Jeep engine knock fix -Cherokee XJ 4.0 Auto, flexplate bolt issue 

You're welcome, glad i could help someone, Make sure you clean the bolts a bit and apply some Loctite, otherwise they will come loose again because the thread is too coarse for the short bolt length. Before i actually found the issue on mine, i ordered some rod bearings, just in case because it sounded incredibly bad, cheers, Mike

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I'm having the same problem. When I start the motor, makes a odd rattle sound and when I turn it off, makes the rattle noise again

Glad it helped, ... hopefully you added some thread lock (e.g. Loctite), otherwise they will come loose again, the bolts are pretty short and the thread is way too coarse.

Glad it helped someone,... when i heard the noise i thought exactly the same but it made no real sense because it disappeared after a minute or 2,....anyway, ordered conrod bearings straight away, just in case. and now they sitting on the shelf ...:-) ...cheers, Mike

Seems to be a common problem of the 4,0ltr with the AW4 transmission. It really sounds like a knocking rod

Oh yes, flex plates are a common issue, loose bolt make them crack too. Alignment and correct torque on the mounting bolts make them last longer. I think i was just lucky, ... at least i could not see any cracks.

you're welcome ....

Best of luck!

@@dynoguy Turned out to be a cracked exhaust manifold....Could have been worse; I hope this helps someone else down the road. Thank you again

If i remember right, some were just loose, but at least one was a bit out

Thanks alot, ... you in my list already ...cheers, Mike

dynoguy I am honored! 👍

Take the starter motor out, that gives you access to the ring gear on the flywheel, then use whatever you can find to block it

turning the alternator is just another way to turn the crankshaft as the pulley bolt is hard to access...

Working on it!

Glad it helped someone, thanks for watching

That's most likely the power steering pump, nothing dramatic as it never really changed over the last 130000 miles

Very hard to tell from your description, can be lifter rattle as well, but can also be just one or 2 bolts about to be coming loose. Checking is easy, so why not just doing it and if they loose tighten it, if it's something else you certainly need to investigate further. A missing bolt will most likely make a hell of a noise because there are only 4 of them.

dynoguy thank you so much for the advice I check it out hopefully they r just loose an need to be tightened thank you again

You're welcome, i would also recommend to put some Loctite on them, stop it from coming loose again.

Glad it helped someone,... In my opinion this is a classic design fault, a coarse thread in aluminium, that simply must come loose under stress, rather sooner than later.

If it's the flex plate bolts, it usually disappears with revs and load. It may be a cracked flex plate, conrod or piston slap, but without hearing it, it's pretty much impossible to figure it out.

@@dynoguy I've gotta 98 Grand Cherokee with a bad knock sound. Seems to go with the RPM and can always hear it, but on deceleration it seems to quieten itself down. What's your opinion? Was thinking it was a lifter collapse but it runs way too good imo.

Manuals are different, they got a flywheel and a clutch, no flexplate at all. The clutch bolts are on the other side and usually don't come loose.

no, just take the cover plate off

Thank you very much,... i did likewise, will have a closer look at your stuff tonight.

front of engine can also be slack of the cam chain, quite common on high mile engines, it usually disappears above idle. The flexplate knock usually disappears when hot, except the bolts are really far put or it's got a crack.

@@dynoguy thanks for the info! Although with mine, the knock consists whether the engine is hot or cold, and it speeds up as you rev the motor. I’m kinda stumped on what it could be

Well, in this case i would say rod knock or piston slap,...also, sometime an exhaust header leak may sound like that, at least for the untrained ear

Hard to tell without hearing it, a cracked flex plate is quite possible, never had a rattling torque converter. Does it disappear when you put the transmission in drive, step on the brake and rev it up gently or does it get louder ? If you tap the flex plate with a hammer, it should (sort of) ring, if it only rattles you most likely have a crack. On various vehicles , I've seen cracks on the outer holes and on the crank bolts holes, but those can't be seen without taking the thing apart. Don't know how many miles your's got, but piston slap makes a tapping noise as well, mine got almost 200k and it's getting a bit more audible now..

