Balancer and Harmonics 6800 RPM

[superstingray77]

Has anyone been successful in locating an affordable balancer for the 4.7 stroker? I can feel vibration around 5200-5400 that bothers me. Defeats the point of a fully balanced engine.
Would like to know that I can rev clean to 7k if I want to without worry.

[CobraMarty]

I'm sure more will chime in, but IIRC ?turboTom said there were 'harmonics' around 5600 cam, timing chain, and it broke ?timing chains. I think that it might be cam 'walk' at that rpm taking out timing chains. Someone made/adapted/machined a belt cam drive to the 4.0 and maybe that is more 'forgiving' to the problem. I would love a proper balancer and a belt drive.

[SilverXJ]

You can get one from ATI, but its a custom unit. IIRC in my build thread the drawing number is mentioned.

It is the cam/crank harmonics that snap the timing chain, not cam walk.

[CobraMarty]

That ATI balancer, is it only for the stroker crank or will it fit a stock 4.0 crank?

[superstingray77]

Silver are you running that custom ATI unit? If so did it make a large difference in the feel of the engine? My E46 M3 spun smooth as glass to 9k so figured fully balanced with harmonics in check this motor should do 7 smoothly..... so I thought anyhow.

[SilverXJ]

The ATI made a bit of difference, not like it turned it into a different engine or anything. But some harmonics you also can not feel. Did you have your stock balancer balanced as well as your flexplate/flywheel? Every stock replacement/stock balancer I have seen has been out of balance by varying amounts.

I don't think any balancer will keep the ~5300-5500 rpm cam harmonic in check. Hesco says you can drive through it, but don't hold it there. It sounds like you are right where the harmonic comes into play. Damaged cam bearings, broken timing chain, and a snapped cam can be the result if the harmonic hits and held. The only similarity between the Jeep I6 and BMW I6 is that they are both inline 6 cylinder ICEs. That is about where it ends.

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

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

[Cheromaniac]

Has anyone been successful in locating an affordable balancer for the 4.7 stroker? I can feel vibration around 5200-5400 that bothers me. Defeats the point of a fully balanced engine.
Would like to know that I can rev clean to 7k if I want to without worry.

Now you know why the stock rev limiter was set at 5200rpm.
Anyway, you should be able to accelerate through that harmomic rpm to 7k without any problem. Just don't hold the engine at 200rpm either side of 5500. There's no cure for the harmonic but Mopar Performance used to make a timing gear drive set that eliminated the chain, and that would alleviate it. Good luck finding a used gear drive though. You might need to have one custom made, and keep in mind that they whine at higher rpm much like a supercharger.

[superstingray77]

I had the flexplate and balancer all spun with the crank.
Somehow with all the research I did before building the engine this topic of harmonics never came up . But yep I know now why they set the rev limit where they did. My engines peak TQ is right around 5100, HP peak is around 62-6300. It makes plenty of power <5200 so I seldom see 3000 RPM in any normal driving scenario. It does pull like my M3 did between 2500-5100 you can feel it come up on the cam big time. Still plan to build a custom intake that will better match the head/cam and curve of the engine as i feel there is a lot of power left on the table due to the crap-tastic intake setup. Nothing like a long runner dual plane with not enough cross sectional area to feed a 3.0 that literally surrounds the headers for maximum hot air zero density . Thanks to Ryan's mad tuning skills it just keeps getting better.