Help OPDA not seating about 1/8th inch off base

Jcraig

Jcraig

TJ Enthusiast
Supporting Member
Joined
Jul 25, 2019
Messages
105
Location
florida
Pinned the old OPDA and removed as described in the several videos. Small dia Phillips head screw driver dropped the shaft through all three holes. However the new OPDA refuses to seat and remains about 1/8 inch out despite attempts to wiggle it in.
Update: Well couldn't leave bad enough alone so managed to get it out of time far enough to so it will not even run.
 
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Follow directions from the FSM. Here's a paraphrased version:

1.) Pull the ODPA
2.) Put the pin back in the OPDA to line up the disk with the housing.
3.) Rotate the crank to get #1 piston at TDC on compression (timing marks on front of motor lined up, feel compression with #1 plug removed).
4.) Install the OPDA. If you have to, use a screwdriver to rotate oil pump through the OPDA hole to allow the OPDA to seat.

Done.
 
g.hayduke said:
Follow directions from the FSM. Here's a paraphrased version:

1.) Pull the ODPA
2.) Put the pin back in the OPDA to line up the disk with the housing.
3.) Rotate the crank to get #1 piston at TDC on compression (timing marks on front of motor lined up, feel compression with #1 plug removed).
4.) Install the OPDA. If you have to, use a screwdriver to rotate oil pump through the OPDA hole to allow the OPDA to seat.

Done.
Click to expand...
Probably was trying that as you wrote your reply. If the timing marks line up, does that mean TDC compression stroke? Or, do I still need to feel the compression on #1 as I am clueless as how to do that. Will google the timing marks location. Thanks for your reply. It is much appreciated.
 
Don't believe there are timing marks on this motor. Only on the crank pulley. It has a single notch. The cover over the timing chain has no marks I have found.
 
Jcraig said:
Probably was trying that as you wrote your reply. If the timing marks line up, does that mean TDC compression stroke? Or, do I still need to feel the compression on #1 as I am clueless as how to do that. Will google the timing marks location. Thanks for your reply. It is much appreciated.
Click to expand...

You will feel the compression as the piston comes up to TDC, once it hits TDC there should be no compression and then the timing mark should be on TDC at the lower accessory pulley.
 
Thanks for your help. I find the notch on pulley but am not able to see any marks recognizable as timing marks any where else. Any idea where they are?
 
Jcraig said:
Thanks for your help. I find the notch on pulley but am not able to see any marks recognizable as timing marks any where else. Any idea where they are?
Click to expand...

This is a pic of a std timing cover for the 4.0. There should be a casting with the marks as you can see.

time cover.jpg
 
The marks are difficult to see looking down from the top. I actually lay underneath and use a mirror. Some remove the serpentine belt for a better view.

On the TDC question, with a 4 stroke motor like this, each piston comes to TDC twice for each full cycle like so:

1.) Piston goes down from TDC to BDC on intake stroke
2.) Piston goes up from BDC to TDC on compression stroke
3.) Piston goes down from TDC to BDC on power stroke
4.) Piston goes up from BDC to TDC on exhaust stroke

Then the cycle repeats. So the marks are going to line up at the top of compression and also at the top of exhaust. You need to line them up at the top of compression.
 
Will look for the timing marks again but located the TDC compression stroke by a balloon taped to the end of a hose pushed into the number 1 spark plug hole. Double checked by removing the balloon tube and used a wire to verify TDC. Moved the oil pump slot about a 16th of an inch and the OPDA Dropped in smooth as silk. Am going back out again to see if I can find the timing marks and verify TDC. The picture of the cover was very helpful. I must just be missing them. Greatly appreciate the ideas and help. Thanks.
 
