hey guys, first post here so lets start with hey! first time jeep owner so im still figuring out all its unwanted surprises....this weeks issue so Ive got a knocking in my wk 3.7. only happens at low rmp, 750ish to1500, 0-20 km/h. im getting a light rotational knocking from what seems to be under the car towards the front. i don't think its the engine, i cant hear it when i lightly apply the throttle in park, i only get the knock in drive or reverse, usually taking off from a stop or backing in my driveway. above 15-20 the knocking goes away, thinking maybe cv joints? ive checked for play in the driver and passenger cv's, they seem good, haven't checked the front drive shaft yet. seems more like a dull knock as opposed to a metallic valve train tick. i thought rod knock or piston slap, but like i said, its not there in park, only in drive or reverse. any thoughts? thanks in advance!!

 

Check for loose torque converter bolts or a sheared harmonic balancer.

 

Welcome to the forum.

This topic shows my loose flex plate bolts.

 

are flex plate bolts really common with the wk? thought it was more of a wj issue.

 

They are common on ANY engine with an automatic transmission if they are not torqued properly when installed. The center of the flexplate that mounts it to the crankshaft will sometimes crack if the bellhousing bolts get loose or the transmission input shaft gets bent by trying to install the transmission with the torque converter already installed on the engine. Sometimes this problem doesn't show up until many miles down the road.

 

Mine were torqued to the correct spec, but the crankshaft bolts loosened.

The FSM does NOT say to use new bolts. The FSM does not say to use Loctite.

New bolts are pre-treated w/ red Loctite.

 

Jason81, welcome to CherokeeForum. Dave1123 and Wingless offer good suggestions/opinions for things to check-out and I suggest you follow through on those points. Other things worth looking into would be motor/transmission mounts, exhaust system support fasteners and pipe clearances.

After installing a new exhaust manifold, my '99 XJ (w/4.0) developed an issue where the front pipe (just after the collector flange) was knocking against the engine cross-member but clearance increased and noises stopped when in gear and under load. I made a dimple in the front pipe with a BFH and that fixed that. At a later date, after replacing motor & transmission mounts, I found the exhaust pipe resting on the transmission cross-member. Apparently, the support-rod weld had broken at the pipe, causing intermittent rattle-rumble and the occasional solid thumps (when I went over speed humps)...a nuisance but an easy fix nonetheless (see clamp-on bracket in pic) which I welded back into place after restoring set-up placement.

 

So it turns out the mystery knock is the crank bearings....ughhhh..so new motor for me! Awesome! What other jeep/Chrysler 3.7's are a direct swap? Gonna try to find a good used one...if I wanted to go to the 4.7 what would be involved? Do they share the same accessories/transmission as the 3.7? Thanks!

 

How could such a new engine have failed so quickly? The 3.7L V6 was introduced on the Liberty in 2002.

Here is a reman long block from Rock Auto.

 

Thanks for the link...hopefully I can find a good used one around here..shipping from the u.s sucks up here. Strange for it to go out with only 150000km on it...think it would have a lot more life it it! Gonna pull the oil pan tomorrow and see if there is anything obvious going on