What to do on top of the engine while valve covers are off?

wicks

Member
I've got leaky/cracked valve cover gaskets on my '94 3.9, so going to replace those. While I've got the top end apart, what else should I replace? Everything is original, untouched parts. Lots of hoses, breather tubes, etc. Also wondering if my oil lines in this year are prone to failure/fire? Have new injectors to put in when I do this as well. Also how to seal the plenum, does someone make a gasket?

What to add:
- Replace valve cover gaskets
- Replace injectors
- Check head bolt torque
- ?
- ?
 

Angus

Well-known member
If your 27 year old oil cooler lines are rubber, they are prone to failure and fire. Not really part of removing valve covers, but you should not wait to get them done. Injectors are easy since you will have the top half of the intake manifold off anyway. I had best results by putting the injectors in the rail, then inserting them into the manifold. Use silicone grease to help them slip in without rolling the o rings. Not much else under there that I can think of. Don't over tighten the cover bolts.
 

wicks

Member
Thanks, yes separate but a thought, will add oil lines to the plan and thx for the tip on mount to fuel rail first. Going to replace the valve cover bolts too, and noting that mine now were super loose, going to use a bit of locktite.

No vac lines are prone to failure here? Nothing seems dry or failing to seal in the hoses department and looks like the heater hoses were maybe replaced at some point.

How to seal intake? Just gasket goo? Hate resorting to that where there should be a gasket.
 
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Angus

Well-known member
I used a smear (very thin coat) of black RTV on the manifold halves. Anything more and you will NEVER get them apart again.
 

evilfij

Well-known member
Manual says hylomar to seal the plenum. Replace the PCV lines if they are suspect and clean out the breather on top of the valve cover (or replace it) and check/replace the vacuum line from the vacuum advance on the distributor. None of these things are that much easier with the valve covers off, but I’d do them especially cleaning the breather (it’s wire mesh so soak it in gas/brake cleaner etc.). If the plenum is full of oil, clean the Idle air control valve where it seats (be careful there is a paper gasket on it).

While the plenum is off, look at the back of the heads and the intake for leaks (heads often drip coolant off the back and the intake gasket can rot and the end seals are prone to fail).

While the valve covers are off, clean out any crap in the corners of the heads. I do NOT recommend removing and cleaning the rockers as my experience is that is asking for ticks going forward but a lot of people do take them off and clean them.

As far as oil cooler lines, I just delete them. It’s a 10 minute job (ask @WreckITFrank )
 
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evilfij

Well-known member
Atlantic British has a PCV hose kit. I’d also replace the flame trap.i also recommend installing new genuine valve cover bolts.

What @jymmiejamz calls the flame trap is what I called the breather. He also has a point on the valve cover gasket bolts. They have 8mm 12 point heads (which is annoying), but you should replace them because they have little sealing bases on them (not sure what to call it but it’s like a dab of silicone under the head that has cured). That being said, I have not had an issue reusing them and they are spendy.

Every time I think, I am going to replace these with the screw head ones off early NAS RRC (and I presume similar and older era ROW engines) but then neglect to order them. I can’t remember now whether those had the sealing bases. I don’t believe they did (I am not even sure they are the same thread pitch and length) but I am writing myself a note now to order some and ask Zach with my next parts order.
 

WreckITFrank

Well-known member
Good discussion. This is in my near future as well. Had the manual up so figured I'd post this. Looks like the 3.9 is showing 2 different bolts for valve covers? 4.0 lists a 1/4UNC bolt which looks like an 8pt from the diagram, but definitely different than the 3.9.

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evilfij

Well-known member
Late 3.9 (NAS era) have the 8mm 12 point valve cover bolts I think (maybe not 110 need to check one of those engines but heck if I know if the valve covers are original). Pretty sure there are no washers under them too.
 

rocky

Well-known member
Having had the original oil filler cap break on me, add one of those to your shopping list.
 

wicks

Member
Great thanks so much gents this is exactly the details I was hoping for - going to replace everything that seals on the valve covers while at it and the flame trap etc. Ordering the PCV kit, already ordered the bolts, but that diagram shows a spring washer and washer on the valve covers, which I don't think are there...maybe these aren't the original gaskets I'll be replacing. Sure seems like those spring washers etc should be there given that the bolts weren't even finger tight. I watched the A/B video on valve cover gaskets and spring washers/washers weren't included there either (that was a 97 motor).

Evilfij - DELETE the oil cooler lines? Is running the oil through the radiator that ineffective?

Will scope out for coolant as well. On my P38 I actually ran that leak seal stuff in the blue bottle through the coolant (for a half hour, then drained and refilled so as not to leave it circulating in there to clog up other stuff), and it cured my leaky head. About 2 years and 3K miles ago now and no other problems arose.
 
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evilfij

Well-known member
8 is a piece of foam and 11 are the things that hold the baffles in the top of the valve covers (you don’t need those, you can clean them out without removing them). 8 you could replace, although it’s probably gone by now.

The new valve cover bolts do not use washers so you don’t need those.

Yes, I delete the oil cooler lines. It’s real simple. You just pull the filter, pull the adaptor, fit a new filter, and remove the lines from the radiator. If I was someplace really hot I would not, but with synthetic I have never had an issue. The oil cooler lines is a terrible design and IMHO is not needed unless you are jumping dunes or driving through Death Valley or something. Early RRC did not have them so I am fine with ridding myself of the problem (YMMV).

BTW call Zach at roversnorth. He always gets you set up right and the cost is comparable to other sources.
 
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chuckc4

Well-known member
I am about to replace the valve cover gaskets on my '97 as a little bit of oils is weeping from the back drivers side corner. My valve cover bolts were really loose all around, I tightened them up and it helped for a while but it was a temporary fix.

Gonna change the springs and shocks too while I am at it. Kind of hoping for cooler weather, but that seems to be a waste of valuable thought processing brain space... Also hoping not to get 'ship fitters" while I am working under the hood.
 

wicks

Member
Speaking of shocks, what is the best bet for replacing without altering (stiffening) the ride? I'd like to keep it comfy on the road, and I've never seen any off-road drivers get better because they had OMEs.
 

rocky

Well-known member
Speaking of shocks, what is the best bet for replacing without altering (stiffening) the ride? I'd like to keep it comfy on the road, and I've never seen any off-road drivers get better because they had OMEs.

Bilsteins.
 
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