Calling out to the 258 gurus

[jamesweed]

Ive just finished a 4.0 head mod with Mopar MPI kit on a mid 80s AMC 258 i6 / 4.2l block. The block has been totally rebuilt, as was the head, all new parts. The jeep runs great, good throttle response cruise up hills no problem(had carter bbd previously), idles smooth. its got about 200 miles on it since rebuild.

However,

I've got an annoying ticking noise seems like coming from cylinder 6, been there since the begining but seems to be getting louder. Leaning over the engine at idle you cant here it, but at around 1500 rpms you barely pick it up. Its very apparent from the INSIDE of the jeep when driving with a load on the engine, and more so during deceleration with engine in gear(engine braking).

I set lifter preloads at about ..055, at the upper tolerance, because I hate valve lifter noise, thought I would avoid that by going on the high side.

I used a stethoscope and probed around and Ive got the loudest noise on the exhaust manifold tube at head, but I can still here faintly on passenger side of engine down by the cam and lifters.

Im thinking exhaust leak, it's a used cherokee header, But Id like your input. Im pretty worried about it.

The back of the head is hard up against the firewall, even more so than the AMC 258 i6 / 4.2l head that was on there, so I hear EVERYTHING from inside.

PLEASE GIVE SOME INPUT!!!!!

thanks, James

 

[IOPort51]

I am hoping that it is an exhaust leak. Instead of a stethoscope use a couple feet of 1/2" plastic hose. one end in your ear and the other in the area of the noise. this will let you "hear/feel" the escaping gas from the gasket if is is in fact leaking.


Did you torque the intake exhaust after it was in the jeep or before you put it in?? Those things are a PITA to get a socket on when they are out in the open, once you are in the engine compartment they are even harder. getting washers that will actually put pressure on both the AMC 258 i6 / 4.2l and 4.0 manifolds at the same time can be a challenge too.

can't wait to see how this turns out.

 

[jamesweed]

IO,
yes I torqued the intake exhaust bolts BEFORE I put the engine in....they are indeed a pain to get a torque wrench on after the engine is in. I thought I saw somewhere these should be retorqued after some running, but never could find that info again. I think the design in mounting these manifolds is total ...uneven thicknesses of mounting bosses from intake to exhaust....

Ill try the hose thing tomorrow. I really hope its a leak....

 

[IOPort51]

OK that's a red flag. How much difference did you have between the intake and exhaust??



If you look at the bottom right corner you can see my front stud bold. Yes I used studs rather than bolts and I cut washers from 1 1/4" cold rolled shaft for the bridge washers. I recommend it. Do you have more difference in thickness than this??

 

[CJ007]

It might just be an exhaust leak and being against the firewall it is magnifying it. Do you have a transfer drop kit? Those can cause the head/valve cover to rub the firewall. The drivetrain lowered in the center/rear down tilts the engine up in the front.

Maybe the spark plug or a cracked wire, I have banged them lighly putting them back in and the gap closes or it can crack. Check the wires by running it in the dark and look for the spark. With all the other cylinders running good you might not notice a minor misfire.

Hopefully its just something simple since you are not past the break in period yet .

 

[Old Dog]

. I thought I saw somewhere these should be retorqued after some running, but never could find that info again. .

Everything on the engine should be retorqued after it has gotton warm and cooled off again.

 

[jamesweed]

OK that's a red flag. How much difference did you have between the intake and exhaust??



If you look at the bottom right corner you can see my front stud bold. Yes I used studs rather than bolts and I cut washers from 1 1/4" cold rolled shaft for the bridge washers. I recommend it. Do you have more difference in thickness than this??

Yes there was more than this, preobably 3/32 to 1/8 difference in thickness, exhaust manifold is thicker than intake. To compensate I made some shims from fender washers cut in half and put them under the domed washer on the intake side of the bridge. I used one on cyl 1 and two shims on cyl 6, as that one looked to be more off. Ill try and pull a shim from that back one and retorque evrything, hopefully Ill hear a difference.

Thanks for the Pic and input, Ill post results.

