I found out the lack of compression problem with my SX4. I heard somewhere that the push rods can come out, so I decided to pull the valve cover to see if that was the culprit.
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AI found two bent (Z shaped) push rods. A trip to my local Pick-A-Part, and I found an old DJ. I could not get the cover off (it had 1/4" hex screws), so I tried a 4.0 L in a Cherokee. I was not sure if they were the same length, but the valve cover was easy enough to remove to check. I got 2 push rods for $1.99 each. After arriving back home with the parts, I put them down in the holes and they were too short! Grabbing a flashlight, I peered down the hole to see the lifters laying sideways in the engine! I was able to use a magnet to pick them up and get them back in the holes without having to pull the head (Thank You LORD!). I put the rockers back on and had a friend crank the engine to make sure everything was OK. Immediately one of the push rods bent again. I was not sure why, but back in the car to Pick-A-Part for more push rods! (I got 4 this time). I took a socket and hammer and whacked the top of the valve spring top to loosen it. That seemed to work, as after putting it all back together, it cranked for a long time an no parts broke, bent or flew off!. I ran out of time, so I will finish putting it back together and fire it another day.
Does anyone know what causes the push rods to bend?..Rich
it sounds like your valves are seized not sure why, but I suggest a tear down of the head and have it cleaned with new valve seals and check for burrs in the valves themselves, Not 100% but that is what I would check, also which cylinder or cylinders? If it is 5 or 6/ or both then I would check for carbon build up on the head of the piston about an inch tall on #6 and 1/2 an inch on #5. I know I had some bad rings and stuff when I first bought my SX/4. You may be in for a bit of work, but since you are already halfway there it wouldn't hurt to take a peak.
I had a problem with bent pushrods. After installing new valve springs I cranked the engine and instantly bent a couple pushrods. Bought new ones, installed them, cranked the engine and bent the 2one new ones and a couple more. It was suggested to me that the lifter may have over pumped and to to install the pushrods and let it sit for a day or two. I waited 24 hours, cranked it up and no bent pushrods. That was 2 years and 20,000 miles ago.
The engine has sat for more years than it has been used. When I first built the car, I used it several times a month (off road). After the first couple years, I only used the car twice a year. I have to say that there is probably less than 5,000 miles worth of driving on the engine since the rebuild (12+ years ago). All that to say that it does sit a lot. I would agree about the stuck valves, as they probably have not had much lubricating since the lifters popped out of their holes. After the second trip to P-A-P for more push rods, I lubricated the valve stems (as much as I could through the springs) and moved the offending valves up and down by hammering a socket against the spring retainers. That must have worked, as it cranks good now with all rockers and valves moving freely.
On my Yamaha TX 750 with sticky valves I put some engine oil in the gas (1:150) like a two stroke. That helped, but note that it will only help the inlet valves.
80-82 4.2L also have an issue with #2 valveguides from the factory in about 20% of the cars and Jeeps.
I have a distributor gear on a power drill attachment for my Jeepster Commando. It gets drived 1 or 2 times a year. before starting it up each time, I pull the HEI distributor and "prime" the system with the drill. This helps lubricate everything before initial start up. I do this because that's what I was taught to do on older engines that sit more than drive. It was under $12 to make the primer and really doesn't take very long to do.
Just a suggestion for starting those 1ce a year drivers and 4x4's.
I know they do this with race engines at the track too.
The 4.0 rods are supposed to be different sized then the 4.2 rods, and that could cause them to continue bending.
I agree that it's probably varnish on the valves. You should drain the old gas out of the tank or it may re-occur.
The engine I just rebuilt had low miles, yet it took three or four times longer to clean than I expected. Years of oil inside had a layer of gunk everywhere. I ended up soaking the lifters in degreaser for a few days because there was visible junk built up around them. I also took an old lifter and drilled a hole in the bottom and made a tool that I could use to clean the cylinder bores down with. I've heard of people draining a third of their oil out and filling it with diesel oil or ATF to act as a lubricating degreaser, then running the car for a 100 miles or so.
The first picture shows the difference in height between a 4.0L and a 4.2L pushrod. The 4.0 is shorter. The second picture is the tool I made.
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(http://i1181.photobucket.com/albums/x427/captspillane/Eagleweb%20Postings/Oct20110616.jpg)
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Lifters are also different