@@dynoguy OK so I went out there with it running and put a long pry bar to the trans and engine, and held byy ear to find out exactly where the noise is. Turns out it's right above the distributer, but only that spot. Could it be a lifter sticking?

High or low pitch noise ? Low frequency "knock" is most likely piston slap or if it gets louder with load, probably a rod bearing, if its more like a higher pitch ticking noise, can be a lifter. How does your oil pressure look ? How many miles have you got on that engine ? ... cheers, Mike

@@dynoguy thanks for the quick response. Truck has 190k it sounds just like a flex plate tap and it radiates from the area above the distributer downward towards the flex plate. I'm sure it's not It's not a rod knock. its not constant it kinda comes and goes and isn't any louder when I give it gas. It goes away at higher rpm. I did have a loose flex plate which was contributing to the issue so I know what that sounds like. This noise is similar. I checked the flex plate for cracks and it looks good.. It's more of a tap that comes and goes but originates above the distributor. Probably about 5 inches directly above it. I'm thinking it's a sticky lifter. The truck has been sitting a while also. It really didn't do this before it sat. Oil pressure is really good. Stays above half way mark at idle when warm and creeps up to 3/4 when driving. Not sure the pressure off hand. Might try to fog the engine through the brake vacuum line with Seafoam. One of those things the t drive me crazy. Even if it isn't bad I gotta fix it or it will be like torture to me driving it this winter. 😂.

You're welcome... So about the same mileage as mine, If you look at my oil filter adapter o-ring video ( ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-aRwNUGu3EKA.html ), from around 17:30 you can hear my engine running. If you listen very carefully (turn the treble down and volume up) , you can hear a slight knock (no, not the blowing exhaust manifold...:-)..). I am almost certain it's piston slap as it is louder in idle, but almost disappears with higher revs. it's louder from the underside and almost impossible to localize it clearly. Does your's sound similar ?

Thanks for interest. .. It was really weird, it actually sounded like a conrod knock, but only when cold. You also need to inspect the flexplate for cracks, If you don't see anything obvious, tighten the bolts one after the other (i suggest a dab of loctite) then hit the plate gently and listen to the sound. If it rings its fine, if it rattles, you got a crack somewhere... good liuck

i ended up checking it out yesterday, flex plate was fine. but the bolts were exactly like yours, one tight, the other 3 were backed out about 1/4 of an inch. used some loctite and snugged em down real good. no issues since. well minus the ziptie my buddy out on my driveshaft lol

glad it worked, ...surprised you got to 300,000 miles wtrhout problems, mine had less than half the mileage and was already rattling like hell,...maybe my driving style ...

funny how those things work, not gonna lie i drive mine pretty hard as well

There is a few more items which may produce similar noise... timing chain rattle (usually only in idle), piston slap, (will mostly not disappear above idle) ... good luck

@@dynoguy Well i did have a knock, nothing on the flexplate. Come to find out, I have some weird thumpy clatter below the head of 3 and 4 piston. Replacing those today and I believe that will cure the problem and can enjoy my Jeep for once.

It is a 2 part cover plate and it does most likely rattle if bolts are missing. Checking the flexplate bolts is easy, so always worth to have a look while you there. However , the noise you describe sounds different to me, but without listening it's pretty hard to tell. Exhaust manifold blowing, perhaps, .. or Evap solenoid does make an intermittant tick noise as well, but that's in the engine bay.

will check out. tried to video it but the sound was just horrible. engine sounds good but on video is counts like a horribly sickened diesel. LOL. I will try again to tape it but the 4 tick then pause sounds like a spinning wheel part . any idea the bolt size of the cover plates?

The gearbox is japanese, so bolts are most likely metric, either M6 or M8, can't remember yet. Still have no idea about your ticking sound, let me know when you got the video up

you know what the sound is like? like a M16 on 3 round burst pause, 3 rds burst pause. the sound of a hollow type sound so that was why thinking g the trans, flex plate. something that rotates and hitting on something making a hollow sound. will take a day to get under there and check, replace the missing cover plates and bolts.

