Hey guys,
I'm after some information on crankcase ventilation in the 4g32. I've searched through the site and there seems to be limited info on the specifics of how it functions.
We all know there is a crankcase breather on the front of the motor. Talking to other car enthusiasts, crankcase ventilation generally works in cycle, whereby the main breather is used to draw fresh air into the motor. A secondary hose draws air/fumes from the motor through the intake to be combusted.
The 4g32 doesnt seem to have this setup. Is the main breather designed to draw air out of the motor? Should there be an air intake into the crankcase? It seems to be a one way system.
There is usually a secondary small hose that connects to the back of the intake manifold from the top of the head, what is the purpose of this hose?
Does anyone use a pcv valve on the 4g32?
The main reason for my question is i seem to be having problems with positive crankcase pressure. Cylinder compression is very good between 190 and 210 (the motor has had some work done to it). I think some of the positive crankcase pressure issues may be because i have blocked off the small hose that connected to the back of the intake?
4g32 Crank Case Ventilation
Re: 4g32 Crank Case Ventilation
The various systems on cars are basically due to whatever anti-pollution rules that were in place at the time.
In the 4G32, it's a really simple system :
- The crankcase pressure is basically caused by blow-by past the rings (you will always get a bit, even in a brand new engine)
- This pressure is relieved by connecting the breather to the air intake (aircleaner), which sucks the oily fumes into the engine & burns them (ie it is a "closed system" with no fumes reaching the outside world).
The down side of course is that crankcase fumes do nothing to improve the quality of the air/fuel mix going into the engine .... they rob power.
Some (many ?) people solve this problem by disconnecting the breather from the aircleaner, and just putting a filter direct on the breather. This does nothing for emissions, but tends to increase backpressure in the crankcase, causing oil leaks etc. (Obviously it's probably illegal from an emissions point of view, but no one really cares .... )
If you are going to disconnect the breather from the air intake (ie. havinhg no "positive suction") you are best leaving it completely "open", or at least running it to a decent size vented catch-can or similar so there is little or no backpressure.
There's no real benefit in fitting a PCV valve .... it's just one more thing to block up & go wrong.
As far as I can figure out, the small hose from the rocker cover to the base of the carb is just a means of getting rid of excess rocker cover fumes into the intake.
In the 4G32, it's a really simple system :
- The crankcase pressure is basically caused by blow-by past the rings (you will always get a bit, even in a brand new engine)
- This pressure is relieved by connecting the breather to the air intake (aircleaner), which sucks the oily fumes into the engine & burns them (ie it is a "closed system" with no fumes reaching the outside world).
The down side of course is that crankcase fumes do nothing to improve the quality of the air/fuel mix going into the engine .... they rob power.
Some (many ?) people solve this problem by disconnecting the breather from the aircleaner, and just putting a filter direct on the breather. This does nothing for emissions, but tends to increase backpressure in the crankcase, causing oil leaks etc. (Obviously it's probably illegal from an emissions point of view, but no one really cares .... )
If you are going to disconnect the breather from the air intake (ie. havinhg no "positive suction") you are best leaving it completely "open", or at least running it to a decent size vented catch-can or similar so there is little or no backpressure.
There's no real benefit in fitting a PCV valve .... it's just one more thing to block up & go wrong.
As far as I can figure out, the small hose from the rocker cover to the base of the carb is just a means of getting rid of excess rocker cover fumes into the intake.
Re: 4g32 Crank Case Ventilation
PCV's are one way valves.
They are only needed if the crankcase is vented directly to the intake manifold (as it is on an A12 out of a Datsun 1200).
If it is connected to the air filter, open to air, or to an overflow bottle, it's not required.
They are only needed if the crankcase is vented directly to the intake manifold (as it is on an A12 out of a Datsun 1200).
If it is connected to the air filter, open to air, or to an overflow bottle, it's not required.
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Re: 4g32 Crank Case Ventilation
Cheers guys, what I thought.
The reason I'm asking is I seem to have some problems with crankcase pressure, filler cap popping off.
I've done multiple compression tests it is really good, between 190 and 210. I want to test it with another compression tester as i have some doubts mine is accurate.
Assuming my cylinder pressure is good, I'm struggling to understand why crankcase pressure is an issue.
The reason I'm asking is I seem to have some problems with crankcase pressure, filler cap popping off.
I've done multiple compression tests it is really good, between 190 and 210. I want to test it with another compression tester as i have some doubts mine is accurate.
Assuming my cylinder pressure is good, I'm struggling to understand why crankcase pressure is an issue.
Re: 4g32 Crank Case Ventilation
How good is the seal on your cap?
4G32's with the oil filler caps popping off are pretty common.
4G32's with the oil filler caps popping off are pretty common.
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Re: 4g32 Crank Case Ventilation
190-200psi compression is really high .... much higher than stock. What pistons are you running ?
re the usual rocker cover venting pipe .... they are such small diameter that I can't see it making a lot of difference, but unblock it & see ?
The usual result of excess crankcase pressure is leaking front & rear oil seals, or the dipstick popping.
As Dave said, it's not unusual for the oil filler caps to lift ..... which is why just about every Saturn-engined rally car you see (including mine) is set up like this :
Easy fix
re the usual rocker cover venting pipe .... they are such small diameter that I can't see it making a lot of difference, but unblock it & see ?
The usual result of excess crankcase pressure is leaking front & rear oil seals, or the dipstick popping.
As Dave said, it's not unusual for the oil filler caps to lift ..... which is why just about every Saturn-engined rally car you see (including mine) is set up like this :
Easy fix
Re: 4g32 Crank Case Ventilation
Yeah very high, the motor has had some substantial work done to it and was running in a rally car prior to me owning it. The guy I bought it off was unable to give me specifics on the motor.
I want to confirm the compression with another tester.
The motor seems to use a small amount of oil and have some blow by, signs of worn rings but my tester shows high compression.
The motor runs pretty well all in all.
I want to confirm the compression with another tester.
The motor seems to use a small amount of oil and have some blow by, signs of worn rings but my tester shows high compression.
The motor runs pretty well all in all.