Cam bearing failure x2.. help...

[MadBill]

... Oh well, I just hope its over.

Yes; after 18 pages, whenever I see there's a new post I think: "Oh no! Not more cam bearing problems for poor old Silver!"

[Kevin Johnson]

First time that I read through it, sorry. Stroker engine -- you adjusted the harmonic balancer? Lots of variations in 258 crank designs too with respect to counterweights. It sure sounds like a harmonics issue. Not surprising it would show up in other straight sixes too.

Very nice job on your windage tray.

[SilverXJ]

No adjustment to the balancer. Every stroker (except racing ones, which usually use some custom job) use a stock 4.0L balancer. Its internal balance. Wouldn't a crank harmonic show up in the crank bearings prior to the cam bearings though?

I'm questioning what weight oil to use for winter. I'm leaning toward 5w-30. I have a HV oil pump and concerned about extra wear on the pump and pump drive gear/cam gear pumping heavier oil. I do have an oil squirter going to the cam gear. Bearing clearances are .0018-.0020", HS roller rockers, and forged 4032 pistons. I don't know if those last two matters any.

[Kevin Johnson]

No adjustment to the balancer. Every stroker (except racing ones, which usually use some custom job) use a stock 4.0L balancer. Its internal balance. Wouldn't a crank harmonic show up in the crank bearings prior to the cam bearings though?

I'm questioning what weight oil to use for winter. I'm leaning toward 5w-30. I have a HV oil pump and concerned about extra wear on the pump and pump drive gear/cam gear pumping heavier oil. I do have an oil squirter going to the cam gear. Bearing clearances are .0018-.0020", HS roller rockers, and forged 4032 pistons. I don't know if those last two matters any.

Reasoning:

The stock 4.0 and 258 (of which there are several versions of 258 crank -- partially and fully counterweighted -- the 4.0 is partially counterweighted) need a harmonic balancer/damper for the normal operating range of the engine. The harmonic balancer dissipates energy by generation of heat. This really has little to do with whether the rotating assembly is balanced. Straight sixes are well known for this fault, e.g. the first group of Datsun 240Z cars shipped to the USA did not have harmonic balancers and there was a very high failure rate.

If the harmonic balancer is not successful in dissipating this energy by generating heat then it can be easily transmitted through the cam drive to excite the long resonating rod there; the chain may also exacerbate spikes by whipping which can also put waveforms out of phase. The waveforms with all sorts of spikes would coexist with those generated by valve train action and may be damped or reinforced depending on the rpm/natural-frequency of the camshaft. Changes in axial alignment of the journals with respect to the bearing bores proper would result in very poor hydrodynamic wedge formation.

Stock elastomeric dampers are known to deteriorate over time so if you have a used one in place this could make things worse.

Note that one of the engineering changes that Mopar made to the 4.0 from the AMC was the addition of a light duty bearing bridge or girdle which was what you took advantage of to construct your tray. You can be assured that Mopar would not have added this device (read $$) whilst still using a stock type damper on a whimsical basis. It probably helps with NVH which is a normal justification for their inclusion.

Lastly, the damage is that which would be predicted and you have essentially exhausted other avenues while leaving this confound common to your builds.

Edit: I recall one reader mentioning to look at the timing gears and chain. It seems likely that these have been damaged (or at least the chain stretched) and it would probably be a good idea to replace them as a matter of sound practice.

[technicaltom]

[/quote]
WOW . Just read the entire thread, Its certainly a thorough detailed breakdown( no pun intended) by Silver XJ . The question that comes to my mind is back on page 14 , the photo of the chain and sprockets , is the discolouration /blueing. of the crankshaft sprocket normal IE a result of a manufacturing process? Or could there be some ecentricity on the snout of the crankshaft? Surely this has been double ckecked many times, its just not been mentioned.
PS I failed to get the correct photo to this page.

[Kevin Johnson]

Silver XJ, see if someone is able/willing to perform a Shore A durometer test on the band (at several locations) in your used harmonic balancer. Compare those values to a new one. I would think that many race teams would have the instrument to check their tires.

[SilverXJ]

Reasoning:

The stock 4.0 and 258 (of which there are several versions of 258 crank -- partially and fully counterweighted -- the 4.0 is partially counterweighted) need a harmonic balancer/damper for the normal operating range of the engine.

