil off so that the spring was the same length as the original bullet one. The pressure with the bullet and its spring was with the engine still warm after the oil change and after a run off approximately 15 mins after it was changed , this was 75 psi at idle and 95 psi when revved at normal driving speeds.

The original bullet did have a few scores on it which I rubbed down with emery tape but not completely perfect would this make a difference or should I buy a new one.

[cal844]

The oil pressure with the ball and its own spring was 75 psi weather the engine was hot or cold and i had cut a coil off so that the spring was the same length as the original bullet one. The pressure with the bullet and its spring was with the engine still warm after the oil change and after a run off approximately 15 mins after it was changed , this was 75 psi at idle and 95 psi when revved at normal driving speeds.
The original bullet did have a few scores on it which I rubbed down with emery tape but not completely perfect would this make a difference or should I buy a new one.

Personally buy new

[tiger99]

Scoring on the parallel portion, if rubbed down so there are no raised areas which could cause sticking, is not going to do any harm. The thing that needs to be good is the conical seating.

 

Is there any way of checking with an independent pressure gauge, i.e. have you got, or can borrow, a different one? This could be a gauge problem, and your pressure may be within the normal range.

 

If the pressure is real, you just need a slightly shorter spring.

[Mervyn]

Sounds to me like a duff gauge

Merv

[gazza82]

The cut down spring might be too strong. Fit a new set especially if the old one is scored.

[Magneto]

What causes the scoring on the side of the bullet relief valve? Mine was scored deeply (just one gouge) so I bought a new one, but I was trying to work out exactly what had done the damage . I figure a small bit of grit did it, but it seems like this is a common issue?

[imack]

The scoring is caused by debris in the oil from the engine and gearbox which is unfiltered when it goes through the pump and oil pressure relief valve.
Years ago I constantly had standard oil pressure relief valves that stuck open resulting in low oil pressure at low engine speeds, used to 'clear' it by a 7000rpm blast. Admittedly in those days I was using worn out second hand £10 austin 1300 engines and boxes and sticking piper 285 cams in and modified heads but the boxes were usually a bit iffy.
I then replaced the thimble type valve with a ball bearing, I think from a cv joint as per vizards how to modify your mini, cut the spring down and made the relief valve adjustable.
I never had a problem with it sticking again.
30+ years later Ive still got the same mini thats had numerous engines since then but I'm still using that same ball bearing, spring and adjustable valve in my latest MED engine.

[nicklouse]

75 all the time with the ball shows a good pressure at all revs with the spring being correct to give 75psi. And your pressure is not dropping below 75 at any time.

But cutting a spring down for the thimble ? Should be correct as supplied. Unless you are talking about cutting down the one that came with the ball kit to use with the cup?

This could be the high pressure as the cut end would be full thickness not variable as they are new. So a little stronger.

[andyt]

The pressure has never dropped below 75psi with the ball and never got any higher either hot or cold. The spring that i'm using with the bullet is the original one that i took out before the rebuild.

[nicklouse]

So what is the cut down spring you say you are using?

[Spider]

Can we eliminate Mervyn's suggestion?

 

Sounds to me like a duff gauge

Merv

 

How reliable is the 75 PSI you are measuring?

 

Have you checked it with another gauge?

 

A 'flat 75 PSI hot or cold' doesn't make sense.