Max RPM of Jeep Engine

[dwg86]

I don't know how a block would be made to have more bearings installed? A new cam would have to be made also.

[1bolt]

Dude, there's no telling whats going on at this stage, hell its just getting more confusing if anything. Drinking or not you may well be right. And I am not defending HESCO though that's probably how it looked. And I'm not ripping on you, that shit was intended to poke some fun at this issue.

Just speculating but he lifted the supposedly "droopy" block when it was completely empty and bare, add the crank back in and the crank girdle and a head and it would stiffen up a whole lot...

Look if the guy had any reason to lie or I had any reason to doubt Plechtan's account, I'd be calling BS on the droopy block thing, it does seem kinda crazy...

But we're talking about a retired NHRA racer with no reason to lie, and Plechtan obviously came in not believing in the cam harmonic at all... So maybe the 4.0 has block rigidity issues? There's certainly ways to find out... Maybe the guy G. Hill refers to as not having problems had a better block?

At this point my theory has gone from needing a stiffer cam (I'm not Cam expert obviously but read the big roller cam thread from a while back all sorts of cam harmonic ideas in there). Thinking maybe Lee Hurley's explanation about needing more Cam bearings was a possible solution. Then wondering if parts are just not that strong because they didn't need to be. Now I'm wondering if the block is flexing at high rpm causing excessive drag on the cam and stretching timing chains and spitting out dizzy's... Lets not forget John's first hand experience with that... If the block flexes enough the dizzy gear could unmesh... Of course it could just have been a weak OEM dist.

Who the hell knows... Anyway... Back to the droopy block... any of you machinists (John?) know a good way to measure droop in a bare block? I can do an unscientific test of several bare blocks I have...

[TurboTom]

Well one way of measuring the droop would be to measure the distance between torqued front and rear maincaps, both supported and just hanging from the engine stand.
That would require either a Looong set of calipers or a short set (or a dial indicator) and a set length, stiff "filler stick".
Maybe the stock girdle, only bolted in the rear with the indicator stuck on the front main?
Putting the crank in should make no difference as the crank never touches the bearings while running.
But here again the crank nor the cam would turn freely once the engine drooped.
I will be back up to the engine shop this week and will try to test this.
I don't believe anyone is lieing. But I do know I have been down some pretty crazy paths when I thought I was "on to something".

Fun stuff!

[John]

1bolt I would start out with the basic test first Mount the block on the best motor stand you can find, remove the oil pan and mark the cleaned mounting surface of the block in 1" increments front to rear. Starret makes a 24 inch precision straight edge that is thick enough to set a magnetic base for a dial indicator, measure and record both sides with the straight edge and dial indicator, remove the head and repeat test. 24 hrs later repeat test, If any change is found...... This has got me thinking far too much, it hurts. The honing plate was pioneered, some say, for the I6 due to its tendency to deform when the head bolts are tightened.. That is quick and dirty. If you have a good Bridgeport mill it would be easy to better search, but quick and dirty should show indications.
John

[SIXPAK]

Droopy block? Homie don't think so

[Flash]

Droopy block? Homie don't think so

That's kind how i fill......................But then again, i never throw out any theory.......until some one can prove it wrong.

as far as hesco adding extra cam bearing.....It wouldn't take much to turn down the "as cast" of the cam to except a couple of bearing..........machining of the block could be tricky, and then, adding pressurised oil as well.

I like the thought that Delk made about a bearing support on each side of the cams distributor gear........would sure keep the distributor gear true and straight motion on the cam.....a specially if the extra bearings were of a thrust design.


Flash

[John]

Ok, I was talking to A. H."Hemi" Adkins today and when we discussed the cam and it's lay out, he wondered aloud if increasing base circle diameter wouldn't stiffen our camshaft, felt the 4 bearing surfaces were marginal for the length of our cam? I toss this into the thought process.
John

[dwg86]

as far as hesco adding extra cam bearing.....It wouldn't take much to turn down the "as cast" of the cam to except a couple of bearing..........machining of the block could be tricky, and then, adding pressurised oil as well.

Flash[/quote]

I'm not trying to be argumenitive... I'm just not sure I get what you are talking about the "as cast" of the cam. Turning down the camshaft to make extra bearing surfaces would't work. The stock or original cam bearing surfaces would be larger than the bearing surface made by turning down the core of the cam, and wouldn't pass through the smaller bearing surfaces...am I making sense?

[Flash]

as far as hesco adding extra cam bearing.....It wouldn't take much to turn down the "as cast" of the cam to except a couple of bearing..........machining of the block could be tricky, and then, adding pressurised oil as well.

Flash

I'm not trying to be argumenitive... I'm just not sure I get what you are talking about the "as cast" of the cam. Turning down the camshaft to make extra bearing surfaces would't work. The stock or original cam bearing surfaces would be larger than the bearing surface made by turning down the core of the cam, and wouldn't pass through the smaller bearing surfaces...am I making sense?