So went out again this morning after finding TDC and finally got the the OPDA reinstalled this afternoon and started up perfectly. Threw a CEL at about two miles from home. Several changes in the OPDA setting kept giving a CEL. So after a ten minute battery disconnect and a 1CM movement in the direction that seemed to be producing positive results I believe the issue is done with. Took what I hope is the final test drive with not another CEL on a 20 mile test drive of errand running in town and highway driving that included a couple of hard accelerations up to 4500 rpms 2,3,and4th gears. Also had 7 shut downs and restarts. Will let finding the timing marks reside on my bucket list for a while. Thanks to both you guys for taking your time to help. Guys like you are an immeasurable asset to the forum and make the experience of owning a Jeep both more enjoyable and rewarding.
 
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Congratulations on getting your problems fixed! I'm sure you learned a lot in the process.

I am about to change out my OPDA. Do you have a sense of how and when things went awry?
 
ike_hike said:
Congratulations on getting your problems fixed! I'm sure you learned a lot in the process.

I am about to change out my OPDA. Do you have a sense of how and when things went awry?
Click to expand...
Not certain exactly what happened but here are some thoughts about what seemed to be potential problems.
1. Probably should have removed the plastic pin from the Crown and used it to pin the OEM OPDA as it would have provided an OPDA removal with less play. I believe the slack left the slot for the oil pump drive in a position so the Crown would not seat on the base.
2.Tried to force the Crown by twisting with more force.
3. Was to late to realize that the oil pump slot could be move a small amount to achieve alignment.
4.*** Pretty sure I tried reinstalling the OEM to try to realign the holes. Had been at it a while and should have quit. By the time I finished on the first start up the engine would only barely run for a few seconds and produced a couple of backfires. I may have at one point tried to turn the crankshaft to align the new OPDA with the oil pump slot. Pretty safe to say probably didn't miss any mistakes.
Sorry I don't have better info but I tried so many things I know I have forgotten some and probably confused on others.
If I were to do another one I would use either the plastic pin from the Crown or an allen wrench that provided a close fit when pinning the OEM OPDA.
One of the things I do not understand is, I had to find TDC of number 1 to get my unit to work. So does that mean when the unit OEM unit is pinned the number 1 is TDC? And if so how is on compression instead of exhaust TDC, when as I understand it must be on TDC compression. I think know the answer but maybe potential confusion might be avoided if one of the members respondes to this.
Best of luck on your install. Don't rush or force it and you should be fine.
 
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On your last question, about the OPDA timing...
There is a 2:1 reduction ratio between crank and cam. While the crank must complete 2 complete revolutions per #1 cylinder combustion cycle, the cam only turns one revolution.
 
djbutler said:
On your last question, about the OPDA timing...
There is a 2:1 reduction ratio between crank and cam. While the crank must complete 2 complete revolutions per #1 cylinder combustion cycle, the cam only turns one revolution.
Click to expand...
Thanks. Helpful.
 
g.hayduke said:
Follow directions from the FSM. Here's a paraphrased version:

1.) Pull the ODPA
2.) Put the pin back in the OPDA to line up the disk with the housing.
3.) Rotate the crank to get #1 piston at TDC on compression (timing marks on front of motor lined up, feel compression with #1 plug removed).
4.) Install the OPDA. If you have to, use a screwdriver to rotate oil pump through the OPDA hole to allow the OPDA to seat.

Done.
Click to expand...
New to the forum but have lurked since purchasing my LJ in 2018. I’ve really appreciated the sound advice from the forum catching/keeping the LJ maintenance up - today in particular. g.hayduke’s summary - especially #4 was key to seating the new OPDA in fully - otherwise it nor the original unit would not seat - even with the plastic alignment pin in and no change to top dead center. I was doubting my work- thinking I missed something or screwed up the top dead center procedure. But....a minor/gentle turn of the oil pump slot down the OPDA hole (using a long screwdriver and flashlight) was needed to align it with the end of the OPDA. I guess this oil pump slot can get turned a bit when you remove the old OPDA, requiring it to be aligned before installing the new one.
 
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