1.6 NA .....Pressure buildup in Valve cover

dkmc · Post by **dkmc** » Wed Oct 29, 2008 3:27 pm

Blowby past the rings will be in the crankcase most, and blowby past the valve guides would lead to pressure in the valvecover area.

Only for the sake of argument and because I think I have a fairly strong background in basic I/C Engine Design, I will argue with that point.
Just because someone does "something" does not mean it's correct.....

Have you seen the oil drain back passages in the head and block??
It's ALL the SAME pressurized "box". Connecting hoses from the top to the bottom of the box does -very little- if nothing to decrease the pressure inside the box.....IMO.

My take is this:
VW vented the cam cover to the intake runners (and thus atmosphere).
That works.....mostly if not prefectly.....when the engine is in good condition and blow by is minimal. But the ports in the runners are too small to handle the increased flow in a tired engine.

Now, it would seem to me if those ports had even 1/8" holes in both of them, that would be plenty of flow.....but maybe not. Surely 3/16" holes would be big enough

But 5/16" as someone mentioned drilling them out to seems quite large......

My key question was:

What I don't understand, is the hose that goes from the cam cover to the No. 2 and No. 3 intake runners.....
Is there a restriction in the fittings someplace that lets pressure build up?
I have never had the hoses off the fittings on the intake runners....what is there?

Although I DID ask........

What is the band-aid fix to bleed off the pressure and stop the oil seepage

But I don't see how running hoses from head to crank case relieves any internal pressure? You could have a balloon with many small hoses connected to the top and bottom of it, and the pressurized air inside will still be.....pressurized....

Thanks again for sharing your experiences!

Post by **Fatmobile** » Thu Oct 30, 2008 12:06 am

The junction between the head and block can cause a restriction and hold pressure in the block.
The best example of this is the 1.5. It had a smaller front oil return hole and after the engine got worn the blowby would keep oil from returning to the oil pan and blow it out the valve cover vent,... into the intake, causing the engine to runaway.
The the tube from the block to the intake made it easier for gasses to pass from block to head so the gasses went slower and oil was allowed to return to the oil pan.
On the 1.6 they made the oil return holes larger but it's still a good idea to put one of the old tubes on if you can find or make one.

I don't think this has much to do with your problem, except I think VW put the restrictions in the intake manifold as means to protect from runaway. I was concerned that drilling out the restrictors would allow more oil to be blown/pulled into the intake and allow a runaway.
I got it running and took it out on the interstate, got it up to 90mph without it running away so I figured it was a safe mod.
I gave it to a friend and he never had a problem with runaway.

82vdub · Post by **82vdub** » Thu Oct 30, 2008 9:08 am

I agree with fatmobile and as I said before, I don't think adding this extra hose will eliminate your present issue.

VW Jon · Post by **VW Jon** » Thu Oct 30, 2008 11:45 am

I have the extra hose, and it didn't help. The additional vent did.

dkmc · Post by **dkmc** » Thu Oct 30, 2008 12:43 pm

And so then I shall DRILL.......

Over the weekend........I will dip the drill in heavy grease in hopes the chips will stick to it and minimal will go into the internal abyss to reek havoc....

Wish me luck!

d

82vdub · Post by **82vdub** » Thu Oct 30, 2008 12:47 pm

dkmc wrote:I will dip the drill in heavy grease in hopes the chips will stick to it and minimal will go into the internal abyss to reek havoc....

Wish me luck!

d

Wishing you all the luck in the world, as that's a bad idea, IMO.

dkmc · Post by **dkmc** » Fri Oct 31, 2008 1:53 pm

Wishing you all the luck in the world, as that's a bad idea, IMO.

Then exactly what would you suggest?
I'd be very curious to hear........

82vdub · Post by **82vdub** » Fri Oct 31, 2008 2:11 pm

Remove the intake manifold prior to drilling it out.

dkmc · Post by **dkmc** » Fri Oct 31, 2008 2:22 pm

.........Ah.......thought you meant 'don't drill it out'.......

I agree.....but........that ain't gonna happen.
I will stick the vac cleaner hose down the runners also.......beyond that, the alu. chips will just have to 'go thru'.......

Wish the chips luck.......

dkmc · Post by **dkmc** » Fri Oct 31, 2008 4:11 pm

GOOD news!

Just drilled it out.....the chip worry is a moot point as the restricted ports are very thin. Only minimal chips made.....and they stuck to the grease on the drill. The orig holes were about .157 (4MM) diameter.....I took them out first to .216 (5.5) and it was better at idle, but still was building pressure. So I went to .295 (7.5MM) and it seems much better. (It looks as though they could go to a MAX of maybe 11 MM diameter).
I revved it to redline a few times, no sign of run-away tendencies.......

I hope this solves or at least minimizes the black spot problem.....

Some approximate calculations:
The original 2 holes at 4mm diameter flow aprox. 8 CFM total at 5PSI
Now, the (2) 7.5MM holes should flow aprox. 15 CFM total at 5PSI.
That's over 7X the flow rate. I doubt there is over 5 PSI in the Crankcase at any time, or it would blow the filler cap off. My vent hose doesn't even have a clamp on it, but it stays on and does not leak oil residue.
How much flow is really needed to fully vent the CC ?? I have no idea......

