Idunno

What I did after removing the breather box for access to the left side -
1. Loosened and backed off 4 trans mounts nuts.
2. Loosened all fasteners on main mounts. Removed the 2 nuts from the through-bolts on both sides, and removed the nuts off the 2 mount studs protruding downward.
3. With a 4X4 between the jack and the forward most part of the oil pan - just aft of the front wall - I jacked the engine to remove the load on the through-bolts.
4. Slid the through-bolt out of the left mount along with the bolt that goes in from the top. Slid that mount off. It fell apart in my hands. The rubber had crumbled away and was sitting there captive in the mount. The through-bolt sleeve fell out.
5, Replaced the left mount. No issues. Went together smoothly and I spotted all fasteners. Did not tighten any of them.
6. Repeated 4 and 5 on the right side. A little more fidgety than the left side but only took a couple minutes longer. This mount was cracked 360° around the sleeve but had not crumbled.
7. Let the engine settle back down onto the mounts. Tightened all main and trans mount fasteners/nuts.
8. Followed the exhaust system back and noticed the pipe/converter joint area touching the trans mount cross member. Loosened the clamp at that joint, placed a jack under it and raised it up to clear, Tightened the clamp. Good clearance.
9. Replaced the breather box.
10. Started the engine and immediately got a very noticeable vibration that was not there yesterday. You can feel it vibrating the doghouse down to and including the front tires.

I got underneath again while it was running and made a study of the underside for any engine/chassis hard contact. Nothing was contacting. There's no way I'm going to accept this level of vibration.

I drove it around to get an idea at what RPMs the vibration is most noticeable. Basically, it smooths out as the RPM increases. It's most noticeable at idle in 1st gear or reverse gear (automatic), and less in neutral.

Could this be a harmonic balancer issue that was not transmitting through the old mounts? Any ideas?

Thanks.

lawsoncl

What type of new mounts did you use? Rubber or polyurethane? Poly is firmer and transmits vibes much more.

Idunno

Rubber. I know the poly isn't exactly vibration damping. It's more for durability. The mounts I used are made by Rusty's -

https://www.rustysoffroad.com/rustys...-xj-tj-yj.html

Idunno

Just a thought; Maybe I should loosen the frame mount fasteners on the main mounts and the trans mount nuts, start the engine and see if it simply needs to self-align the new mounts onto the chassis up front and trans cross member. I tightened up everything before starting the engine. Maybe it's sitting there all locked down but kinda kinked.

Would that make a vibration difference in Park?

Going to give it a go.

Idunno

Loosened up the frame fasteners and trans mount nuts, started the engine and revved it a few times. The vibration immediately fell off to a more tolerable level. Tightened everything back up with the engine running. I can live with it now. I expect the new mounts to settle in. Over the next couple months I'll repeat the foregoing just to see if the vibes settle down more.

playbass

The vibes will likely settle after you drive it a while with rubber mounts. Doesn't sound like you replaced the transmission mount which could be shot too and causing more vibrations.

Idunno

Yep, replaced it same time as main mounts.

Reading around a bit the vibration I have sounds like the harmonic balancer is giving up the ghost. The vibration is rhythmic, like an oscillation changing from crescendo to decrescendo, and probably not noticeable before with the crumbled old mounts installed. Closest I can relate it is a twin engine propeller driven airplane when the prop speeds aren't synchronized. It sounds like a Wah-Wah-Wah oscillation. Located a new balancer and will attempt to change it this coming week night.

cruiser54

You beat me to it.
Also, how tight did you make the horizontal bolts and nuts from mount to engine bracket?

Idunno

Ah, thanks for stepping in here, I backed those off just enough to see air then snugged them so that the bolt heads and nuts are just snug against the brackets to prevent fwd/aft slop. I left the frame attaching fasteners torqued (by Armstrong, Wrist & Company).

Now, after that did not bring the vibration back to where I think it should be (nil, if possible) I began running around the internet looking for clues. Some off-roaders pointed out the bracket bolts will sheer (off-road terrain use) at the block bosses because the factory bolts are too long for the holes and tightening them bottoms them versus stretching them into their elastic ranges. Reading that, I dove beneath the bumper again to see if either side brackets had busted bolts causing the vibration. I realize if one side had all bolts broken the calamity would be obvious. But, if the brackets are "working" on the bolts because they are not actually retained dead-snug against the block perhaps they might be vibrating freely. I still need to check that and then get some washers underneath those bolts and Torx fastener heads to space out the bolts. Will probably get some grade 8 replacements.

