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Big block oil pressure

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Jools View Drop Down
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    Posted: 31 Oct 2017 at 12:02
I acquired my '78 G5 last year as a bit of a running project; my attention has chiefly been confined to cosmetics/electrics/general refurbishment so far, but I'm now going further on the mechanical front.

fitted a deep-sump conversion earlier in the summer and noticed immediately afterwards that the oil pressure warning light began to flicker on tickover once the engine was hot. 

I fitted an oil pressure gauge to check things out and found that the pressure starts off at 35 - 40psi when cold and then falls to 20 - 25psi at around 3500 - 4000rpm when hot. On tickover, the pressure falls to absolute zero!!

I have no idea how many miles the engine has covered as the speedo has been changed in the past, and it shows no signs of having been rebuilt in the past. I'm assuming that the oil pump is knackered and requires replacement. However, am I correct in my assumption that the oil pump is solely responsible for providing the pressure? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken-Guzzibear Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2017 at 12:13
Before you panic check the oil pressure relief valve in the sump and that the oil is as per manual ....My V1000 has covered 265,000 miles never had to look at the oil pump If you look in the online V1000 workshop Manual there is a section on how to check this as well as info about engine oil and working pressures Greg Bender Moto- Guzzi ...by the way the same as in the Spada and T3......
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Jools View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jools Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2017 at 13:20
Thanks Ken. The same thought had occurred to me, though the flickering oil light post the deep-sump addition made me wonder if the extra 'lift' (even though small) was now causing an underlying problem to finally surface. 

I'll have it apart in due course and test it. 
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 31 Oct 2017 at 21:53
My memory (but which is unreliable) recalls 60 - 80 psi from what’s in my manuals.

You say “after doing a sump extension conversion” have you now got a partially blocked oilway or gasket leak? I.e. fault has occurred after you did something.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2017 at 07:58
OK, one silly question, what grade of oil have you put in?
 
A temporary solution would be to use one with a higher hot viscosity. If you put in 10W40, try 10W60.
 
But well worth pulling the oil pump, though under normal conditions they do last well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2017 at 09:03
Originally posted by Jools Jools wrote:


fitted a deep-sump conversion earlier in the summer and noticed immediately afterwards that the oil pressure warning light began to flicker on tickover once the engine was hot. 


Extension or replacement sump?

I fitted a G&G deep sump to mine that has the filter screw in from the outside and whilst I reused the oil pressure relief valve, I had to grind some ally away from the sump to get it to fit properly as it was too wide to fit the small gap they left.

I didn't check the bypass pressure as it never occurred to me that it might be suspect and I've had no oil lights or problem that I'm aware of but I would say if it wasn't screwed in properly (due to being too tight a fit in the gap) that it could leak around the base and therefore not do it's job.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken-Guzzibear Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2017 at 12:24
I have deep sump and ext oil filter on the V100 been there over 20 yrs no issues whatsoever
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jools Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2017 at 20:17
Thanks Guys, answers as follows;

1). I was expecting around 60psi max, in accordance with the manuals

2). The sump extension used was a simpler 'spacer' type

3). Oil used is 20/50 - the same type as used immediately before the swap

The gaskets used were new ones, with the holes checked for alignment before fitting. The sump bolts were tightened progressively, with a final check the following day to allow for any 'sinkage'. 

However, what's the consensus on the key question - is it the oil pump which is solely responsible for generating the oil pressure? Indeed, any restriction or leakage will affect the pressure as read on the gauge, but how is the pressure generated in the first place? 

I'll tear it apart at the end of the month when the tax runs out. Meantime it's still rideable so it'll get ridden!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2017 at 21:52
The oil pump generates the pressure (and therefore the flow), in fact they can develop too much pressure at high RPM which is why there's a relief valve to stop it being too high.

Low pressure could be a few things; the pump not generating enough pressure, the valve 'blowing off' too soon, a leak or blockage in an oil way or, worse case scenario a knackered engine.

If there's no or low pressure and therefore little oil circulating, I wouldn't ride it until you've found why because, something simple could become something complex and expensive in a short time... 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 01 Nov 2017 at 22:04
If you think about it, the difference between having the standard sump and adding a spacer is that the oil intake is moved about 2 inches? lower, considerably increasing the distance below the oil pump.
As this requires the pump to suck, I would imagine that the likelihood is that the oil pump will not suck up as quickly, probably reducing the oil pressure.
Added to that you would only have to have a slight flaw in one of the sump gaskets around the pickup drilling to greatly affect the pick up efficiency. Equally any slight restriction in the pickup system will again result in reduced flow which will show as reduced pressure.
Again, any slight wear in the pump itself will again be accentuated with the increased height above the oil.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gianni Quote  Post ReplyReply Direct Link To This Post Posted: 02 Nov 2017 at 09:40
I had this on my Quota.
 
Did an oil and filter change, fired it up and exactly that: light flickering on tickover but OK at higher revs.
 
I had put the sump spacer in the wrong way round. Only half the oil ways line up that way.
 
If that is your problem, DO NOT RIDE IT, it will F**K your engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gianni Quote  Post ReplyReply Direct Link To This Post Posted: 02 Nov 2017 at 10:00
vs.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote red leader one Quote  Post ReplyReply Direct Link To This Post Posted: 02 Nov 2017 at 11:42
Which is the right way round then?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote italianmotor Quote  Post ReplyReply Direct Link To This Post Posted: 02 Nov 2017 at 11:57
The right way round is when all the holes on the sump gasket line up correctly with all the holes on the sump AND the bottom of the crankcase. If I were you Jools I'd put it back to standard and see if the issue is still occurring.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 02 Nov 2017 at 12:20
Originally posted by red leader one red leader one wrote:

Which is the right way round then?

This one;

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