up to date stroker info

[Torqsplit]

This thread is a fun read! Great brain-teaser. I don't challenge any of the theories offered here on the various factors that cause 'bad vibrations'. Sadly whoever had/has 1st hand experience with cam harmonics on these engines apparently isn't readily available to ask or post here. I've heard tails of broken cams in these engines when pushed to outer limits. My feeling is that the cam harmonic is a torsional problem, not so much a balance issue, and comes about as a result of the timing of the valve-train events. At a case-specific rpm, these events cause the cam to effectively wind-up and release, torsion bar style, as the lobes encounter resistance alternately at opposite ends of the cam(and its a long cam at that!). At some point, based on many variables already mentioned, the cam will twist itself beyond its ductile threshold, and snap. I've often wondered when degreeing the cam, just how accurate the valve timing truly is on those back few lobes when this thing is fully heat-soaked and near redline? Depending on the firing order, many 6-cyls have Crankshaft harmonics around 5500 as well, the trick is to not hang out there long. The longer you spend there, the longer the harmonics have to compound on the affected components. Drags don't tend to leave you in those revs as long as guys on the back straight of a road course, or the guys at Bonneville. You might be fine? There is the piston-speed issue on a stroker at higher revs. I think a stock stroke 4.0 could handle it with rods & forged slugs but, as was mentioned, the piston mfg'r would be the ones to advise you on that. Crank flex may become a problem at some point? Cam life could suffer as well, likely that the spring rates needed to control the valve-train at 7k+ rpm would smear the lobes off in short order. It could be done tho. I'd sure love to see somebody give it a shot! Power to you :cheers

[Cheromaniac]

I guess we'd have to pick the brains of guys like Rick Mudge and others who've built Jeep I-6's that have revved past 8000rpm and lived to tell the tale.

[mountaineerjeff]

Given that I'm already running a 99 motor and have another as a spare, I'm honestly thinking about just raising the red line to like 6500 and just see what happens. If something blows apart then I dont have any money invested. I wonder what the stock valvesprings will rev to. I'm still on a stock cam and lifters/pushrods but I am running HS 1.7 rockers.

[mountaineerjeff]

Even on the stock cam this thing hits my current 5250 limiter like a brick wall, seems like it still has a lot to go. I always feel like I'm short shifting it.

[jeepxj3]

I wonder what rpm 'valve float' occurs on those stock springs?

[SilverXJ]

This back and forth movement of the cam PLUS the rotation of the cam, sets up a harmonic frequency which depending on the above variables, valve spring tension, lifter face taper, cam lobe taper helical gears, on the 4.0 occuring around ?5600 rpm.

It is the cam walking/movement PLUS the spinning of the cam that causes the problem of harmonics.

If that was the case you could simply setup a plate style cam and eliminate the harmonic issue. But that isn't the case.

No cam walk, no problem harmonics. Remember, need cam walk and a spinning cam to produce the problem harmonics.

You are confusing two different problems.

The harmonic issue that happens at higher RPMS (can't recall off the top of my head the exact figure), causes the cam to snake around in the block, basically act like a piece of spagetti. Its not the walk that is the issue here.

The old timers, HESCO, turbo tom, and others, were all NOT using the cam retention plate(CRP) as no cams were available for the CRP in the grinds that they desired. .

Hesco tried to solve the cam harmonic issue long ago when they were still racing the 4.0l/strokers. The problem they were experiencing happened when the drivers held the engine at the harmonic rpm. This resulted in repeatable damage. Now, if they had pushed through that RPM there wasn't a problem. Hesco tried many different solutions. Different timing sets (gear, chain) and even tried adding extra supports to the cam. The gear drive seemed to be the best solution according to Lee. Hesco had/has the resources to create any cam setup they desired, so it wasn't like a particular grind was unavailable to them.

The harmonic problem came about with a ROAD RACE vehicle where the driver wanted to let the engine speed (under power) stay the same rpm so he would not have to shift two extra times.

The engine broke the timing chain on first try. Second engine broke with in 10 ft of the first engine.

At this time I had 5 race cars running the engines. all but one broke the timing chain at the same place on the race track that race week.

Back at the dyno I tried to simulate the problem. With some success I was able to break timing chains by holding a load at 5375 rpm and the chain would break. With a cut away timing cover on the dyno and watching with a strobe I could see the chain start to wrap up and break.

The next project was to watch the cam do a harmonic warp. Added two extra cam supports with little help. Still broke!

I don't believe I have any video or photos left. I am sure there is not any engineering data that would be of any help.

I did make a gear drive set up that would not break. But all of those are long gone.

