Pilot bearing failure again? Opinions needed

[BlurpleXJ]

Gentlemen of the SEC! I'm back for a bit and trying to get the Blurple in proper shape before I stable it for two or three years. I am going to a new post in South Korea and the Army won’t ship cars there. I don't want to come back to the US and immediately have to work on the jeep. I need your wisdom.

I know this is long, but I'm trying to get the detail questions out of the way up front.

- problem -

The problem is that I was having a really hard time getting the trans in gear (AX-15) sometimes especially when stopped. First gear required a lot of hunting for Fourth or Second and Fifth and then I could catch First. This is frustrating spending three or four seconds doing this at every stoplight - though I could usually get the jeep in First at a slow rolling speed that meant holding the clutch in for the whole time the light was red and eventually that'll ruin the throwout bearing.

I took the jeep to a local shop in Lawton, OK and they separated the engine and trans and supposedly the pilot bearing just fell right out of the back of the block. They replaced the pilot bearing with a poly bushing (much like the 258 ci engine takes) and the problem was fixed for a while, but it has reared its ugly head again in exactly the same way. I have a Hurst short-throw shifter on the trans which I am sure is exaggerating my problem, but I don’t think it is the source as the issue comes and goes mysteriously. I’m removing it shortly to compare how it feels with the old stocker.

- background / other info -

The jeep is a 1998 with a Russ Pottenger-built 4.5L stroker made out of a '96-98 block, and the original AX-15 rebuilt ~17,000 miles ago. I have been chasing vibrations on and off, and I keep wanting to blame the vibes on the engine because they're bad enough that I’ve lost two fuel rail bolts and the rear header/manifold bolt keeps backing out and my exhaust downpipe flange bolts keep vibrating loose as well (with new exhaust hangers). I also had to change the rear main seal twice since the engine swap and it looks like the new one is seeping almost immediately.

The engine is largely smooth at idle but using the A/C brings on a nasty vibration that I'm still trying to understand, and I am wondering if something is off in the balance of the engine internals. Or possibly the harmonic balancer as I am not entirely sure how that works or how I would determine it was failing at its job. Under load the A/C vibe seems to smooth out. The jeep does have some highway vibes from ~58-65 mph that feel similar to the A/C vibes, and can be felt in the gas pedal particularly.

I also wonder if I have an engine vibration caused by the A/C compressor (aftermarket), the 136A alternator (aftermarket) or even the power steering pump (sourced new from PSC but works badly at idle). I’m a little at a loss, I thought the straight six was supposed to be a helluva smooth configuration.
The engine and trans internals are still something I don't completely understand, so I'm not sure whether to blame this on the stroker motor or the AX-15 that I had rebuilt. I don’t have time before I fly off for my next station in South Korea to just throw parts at this.

- recent work -

The jeep's at almost 252,500 miles now, and the new pilot bushing was put in around 4,000 miles ago. It took probably 1,500 miles for the shifting to start getting worse again, and it's now sometimes bad enough I am concerned I won't be able to get it in gear.

As far as the highway vibe, the driveshafts are probably OK. The rear was professionally balanced at a driveline shop, and has received a new CV yoke after I forgot to lube the old one. The front seems OK as received from Tom Woods. I removed and greased both driveshafts 1,300 miles ago and inspected the U-joints and brought them to a shop for a second opinion. I was told they’re fine.

The outer yoke nuts on the diffs are tight. The rear yoke on the T-case was pretty loose for awhile, and tightening it has gotten rid of some vibes I was chasing at the time ~2000 miles ago. Front yoke nut was fine.

I’m going to recheck my driveline angles hopefully today in between other errands, but they were shimmed as part of the lift kit I bought from DPG Offroad.

The axleshafts are a possible vibe source as they’re aftermarket. The rears are Yukons. Forgot the front brand.

Tire balance is another vibe source I know. I have black Cragar steelies all around (one new) that have been somewhat abused but professionally balanced by a Goodyear outlet in OK and are as smooth as they've ever been. They might cause my highway vibe, might not.

I have changed so much on this jeep it’s hard to eliminate various factors, but I’m trying.

 

[BlurpleXJ]

The point of all this ramble is to ask yall whether you think some sort of internal balance issue with the engine is likely here. If the jeep has eaten the pilot bushing just like the pilot bearing, I am at a loss for what the most likely culprit would be. I'm trying to decide whether to have a machine shop tear the block down to check the balance of the crankshaft or something like that.

 

[David_Bricker]

I have a very similar setup to yours. 4.6L Russ motor, AX-15 new from Novak, Hurst short throw shifter, which I love.

Before going after anything in the motor, please check two things.

