I need some advice on this project. I’ve searched through the forums, but haven’t been able to find many posts about this specific issue. Maybe it is too general a question. So I thought I’d post my first thread. Sorry if it is long, but I figured the more info, the better.


I recently decided on the APN manifold to replace the stock cracked manifold on my bone stock 98 Cherokee. The install went well. I also replaced both motor mounts and the lower radiator hose (it was leaking). When I put the manifold in, I had no clearance issues with the 98 intake. When I fired it up I had a very high idle. I let it run for 5-10 minutes to let the pipes heat up and smoke out thinking the once it was warmed up a bit the idle would settle down, and it eventually dropped to 1200 RPM. I drove it around the block, no change. I went to bed because I had to be at work in 4 hours.


4 hours later, I couldn’t get my old Wagoneer started so had to drive the Cherokee to work (10mi round trip 40mph) I noticed that after firing, the RPMs jump to just over 2k, then settle down to about 1200, 900 in drive. Also the transmission is shifting early. I’m suspecting a vacuum leak.
On the way home I stopped and picked up a new fel-pro and some copper spray. Once I got home I sprayed around the intake with some TB cleaner and bingo, big air leak on half the runners at the head.
I let the engine cool down and took everything back apart. I sanded the header flange smooth again and reinstalled everything with the new copper sprayed gasket and torqued the bolts back down to 24ft-lbs per spec. (except for the one behind the #4 pipe which I guessed at with wrench) in the order on the APN installation instructions. This is when I noticed the difference in thickness between the new header flange and the intake flange. I plugged all the vacuum ports on the intake just to rule them out. I fired up the jeep once again and this time the RPM’s didn’t shoot up past 2k, but the idle still settled around 1k RPM. Still too high. I hooked the brake booster back up and drove around the block. No change.
When I got back to the garage, I sprayed around the intake again with TB cleaner and still have an air leak. So I grabbed a wrench and tightened the top bolts on the intake about a 1/8th turn. The RPMs immediately started dropping. I think I ended up adding 1/4-1/2 turn past what my torque wrench said was 24ft-lbs.


Now the Jeep is running well and idles smoothly. However I am worried that I over tightened the bolts to get the intake to seal enough. The transmission still shifts between 1st and 2nd quicker than I remember and I still think there is a leak on cyl 1, but I don’t want to crank down on the bolts any more. What kind of damage could I be doing in the long run by over-tightening them?


I could take the header back off and remove some material where the washers sit, or I was thinking I could cut a washer in half and place it on the intake to add some material there. What do you guys think?
Here is a picture of the bolt on cyl #1







Thanks for the help!

 

It looks to me from the photo that the new exhaust manifold is thicker than the intake manifold so the washer that is meant to hold both down isn't really making contact with the intake manifold much. Is it even necessary to remove anything other than the bolt/washer to remove some some metal and make the area flat?

 

I could try to do #1 without removing anything. I would want to do the rest though since I think the entire flange is the same thickness. Also, isn't it dangerous throwing sparks around the engine from a grinder?

 

I have always used thin bead of Permatex ULTRA Copper RTV with the gasket per a drag racing buddies suggestion, and I have installed a bunch of after market headers with no leaks, I would not worry about torquing it down some more... (Just don't snap the bolt) PS: I use a torque wrench on a lot of things, but Jeep intake/exhaust bolts I generally don't bother.

http://shop.advanceautoparts.com/p/p...2160/7160075-P

 

Did you use the RTV around just the intake ports, or both intake and exhaust?


Looks like I'll be pulling it off again. After messing with the transmission linkage I took it out on the freeway. I fixed the shift problem, but when I got off the freeway I didn't have as much deceleration, I hit the throttle in the parking lot and the RPMs hold high (1500) for a second or two before dropping back, and I can almost hear a hiss. The idle is OK, but I think the leak is back. Should I tighten the bolts again for the drive home?

 

Not uncommon with the APN manifolds that intake manifolds need some filing.

Forget using RTV.

 

I use the Ultra Copper RTV on both Intake and Exhaust part of the gasket.

Lately I have been using the eBay dual pre-cats header (00-01) because I do a lot of motor swaps into those years of earlier motors and they need a header to fit the larger exhaust ports, I do recall a couple of them having different heights between the exhaust and intake, but not sure how bad they were. My daughter's DD Cherokee was around 4 years and 20K plus miles and never leaked, her trail rig has been done for 2 years but only a few miles on it, but still no leak, the rest have been sold shortly after swapping but never heard a complaint.

 

As far as torque specs. Someone correct me if I'm wrong but...

24 lbs is cold torque. I found some info that suggested tightening everything to 24, letting the motor come to temp, let it cool, then re torque to 39 ft/lbs. I skipped the warming up step. But I tightened to 24 in the correct order, then retightened to 39 + a slight nudge, in that same order.

But it does look like flange thickness is what you're running into. Don't be afraid to torque those bolts. Just do so in small increments instead of going fully tight one by one.

 

This is from ALLDATA