Well, what you describe appears to be more like an exhaust manifold leak, does it get louder with load/throttle and does the "shooting" frequency increase with engine speed ? The stock manifold is not exactly well designed and tends to crack around the weldings.I am on the third now and it starts banging at the cyl 4-5-6 joint, exactly as the previous 2 did. Also got a crack at the end where it joins the downpipe. Welding is hopeless, after a while it just cracks again. I do a lot of short runs from cold, we also have alot of rain here and every puddle is a temperature shock for the manifold, that puts alot of stress into it and makes the material rather brittle, long highway runs and warm/dry climate makes them last alot longer.

Well,... can't see the point of your question, ... just a set of spanners required to do the job

+HolzMichel .. It's the same gearbox as yours, but that's not a Toyota, it's actually an Aisin Warner AW4, no idea why so many people call it a Toyota box. Aisin Warner was formed at the early 70s and is a Joint Venture of Aisin (JP) and Borg Warner (USA). The Toyota box is similar and most likely made by AW as well, but certainly not exactly the same, i think Toyota is somehow involved in AW as well, not quite sure. It's a pretty bullet proof transmission, keep it cool and check oil regulary and it will last, only downside is rather poor efficiency., so it wastes alot of power (and fuel). The US market is quite price sensitive and in the desert it has to be simple to fix, that's why they put the cheapest/simplest manual transmission in they could find and together with no bells and whistles it made a cheap farmers ride. Just look at US trucks, cheap and simple, no one in Europe would buy a non-synchronised gearbox anymore, but US truckers are used to it. Over here, all XJ Diesels and most (if not all) 4 cylinders came with the manual box, i've seen some I6 engined ones with MT as well, but most had AT. Strange thing here is that rear LSD was a rare option which is pretty hard to find, searching for years now, but all i found was scrap metal. Apart from that, mine got all the bells and whistles, except the factory tow bar, that's why i bought it. No hitch bar means most likely not being abused, i fittied one off fleabay, they sell pretty cheap here. In the 90s, the rather rough Cherokee had to compete with Range Rovers + Co, so leather seats, plastic wood trim, AT, Aircon and electric windows were essential to reflect a similar status symbol. I recently found an old video from the 90s here on YT where Jeremy Clarkson (Top Gear) tested a 4.0 XJ, ... he saiid something like "perhaps the best 4x4 money can buy ...." ...i think he's right. Swapping the AT box into a manual car is quite challenging as this is not your old fashioned hydraulic TH700 anymore, it's all electronic, so it's not just swapping tthe transmission, you need all the wiring, the TCU, engine mapping is different on AT's so you need an AT engine ECU, radiator with oil-water trans cooler, the oil to air trans cooler in front of the radiator, all the oil pipes and hoses. Not sure if the starter motor is the same as the ring gear on the flexplate looks a bit different to the MT flywheel. Axle ratios are different with AT as well, usually 3.55,... pretty sure i forgot something...most likely easier to buy one with broken engine/gearbox and swap your good bits in.

dynoguy lots of info there :) good to know about the automatic tranny. guess i'll look to scrounge up another used B10 to keep around as a spare and sell the automatic. i have a limited slip differential in my dodge and it has pluses and some minuses. the plus side is that it does pretty good on slick and icy roads. the HUGE drawback is that the truck likes to bunny hop and go sideways on washboard gravel roads when running without a trailer behind it. especially in curves, which can get real interesting when you have oncoming log truck traffic...lol the diesel XJ was never marketed in the US as diesel vehicles aren't real popular. the only thing that really took off was dodge cummins. ford and chevy have been dinkin around with diesels too but not had the market share dodge has if i'm informed correctly the diesel XJ has a perkins diesel in it? one idea i was mulling around when it come time to do an engine swap (mine has some 300 000 miles on it) is to dig up a volvo diesel (the inline 6) and shoehorn it in there. i've been trying to find out dimensions of the stupid thing, but i guess it's gonna be a matter of actually going to a wrecking yard and putting a tape measure on it to know for sure if it's gonna fit. if you think the XJ is easy to fix then you'd love the CJ.. those things are like working on a 50's or 60's vintage chevy pickup... not much to them. my mom bought a '78 CJ7 brand new and i can still hear the whine of the tranny as the thing went down the road. it was a 3 speed on the floor and first gear wasn't synchronized at all.. the roof (hardtop) leaked like a sieve. it had the 4.2l inline 6.. that hing would climb a tree if it could traction.. mechanically the only thing that went wrong with it was the clutch went out after my folks went out pulling willow stumps out of the ground.. mom didn't have much finesse when it came to machines or driving..

