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Dodgy Oil Pressure


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#1 fortythree

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Posted 21 June 2020 - 10:30 AM

Hi.

I'm having some oil pressure problems with my SPI (93, 1275). It's not injection related so I'm posting this in the general forum - hope that's OK.

 

So, here are the symptoms:

The oil light comes on every now and then. Only at idle and it seems that it is only when the engine has warmed up a bit (doesn't have to be hot, but the light doesn't seem to come on after a cold start). I have the original (7-10psi) oil switch and the pressure release valve is the non-adjustable spring and cap type. I hooked up an oil pressure gauge and the pressure seems to creep up very slowly on start-up. it will then sit at about 20-25psi if the engine isn't revved. A decent bit of gas (~3000rpm) and the pressure shots up and hovers around 50-70psi. It isn't all over the place, but it does go up and down a bit - there don't seem to be any sharp jumps in pressure, but that may be the gauge. After revving it sit's at 50-70psi for a while, even at idle. After about a minute of idling the pressure slowly drops until the light goes on (0-5psi!!), a quick rev and it shoots back up and stays high until it's been idling for while. The cycle continues...

 

My thoughts:

I thought the release valve may be sticking open. I pulled it out and it has some serious gouges in it (I recently rebuilt the gearbox and the amount of loose metal in there was unreal - there was even a munched up needle bearing cage attached to the sump plug). I am a bit concerned about this but confident that I won't see this again if I replace it. I cleaned it up a bit but couldn't get a good look into the recess to see if the guide in the block has been chewed as well. Cleaning off the burrs didn't make a difference, my next step would be to replace it with a ball and spring type valve and to make sure the guide is smooth.

I am also wondering if the oil pump is on the way out. I don't think so as the pressure is good most of the time. I can't imagine how the pump could cause this sort of problem - but I'm open to an education :)

If it is the pump I think I'll have a breakdown - I just got the gearbox rebuilt and the motor back in! I didn't bother to look at anything attached to the block as it 'was running really well'! Live and learn I guess.

 

This problem is new since the gearbox rebuild. The only change that I think could affect the pressure would be the central oil pickup I installed.

Any thoughts/ideas or even better solutions? 



#2 nicklouse

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Posted 21 June 2020 - 10:42 AM

Sounds like the typical worn out engine. Pull it and measure and remedy the mains and Big ends. And replace the oil pump. I would also have the oil ways cleaned out as you will have crud in them.



#3 fortythree

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Posted 21 June 2020 - 10:50 AM

Thanks - but not really what I wanted to hear  >_<

Can you help me understand what is going on? If the bearings/pump were on their way out surely the pressure would always be a bit ****. Also, wouldn't the pressure tank pretty much as soon as it gets back to idle?



#4 fortythree

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Posted 21 June 2020 - 11:19 AM

I forgot to say that when revving to about 3000rpm (after start-up with oil pressure at about 20psi) the pressure doesn't really change for a couple of seconds and then shoots up to 60-70psi. After that, as mentioned, it levels out at somewhere between 50-70psi. The time it takes seems to be longer than it would take for the pressure to build up.



#5 cal844

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Posted 21 June 2020 - 11:26 AM

I'd replace the oil pressure relief valve and also the pressure switch first.

Although it does sound like you need to remove the motor and inspect it all, also the gearbox to see what bearing cage has failed

#6 nicklouse

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Posted 21 June 2020 - 11:39 AM

I forgot to say that when revving to about 3000rpm (after start-up with oil pressure at about 20psi) the pressure doesn't really change for a couple of seconds and then shoots up to 60-70psi. After that, as mentioned, it levels out at somewhere between 50-70psi. The time it takes seems to be longer than it would take for the pressure to build up.

that does sound more like a valve issue.



#7 fortythree

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Posted 21 June 2020 - 11:44 AM

Thanks. I'll replace the valve and see if it solves the problem. I need to make sure the guide is still good as well otherwise it may just chew up the new ball bearing steel ball.

 

I have completely rebuilt the gearbox so that's all good now. The PO had made a bit of a hash of it and there was a lot to be done. With all the waiting for parts and then discovering I needed more parts and then waiting for those parts... by the time I had the gearbox, wire harness, clutch etc. done I just ignored the block and went with the old: it was running fine, it'll be fine, I'm sure everything will be fine... Beginning to regret that now.

 

Definitely won't be removing the motor until after summer. Pressure is good when it's running and idling at the lights for a minute or so is OK. Just need to avoid traffic jams or kill the motor stopped for too long. Basically, a complete rebuild in winter is still cheaper than a divorce ;)


Edited by fortythree, 21 June 2020 - 11:52 AM.


#8 nicklouse

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Posted 21 June 2020 - 11:47 AM

Thanks. I'll replace the valve and see if it solves the problem. I need to make sure the guide is still good as well otherwise it may just chew up the new ball bearing.

 

hang on. Valve or ball bearing? which?



#9 fortythree

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Posted 21 June 2020 - 11:49 AM

 

that does sound more like a valve issue.

 

 

I must admit I haven't really got into the mechanics of the valves on the mini. I usually deal with bikes. I did check the clearances a while back but didn't really have a good look in there. How would the valves affect the pressure? How do the oil passages run through the valve train?

 

I'm an idiot sometimes... That valve! It has the old spring and cap at the moment. There is another version with a steel ball (sorry, didn't mean a bearing) which I will get to replace it.


Edited by fortythree, 21 June 2020 - 11:51 AM.


#10 fortythree

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Posted 21 June 2020 - 11:59 AM

Just to clarify:

This is currently installed (and a bit chewed up):

http://www.minispare...c/6K853KIT.aspx

 

And this is what I will get to replace it:

http://www.minispare.../AEA536KIT.aspx


Edited by fortythree, 21 June 2020 - 11:59 AM.


#11 nicklouse

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Posted 21 June 2020 - 12:00 PM

 

 

that does sound more like a valve issue.

 

 

I must admit I haven't really got into the mechanics of the valves on the mini. I usually deal with bikes. I did check the clearances a while back but didn't really have a good look in there. How would the valves affect the pressure? How do the oil passages run through the valve train?

 

I'm an idiot sometimes... That valve! It has the old spring and cap at the moment. There is another version with a steel ball (sorry, didn't mean a bearing) which I will get to replace it.

 

dont use the ball type.

 

read this first

http://www.theminifo...huttle-vs-ball/

 



#12 nicklouse

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Posted 21 June 2020 - 12:00 PM

Just to clarify:

This is currently installed (and a bit chewed up):

http://www.minispare...c/6K853KIT.aspx

 

And this is what I will get to replace it:

http://www.minispare.../AEA536KIT.aspx

read link above.



#13 fortythree

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Posted 21 June 2020 - 12:16 PM

Thanks! That's a good post, didn't think about the back pressure. Also saw that I can remove the guide/seat which will make inspection a bit easier.

 

Will order the parts and then report back. 



#14 whistler

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Posted 21 June 2020 - 12:53 PM

I made the mistake of replacing the standard sping and metal cap with a spring and ball. Oil pressure went up to 100psi+. Replaced with new standard setup and presure around 75psi. Much better.



#15 fortythree

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Posted 21 June 2020 - 03:58 PM

That's some serious pressure! 

I'm very glad I posted this here before ordering. Ordered a standard valve kit and a 20psi switch from minispares, usually takes about a week to get here. Enough time to try and fix (read: bodge) the oil leak at the u-seal on the gearbox.






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