The 258 came in 4 and 12 counter weights versions, and IIRC the 4.0L may have 8. I have a 4 counter weight.

If the harmonic balancer is not successful in dissipating this energy by generating heat then it can be easily transmitted through the cam drive to excite the long resonating rod there; the chain may also exacerbate spikes by whipping which can also put waveforms out of phase.

There is a documented cam harmonic around 5400-5700rpm, but I don't go that high. The transmission shifts around 4900 RPM. The cases I have heard of people staying in that RPM range have resulted in snapped timing chains.

Stock elastomeric dampers are known to deteriorate over time so if you have a used one in place this could make things worse.

I have a new Powerbond balancer. The balance was also checked by the machine shop. Also, I found that ATI makes a damper, but I don't have many details other than the hub has to be made to work, as its too long or something. I'm contacting ATI about that. I believe the part number is 917071, but I think that is only for the hub.

You can be assured that Mopar would not have added this device (read $$) whilst still using a stock type damper on a whimsical basis. It probably helps with NVH which is a normal justification for their inclusion.

Yes, the main girdle was one of the changes they made to combat NVH.

Edit: I recall one reader mentioning to look at the timing gears and chain. It seems likely that these have been damaged (or at least the chain stretched) and it would probably be a good idea to replace them as a matter of sound practice.

I didn't see any damage on the chain or the gears. I had though about replacing them but... I just buttoned it up yesterday. Now I'm second guessing myself.. take it apart again to replace the timing set?

the photo of the chain and sprockets , is the discolouration /blueing. of the crankshaft sprocket normal IE a result of a manufacturing process?

Its normal and part of the manufacturing process. It came like that.

[Kevin Johnson]

I looked a bit at the discussions of AMC six cam harmonics on other forums just now. The harmonics will be complex and you have (apparently) found one that does not destroy the cam but torques/distorts it such that the oiling is affected. The system will be a combination of cam and crankshaft harmonics interacting (primarily) through the timing gears and chain. It is probably an rpm you spend much of the time at or perhaps when the motor is at hot idle or??? Perhaps when Chysler re-engineered the block it removed another sort of crankshaft "damping via slight block flex" that is now energy that is transmitted through the timing gears to the cam. NVH does not magically disappear without the energy being accounted for somehow.

I am not sure if you are saying that you have always used the same new aftermarket damper in both builds or have just added it. You also wrote that people are successfully using stock dampers. How do you know that aftermarket versus stock dampers work as well and one or the other may not quite extend into the range your stroked system operates in. I know there were a few people that thought all plastic slant six distributor gears were the same. When I looked into that, all the examples I found spanning about 45 years manufacturing time were different. Perhaps there is someone with access to the AMC archived info at Chrysler that could provide engineering specs for the dampers over the lifespan of the engine. Does Mopar supply dampers? Do they supply the same part numbers? The same Durometer specs? Were they always the same numbers?

In any event, I think about a $400 instrument (Durometer) would allow you to do some investigating. You might be surprised at what you find. Good luck.

Reasoning:

The stock 4.0 and 258 (of which there are several versions of 258 crank -- partially and fully counterweighted -- the 4.0 is partially counterweighted) need a harmonic balancer/damper for the normal operating range of the engine.

The 258 came in 4 and 12 counter weights versions, and IIRC the 4.0L may have 8. I have a 4 counter weight.

If the harmonic balancer is not successful in dissipating this energy by generating heat then it can be easily transmitted through the cam drive to excite the long resonating rod there; the chain may also exacerbate spikes by whipping which can also put waveforms out of phase.

There is a documented cam harmonic around 5400-5700rpm, but I don't go that high. The transmission shifts around 4900 RPM. The cases I have heard of people staying in that RPM range have resulted in snapped timing chains.

Stock elastomeric dampers are known to deteriorate over time so if you have a used one in place this could make things worse.

I have a new Powerbond balancer. The balance was also checked by the machine shop. Also, I found that ATI makes a damper, but I don't have many details other than the hub has to be made to work, as its too long or something. I'm contacting ATI about that. I believe the part number is 917071, but I think that is only for the hub.

You can be assured that Mopar would not have added this device (read $$) whilst still using a stock type damper on a whimsical basis. It probably helps with NVH which is a normal justification for their inclusion.

