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MG Midget and Sprite Technical - Midget 1500 - coldstart oil pressure

I've recently (sept 2008) done an overhaul of the engine of my midget 1500 of 1978 (new bearings,pistons,cilinderhead....)
I also added a 10row oil cooler , since I had cooling problems when cruising at 60Mph

Now I have a problem with the oil pressure built-up during coldstart : during 10 seconds the engine produces a metal/rattling sound before I reach the optimal oil pressure of 42 PSI.
As soon as oil pressure is 42 PSI, the sound is gone.

I use an anti-drainback oilfilter so this can't be the problem.
* Could it be the oil cooler, since the oil pump has
to fill the complete oil cooler when starting cold.
* has it something to do with the oil pressure-
relieve valve ? Needs this also be adjusted ?

I don't have this problem if the engine is warm.

Can someone please help me since I'm afraid I will ruin my new bearings after a while....
Gerrit

When we had a Spit, we'd turn the engine over with the choke in so the engine woudl not start, until the oil pressure light went out. This would allow it to start with no rattle...


A
Anthony Cutler

If you run an oil cooler on the Triumph 4-pot then you need to fit an uprated oil pressure release valve spring (or shim the plunger).

Springs are available from Rimmer Brothers or Moss.
Deborah Evans

Hi again, Gerrit! Great to see you on the BBS!

Just my opinion here, but I'm surprised you're getting ANY rattle on startup. Seems to me that with a fresh rebuild, you shouldn't be hearing noises like that. My engine's done over 85K, and I get no rattle whatsoever.

Deborah's advice sounds reasonable. I don't use an oil cooler on my 1500, so I can't comment knowledgeably.

-:G:-
Gryf Ketcherside

Gerrit, sound like your oil system is a similar spec to mine. As long as I drive the car daily it is fine but I get the Triumph "death rattle" if I start the car after its been sitting around for a few days.

Anthony did what I usually do. Turn it over a bit first before trying to start. That way it primes the oil pump nicely.

Also, the advice for fitting a better pressure valve spring is sound as this will make sure it come up to pressure quicker. I got mine from Moss for a few pennies so a good investment!

Even when hot I get an oil pressure around 15-20psi at tickover and a maximum of about 60psi at 3000rpm+.
Bob T

Hi mg friends,

I've some update on my oil pressure issues...

apparently it has indeed something to do with the oil pressure relieve valve !

I disassembled this valve and saw nothing unusual. Then I thought, mmm perhaps the spring is worn and thus lost some strength during the years.
So I decided to try something and added an extra washer to have more stiffness of the spring.

Guess what : my oil pressure went from 40psi (idle) to 60psi, and from 60psi (cruising) to 74psi :-)
I can also suspect that when coldstarting and the valve doesn't close tight, the oil will drainback into the sump after shutting the engine.

I will immediately purchase a new valve (uprated valve) since when placing an oil cooler this valve needs to have more strength, stiffness to achieve
good oil pressures. (Thanks Deborah for your advice !)

Thank you all for helping me with this rather difficult diagnose :-)

Cheers
Gerrit

>>> Even when hot I get an oil pressure around 15-20psi at tickover and a maximum of about 60psi at 3000rpm+. <<<

Those are the numbers I see on my basically stock 1500, which to my knowledge has never been rebuilt.

>>> I can also suspect that when coldstarting and the valve doesn't close tight, the oil will drainback into the sump after shutting the engine. <<<

As far as I know, the pressure relief valve doesn't have anything to do with oil drainback, which is controlled (hopefully) by a rubber membrane behind the inlet holes in the base of the oil filter.

-:G:-
Gryf Ketcherside

Another problem arose yesterday : oil gauge is not displaying the correct oil pressure. When tampering on the oil gauge by touching the connection pipe, the gauge displaced for about 15 PSI downwards !
So I immediately replaced the oil gauge by a new one.

Now I can read : 40 PSI at idle and 60 PSI at 3000rpm
remark : I'm using 20W50 oil and an additive (Lucas Heavy Duty Oil Stabilizer )

But I'm almost sure that the oil pressure relief valve is causing all these problems. I noticed wear on the spring and piston of this valve.

Griff, I was told that oil drains back to the sump via this oil pressure relief valve in case of too much pressure....
remark : the oil pressure relief valve is situated just under my oil filter...
DJ Overall

This thread was discussed between 12/12/2008 and 16/12/2008

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