If anyone wants to try to calculate the aprox. MAX flow rate of crankcase
vent air including blow by and "2 pistons going up/ while 2 are going down".....please feel free....!!

dk

vanbcguy · Post by **vanbcguy** » Fri Oct 31, 2008 5:18 pm

dkmc wrote:.........Ah.......thought you meant 'don't drill it out'.......

I agree.....but........that ain't gonna happen.
I will stick the vac cleaner hose down the runners also.......beyond that, the alu. chips will just have to 'go thru'.......

Wish the chips luck.......

There was a great pic around here somewhere once upon a time of a cylinder that had a small piece of something bouncing around inside of it... Scored cylinder walls, nicks all over the crown of the piston, head and valve faces... It was great.

Things don't "go thru", they "go in" and find somewhere expensive to lodge themselves. Gravity is funny that way...

dkmc · Post by **dkmc** » Fri Oct 31, 2008 6:30 pm

Things don't "go thru", they "go in" and find somewhere expensive to lodge themselves. Gravity is funny that way...

I guess you didn't get to the next post before you posted that.......

"Just drilled it out.....the chip worry is a moot point as the restricted ports are very thin. Only minimal chips made.....and they stuck to the grease on the drill"

NOT WORRIED ABOUT THE CHIPS

82vdub · Post by **82vdub** » Fri Oct 31, 2008 6:55 pm

dkmc wrote:"Just drilled it out.....the chip worry is a moot point as the restricted ports are very thin. Only minimal chips made.....and they stuck to the grease on the drill"

The one's you saw stuck to the grease on the drill............

dkmc wrote:NOT WORRIED ABOUT THE CHIPS

Hopefully nothing will happen down the road. There's a reason why there's an air filter in the intake manifold air stream. I am glad that this seemed to mimize your pressure issue and the technical analysis.

Post by **Fatmobile** » Sun Nov 02, 2008 12:56 am

I put a vacuum cleaner hose around the bit so it pulled the pieces toward/through the bit.

Quantum-man · Post by **Quantum-man** » Sun Nov 02, 2008 12:26 pm

nice to see you seem to have cured/alleviated your pressure issue.

dkmc wrote:
Blowby past the rings will be in the crankcase most, and blowby past the valve guides would lead to pressure in the valvecover area.
Only for the sake of argument and because I think I have a fairly strong background in basic I/C Engine Design, I will argue with that point.
Just because someone does "something" does not mean it's correct.....
Yep never have blind trust
Have you seen the oil drain back passages in the head and block??
It's ALL the SAME pressurized "box". Connecting hoses from the top to the bottom of the box does -very little- if nothing to decrease the pressure inside the box.....IMO.

My take is this:
VW vented the cam cover to the intake runners (and thus atmosphere).
That works.....mostly if not prefectly.....when the engine is in good condition and blow by is minimal. But the ports in the runners are too small to handle the increased flow in a tired engine.

Now, it would seem to me if those ports had even 1/8" holes in both of them, that would be plenty of flow.....but maybe not. Surely 3/16" holes would be big enough
But 5/16" as someone mentioned drilling them out to seems quite large......

My key question was:
What I don't understand, is the hose that goes from the cam cover to the No. 2 and No. 3 intake runners.....
Is there a restriction in the fittings someplace that lets pressure build up?
I have never had the hoses off the fittings on the intake runners....what is there?
Although I DID ask........
What is the band-aid fix to bleed off the pressure and stop the oil seepage
But I don't see how running hoses from head to crank case relieves any internal pressure? You could have a balloon with many small hoses connected to the top and bottom of it, and the pressurized air inside will still be.....pressurized....
Pressure equalisation in 2 chambers, seperately fed by differently 'valved' supplies, joined by finite tubes is a function of several factors including #1 time, #2 pressure drop through 'tubes' and the important factor that these are not static pressures, but assuming venting pipes not blocked, 'pressures with drops due to exiting flow'...
Eliminating one or other or both of the sources, ie duff rings , or slack stems/stem seals will definitely alter the experiment. At 2500 to 3500 rpm, I assume that you are adding a significant volume of air. Doing as youi have done, and increasing the size of the plughole, will also help reduce pressures.

Thanks again for sharing your experiences!

Why do people, including 'experts' assume there is no vaccuum in a diesel intake? When a carburetter butterfly is wide open, is that causing a vaccuum? No... it's the venturi sucking the fuel in at that point. Look along the intake of a diesel, do you see any venturi's especially where pipes join etc. Granted it's not great, but it is amplified by the use of an air filter in the case of the valve cover offtake . I don't know of non TDset up though but speak with authority for TD's and a QTD in particular. [ I have in my QTD a gauge that measures both boost and vac. It does move into vac before boost, be it only a little!] I have in my shed a mechanical indicator that I stole from a big truck that 'pops' when vac gets too high [ a sign of a degraded airfilter ]