Max RPM of Jeep Engine

[Plechtan]

I was taking apart a 4.0 from a 2000 Grand Cherokee. I noticed that the timing gear was not attached to the cam the same way the older gears were. The old ones had a bolt in the center and a locating pin. The new design has the camshaft extended and a keyway to locate the gear. It would seem to be a better way to center the gear in the camshaft. with the single bolt in the center, the gear could run off center. It would all depend on the fit of the bolt into the gear and how much play you had in the threads. The new design, the gear is a tight fit on the Cam. The new design also has a thrust plate for the cam, i do not believe the older design does.

[Mgardiner1]

The old style gear is reccessed so that the cam shaft fits into the gear. The cam itself centers the gear, and the pin locates its relationship to the cam, and the bolt torques it all together

[John]

I was taking apart a 4.0 from a 2000 Grand Cherokee. I noticed that the timing gear was not attached to the cam the same way the older gears were. The old ones had a bolt in the center and a locating pin. The new design has the camshaft extended and a keyway to locate the gear. It would seem to be a better way to center the gear in the camshaft. with the single bolt in the center, the gear could run off center. It would all depend on the fit of the bolt into the gear and how much play you had in the threads. The new design, the gear is a tight fit on the Cam. The new design also has a thrust plate for the cam, i do not believe the older design does.

As was correctly pointed out above the camshaft/timing gear centering is machined fits with indexing by the pin and methods of clamping. It is a properly tight fit to the cam. I have not ran into any issue here.

Thrust plate.. if you remove that , install a aftermarket or a older OEM camshaft, new,correct for the camshaft, timing set, install the correct end bolt (With the thrust pin and spring) Reuse the OEM timing set cover. This reverse engineers the later upgrade.

Since seeing the results of us running a I6 as hard as possible (spit the distributor). We may have bumped 5700-5800 rpm, We were doing pretty good we thought, the long rod slant sixes were pushing it at 4500. rpm's. We never did get running at much more rpm if any, but we never had problems after converting the thrust pin/spring in the cam bolt to fit to zero clearance with the timing cover thrust surface. if you think about it, the factory fixed it in place with a plate, I fix them in place by modification. No problems yet. We have a gear pump via cam/dis gears for our lubrication as well as the cam lobe taper/valve train providing thrust to our camshaft that was retained by a floating pin backed by a spring.How much of our camshaft harmonic is influenced by end play issues? Always change dis gear when swapping cams. I like Hesco's bronze one. Always check the clearance between the camshaft and the frost plug directly behind it with the camshaft physically to the rear.
John

[Plechtan]

Can you get aftermarket cams with the new design, or do you have to revert back to the older design? I guess same question on the Timing chain, any performance ( double row roller) available for the 99+ motors?

[John]

I do not know of a source of a +99 aftermarket camshaft. I remember someone on this board reporting on a discussion that a new mold box was considering being made to produce different blanks. Timing sets are the same for aftermarket manufactures, no known source for 99+ sets. If you are requiring a 99+ camshaft design, consider a quality regrind of the profile.
John

[dwg86]

I do not know of a source of a +99 aftermarket camshaft. I remember someone on this board reporting on a discussion that a new mold box was considering being made to produce different blanks. Timing sets are the same for aftermarket manufactures, no known source for 99+ sets. If you are requiring a 99+ camshaft design, consider a quality regrind of the profile.
John

I had been talking to CWC about making a cam for the later engines. I thought since they had made them before for Chrysler, it wouldn't be a big deal to have blanks made for the aftermarket companies(thought they might still have the molds). Well, I got tired of "chasing the wind". A single person doesn't have enough influence to having new blanks made. I even talked to Crane, Comp and Reed. They seamed interested in what I had to say about the newer cam design and the wide vs narrow lobe, but not enough to have the newer cams made.
The last time I talked to CWC, they said they had looked at using the older cam blank and machining the front to make it like the newer style, but it wouldn't work. I called a few more times and left messages, but no returned phone calls...I gave up.
I like the way the newer style cam is held in with a thrust plate vs the spring/pin. I finally got a couple days off and I will be comparing the 2 cams and see if there is a way of using the retaining plate on the older style cam. It may be as simple as cutting a groove in the part of the older style cam that sticks out the front of the block and cutting a section out of the retaining plate to install it from from the side. My stroker is going to be a DD, and won't see high RPM's(above 4500), so I don't know if it will be worth the money in machining cost to have it done, but I am curious...