First, the Hurst shifter in mine has a tendency to come loose, where the shift lever meets the shifter assembly. It's done that more than once to me, and creates a very sloppy shift pattern.

Second, since you have a stroker, at least my crank takes a different size bushing that does the one for later models. I owe my son the numbers, so I'll dig them up. Initially, I had the 4.2L bushing that fit the crank inside diameter. This, however, is loose on the input shaft of the trans, and made a ton of noise. I suspect eventually, it would have caused the trans input shaft to break. A shop in New Jersey where I bought my Kevlar clutch was able to cross reference and find a bushing that matched both the stroker crank and the AX-15. After installing that bushing, the noises have gone away.

I'd be very surprised if there was a balance issue within the motor.

David Bricker / SYR

 

[Ghost]

I don't think your vibrations are from the engine. If the harmonic balancer is it might have cracks in the rubber part of it or maybe even have it missing. I had one that was bad once and it was easily noticeable. I'd check the shifter like suggested and Try that pilot bushing that was suggested. Feel free to shoot me a text or call if I can help you out. You are kind of in uncharted territory for me but I'll do what I can.

 

[BlurpleXJ]

I don't think your vibrations are from the engine. If the harmonic balancer is it might have cracks in the rubber part of it or maybe even have it missing. I had one that was bad once and it was easily noticeable. I'd check the shifter like suggested and Try that pilot bushing that was suggested. Feel free to shoot me a text or call if I can help you out. You are kind of in uncharted territory for me but I'll do what I can.

Thanks Ghost!

I have a very similar setup to yours. 4.6L Russ motor, AX-15 new from Novak, Hurst short throw shifter, which I love.

Before going after anything in the motor, please check two things.

First, the Hurst shifter in mine has a tendency to come loose, where the shift lever meets the shifter assembly. It's done that more than once to me, and creates a very sloppy shift pattern.

Second, since you have a stroker, at least my crank takes a different size bushing that does the one for later models. I owe my son the numbers, so I'll dig them up. Initially, I had the 4.2L bushing that fit the crank inside diameter. This, however, is loose on the input shaft of the trans, and made a ton of noise. I suspect eventually, it would have caused the trans input shaft to break. A shop in New Jersey where I bought my Kevlar clutch was able to cross reference and find a bushing that matched both the stroker crank and the AX-15. After installing that bushing, the noises have gone away.

I'd be very surprised if there was a balance issue within the motor.

David Bricker / SYR

David, the bushing I had installed was made from the stock bushing for a 258ci inline six. The shop told me they bored it to .750" to match the input shaft. It did fix my issues, for while. If my problem is that the bushing has gotten hogged out, I am at a loss for what would have done it. Probably whatever ruined the pilot bearing the first time. I was hoping I had just gotten a bad bearing.

I just now replaced the Hurst shifter with the stock one (which I took fully apart, cleaned, and reassembled with a decent rebuild kit). When there is no 'bind' trying to get into first, it shifts smoothly and cleanly. It has changed nothing about my problem which seems to come and go. I also can't find anything outright wrong with the Hurst. Looks and feels tight and clean.

Any other suggestions, gents? What would make an engine eat pilot bearings/bushings?

 

[old_man]

They said they bored it to .750", the real question is....what was the diameter of the shaft? The hole needs to be several thousandths larger than the bushing.

Did you lube the bushing before you put it all together.

Now to the real question. Were the locating dowels in the block when you mated the tranny to the engine. If not, the tranny can shift off of center and make the shaft rub and bind in the bearing.

 

[Ghost]

They said they bored it to .750", the real question is....what was the diameter of the shaft? The hole needs to be several thousandths larger than the bushing.

Did you lube the bushing before you put it all together.

Now to the real question. Were the locating dowels in the block when you mated the tranny to the engine. If not, the tranny can shift off of center and make the shaft rub and bind in the bearing.

Every pilot bearing I ever saw was a needle type bearing. If they drilled something out was it impregnated brass? When replacing that I'd check that front input bearing. If it's going that front shaft is going to move and hence wear out the pilot bearing.

 

[Cottontail]

If they drilled something out was it impregnated brass?

I always heard that if you drill in the brass you can't get pregnant??? :dunno:




Was that too much??? :doh:

 

[David_Bricker]

It isn't a pilot bearing, it's a pilot bushing.

