How can air pressure leak from intake manifold to cam assy?

[bebbetufs]

I have found a large vacuum leak from the cam assy seal. When pumping air into the intake system it escapes from a rupture in the cam assy seal above cyl#4.

What I would like to know is what is the most likely path for of the air from the head to the cam assy?

B

[robm-951]

Valve guides and seals.

[bebbetufs]

Thanks.
I'll do the seals then. The engine has only done 62k miles. Do I need to fear that the guides are gone too? Is there any way I can get a feel for this without buying tools or pulling the head?

[Rasta Monsta]

Might as well pull it and take it to the machine shop unless you are on a very low budget. Shouldn't cost you much more than $100, and it will be done for another 75-100k miles.

[bebbetufs]

I apreciate your advice and I do agree but my budget is blown by about $4000. I'm now on borrowed money so I won't do anything I don't absolutely have to do.

So do I only feel for play? How much play is considered too much?

By the way, machining a head here in Norway starts at around $500) if you do valve seats as well it's about $4000 It is probably cheaper to ship it to the states to get it done.

[Rasta Monsta]

Hmm, maybe I should move to Norway and open a machine shop.

[robm-951]

Unless you are boosted, the intake valves won't see any positive pressure like you are applying. How much pressure are you applying?

Assuming you are not a turbo car, your crankcase should be hooked up to the intake boot between the throttle body and afm and should only be at atmopsheric pressure or below.

Is there a problem you are trying to correct. i.e. are you burning oil through the exhaust or something?

[HondaDustR]

Depending on where you sealed off the intake, pressure can also go through the big vacuum lines from the J-boot, through the air/oil separator (crankcase breather system), into the crankcase, up the oil return passageways and into the cam area. That would probably be the easier path than through the valve guides and stem seals, unless the guides and valve stem seals are REALLY worn. If you are able to create pressure inside the engine to get it to leak out of a bad cam housing gasket, then that means either the air/oil separator hose has been plugged to contain the pressure for the test and it is in fact leaking through the valve guides to get into the engine, or the AOS system is left unobstructed and part of the pressurized test, which means that's probably where the cam gasket leak is getting it's pressure from. It is not at all uncommon for leaks to the crankcase to cause symptoms of a vacuum leak, since they are essentially all part of the same system. The crankcase is kept under vacuum through the AOS from the intake J-boot. A telltale sign of crankcase vacuum leaks is oil in the throttle body. The extra airflow through the AOS carries oil mist out of the crankcase with it into the intake.

[bebbetufs]

Thanks all for your effort to help me out.

- I plugged the J-boot where the MAF goes, so the entire intake system was pressurised.
- The leak is so big I can hardly get it to build enough pressure to show on the guage (bar).
- My car is an 1990 Turbo.
- I have not noticed any dark exhaust at all, but I am loosing some oil somewhere.
- I found some oil in the intake system. most notably on the lip created by the intake to the intercooler and on just before the throttle body. Throttle body also has oil in it but it seemed crusty and dry. J-boot is quite crusty.

I'm thinking HondaDustR is on the right track and that the air does come via the cranck breather. In that case I only need a new cam assy seal?

[robm-951]

ok, just remeber that all the connections prior to the turbo normally don't see positive pressure like you are applying. This means you are pressurizing your crankcase that should only see atm. pressure or below as well as a couple of other valves like fuel tank vapor purge system and one port of the cycling valve.

A better test would be to connect your pressure source directly to the turbo inlet or outlet.

A small amount of oil in the after turbo intake plumbing is normal.

[bebbetufs]

Originally Posted by robm-951

A better test would be to connect your pressure source directly to the turbo inlet or outlet.

I believe your'r right, but I would never have picked up on the blown cam assy gasket that way. How sensitive do you think the components you mention are to positive pressure? Wouldn't they be able to deal with some positive pressure considering they can deal with a vacuum?

Originally Posted by robm-951

A small amount of oil in the after turbo intake plumbing is normal.

Good news

[robm-951]

Originally Posted by bebbetufs

I believe your'r right, but I would never have picked up on the blown cam assy gasket that way. How sensitive do you think the components you mention are to positive pressure? Wouldn't they be able to deal with some positive pressure considering they can deal with a vacuum?

I'm not sure really. I would think most can handle some positive pressure without damaging them or pushing seals out. But it may also have you chasing air leaks that you wouldn't get during normal running conditions. This is because they are designed to seal at atmospheric pressure and below. I would also imagine a boosted engine might slighly pressure the crank case as blowby increases and/or there are leaks in the crankcase evacuation system. Personally I wouldn't put too much air pressure on anything hooked up pre turbo. Maybe a few pounds.

[HondaDustR]

I don't know how much pressure that crankcase is subjected to with a turbo vs a NA, but at least with the NA the crankcase is kept under vacuum through the AOS from the J-boot. Any significant leaks will make the engine run lean, since it is air entering the intake after the AFM (pull the oil cap off with the engine running and it gets really rough...then seal the palm of your hand over it and feel the vacuum). If the rings are worn, you'll get positive pressure in the crankcase under boost, which will go through the AOS, taking oil with it. If the rear plugs on the balance shaft housings are really loose, the o-rings have shrunk and vacuum will leak there, as well as the dipstick tube seals, oil cap seal, AOS to block o-rings. Believe me, I've been through this...any extra air leakage not only leans out the engine if it's bad enough, it also carries oil mist with it. Oil mist decreases the octane rating of gasoline...not so big of a deal on a NA, but can be a real problem on a turbo if it's bad enough, besides coking up the turbine wheel and gumming up the intercooler. Oil film in the intercooler would most likely reduce the thermal transfer to the outside air.

This I heard is a really good product, especially for turbos. I almost bought one until I got the balance shaft rear o-rings replaced and it solved my oil sucking problem. http://www.saikoumichi.com/951_page.htm
Fixing the cam housing seal is definitely a good thing to do as well.

[bebbetufs]

Thanks to all of you.

I'll change the cam housing seal as soon as I've completed a leak-down in case I need to pull the head while I'm at it.