[dwg86]

After looking at both cams, I don't think it would work(trying to use the cam plate on the old style camshaft). I posted some pics in a new thread(cam pics). If you think that cam walk might be the problem with the harmonics, it might be best to use a solid rod with no spring, or build up a weld on the head of the cam retaining bolt. You would have to remove the rear cam plug and put a dail caliper on the back of the cam, install the cam sprocket, timing cover and gasket. Then keep grinding the pin or weld down until you maesure .003-.005 camshaft end play on the dail caliper installed on the rear of the cam. Some people used to do this on the AMC V8's(they have no cam plate or spring to prevent cam walk).

[John]

Measure the distance the end of the cam bolt is to the face of the motor with the camshaft seated to the rear. Measure the depth of your timing cover from the gasket surface to the boss the spring pin centers on. Measure the thickness of the gasket. Throw the spring away that seats behind the pin and cut drill rod to a length that will bring the radius of the pin to 0.00 clearance between the cover boss and the pin when assembled, substituting the drill rod for the camshaft bolt spring. The cover for your timing set just became the cam retainer, Works well and have no problems with gasket or cast cover. I haven't, but you could just make up a drill rod and radius polish the end to replace the spring and hollow pin both.
John

[1bolt]

Interesting, here's a thought; With the distributorless ignition the cam sensor is just a cut down distributor right? What if we eliminated that and figured a way to replace that sensor with an Edis tone ring. Does the harmonic even exist or remain the same "pitch" without any contact at the dist. gear? What if like John said the harmonic is an end play issue, and the dist. gear is playing the cam like a violin string? (so to speak)... it certainly has some effect one way or another judging from the repeated assertions that it gets spit out around 5800 RPM's... Obviously would require aftermarket fuel and spark.

[John]

1bolt as I used to hang out with Bobby Taylor at Galax, I prefer fiddle strings, Prim brand. Ahem.. There is several variables that are changeable on our valve train camshaft, we might not be able to eliminate it, but we should be able to reduce it from a 3rd order or relocate it to a less troublesome rpm. I keep thinking of a means to test that is less destructive than trying something and then attempting 6k+ rpm. Vibration analysis with monitored runs would be the best. Anyone have a source of quality magnetic coupled sensors, three would be required.
John

[1bolt]

someone could take a core engine to a NASCAR shop that has a spintron short of something like this I don't see a practical or even feasible way to spin it up to 6k.. And even if you did without the thrum of real combustion events hammering down the crank and up to the cam, and up the valves and down the pushrods I suspect the various "bows" or "picks" that actually cause the harmonic to set up wont be there.

On the other hand, intuitively speaking, if you got rid of a major source of friction (helical gears meshing) right in the middle on the long "string" of the cam shaft, it would just have to have some significant effect. It doesn't even matter which way the cam flexes whether its across the axis (like a string) torsionally (twisting along the long axis which is how I envision it) or a back and forth jitter (end play); the dist. gear it seems to me is a lot like a "fret" and should have some significant effect on the "tune".

I can't help but think that spitting out distributors suggests there's a whole hell of a lot going on right there where the gears mesh.

[John]

I Agree that this test would really need to be performed on a operating engine to be accurate. This would allow a motor to be brought up to speed while monitoring real world vibrations.
John

[Mgardiner1]

True, but maybe spinning each component individually could help "clue" into the dynamics and harmonics of each piece

We all love to say the distributor is bad for harmonics, but wouldn't one consider that the fact it connects to the oil pump, maybe the oil is helping create a "dampening" effect? I would be more so inclined to think that the extra force and side load to the cam is no good myself. Just pondering thoughts

[TurboTom]

I Agree that this test would really need to be performed on a operating engine to be accurate. This would allow a motor to be brought up to speed while monitoring real world vibrations.
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.

[gradon]

Now that you got me thinking musically, I have the thought that besides the issues of cam walk and distributor popping out, the distributor shaft will help support(might not be much, but it's a guide of sorts) the cam in the middle and make the cam "wobble less" @ high rpms and in the fret sense, help make a higher note/higher harmonic. Could the harmonic be lower w/o it? Or could it be like whiny differential gears and that harmonic is due to the mesh and if you used a different cam position sensor(a tone ring for eg) that didn't use the cam's distro gear there wouldn't be a harmonic? Hmm