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PollyMobiles Rebuild

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pollyp

pollyp

Club Member
hmm I musta assembled something wrong or trapped an o-ring? do you leave ur timing cover oil pump o-ring bit dry or you also smear some sealant on it?

wonder if my socket will reach the timing cover bolts and need to get my endoscope back from a m8.

haven't checked the crankcase hose. previously with alot of crankcase pressure on the old NA block, the bottom of the inlet mani usually pools with oil from the PCV vapours but its mostly dry here.
 
i,ve used both types of O ring no probs paul, is there a lot of crankcase pressure ?

was just about to suggest this, years ago i had the same issue on my mini when one of the breathers got blocked, the extra crank case pressure forced oil out where ever possible.
 

frank

Club Member
hmm I musta assembled something wrong or trapped an o-ring? do you leave ur timing cover oil pump o-ring bit dry or you also smear some sealant on it?

wonder if my socket will reach the timing cover bolts and need to get my endoscope back from a m8.

haven't checked the crankcase hose. previously with alot of crankcase pressure on the old NA block, the bottom of the inlet mani usually pools with oil from the PCV vapours but its mostly dry here.
i smear the joint and O ring paul, and if its leaking oil pressure i doubt if the rpm would factor much, but crankcase pressure would climb more with the rpm eh (if you had a breather blockage or whatever that blew it out the crank seal ?)
 
i smear the joint and O ring paul, and if its leaking oil pressure i doubt if the rpm would factor much, but crankcase pressure would climb more with the rpm eh (if you had a breather blockage or whatever that blew it out the crank seal ?)
Along those lines if its on boost and the existing vacuum lines to the inlet mani havent been moved is it possible the boost is forcing air back through into the engine and increasing pressure? (frank feel free to shoot me down here lol)
 

frank

Club Member
Along those lines if its on boost and the existing vacuum lines to the inlet mani havent been moved is it possible the boost is forcing air back through into the engine and increasing pressure? (frank feel free to shoot me down here lol)
the PCV valve is 1 way joe, so you should,nt be leaking any boost into the crankcase tbh :)
but................if that valve was to fail, then yes ;)
 
Also been as we're on the crank case pressure theory, it's also possible that with enough pressure it can force oil past the rings which might explain the oil in the cylinders :-/
 
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pollyp

pollyp

Club Member
so tday to try see if its leaking from behind (can't get the camera pointing at the timing cover side of the block where the oil pump feeds the block)

DSC08368.JPG


went for a quick blast but prob went too short cos it hasn't leaked much and can't see any signs


fellas I think you've all helped me possibly find the cause just now, not tested yet till tomorrow.

The PCV is a 1-way valve as frank said.
During +ve boost it closes and stops the pressure going into the crankcase. The top section of the engine is always vented open via the PCV breather so when the PCV is shut under pressure, any excess blowby can flow out this breather port.
I have a oil catch can (motorcycle oil filter) plumbed to the PCV breather and the filtered gases then flow back into the turbo inlet. the catch can isn't soaked much and the turbo inlet isn't soaked so not much blowby/oil vapour has gone out this port.

during closed throttle vacuum the PCV allows the crankcase vapours to be sucked up the front hose, through the rocker cover, PCV and into the inlet mani. Meanwhile fresh air from the turbo inlet flows into the PCV breather port to fill the crankcase void.

I checked the PCV and it functions perfectly.
ok so the pcv and the front crankcase hose flows fine but haven't checked the catch can plumbing side yet.

as everyone says a blocked breather especially at higher rev/blowby rate could increase case pressure n cause all the issues.

so I unplugged the PCV breather / catch can hose, blew through it hard (to simulate loadsa blowby under boost) and it seemed kinda restrictive.
replaced the motorcycle oil filter with a new one and yea flows better (not completely freely cos of the paper filter but free enough).

and then inspecting the used oily filter I realised hang on, these oil filters have a 1-way valve to normally stop the thick oil from draining back down the sump, so they flow freely from the outside to the centre but restricts when flowing from the centre to the outside.

looking at my catch can plumbing, the PCV breather (source of the blowby pressure) leads to the "center" of the oil filter while the "outer" bit leads back to the turbo.

DOHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

I feel so stupid if this is the cause in the end, so stupid of me!

so the new theory of cause is:
  • during boost the PCV shuts to prevent boost going into the crankcase, fine thats normal.
  • at normal low rpm there ain't enough blowby out the PCV breather to cause a problem so it doesn't leak oil much.
  • but at high rpm with more crankcase blowby pressure coming out the PCV breather, it wrongly enters the middle of the oil filter catch can where the 1-way valve restricts flow. the damp oil residue further improves the rubber valve (further restricting it) and the damp paper filter further restricts flow.
  • with the catch can preventing the blowby from easily escaping, all that pressure has to find another exit route ie piston rings and seals
  • the massive built up crankcase pressure under high boost high rpm forces the vapours and oil out through the rings (hence wet oily pistons and smoky exhaust under boost) and out the front/rear crankcase seals (hence massive visible oil leak)
I just quickly swaped round the catch can pipes n hope it fixes it tomorrow
 
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pollyp

pollyp

Club Member
Pressure comes from in Mani to cam cover port on the left. Right allows pressure out?
as previously explained, (looking at the engine) the PCV at the rear left of the cover only allows gasses from down the crankcase to go up the front pipe, through the cover and into the inlet mani during cruise/deceleration but not the other way.

the PCV breather at the rear right of the cover is fully open to allow gasses to flow in/out of the top of the engine.

gasses can flow between the top of the engine and the crankcase down below via the timing chain void
 
yes they are. I can't kick my own backside hard enough for such a silly schoolboy error
lesson learnt now pay closer attention next time little polly :p
Believe me were all the same. I couldnt wprk out why my brakes weren't working after the ga transplant... one way valve for servo...
We can build engines, fast cars etc but cant put a one way valve in right :p
 
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pollyp

pollyp

Club Member
hehe I'm only human with some good and faulty bits.

just hope all this leaky oil past rings hasn't hindered the breaking in process too much. compression is good and if the wet piston and external leaking stops then I'll be very relieved the crisis is over
 
I have a oil catch can (motorcycle oil filter)
Personally I'd replace it with a proper catch can

that breather port has to flow in both directions (allow air in during idle/low revs then allow gasses out at medium to high revs) so a one way valve is going to cause problems
 

frank

Club Member
i dont get this "catch can" stuff personally ?? factory fitted turbo cars dont have one, and i shoved my crankcase breather pipe into my clear plastic coolant spill bottle for the 1/4 mile runs (scrutineer insisted) and there was no oil in it after a few weeks of driving.
if you are venting oil mist, then the rings are shot imo (or ringlands are busted :D)
 
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pollyp

pollyp

Club Member
Personally I'd replace it with a proper catch can

that breather port has to flow in both directions (allow air in during idle/low revs then allow gasses out at medium to high revs) so a one way valve is going to cause problems
indeed, was being a cheap skate n fitting a £25 make-do oil filter than fork out for a £50 catch can but will get round to it.

for now maybe I should try ripping out or puncture that rubber oil filter valve
 
i dont get this "catch can" stuff personally ?? factory fitted turbo cars dont have one, and i shoved my crankcase breather pipe into my clear plastic coolant spill bottle for the 1/4 mile runs (scrutineer insisted) and there was no oil in it after a few weeks of driving.
if you are venting oil mist, then the rings are shot imo (or ringlands are busted :D)

on factory cars it just goes to the air box, what a catch can will do is remove any oil vapor (all engines will vent mist regardless of condition) before it reaches the inlet tract. catch cans are not really needed but removing oil vapor will reduce emissions and stop build up of oil in the manifolds
 
indeed, was being a cheap skate n fitting a £25 make-do oil filter than fork out for a £50 catch can but will get round to it.

for now maybe I should try ripping out or puncture that rubber oil filter valve
The catch cans ive used past and present were £20. Add some proper orings and thread lock the hose joiners. They've been brilliant. Just an idea for you there
 

frank

Club Member
on factory cars it just goes to the air box, what a catch can will do is remove any oil vapor (all engines will vent mist regardless of condition) before it reaches the inlet tract. catch cans are not really needed but removing oil vapor will reduce emissions and stop build up of oil in the manifolds
the PCV valve is fulltime open under all but positive boost conditions tho eh (so all the vapor,s are being draw into the engine regardless of having a catchcan or not) , and its connected to the bottom of the mani (thats why and where the oil collects in the bottom of the mani).
and emissions laws are why PCV valves/systems were fitted in the first place
all these extra pipes and stuff complicate everything imo paul KISS i say :D
 
Not sure if it has already been posted in this enormous thread (and pollyp has probably already read it), but here is the Nissan SR20DE Crank case ventilation fully explained:

N/A: http://www.sr20-forum.com/informati...d-naturally-aspirated-edition.html#post446849
Turbo: http://www.sr20-forum.com/informati...ion-fully-explained-turbocharged-edition.html

Hope you get your forged engine sorted. Those unlucky moments are what's holding me away from putting really expensive engine parts in my SR20 build, I just couldn't cope with the potential economical loss.

