Max RPM of Jeep Engine

[John]

John did you wittness the distributor being spit out? I am just doing research here and trying to learn. Could this also have been caused by the cam walking forward?
Does the 4.0 with it shorter stroke have a problem at the same RPM? Did the problem accure when the engine was held at a certain RPM or was it being driven through it?
I have learned an NHRA comp racer was staging at 6500 and shifting at 9200 rpm with a cryroed,nitrided reworked but stock core 4.0 crank.
Oh, and what part of W.Va are you from? I am in Va.

I was with Kent when the motor died at the track, but he was driving, ( I was the mechanic) the cause was determined when the rig was pushed to the pit area. Quite a surprise when we raised the hood. That was on a 258. I haven't seen a 4.0 do this myself. I am skeptical about the motor you heard about. That would be a very interesting motor to see. We are located along the Ohio river in the western part of the state. Do you have any more info on the high revving 4.0?
John

[1bolt]

I have learned an NHRA comp racer was staging at 6500 and shifting at 9200 rpm with a cryroed,nitrided reworked but stock core 4.0 crank.
Oh, and what part of W.Va are you from? I am in Va.

Wouldn't be "Garth Hill" would it? Reminds me of something I've been meaning to post for months now... look for a new thread titled: 580hp 4.0 NHRA dragster motor 8000 RPM.

How he ran 8k RPM's with a cam harmonic I don't know... because so far there's no mention of it... He ran a dry sump system, don't know if it was a remote electric pump setup maybe that plays some part.

There's a hell of a lot of drag between the distributor and the oil pump, especially the oil pump, creating 60 PSI of oil pressure takes energy just like making boost with a belt driven Supercharger takes energy. Drag on both sides of the gear means a lot of loading forces at the teeth. Could be that just changing this part of the equation a bit would have some beneficial effect.

[Mgardiner1]

You know what, its starting to make a little more sense now...... the higher RPM, the more oil pressure, the more the helical gear will try to force the cam either forward or backward. If its forcing the cam forward, then the spring and pin design can only take so much, not to mention the cheese aluminum front cover wouldn't provide much support for those kinds of forces....

[John]

The front cover is a lot stronger than you think. Te way I set them up places the front cover as the retainer. It handles the stress very well. No failures.
John

[Mgardiner1]

I realize it is strong, and after reading the 540hp thread, there was a comment about an aluminum plate front timing chain cover

Just because the timing cover is strong, doesn't mean that it won't "harmonize"

[TurboTom]

John did you wittness the distributor being spit out? I am just doing research here and trying to learn. Could this also have been caused by the cam walking forward?
Does the 4.0 with it shorter stroke have a problem at the same RPM? Did the problem accure when the engine was held at a certain RPM or was it being driven through it?
I have learned an NHRA comp racer was staging at 6500 and shifting at 9200 rpm with a cryroed,nitrided reworked but stock core 4.0 crank.
Oh, and what part of W.Va are you from? I am in Va.

I was with Kent when the motor died at the track, but he was driving, ( I was the mechanic) the cause was determined when the rig was pushed to the pit area. Quite a surprise when we raised the hood. That was on a 258. I haven't seen a 4.0 do this myself. I am skeptical about the motor you heard about. That would be a very interesting motor to see. We are located along the Ohio river in the western part of the state. Do you have any more info on the high revving 4.0?
John

Was the clamp still in place? Did it break the dist. base, push the clamp up? Not doubting you, it's just I should have mine on the dyno next week and want to get as much info as possible.

[John]

Clamp was still in place, pushed the shaft through, it busted the dis body.
John

[Mgardiner1]

So then maybe the distributor is "top heavy" and when the vibrations are sent through it, it can turn it into a turning fork. Maybe a billet distributor would aid? or even the coil packs as previously mentioned?

[John]

I can see the dis top vibrations, I wish I remembered more of the small details but this was many years ago, since I have turned blond, the memory is not as good as it once was.
John

[TurboTom]

I don't believe it is in the dizzy. Could be wrong, but I doubt that is the culprit.

[seanyb505]

Probly not the culprit, but it could be the manifestation of the harmonic. I think it would be difficult to spit the cam out, no matter how much it was wriggling.

[TurboTom]

OK lets recap this thread.
John has seen a dizzy broken, the ONLY first hand evidence I could find here. Could be a harmonic could be other causes. Not trying to insult John, just stating facts as I see them.
Hesco says there is a problem, say's they know the fix but is not forthcoming with any hard evidence or actuall testing.
I know Sixpack turns his engine 6400 and has went 7800 on occasion. Says the AMC 6 is hard on timing chains..now runs a gear drive...no more problems. Did not break timing chains, just streched them. Never broke a dizzy.
A comp racer left at 6500 and shifted at 8400, no mention of harmonics.
Maybe I missed it but did not see this 5600 harmonic in Navarro's engine post.
Is this harmonic an urban mith?? Like people still not wanting to sit a battery on concrete?
If I missed something please speak up. I am all ears.
I will be going to the dyno this week with my Turbo 4.0 on E-85. I am going to learn something!!

[John]

Excellent recap, and yes we do not know for sure what causes some of the I6 motors to have problems revving on up. (No insult or injury taken TurboTom) Kent's distributor was the only one that I have encountered. The mod that I do to attempt to improve camshaft positioning was a attempt to improve any parameter we felt might have influenced the failure. The oil pump was even suspect for some time as the cause. Hell it may have been a bad casting?
The Navarro motor was reported as cruising comfortably at 6k RPM. The Hill dragster . I wish I knew more, I sent 1bolt some info that might help us find more about this one?
Urban myth, don't know, years after our failure I learn from Lee Hurley of a harmonic issue. I think there is something, the factory computers rev limiter was set 5200 rpm, but we do not know why this point was chosen? Sixpack reports the motor as hard on timing chains but found the gear drive got around this. Good sets of double roller timing chains are hard to stretch.
One of the near end of production changes to the design was to change the method of retention of the camshaft and casting changes stiffen the block and to improve the cam support. That was not a cheap change over for the manufacturer, NVH markings on these castings were reported to be for the noise, vibration and harmonic reductions.
I'm not chicken little, the sky is not falling. Most I6 motors never bump the rev limiters, there really is not that many owners trying to take them above factory setups to have generated answers. We do know
our I6's can be made to operate above 6k.
Keep us posted on the dyno run.
John

[1bolt]

There does seem to be a body of experience just coming out now that suggests the "harmonic" is either not all that its cracked up to be or maybe just isolated incidences of the "weak link" in the chain being found.

We can say for sure that Oil pumps and Distributors and timing chains for the 4.0 (at least) are all almost purely OEM design standards... If they don't need to rev to even 5500 then they probably aren't overbuilt to be able to withstand much more.

Double roller timing sets are not easy to come by, the last build I did I was unable to even find an actual double roller for the 4.0 (I didn't ask HESCO as I'm sure anything they have is not affordable).. Race prepped (ported to lower resistence of oil passing through) and overbuilt oil pumps may be out there, but most of us are using OE standard or "high volume" Mellings.

We can also say for certain that most builds will have an OE distributor... MSD makes a Billet distributor for Jeep I6's that will almost surely be stronger, better balanced and lower friction than an OE, but its for a 258 without computer controlled Spark.

So It would be extremely interesting to see what would happen with a build that replaced these components with better than OE parts.

[John]

Ever notice the last photo here http://www.hesco.us/customergallery.asp ... rdID=90225
John