87951

Anyone familiar with the operation of crankcase ventilation system and how it relates to the turbocharged engine when under boost? I'm on my 2nd cam housing gasket in a week and just discovered my blowoff valve was shot. Is it possible when under boost and then after throttle lift off that because the blowoff valve wasn't relieving the boost pressure that it is being forced back into the crankcase? I would think there would be a check valve in the line but i can't find much info on the system. Question 2 - Anyone know where the vacuum hose diagram is posted lately?

tazman

Here is a copy scaled down a little

Luke

now what do you do with the crank case ventilator line that used to feed from the cyclic valve, before you removed it? <img src="confused.gif" border="0">

Danno

Luke, not sure what crankcase ventilation line you're talking about. The only line that the CV does as far as crankcase goes is the pressure return to the intake manifold. Just plug that up.

It's not likely that the cam gasket is blowing because of the bad/disabled compressor bypass. That will just make your boost drop off faster between shifts and may possibly damage your turbo. But that pressurized air has no way to get into your engine.

Most likely someone used the wrong gasket sealer on your cam gasket (no silicone allowed!).

Luke

"plug it up"


thank you danno.

Danno

Whoops, I didn't mean "intake manifold" is where the CV vents its pressure. It should go to the piping right before the turbo. You can cap the hard pipe under the intake manifold, or the nipple on the manifold right before the turbo.

Peckster

My engine recently started leaking oil at a few places (pan, oil filter housing and rear seal) and I'm hoping it could be caused by a plugged PCV valve or something like that. I know, I'm clutching at straws to try to avoid this job. Do these cars have PCV valves?

jp

Danno

Nope, no PCV valve. The crankcase is pretty much vented directly to the intake of the turbo. That's why we don't need a TAC-Thermostatic Air Cleaner (sealed airbox). The turbo in effect, IS the PCV valve. At idle and low-RPM/low throttle, the turbo sucks in little air and little from the crankcase. At higher-RPM and larger throttle-openings, the turbo spins faster and sucks in more air and more from the crankcase.

In your case, you could have worn-out and leaking turbo seals which is allowing oil that lubricates the turbo bearings to get into the intake tract. Most likely though, it's your pan gasket, oil filter housing and rear seal that's leaking.

951and944S

Danno, turbo engines and NA engines alike, can build high crankcase pressures due to compression passing the rings, from worn cylinder bores, excessive clearance and such, seems even more likely on a turboed engine although all engines have pressurized cylinders.
I've seen your post regarding your engine's mileage, some percentage being accumulated during track use, and when I read "SFR Pizza Run" #1 Danno's oil pan gasket blown out again, it's the firt thing I thought of, compression bypassing the rings to your crankcase..

Cheers

Danno

Yeah, but it happened overnight! Yes, I had a perfectly sealed engine one day and the next it was blowing out oil at 1qt/day. I don't think the rings and valve guides can wear out that much in a day.

Although in John's case, it could be excessive crankcase pressure since he's leaking from several places; I'm only leaking from the oil-pan.

Discovered my mistake today after I tore out the oil-pan again. The new #2 bearing looks fine. I had stupidly used some of that copper-silicone sealant on my oil-pan gasket. Should've known better since it felt kinda 'slick' to the touch. Anyway, some Yamabond-4 took car of that and no more leaks! Yayyyyyyy!

Bri Bro

Is the Yamabond #4 sold at Yamaha motorcycle shops and the Three Bond 1104 the same thing?
<a href="http://www.twobros.com/cgi-bin/shopper?preadd=action&key=032-TB1104" target="_blank">Three bond 1104</a>

Danno

I don't think so. The Yamabond-4 comes in a black tube (part# ACC-YAMAB-ON-D4). It's not really a gasket sealant, closer to a gasket maker; it's thick, has high viscosity and never really dries. Really good for those two-part crankcases on motorcycles that have metal-to-metal mating surfaces that doesn't have a gasket. The Yamabond will fill the gaps and seal even when the surfaces fret against each other. Good for headgaskets too.

What threw me off on the 951 oil-pan gasket was that we're joining rubber to metal. But the stuff works wonders here too. Here's where I found out about the virtues of Yamabond:

<a href="http://www.landsharkoz.com/articles/jatmm02.htm" target="_blank">928 Australia</a>

Some more after some searching:

<a href="http://www.italian-cars.com/html/tech/biturbo.html" target="_blank">Maserati Tech Page</a>

Luke

So you would reccommend using a gasket sealant/maker no matter what when replacing? <img src="confused.gif" border="0">

Danno

I don't know... I think a dry gasket with just sealant on the corners would work fine. I just blew it in my case and used that silicone stuff (big no no). So I might have gone overboard and went to the other extreme and really sealed it in with some other goop.

Peckster

Still with the straws, is it possible to tighten up all or some of the bolts on the oil pan, or will this make it worse?

jp