In the meantime, tonight I removed the harmonic dampener and I'm glad I did. The rubber is like plastic and chipping out from between the hub and belt pulley ring. Plus, there's a slight groove worn on the inside surface of the pulley ring that spins adjacent to the timing cover. I looked at the timing cover but it's piled with crud that needs to be scraped off and then cleaned. A corresponding damage arc in the cover matching the pulley ring groove was not immediately visible on the cover. I thought it would be obvious. Maybe a stone got lodged between the balancer and timing cover and then spit out at some earlier time and the crud built up after on the cover. Once I get it cleaned off I can inspect it further. I did not have a leak out of the seal and the old balancer sealing journal is smooth. Probably should R&R that too. That said, a seal in good condition here tells be my crank is spinning true.

Idunno

Well, gents and otherwise, change your harmonic balancers. If you're on either side of 200K miles just do it for the fun of it. I didn't suspect mine because it looked like it was in good condition. But, because the rubber had age-hardened into plastic it wasn't damping anymore and that turned out to be a big contributor to the vibration this thread is all about.

I still have some vibration and will continue chasing it down. Next comes the mount bracket bolts. Going to remove them this coming weekend to put washers under the heads. Then I'm doing a compression check followed by a look under the valve cover.

Spencer_P

You make it sound easy, I thought it was a pretty difficult task?

Idunno

Not hard. You can find videos of people changing the balancer but they kind of go over the top removing stuff.

The way I did it - You may have to remove your electric radiator fan if you can't fit a breaker bar with a 15mm socket to loosen the center bolt on the tensioner pulley, but that's about it. I didn't have to remove the fan or anything else. I loosened the tensioner, got the serpentine belt out of the way (not off) and removed the harmonic balancer by accessing it from beneath the front end. It's plainly visible and accessible from beneath and pretty easy to bolt up the puller as well. You just need to get comfortably situated and have a decent light positioned correctly. I did have to get shorter bolts for the puller than the ones supplied with it because the puller would otherwise be spaced too far out and conflict with the front clip.

The center bolt on the balancer is pretty tight and you'll spin the engine trying to break it free. I took two of the puller bolts and threaded them into two of the three threaded puller holes in the balancer. Then I used a breaker bar & socket to loosen the center bolt while holding the balancer from rotating with a pry bar slipped between the two puller bolts. If you have a breaker bar long enough you can support the free end using the floor rather than your other hand. Once you break the center bolt free you can spin it out by hand. I did not have the installation tool but I made one from a piece of 1/2" X 20TPI all-thread with a nut welded onto it to create a bolt. I did that because I could not find a suitable bolt that size with full threads, whereas I could find the 1/2" all-thread locally. The tool consisted of the bolt I made (about 4 inches long), eight 1/2" fender washers and two additional 1/2" X 20TPI nuts. You can find videos on how to make the installation tool. Using this tool it took me about 10 minutes to install the balancer.

Spencer_P

Awesome, thanks!

Idunno

You're welcome.

Precautionary note: When you thread your puller onto the balancer use bolts that will allow it to fit flush against the front of the balancer but won't be so long as to protrude through the balancer and into your timing cover (possibly damaging it). Take a small rod (piece of coat hanger wire or similar) and slip it through one of the balancer puller holes until it contacts the timing cover. Note the length from the timing cover to the front face of the balancer puller. You don't need to hold the puller against the balancer while you do this. Just don't forget to add the thickness dimension of the puller to the distance between the timing cover and the front face of the balancer. Get bolts that are about 1/4 inch shorter and you will be good. The reason for this is because you want an even pull on the balancer and the only (best) way of doing that is to start out with the puller bolted flush against the front face of the balancer. If the puller is even slightly cocked the pull won't be even and it will bind on the crankshaft when removing it.

Also, use some motor oil on the puller and installer threads to reduce the friction. Lube the new balancer outside seal journal and center crankshaft mating hole as well. The new balancer will slip over the crankshaft extension by hand enough to line up with the woodruff key on it.

Idunno

Update: Vibration resolved. The new Rusty's off-road mounts were causing the vibration. They're just too rigid even though they're rubber (not polyurethane). I bought another set of main engine mounts from O"Reilly's and they completely tamed the vibration. The 96 is now almost as smooth at idle as my wife's 2007 Toyota Pilot. The mounts I bought from O'Reilly's are made in China for the brand Power Torque (P/N B2572). They are the spitting image of the original factory mounts. Will see if the rubber holds up over time. The Rusty's mounts aren't bad, BTW. They're just poor vibration isolators. They have about 1/2 the rubber height between the through-bushing and the bottom steel frame than the factory mounts do.