The drag car does not seem to have the problem as the engine will go thru the harmonic range quickly. I have turned the 3.0L engine 7500 for long periods with out a problem.

http://www.hesco.us/forum/forum_posts.asp?TID=994

http://www.hesco.us/forum/forum_posts.asp?TID=1320

Incidentally, the damage pattern to the cam bearing are different between the cam walk issue and harmonic issue. The cam walk makes the bearings look like they were squeezed out like crazy cheese. The harmonic makes the bearings look like they were hit with a hammer.

[jeepxj3]

So besides Lee Hurley breaking 3 timing chains, no cams, has anyone else broken timing chains that were not worn out chains?
What timing chains were broken? single row, double row?
Maybe not even cams but harmonic balancer problem.
IDK.

[jeepxj3]

I still think that all of Hurley's failed engines were non-CRP engines and he was not using or regrinding any '99+ CRP cams. Maybe not? Just saying.
Has there been any reports of 'cam harmonic' problems and timing chain breakage on CRP preped engines?

[mountaineerjeff]

5375 is a lot scarier than the 5600 we were previously talking about.

Any idea on stock valve float rpm? Given our relatively low operating rpm I've always thought guys tend to run too heavy of a spring.

I've seen some 4.6/4.7s that rev to 6500. There's one on YouTube that didn't pull it's max HP until 5800.

I'm torn between displacement/cost vs rpm/reliability.
If I'm stuck at 5300 then I might as well go with a 4.6. But then I'm worried about block strength once it's bored. Example, would a 250hp 4.0 hold more spray then a 350hp 4.7. If a standard bore 4.0 block will hold 800hp but a 4.000" bore block will only hold 650, then I'd rather have less power NA and make up the difference on the bottle.

[jeepxj3]

I re-read those 2 Hesco links.
Lee said this occured, broken timing chain, in a race car during IMSA road racing, late 70's ?is that right?, and re-created timing chain breakage on the dyno under load at 5375rpm.
Also said the timing chain was the weak link and that maybe a different dampner would help.
And that there has been some development in the timing chain area to rev higher.
And he tried and added 2 cam supports, I guess in addition to the stock 4 bearings, and it still broke. Doesn't sound like a cam flexing issue.

So many theories, too many unknowns, maybe not even a problem since those 4-5 occured. All by same engine builder.

[SilverXJ]

I still think that all of Hurley's failed engines were non-CRP engines and he was not using or regrinding any '99+ CRP cams. Maybe not? Just saying.
Has there been any reports of 'cam harmonic' problems and timing chain breakage on CRP preped engines?

You really think that Hesco was using anything stock on the cam setup while trying to alleviate the problem? He even added extra support to try to help, which probably wouldn't have been done with a stock cam. I'm pretty sure they took care of any potential cam walk.

This is some of the work Hesco has done from one of Plechtan's threads


Here is a good thread on the max RPM:
http://www.jeepstrokers.com/forum/viewt ... 4383#p4383

[SilverXJ]

Any idea on stock valve float rpm? Given our relatively low operating rpm I've always thought guys tend to run too heavy of a spring.

There was a thread on here where someone was experiencing a wall around 4k rpm (IIRC) and it turned out to be the stock valve springs with a comp cam. Xxxx rpm really isn't a good indicator of anything as there are many variables that need to be taken into account such as valve and retainer weight and the cam lobe's ramp rate.

[SilverXJ]

http://www.hesco.us/forum/forum_posts.a ... t-5600rpms

[SilverXJ]

So you're saying 99+ blocks. I'd always heard 96+ as being the block difference. And I've also heard there was a 02+ change but that has yet to be verified in this thread.
So you're saying there are 91-95, 96-98, 99-01, 02-06 blocks? Or is it possible that the 02+ I've heard about is a chassis difference and is actually the same as the 99+ you are referring to?

96+ blocks had the extra ribbing, NVH enhancements, and the girdle. I've heard that there was some metal removed and need the girdle.

99+ blocks received the cam retainer plate and new cam shaft

53010327AB, 53010328AB: 1999-2004 WJ & 2000-2006 TJ blocks have different engine and accessory mounts. These block will not interchange with earlier blocks. I've also heard that they have thicker cylinder walls to allow a thicker bore.

I actually had to reference my chapter in the XJ performance book to refresh myself. LOL.

See here as well: http://www.jeepstrokers.com/forum/viewt ... ?f=34&t=52

[beiwulf]

Would having a dizzy vs. cps stick be any improvement - vs. a billet piece here? And was there any evidence showing that the cam retainer plate in the NVH 99+ blocks did any good with higher revving?

Brian