Jeep Strokers

We're talking about this in a few threads that have migrated from the original topic. So here is a place to discuss this.

A few things to start off with. The Gear drive timing set with two idlers. Gear drives are the worst setup for harmonics and long term use. The only engines that use a gear drive timing set are Diesels, tractors and low RPM boat/industrial engines. Here is something I found while trying to find out more info on the 4.0 gear to gear timing set. This is from a Duramax site. http://www.duramax.bizhosting.com/My_Tr ... -drive.htm
Since there are accounts of engines being spun over 6K with a gear to gear timing set could it be that the harmonic that many are saying is in the cam actually in the timing chain? It would explain why they are reported to snap the timing gear off at 5700 RPM. That is why I am checking into a belt drive for the cam. They dampen harmonics the best and isolate the cam from the crank. Comp Does have a timing set that is designed to fit under a stock cover and run with stock splash/drip oiling. The only problem is that the belt they have listed is too short, I'll see what I can do.
From what I've heard and learned in class a harmonic that exists inside an engine should cause a failure in the middle of the piece and not at the very end as the story on the 4.0's.

~Alex

They will also spit the dizzy out of it's mount. Many think the gears work because they will allow more unrestricted movement. I am sure that the chain set is one of the inputs to the harmonic failure. I have been sorely tempted to get a scrap block, put new cam bearings in place and run the cam up to speed with a chain set operated with a speed controlled motor to see what happens above 5k. With valve train in place but crank/piston/rod out of the picture, I might be changing operations enough to completely screw up the results, but it could be easily controlled and monitored.
John

I'm really interested in the idea of lightening the valve train. Mostly because titanium valves, springs, keepers and retainers for SBC's pop up all the time on Ebay and are not all that expensive. Lowering the valve train mass is a multi-fold performance magnifier. Lower friction, less wear, higher RPM's better stability and reliability... basically as can be seen with overhead cam engines... there's a lot of efficiency, performance and reliability given up pumping all those heavy parts up and down.

yep... pushrods r bad for high rpm's. I won't go for Titanium valves in my engine because they don't have the durrabality of a steel or stainless steel valve. I have seen the damage a broken Ti valve can do to an engine. One customer bought the car with an unknown history and unknown engine specs & dates. Not too far into the season an intake valve lost its head, only the camshaft and one cylinder head were able to be reused in the new engine. I will say that I don't know how long a Ti valve will last in a low stress environment such as a Jeep 6cyl. I would be cautious using Ti valve springs because I just don't know anything about them, yet, last I heard it didn't have the elasticity to make a decent spring. Those SB2 springs listed on eBay are some very strong springs and would be complete overkill for a stroker engine, also too cheap to be believable. Ti retainers and keepers are a good way to save on weight. A beehive (progressive) spring would be the way to go because they are generally lighter and will resist a harmonic while using a smaller diameter valve retainer (lighter). Also one other note on Ti components. Don't use brake clean or carb clean on them it is bad for the anti-galling coating and maybe the Ti its self.
I've gotta look into the distributor issue soon as well.

John, ever hear of Spintronics?

~Alex

Alex22 wrote:I would be cautious using Ti valve springs because I just don't know anything about them, yet, last I heard it didn't have the elasticity to make a decent spring.

I take that back. After finding out more about them, Ti does make a good automotive valve spring, but durability can be an issue for a daily driver.

~Alex

John, ever hear of Spintronics?

No but feel free to educate me.
John

John wrote:John, ever hear of Spintronics?

No but feel free to educate me.
John

I tried to find the company's website but couldn't. It is used by most of the cup shops (Winston & Nextel cup) to analyze the engine's valve train for harmonics and other problems. The setup uses a 100 HP electric motor in place of the crankshaft to turn a fully assembled valve train at whichever RPM they want to. There are high speed cameras and strobe cameras to record what is happening so they can find their problems and test new ideas without the risk of grenading an entire engine on the track or dyno.

Basically a $30K version of what you are planing on building.

~Alex