Crankcase pressure and breather pipe

[Vertigo]

So my rebuilt smallport 4AGE just went for its first drive by my mechanic. He said it was well down on power, and the front main seal blew out, leaking oil everywhere. So suggests quite a bit of crankcase pressure. (Also cam timing is probably out, as I didnt have a degree wheel, and just eyeballed it. Starts and idles decently though. Was going to come back to this as needed.).

Now, I had to use my bigport throttle body on the smallport manifold, as the TPS sensor was way different, and it was the only way we could get it sorted out. I have since read online that the 4AGE breather pipe actually vents into the throttle body rather than the manifold itself - is this true? Could I have inadvertently blocked the breather completely? He wants to drop the engine and rebuild it again, but Id like to avoid that if possible. That said, its probably a good idea anyway (Im the one who built it, and while I was sure I did everything correctly, it wouldnt hurt to have it looked over by someone who has done it a thousands times already).

Assuming the breather is blocked, would venting to atmosphere instead resolve the issue?
How much blowby is needed to blow out a main seal like that, anyway? Normal amounts, or does it suggest my ring installation was bad?
Fuel injectors had to be replaced - 200cc vs the 186cc that were originally used. Would this combined with no o2 sensor (custom exhaust) make AFR so rich that it runs poorly?
What else should I be thinking about at this stage?

[QikStarlie]

smallport does vent back through the throttle body, to the other side of the throttle plate. has an internal passage in the inlet manifold that goes to the throttle body flange. haven't delt with bigport stuff. but guessing is plausible that you've blocked the breather by using the bigport throttle body. venting to atmosphere will solve problem.

you'd have to have shitloads of crankcase pressure to pop the seals out, if installed correct. breathers blocked etc.. as you suggested

[matt dunn]

you'd have to have shitloads of crankcase pressure to pop the seals out, if installed correct. breathers blocked etc.. as you suggested

Probably not
as if there is no where for it to escape, a small amount getting past the rings each stroke
will eventually build up to quite a pressure and pop out the seals.

You would be surprised how much comes out even on a good engine under load.

[jondee86]

If you mix and match RWD and FWD parts, it is possible to block the
vent hole for the crankcase...



It is also possible, if you have a gasket that only has one vent hole, to
put it in backwards and block the vent, even if the holes in the throttlebody
and the manifold match up.

Cheers... jondee86

[Vertigo]

Thanks guys, good info. Id need to compare to two throttle bodies to be sure, but this is a good avenue to pursue.

[QikStarlie]

you'd have to have shitloads of crankcase pressure to pop the seals out, if installed correct. breathers blocked etc.. as you suggested

Probably not
as if there is no where for it to escape, a small amount getting past the rings each stroke
will eventually build up to quite a pressure and pop out the seals.

You would be surprised how much comes out even on a good engine under load.

Thats what I said; The breathers blocked = shitloads of crankcase pressure = seals out
If the stock breather was in place and working correctly, seals would not likely pop out, on any engine that is actually mechanically good enough to run.

[Vertigo]

Turns out the manifold passage is blocked - probably was done by the previous owner for his turbo build, now that I think about it.
I now have a catch can with filter, which will go in this weekend.