 

[jamesweed]

It might just be an exhaust leak and being against the firewall it is magnifying it. Do you have a transfer drop kit? Those can cause the head/valve cover to rub the firewall. The drivetrain lowered in the center/rear down tilts the engine up in the front.

Maybe the spark plug or a cracked wire, I have banged them lighly putting them back in and the gap closes or it can crack. Check the wires by running it in the dark and look for the spark. With all the other cylinders running good you might not notice a minor misfire.

Hopefully its just something simple since you are not past the break in period yet .

No transfer drop kit, Its all stock from bell housing back. Id love to find a way to get some space on that firewall for the back of the head though, the Alum cover on there now seems much beefier than the plastic AMC 258 i6 / 4.2l one was.. its really jammed up on there, Ball peen hammer next time the head is off maybe.

 

[73CJ]

My head was up against the firewall. Main cause was deteriorated front body mounts. The tub was also on top of the bell housing.

A body lift might help too. Take a look.

 

[Torxhead]

Having little or no clearance between the valve cover and fire wall is a common issue with the AMC 258 i6 / 4.2l and the aftermarket valve covers seem to make it worse. I was able to get a little more by loosening the body mount bolts and prying the body back. Having tired engine mounts will also be a cause of this issue, but in your case, with a rebuilt engine, they are probably in good shape. I also got some more clearance with a 1" body mount installation. The aluminum valve cover that I paid a fortune for years ago is up in the rafters.

 

[bondo258]

RE: Firewall clearance.

Which set of engine mount bracket holes are you using?, also maybe mount the Tranny Support "shovel' forward one set of holes, if you're on the forward most set of tranny mount holes.

Will probably be a problem if you use a fan clutch, and have a three row rad. A ten dollar spacer, in place of the clutch should work.

Check your prop shafts for binding, too. if you do this.

My stock body mounts are also in need of repair, and until last week my AMC 258 i6 / 4.2l had the rear heater hose behind the aftermarkrt Alum valve cover, with no rubbing whatsoever. Moved it topside when I replaced my hoses last week.

 

[jamesweed]

RE: Firewall clearance.

Which set of engine mount bracket holes are you using?, also maybe mount the Tranny Support "shovel' forward one set of holes, if you're on the forward most set of tranny mount holes.

Will probably be a problem if you use a fan clutch, and have a three row rad. A ten dollar spacer, in place of the clutch should work.

Check your prop shafts for binding, too. if you do this.

My stock body mounts are also in need of repair, and until last week my AMC 258 i6 / 4.2l had the rear heater hose behind the aftermarkrt Alum valve cover, with no rubbing whatsoever. Moved it topside when I replaced my hoses last week.

Im using the rear holes, I do have a fan clutch. Def will investigate this. As for the ticking, I removed a shim that I made for cyl 6 and retorqued every bolt in order and no change. MY gut is telling me that if I cant hear it leaning over the engine without a tube or stathscope then it cant be so bad...or is that wishful thinking? It idles smooth, runs smooth, if it was a bad lifter I think It would be obviously a bad lifter, like serious noise at all rpms and crappy running. My exhaust manifold was a junkyard donor off a wrecked cherokee. could be that it has a crack somewhere, Im gonna pull it and DYE Pen. it. Shoulda done that first but I was in a rush I know. But thanks all for your comments.

 

[reckboy]

Im using the rear holes, I do have a fan clutch. Def will investigate this. As for the ticking, I removed a shim that I made for cyl 6 and retorqued every bolt in order and no change. MY gut is telling me that if I cant hear it leaning over the engine without a tube or stathscope then it cant be so bad...or is that wishful thinking? It idles smooth, runs smooth, if it was a bad lifter I think It would be obviously a bad lifter, like serious noise at all rpms and crappy running. My exhaust manifold was a junkyard donor off a wrecked cherokee. could be that it has a crack somewhere, Im gonna pull it and DYE Pen. it. Shoulda done that first but I was in a rush I know. But thanks all for your comments.

Just curious if you got this sorted out and if it was a manifold/gasket issue?