Maybe John can repost the discussion on this, on the hesco sight.........would be simpler then trying to explain my self.[/quote]
Flash

[TurboTom]

Well took a long hard look at my 2000 4.0 today.
I am now not even going to try to measure the "Droopy block theory" It's just not happening.
So what's next on the list?

[John]

Flash hang in there, one of has to keep a working memory and mines trying to retire. How about 3 links on this topic, including the one we discussed, that's the second link.

http://www.hesco.us/forum/forum_posts.a ... W=5600+rpm
http://www.hesco.us/forum/forum_posts.a ... ar+failure
http://www.hesco.us/forum/forum_posts.a ... W=5600+rpm

John

[1bolt]

Yawn... having reread those threads so many times and going back through this one it almost seems like we're going in circles... Lee is absolutely sure of himself when he says its a cam harmonic. We all knew that, the droopy block thing sounds crazier and crazier but WTF would probably the only guy to ever take a 4.0 down a 1/4 mile in 8 or 9 seconds lie about that?

My unscientific test will be to put each of my bare blocks on the stand let them sit for a week and try to install a couple of the junk cams I have laying around.

Seriously why would Garth Hill bull shit something like that. No offense to you all, I know some of you actually race, but until one of you spins yours up to 8,000k 140 times I'm going to give Mr. Hill the benefit of the doubt.

[TurboTom]

1 Bolt:
It is not a lie or BS if Mr. Hill believes it. But just for a minute consider he could just be wrong. Maybe he had trouble getting a cam in, and while lifting the block he twisted his arm just right and it slid in. He could then conclude the block was drooping. I can tell you that if the block could "bend" enough from it's own weight to misalign the cam journals there is no way these engines could go 150,000 miles without constant main and cam bearing issues. And if it bent on the stand THEN THE CAM NOR THE CRANK WOULD TURN AFTER HE LET GO OF THE BLOCK!!. I have shared this "theory" with 3 different engine builders. They all called BS. I myself have ported and built the heads, and ran the dyno for the BMW of North America factory road race team (Prototype Technology Group). We won our class in the 24 hours of Daytona and the 12 hours of Sebring 2 years in a row. We won 7 championships in 5 years... all with straight six's turning 8400-9200 RPM. So the people I have discussed this with have as much working knowledge as anyone.
Every crankshaft has a harmonic (and straight sixes are worse due to their length) but generally if you "drive through" these spots there will be little damage.
There is alot of BMW engineering history behind my last statement.
Also the factory damper may be tuned for highway RPM. According to my engineer friend, we should be using a fluid dampner as they are better at absorbing harmonics over a wider range of RPM's.

By the way i have started a new thread at Hesco to try to get to the facts.

[1bolt]

Good info, I agree on the fluid damper. Those are some impressive credentials BTW nice to see the mix of experience on Jeepstrokers is growing.

Hopefully you can get more out of Lee than his usual terse responses that somehow always seem to need more elaboration He's a busy guy which I completely understand but his reponses always seem to just tease at the details.. Maybe its just me.

I wonder if anyone makes a small damper that could ride on the cam timing sprocket? Or if that would help. The Navarro engine had a fuel pump on the cam snout...

[Plechtan]

I have been out of town for a bit, so i have been catching up on the thread. I guess I am generally suprised that very few people in this group seem to have any experience raving a jeep engine over 5,500 rpm. The reason i started this thread was that I was hoping to learn form other peoples experiences. The guy with the most experience: Lee Hurley. he is 82 years old and has been working on engines for 60 or 70 years. He says the jeep engine has a harmonic at 5600, he also in one of the posts on his site the the 3.0L stadium engine does not have the harmonic. This was previously mentioned in this thread. Could it be that the choice of components that Hesco uses is prone to the harmonic? For example, maybe they are using 4.0 main bearing caps. The stadium motor is based on a 258 block and a 3" stroke so i would assume that it uses 258 main caps. I think the best idea so far is to set one up on a dyno and see what happens.

As for some of the posts about Dampers, I spoke to the chief engineer of ATI at the SEMA show. He does not believe the harmonic is originating with the cam, he thinks the crank is the cause ( of course they sell crank dampers) . I did ask hin about Cam Dampers, and he said that they have done some work with them but it is ant a product that is currently for sale. I really like the ati product for 3 reasons, it seems to work very well, it is tunable, and it is rebuildable. The ATI unit is used by allot of the NASCAR teams, they only use the things that work the best.

As for the Block stiffness issue, I don't know if Garth was mistaken or not, but i do know that looking at the support for the main bearings on the blocks that i have, the support stinks. The center main has almost no support going over to the Cam side of the block. I can see why they didn't use the center for the thrust bearing . The center support has a hole in it for the oil pump. The supports are thin on all of the mains except the front and rear mains. It doesn't look like the bottom end of a 500 hp motor to me.