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(help) Too much pressure, not enough ventilation?
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Author:  spathi [ Fri Dec 10, 2004 8:49 am ]
Post subject:  (help) Too much pressure, not enough ventilation?
For the doc, or anyone else who may know,

I was playing with the matic engine the other day, after fitting the facet solid state fuel pump (works excellent btw, thanks to all that contributed to the thread on that one.) and I thought I'd check to see how the oil was flowing at the top of the head, so I took the oil cap cover off. It made a noise, kind of like a release of pressure (or maybe sucking) when i took the cap off, the engine then started to idle much slower, sounding a lot more lumpy then stalls. (the engine was tuned and timed with the cap on)

question is, is this normal for a matic? or for a mini in general? the cap i have on there is non ventilated, the engine has one of those oil seperator side plate covers, that connects to a PC Valve, which connects to one side of the redline manifold. Im not aware of any other forms of ventilation from the car, does it need any? the rocker cover has no provision for it.

Any insight would be appreciated :D
Author:  TheMiniMan [ Fri Dec 10, 2004 8:57 am ]
Post subject: 
sounds pretty normal to me,,,the oil cap has a small breathing section, only allows so much air in, if you remove the oil cap then heaps of air is sucked in through the engine via the PCV Valve (positive Crankcase ventilation Valve) it`s low pressure is drawn from the manifold, through the PCV Valve & through the engine internals, so any gapping hole anywhere in that system, will allow air to be sucked in & run the engine mixture very lean,,,rough idle & stop,,,

quite normal

:-)
Author:  spathi [ Fri Dec 10, 2004 9:03 am ]
Post subject: 
Thanks matt! wasn't to sure, i don't remember my last engine doing that (it was manual, with no PCV Valve) didn't want to break anything. Something else I don't have to worry about

Cheers :)
Author:  drmini in aust [ Fri Dec 10, 2004 10:05 am ]
Post subject: 
Yep Matt's got it right. PCV system is workin'... :wink:
<edit> the vacuum in the crankcase also reduces oil leaks from seals, while it's running, anyhow. :lol:
Author:  spathi [ Fri Dec 10, 2004 11:39 am ]
Post subject: 
thanks doc, its good to know all these interesting facts. Im learning it all, slowly..

while im on the subject, how much oil should be running around in the head?

On my old mini it was virtually splashing around, quite a lot of oil, on the matic its not as much, i can still see it flowing but its not a huge amount.
Author:  redfive [ Fri Dec 10, 2004 11:54 am ]
Post subject: 
So if you pull off the oil cap while the engine is running and it doesn't change how its running, what does this mean?
Author:  drmini in aust [ Fri Dec 10, 2004 3:58 pm ]
Post subject: 
Spathi,
If there's a heap of oil around the rockers maybe the rockers & shaft are a bit worn. Should not be a heap in there- it's an intermittent flow from the slot groove on the cam's front journal.

Redfive- depends what PCV system you have. If it's the one talked about here with the Smiths PCV valve into the manifold, it's probably blocked with crud & varnish.
If it's a later one that goes into the carb, these are less sensitive to this test. To check if working pull the hose off the side of the carb body, and feel for suction on the carb pipe.
Author:  spathi [ Fri Dec 10, 2004 4:04 pm ]
Post subject: 
thanks doc, i think my old engine was just stuffed :) the matic engine seems like you have described.
Author:  Christoph [ Fri Dec 10, 2004 10:53 pm ]
Post subject: 
To avoid confusion it doesnt matter whether it is a manual or automatic motor. Its all down to whether or not a PCV system is installed or not. I know the mkII s's had them, not sure about the other models.
Author:  drmini in aust [ Sat Dec 11, 2004 6:10 am ]
Post subject: 
The Smiths PCV into manifold was used on the MK1 & 2 S's, Morris 1100S/1300 auto & manual, and I think my MiniMatic had it too? (they were UK built motors). Can't remember now... long time ago. :?
Most 998 Clubbies had the PCV plumbing hooked into the side of the HS4 carb's suction chamber. Worked similar but had no PCV valve to clog up, or break diaphragms. :wink:
Author:  TheMiniMan [ Sat Dec 11, 2004 8:02 am ]
Post subject: 
& that later type breathing system, into the side of the carb, doesn`t actually work anywhere near as good as the good old original PCV system

but still,,,it`s some sort of suction breathing, better than just open to atmosphere

You should notice a small change in engine revs when you take the oil cap off the later cars , just not as much as the dramatic change evident in the PCV fitted cars
Author:  68matic [ Sat Dec 11, 2004 10:56 am ]
Post subject: 
my pcv fitted matic
chokes and splutters like its first ciggy
without the pcv fitted
makes me think i should carry round a spare
chuck it amongst the spare plugs dizzy fuel water ...
Author:  Gezo [ Sat Dec 11, 2004 12:25 pm ]
Post subject: 
Hi,
I have a PVCfrom the crankcase going on to the manifold (twin 1/1/4) carbies and a breather oil cap. When I take the oil cap off the motor, the motor picks up revs. Is this correct.
Thanks
Author:  drmini in aust [ Sat Dec 11, 2004 1:58 pm ]
Post subject: 
Yes.
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