So much time and effort has gone into your car, hope you can enjoy it fully soon :D
 
the PCV valve is fulltime open under all but positive boost conditions tho eh (so all the vapor,s are being draw into the engine regardless of having a catchcan or not) , and its connected to the bottom of the mani (thats why and where the oil collects in the bottom of the mani).
and emissions laws are why PCV valves/systems were fitted in the first place
all these extra pipes and stuff complicate everything imo paul KISS i say :D

Yep, on a na engine the catch can would go between the pcv and manifold to stop oil collecting in the manifold. Problem here is the valve shuts off when under boost so the crank case pressures got to then leave via the breather.

You could connect the breather straight to the inlet side of the turbo but then oil would form in the turbo etc so a catch tank is needed to keep it all clean or the easiest solution would be to just let it vent to fresh air via a filter
 

frank

Club Member
the easiest solution would be to just let it vent to fresh air via a filter
yes, thats what i,m saying :) that vent on the cam cover that people fit a little filter or catchcan onto is the atmospheric breather, and is under vacuum in most conditions (even when revving) so any crap that is blown out under boost is sucked back into the crankcase when off boost.
you are better of just venting it into the engine bay, or vent it to the air filter (to burn it off) if you,re concerned about emissions
and for N/A its pointless fitting a catchcan to a pipe that is only sucking and not blowing
 

SuperUno

Buy & Sell Member
the PCV valve is fulltime open under all but positive boost conditions tho eh (so all the vapor,s are being draw into the engine regardless of having a catchcan or not) , and its connected to the bottom of the mani (thats why and where the oil collects in the bottom of the mani).
and emissions laws are why PCV valves/systems were fitted in the first place
all these extra pipes and stuff complicate everything imo paul KISS i say :D
Where does this connect to the inlet manifold? Will have to fit a catch tank soonfor MSA regs, currently got a little filter on the right hand vent are there others? I dont want the oil mist being burnt by the engine.
 
Where the little filter is thats where the catch tank should tank over and reroute it to your inlet. The oil should be swirled out in the tank.
The other vent can be filtered off too. The catch tank should provide enough vacuum for crankcase pressure. So just the tank and no other pipes. Less complicated that way
Its late and ive no idea if what ive wrote makes sense :p
 

frank

Club Member
Where does this connect to the inlet manifold? Will have to fit a catch tank soonfor MSA regs, currently got a little filter on the right hand vent are there others? I dont want the oil mist being burnt by the engine.
the black pcv valve on the offside rear goes to the underneath of the inlet mani matt, and the atmospheric breather is on the nearside rear (where you have fitted the little filter)
a catchcan fitted in place of the filter will pass scruting, but it wont serve any purpose tho :)
if you want to create (the ideal) constant vacuum condition in the crankcase at all times, then you would need a slashcut pipe mounted in the inlet tract or exhaust system.
the stock system draws the crankcase fumes fulltime through the pcv valve, but there is an oil separator under the lid of the cam cover, so as long as your rings are healthy, you wont be consuming/burning oil, (you will only be burning water condensation and fuel residues)
 

SirChris

Educated Bodger
as previously explained, (looking at the engine) the PCV at the rear left of the cover only allows gasses from down the crankcase to go up the front pipe, through the cover and into the inlet mani during cruise/deceleration but not the other way.

the PCV breather at the rear right of the cover is fully open to allow gasses to flow in/out of the top of the engine.

gasses can flow between the top of the engine and the crankcase down below via the timing chain void
I thought you might just want to block the PCV and fully open in the breather. Would that not be the best of both worlds?

**edit of course bloking the mani as well eh? What does the vacuum actually help with?
 

frank

Club Member
I thought you might just want to block the PCV and fully open in the breather. Would that not be the best of both worlds?