Here is the info I have from my research:

Pilot bushing #PB-122
ID: 0.580"
OD: 1.055"

Pilot bushing #PB-117
ID: 0.755"
OD: 1.055"

Pilot bushing #PB-207
ID: 0.755"
OD: 1.001"

I got this info from Phoenix Friction Products, from whom I bought my kevlar clutch kit and flywheel. They can supply those bushings, though they should be able to be cross-referenced at a local parts store. This was the clutch kit I used: http://www.phoenixfriction.com/p-40...rand-cherokee-wagoneer-wrangler-10-12-in.aspx

The 4.2L crank that is used on a stroker has a hole of 1.056"
The 4.0L crank that is in Renix and HO motors has a hole of 1.001"

The early model AX-15 trans (before 1991-ish?) has a input shaft of 0.580"
The later model AX-15 trans has an input shaft of 0.755"

Note that these sizes aren't exact. For example, the trans input shaft is slightly smaller. My trans mic'ed at 0.752".

I think drilling out the bushing is likely to not be all that accurate.
In my case, you could see the bushing had quite a bit of wear on the trans side of the bushing. I'm guessing they used a PB-122 bushing, which would have required drilling it out. The ID of the bushing, when removed, was 0.768".

When putting things together the second time, since I had a 4.2L crank with late model AX-15, I used bushing PB-117. Putting together my son's stroker, he will use PB-122, as he has an early AX-15.

Novak's website also has some description, without the sizes, that discuss the differences in pilot bushings. https://www.novak-adapt.com/catalog/pilot-bushings/amc-ax15

David Bricker / SYR

 

[old_man]

I think drilling out the bushing is likely to not be all that accurate.
In my case, you could see the bushing had quite a bit of wear on the trans side of the bushing. I'm guessing they used a PB-122 bushing, which would have required drilling it out. The ID of the bushing, when removed, was 0.768".

Drilling out the bushing is a crap shoot. The problem isn't the size of the hole, but the concentricity. In other words, is the hold centered. Drilling the hole, even in a mill and setting everything up correctly is even hit or miss. A drill may catch on one side and veer off center if it is too close in size to the existing hole. A reamer is the best way in a mill or drill press, as they tend to center. The other way is to chuck it into a lathe.

I find way to many people who do not lube the sintered bronze bushings when they put everything together. I use a dab of high temp molly lube.

 

[Ghost]

It isn't a pilot bearing, it's a pilot bushing.

Here is the info I have from my research:

Pilot bushing #PB-122
ID: 0.580"
OD: 1.055"

Pilot bushing #PB-117
ID: 0.755"
OD: 1.055"

Pilot bushing #PB-207
ID: 0.755"
OD: 1.001"

I got this info from Phoenix Friction Products, from whom I bought my kevlar clutch kit and flywheel. They can supply those bushings, though they should be able to be cross-referenced at a local parts store. This was the clutch kit I used: http://www.phoenixfriction.com/p-40...rand-cherokee-wagoneer-wrangler-10-12-in.aspx

The 4.2L crank that is used on a stroker has a hole of 1.056"
The 4.0L crank that is in Renix and HO motors has a hole of 1.001"

The early model AX-15 trans (before 1991-ish?) has a input shaft of 0.580"
The later model AX-15 trans has an input shaft of 0.755"

Note that these sizes aren't exact. For example, the trans input shaft is slightly smaller. My trans mic'ed at 0.752".

I think drilling out the bushing is likely to not be all that accurate.
In my case, you could see the bushing had quite a bit of wear on the trans side of the bushing. I'm guessing they used a PB-122 bushing, which would have required drilling it out. The ID of the bushing, when removed, was 0.768".

When putting things together the second time, since I had a 4.2L crank with late model AX-15, I used bushing PB-117. Putting together my son's stroker, he will use PB-122, as he has an early AX-15.

Novak's website also has some description, without the sizes, that discuss the differences in pilot bushings. https://www.novak-adapt.com/catalog/pilot-bushings/amc-ax15

David Bricker / SYR

Good info! I am going on my experience and my memory with my 2.5 with an ax-5 I had for a few years long ago. I could have sworn the pilot in that one was a bearing. I figured they would be the same type bearing.

 

[David_Bricker]

The 2.5 may use a bearing. The older 4.2L with a BA-10 trans may also use a bearing. I know there were some bearings in the mix.

David Bricker / SYR

 

[David_Bricker]

I find way to many people who do not lube the sintered bronze bushings when they put everything together. I use a dab of high temp molly lube.

Lube is important, but from what I've heard, grease is not recommended, as it will clog the pores of the bushing. Soaking in motor oil overnight is the preferred method. A molly lube like assembly lube might be good as well.

David Bricker / SYR

 

[BlurpleXJ]

Some great references and insight, thanks everyone. I hope that I have simply replaced a bad bearing with a bad stopgap bushing, and that obtaining the correct bushing will solve my shifting woes.