Knocking sounds at idle?

1993 XJ 4.0L, AX15 w/ NP231 Transfer case, stock. 218K miles

I've been hearing this knocking / banging sound coming from the area of the bell housing while sitting in neutral at idle RPMs (700 or less) If I rev the engine to 1000+ rpms the sound goes away, but comes back as soon as the rpms drop back to idle. Been going on for a couple weeks now, and seems to be getting worse. Sounded like it was missing on a cylinder at first, but I do not think that is the case.

Purchased this XJ three months ago and have done the following so far:
-Spark Plugs
-Air Filter
-Valve cover gasket
-External Slave cyl. swap ( Used throw out bearing retainer, bell housing, clutch fork & new retainer spring)
-New Clutch (pilot bearing, throw out bearing, flywheel, friction plate & pressure plate)
-Replaced transmission and transfer case fluids
-Heater control valve delete

I recently replaced a leaky valve cover with a felpro cork gasket, which hopefully has resolved some of the vac leaks. I still need to go through all the hoses, but the idle rpms are pretty steady. I have the rest of the top end felpro gasket kit that I plan to install at some point.

I can't recall I there was any knocking before I replaced the clutch, but it is certainly there now. Not sure if I messed something up on the install, but the clutch engages and disengages normally. There is a bit slight of a knocking/banging sound when first engaging 1st gear occasionally, but that could be user error.

I plan to investigate the motor mounts, trans mount looked fine when I was working with it. Should I also check the harmonic balancer? Could it be anything else?

I have not checked the compression yet either, the battery would die quickly when I tried. Starts and runs fine... I am going to try a compression test again since the battery could have just been weak from sitting. I've been driving it daily since purchase.

Always suspect recent repairs or modifications when new noises appear. I would start with checking the flywheel/flexplate bolts.

I was hoping not to have to pull the transmission again, but yes, it's probably a good idea to recheck the torque on those bolts.

Should I just replace with new ones while I'm in there? I definitely reused the flywheel bolts, can't remember if I replaced the flex plate bolts...

I'll probably switch the slave cylinder over to a metal body one from the cheap plastic one that came with the clutch kit.

You don't have a "flex-plate", you have a flywheel and yes I would replace the bolts with preferably some ARP's to call it good. That may not solve your problem, but it will eliminate any question as to the work you did.

RCP Phx said:

You don't have a "flex-plate", you have a flywheel and yes I would replace the bolts with preferably some ARP's to call it good. That may not solve your problem, but it will eliminate any question as to the work you did.

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Yes you're right, I meant pressure plate...

Any good vendor recommendations? I used to use Rock Auto, but they will not ship to CO over sales tax complications..

SV-BDN said:

Yes you're right, I meant pressure plate...

Any good vendor recommendations? I used to use Rock Auto, but they will not ship to CO over sales tax complications..

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Rock Auto will ship to some cities in Colorado.
Searching, I found this response fro Rock Auto when questioned about Colorado sales. I would imagine a lot of smaller businesses are being impacted by the new rules. Colorado needs to change its sales tax collection laws to ones similar to the rest of the states where the State itself receives the taxes and redistributes them locally .

"In response to the Supreme Court decision (South Dakota v. Wayfair), Colorado now requires online retailers, like RockAuto, to collect sales tax on orders shipped to that state. Your state forbids us to ship orders to some cities (but not all) because we do not have enough accountants to comply with their complicated tax rules.

However, we can still ship your order to any Colorado city that relies on the state to collect its sales tax. Cities that we can ship to are listed on the state website. (Hint: the list of cities with "State-Collected City Sales Tax" starts on page 4). Please consider shipping your order to an alternative address in one of these cities, such as your mechanic, your work, or a friend's house.
Thank you,
Bryan R.
RockAuto Customer Service"