**edit of course bloking the mani as well eh? What does the vacuum actually help with?
the pcv end has the benefit of the oil separator eh chris, so you could block the mani port and fit a catchcan there i guess :)
and half a bar of vacuum in the crankcase is supposed to help cut the windage from the crank ??
a proper pcv valve should regulate the vacuum apparently (with a pintle) ours is just a 1 way valve to check against blowbacks tho eh
 

SirChris

Educated Bodger
the pcv end has the benefit of the oil separator eh chris, so you could block the mani port and fit a catchcan there i guess :)
and half a bar of vacuum in the crankcase is supposed to help cut the windage from the crank ??
a proper pcv valve should regulate the vacuum apparently (with a pintle) ours is just a 1 way valve to check against blowbacks tho eh

Wheres the figures on that? wheres the research :D They lie, na I wonder if it makes a massive difference. I suppose if its vacuum it would create less air disturbance thus creating less windage, I think block ing and using a catch can makes sense.. at least we then we know when things have gone tits up eh?
 

frank

Club Member
just threads that i have read chris, and i just prefer to keep it simple personally (if it aint broke..................) :)
 

SuperUno

Buy & Sell Member
Thanks for that Frank and explains the oily stuff in the bottom of the inlet mani, as have been asked really i need to link the catch tank to the output from the offside one rather than the nearside one. Thanks for the info. you learn something new everyday! :) :)
 
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pollyp

pollyp

Club Member
thanks for the info guys. editing and uploading the videos been taking ages but here's what happened the other day.

4th June

after replacing my catch can oil filter and correcting the plumbing I started her up.
lumpy rich 9afr cold start cos of oil in cylinders, soon clears and O2 makes it 14.7 afr.
warm up driving through town sounding like a diesel.
once a can open the revs at the country roads it doesn't smoke or leak oil as badly as before so the reduced catch can breather restriction has improved it.


after the first blast, cylinders are no longer oily :) and compressions good. its not raining oil anymore but still some drips

so continued driving to work but then hit traffic. not letting it idle but once I reached work n recheck, once of the cyl was damp again prob from the low loads but compressions still good.


after work I drove back to the open roads and commence bringing the revs n load upwards. she still smokes abit at high rpm & boost (oil leaking n burning in cyl during high crankcase pressure?) and the trickling oil leak it still there at high rpm. back at home after the run, the cyls are again drier without the oil pool (not bone dry but just damp - seems to say that its fine n dry when under low load/low smoke but once under high load/high smoke the oil leaking past the rings douse the pistons in some oil hence smoke)


the next test is to disconnect the restrictive catch can to eliminate it out of the equation and see if the free flowing breather port will further improve the damp cyl and smoke and oil leak
 
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pollyp

pollyp

Club Member
oh btw frank I unplugged that front crankcase breather pipe n blipped the throttle to 4k and looking at the faint steam trail the crankcase doesn't have any +ve blowby at such low rpm under no load.
don't wanna rev the nuts off it n scare the neighbours lol
 

SirChris

Educated Bodger
use evian bottle like frank... drill tones of holes out top.. you can test then. no point spending if you dont need to :)
 

solarice

Ex. Club Member
Regarding catch tanks, the only side on mine where oil vapour is present is on the left rear (to underneath intake)...the other filtered pipe never has any oil etc near it. Which is why i put a catch tank attached to left rear to try and eliminate some of the theoretical power stealing vapour / mucking up the intake.

Good to see you're starting to get ahead with this polly, fingers crossed everything starts going super smooth :D
 
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pollyp

pollyp

Club Member
cheers chris n frank. remember when I made a rough evian catch can the last time this forged engine burnt oil?
I'll def try that evian trick again
 
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pollyp

pollyp

Club Member
so I drilled 4 holes in a bottle and taped the breather pipe to it

DSC08369.JPG
DSC08370.JPG


cold starts very rich n lumpy n too slow again before clearing up.

warmed up and gave a blast and behold no more oil leak and minimal smoke


cylinders quite dry and reading 11.2 11.4 11.8 11.3 bars at 238m.

continued the high rev runs and not a drop of oil leak. still a small hint of smoke the moment it resumes combustion but I think thats prob cos its only done 250m and during high rev overrun it sucks abit of oil into the cylinders and once it resumes power it burns that tiny oil residue off. will hopefully stop smoking after overrun once we reach 1000m.


tdays 30mile blast has consumed 1/4 dipstick of oil so still early days in its break-in
back at home after a cooldown run through town, compressions at 11.2 11.4 11.8 11.2 bar so very consistant and even which is luvely

so there we go, the cause all along has been that silly oil filter catch can. evian bottle catch can ftw for the moment :p
oh and after all that revving tday, there's only the tiniest speck of condensed oil droplet in the evian bottle.

now got a messy underside to clean, added to checklist, which coulda all been avoided if I'd noticed the catchcan plumbing but meh at least its finally fixed n didn't resort to pulling the engine out or other extreme measures. relief
 
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