Yes, the main girdle was one of the changes they made to combat NVH.

Edit: I recall one reader mentioning to look at the timing gears and chain. It seems likely that these have been damaged (or at least the chain stretched) and it would probably be a good idea to replace them as a matter of sound practice.

I didn't see any damage on the chain or the gears. I had though about replacing them but... I just buttoned it up yesterday. Now I'm second guessing myself.. take it apart again to replace the timing set?

the photo of the chain and sprockets , is the discolouration /blueing. of the crankshaft sprocket normal IE a result of a manufacturing process?

Its normal and part of the manufacturing process. It came like that.

[SilverXJ]

I am not sure if you are saying that you have always used the same new aftermarket damper in both builds or have just added it. You also wrote that people are successfully using stock dampers.

I had a "Professional Products" (IIRC) balancer earlier. That was replaced with this Powerbond unit as I noticed a slight wobble in the Professional products one.

How do you know that aftermarket versus stock dampers work as well and one or the other may not quite extend into the range your stroked system operates in.

I don't I have no way to tell other than visual, check for wobble, check for balance, etc.

Does Mopar supply dampers? Do they supply the same part numbers? The same Durometer specs? Were they always the same numbers?

You can still but a balancer from the dealer, if that is what you are asking. The one for the Cherokee has always been pretty much the same aside from the hob lengthening ~.030" to account for the removal of the oil singer. They don't publish any specs for them other than it will fit. What would one look for in the durometer specs? Harder is better?

[Kevin Johnson]

Example of a substituted Mopar number/part off the top of my head: the Mexican turbo 2.4 in the 90s had scraper and tray integral with the gasket. After that supply was exhausted it went to a simple gasket.

You might also examine parts headed for dedicated truck motors. Maybe the universal replacement part is too much of a compromise especially when you're pushing the envelope with a 4.6 stroker.

Harder better? Maybe not. Possibly a tradeoff is being made in sacrificing low rpm vibration dampening when a higher number is used. Could be what you are seeing is a consequence. Data, data, data. Think of the straight six community service you'd be providing by roaming auto supply houses and wrecking yards with your trusty durometer in hand.

[SilverXJ]

I have been alerted that I never posted the resolution to the problem here.

As far as we can tell it was cam thrust. I had the block checked over by MotionMachine and nothing was found wrong with the cam tunnel or anything significant. Dale was very through and precise. The best conclusion we could come up with was the cam bouncing in and out of the block with the stock pin and spring configuration. Which caused the hydrodynamic oil wedge to break down. The first fix was using a solid pin and setting the end play manually by removing material from the pin. This stopped the bearing failure. I wasn't too thrilled with this idea as I was concerned with the pin wearing out the timing cover since it was such a small area and I also wanted to try a different cam. So after the Melling stock replacement cam for the 98+ engine that uses the thrust plate came out Jones Camshafts ground a custom cam on the blank that Melling uses. Out of the 5 cam companies I contacted he was the only one willing to help since there isn't a performance cam for the thrust plate style camshaft.

Its been an experience but I now have around 15,000 miles on it since last bearing failure. And I have checked the bearing several times. An Mp90 supercharger is now in the works. I'm still don't understand what force would move the cam like that though. Thank you all that offered assistance on this.

[Dan Timberlake]

Do you have any of the old "bad" cams and lifters around, and the original "good" Crane?
I'm glad the problem is gone, but I wonder about stuff like cam lobe taper (maybe somehow driving the axial bounce) and especially journal polishing direction.

I'll have to look up the AMC cam thrust related parts.

[SilverXJ]

Yes, I have a couple cams lying around. I wouldn't call them bad though. I know I have one cam with its matching lifters.

[Dan Timberlake]

Yes, I have a couple cams lying around. I wouldn't call them bad though. I know I have one cam with its matching lifters.

I was calling the cams that ate the bearings "bad" since I think you found some cams did not do that.

My first test would be to run my finger nail in each direction on the cam bearing journals after cleaning with brake clean, etc..
Then maybe rub thejournals each way with one of those micro fiber cloths. First lightly, then firmly.
I'd be feeling for some "directionality" in the rotating direction of the good and bad cams' journals.

[SilverXJ]

That wasn't the issue.