4.2 to 4.0 head conversion
06-09-2012, 06:29 AM
#1
Newbie
Thread Starter
4.2 to 4.0 head conversion
I did the 4.2 to 4.0 head conversion on 258 J10. The only problem I'm having is an oil issue. I was using the plastic jeep pcv for the new head the one that your supposed to use for that year, it's just a plastic elbow with a small opening in the bottom. That was causing oil to come from the line running out of the 2nd opening in the valve cover in the middle that goes to the bottom of my Weber 38 air box and getting oil everywhere. I assumed I wasn't getting enough vacuum through the very small opening in the plastic pcv elbow. So I drilled it out to a 1/4 inch. This seemed to solve the problem, no more oil running out of the air filter. The new problem is that after 100 miles I've gone through a quart of oil. So then I rigged a "real" metal pcv to fit and tried again. Now I'm back to the original problem of oil filling up the air filter after 30 miles. So I've done a compression check and these are the results: 145, 150, 150, 160, 150, 150. So am I safe to assume it's not a blow by issue. Could it be the wrong valve cover for the head I'm using? The head is a from a 95 and the valve cover from a 91, at least that's what the salvage place told me. Should I move the pcv to the middle opening, or is this something else?
06-09-2012, 08:20 AM
#2
CF Veteran
This is a problem on the 4.0 too.
my 87 4.0 will slobber oil from that stupid idea too.
You made the problem worse by enlarging the hole.
There is a small baffle there that is suppose to kind of cure that.
But it doesn't and like you mention it doesn't take a lot of blow
by to overcome it.
Heres a fix from another forum:
Happy Trails.
Did you notice a power increase without doing a cam swap too?
my 87 4.0 will slobber oil from that stupid idea too.
You made the problem worse by enlarging the hole.
There is a small baffle there that is suppose to kind of cure that.
But it doesn't and like you mention it doesn't take a lot of blow
by to overcome it.
Heres a fix from another forum:
My old beater Jeep (winter driving and trips to the home improvement stores) suffered from a common problem. Starting around model year 1987 the 4.0L Jeeps used a CCV (crankcase ventilation system) instead of a PCV (positive crankcase ventilation) valve. The difference being that the CCV is a "closed" system on the Jeep 4.0L requiring two ports in the valve cover. One large hose was for intake/return air from the airbox and one tiny (inside diamter of the tube is smaller than #2 pencil lead) tube for the crankcase gases to escape into the intake manifold.
The problem with the system is that the CCV valve (which is inside and built in to the valve cover -a nonserviceable item unless the entire valve cover is replaced) often got clogged up no matter how good the maintainence on the vehicle. This causes gases and oil mist to flow backwards through the system (it has to have some way to escape) through the larger tube and into the airbox fouling the filter with oil.
I replaced all the hoses in the CCV system about 2 years ago (~$115), but it kept fouling the air filter. I was going to break down and buy a new valve cover (at the cost of $200) but ran across a recommendation on a jeep related site buried within the forums there.
The solution is to remove the grommet on the valve cover (for the small line) and replace it with a grommet for a 1985 CJ7 along with the PCV valve for the CJ7. Prior to replacing the grommet, you must bend a metal tang inside the valve cover using a screwdriver. This tang is what forms the "spring" in the built in CCV valve. Bending it up, opens the valve all the way permanently.
Next, take a 3/8 inch quick connect air chuck (the kind you screw into a blow-gun or tire chuck for use on an air compressor equipped with quick connect fittings) and replace the screw in nipple on the manifold (where the original tube attaches) with the air chuck. The chuck is an exact fit (threading and length)but has a much larger internal diameter for the crankcase gases to flow. Finally run a section of 3/8 inch fuel line from the newly installed PCV valve to the new air chuck nipple you screwed into the intake manifold. Attach a hose clap at each end of the fuel line and you're done.
I just completed this permanent fix for the idiotic and horribly designed system Jeep/AMC/Chrysler designed way back in the 80s. It works like a dream. No more blow back into the air box.
Total cost for this fix was $15 and that included a new air filter.
The problem with the system is that the CCV valve (which is inside and built in to the valve cover -a nonserviceable item unless the entire valve cover is replaced) often got clogged up no matter how good the maintainence on the vehicle. This causes gases and oil mist to flow backwards through the system (it has to have some way to escape) through the larger tube and into the airbox fouling the filter with oil.
I replaced all the hoses in the CCV system about 2 years ago (~$115), but it kept fouling the air filter. I was going to break down and buy a new valve cover (at the cost of $200) but ran across a recommendation on a jeep related site buried within the forums there.
The solution is to remove the grommet on the valve cover (for the small line) and replace it with a grommet for a 1985 CJ7 along with the PCV valve for the CJ7. Prior to replacing the grommet, you must bend a metal tang inside the valve cover using a screwdriver. This tang is what forms the "spring" in the built in CCV valve. Bending it up, opens the valve all the way permanently.
Next, take a 3/8 inch quick connect air chuck (the kind you screw into a blow-gun or tire chuck for use on an air compressor equipped with quick connect fittings) and replace the screw in nipple on the manifold (where the original tube attaches) with the air chuck. The chuck is an exact fit (threading and length)but has a much larger internal diameter for the crankcase gases to flow. Finally run a section of 3/8 inch fuel line from the newly installed PCV valve to the new air chuck nipple you screwed into the intake manifold. Attach a hose clap at each end of the fuel line and you're done.
I just completed this permanent fix for the idiotic and horribly designed system Jeep/AMC/Chrysler designed way back in the 80s. It works like a dream. No more blow back into the air box.
Total cost for this fix was $15 and that included a new air filter.
Did you notice a power increase without doing a cam swap too?
06-10-2012, 02:39 PM
#4
Newbie
Thread Starter
I'm a little confused by "you must bend a metal tang inside the valve cover". Both openings in my valve cover look the same on the inside, there does appear to be a metal "tang". But it's in both and they are both open already. They are at an angle with a 1/4" gap at one end with 2 feet holding it up then attached at the other end. These are not moveable, there is no spring action to them. So after doing this mod expect for bending the tang that is already always open, I'm still having the same problem. Just drove 5 miles and the oil is dripping out of the air filter already. Maybe I should back up a little and say that it didn't do this at first, it's only been for the last 500 miles that I've been having this oil problem. I should add that I have noticed one other oil problem recently and that is that after you drive for several miles and come to a stop the oil pressure drops to 0 then comes back up when you accelerate. My plans is to pick up a mechanical oil gauge and temporarily hook that up and see if I still get the same readings. Are these two problems related?
Last edited by akellym; 06-10-2012 at 03:02 PM.
06-11-2012, 09:25 AM
#5
CF Veteran
Join Date: Dec 2011
Location: Pasadena, MD
Posts: 4,006
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Year: 1987
Model: Wagoneer
Engine: Renix 4.0
had the same issue on a 87 4.0. i was getting blowby because of incomplete burn. replaced plugs, issue solved. and i didnt replace anything on the CCV system.
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