+HolzMichel If that would be a Perkins i probably would like one, but as far as i know all European XJ Diesels had a VM engine. This lump wa produced by VM Motori spa in Italy and was not really designed as a car engine which caused several problems. Target application was generators and agricultural machinery and that exactly how it behaves, pretty rough. I can't tell you any dimensions of the Volvo, but it happens that i will be playing with a Perkins/CAT 4.4 I6 next week, happy to take some measurement if you like. From memory, i think it's not longer than the 4.0 I6. but it's quite tal. The general problem with diesel conversions is that your gearing becomes too short, unless you use one of these modern TDI car engines, your rev limit is around 3000rpm, that's at least 2500rpm less than the gas guzzler, so your top speed will hardly reach 60mph. I'd love to have one of these Chevy stepside pickups from the 50's but they fetch astronomical prices over here, even if almost scrap condition.

dynoguy hmmm.. i've never actually seen an XJ diesel in the flesh.. my dad used to pull wrenches for a living and he knew a guy that had one. so that's where i got my info from. so the italian engine is probably closer to truth. maybe the perkins diesel was a custom job.. hard to say the italian diesels have a heating problem in the rear cylinders.. seems to be a common thread with them. i worked on a pistenbully once that had a lamborghini diesel in it. # 4 and 5 burned up in it.. the volvo can rev a little higher than other little diesels which is part of the reason i've been tinkering with that idea.. think it winds out around 4g.. not that i would ever run up that high but at least it won't be throwing a rod if a guy did by some dumb luck run it up that hi. of course there are differential kits a guy can get aftermarket to run the gearing out a little further. i wonder how heavy the perkins/CAT engine would be? the dimensions of course would be of interest as well. ah yes.. the ubiquitous chevy stepside.. that's when GM still knew how to make a decent pickup.. they fetch insane prices in the states as well.

+HolzMichel Didn't know that Kaessborer used Lombardini engines (don't think it was Lamborghini as tou said), i was always under the impression they used something German made. The VM and so the Lombardini is not a bad engine when used for it's initial purpose, the problem starts when you try to adapt it for something else but don't think it to the end.The most common issue is aiflow around the engine to get rid of radiated heat. I'll see what i can do with the Perkins spec and let you know next week. And for gearing, bigger tyres are the smplest method

done,...thanks alot.

Which tools ?

the little piece that you used to hold the flywheel

That's not a special Jeep tool, it's just a generic flywheel locking tool. Can't remember where i got mine had it for decades, it came in a set with some camshaft pulley lockers. Just search fleabay and you'll find them in various shapes.

If you need a means of securing a bolt from coming loose and if there is no other way (e.g. a wire lock), Loctite is a widely accepted procedure. A bit of heat and the bolt can easily being removed, i don't see a problem here.... But if one of the flex plate bolts comes out, you will very likely have a catastrophic failure which may cost you thousands of $$ to repair. That's why you need to secure them, the manufacturer was rather careless here, the material combination and design must lead to loose bolts, sooner or later.

@@dynoguy i dont take kindly to locked BOLTS round errrrrrrr!!!!!

@@dynoguy i dont abide by no larked up bultz on me JERPP!!!!!

Maybe if you actually knew how to fix it it would run lol

Fully agree ..:-), ....mine runs just nice