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Discussion Starter #1
If an engine suffers from bad harmonics at a certain rpm what measures can be taken to elimenate/shift harmonic point primarily in inline 6 cyl engine.
Any input appreciated.
Thanks
 

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out of work hair dresser
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Determine the "why" first and foremost.
 

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there are a few inline 6's around with destructive harmonics at certain rpm points, the little I know of the subject says there are orders of magnitude that means that the harmonic is present at a bunch of points in the rpm range but it gets nasty when you sit on the "worst" rpm point for extended periods.

Circuit engines are particularly susceptible if they "hover" around the damage point, in most of the stuff im familiar with (admittedly not much) the consensus is to move THROUGH the rpm point to a less "destructive" region and its not "too" bad.

The usual attention to balancing, tune etc etc might lessen its effect but in some cases it just cant be eliminated so you deal with it and move on.

Might help for you to list the engine type etc for the more learned chaps to chime in and id suggest you find someone successful in the racing you want to do, with the engine you want to use and start there because you can bet theyve killed a bunch of engines and tested plenty to try and fix it.
 

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out of work hair dresser
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Start with potential obvious things like...........condition of harmonic balancer used, and question the flexplate or flywheel. Ask yourself, is the problem new? When did it start? Has it always been there?

What RPM does the vibration occur?

Inline 6 cranks are very prone to twisting at upper RPM levels, perhaps your problem is in the where-abouts?

More info helps.
 

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Discussion Starter #6
there are a few inline 6's around with destructive harmonics at certain rpm points, the little I know of the subject says there are orders of magnitude that means that the harmonic is present at a bunch of points in the rpm range but it gets nasty when you sit on the "worst" rpm point for extended periods.

Circuit engines are particularly susceptible if they "hover" around the damage point, in most of the stuff im familiar with (admittedly not much) the consensus is to move THROUGH the rpm point to a less "destructive" region and its not "too" bad.

The usual attention to balancing, tune etc etc might lessen its effect but in some cases it just cant be eliminated so you deal with it and move on.

Might help for you to list the engine type etc for the more learned chaps to chime in and id suggest you find someone successful in the racing you want to do, with the engine you want to use and start there because you can bet theyve killed a bunch of engines and tested plenty to try and fix it.
Cheers for reply.
Yes all points you have made have been considered. Engine performance is ahead of anyone who has tried with this particular combo and reliable provided rpm is kept in check. Harmonic occurs close to peak power which is a pain. Engine is notorious for it.
 

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Discussion Starter #7
Start with potential obvious things like...........condition of harmonic balancer used, and question the flexplate or flywheel. Ask yourself, is the problem new? When did it start? Has it always been there?

What RPM does the vibration occur?

Inline 6 cranks are very prone to twisting at upper RPM levels, perhaps your problem is in the where-abouts?

More info helps.
Std balancer originally then ATI (new)
Originally Flexplate with multiplate adapted now billet flywheel, all balanced etc.
No, inherent problem with engine type.
Harmonic can be felt around 7 k.
Will provide more details if needed. Dont want to cloud the ideas at this point.
Thanks for input
 

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is it a definite engine problem or could it be valvetrain related?

is there any scope to move the power band or rev further past peak power?

my ability to help is limited, im just throwing out some ideas.
 

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out of work hair dresser
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out of work hair dresser
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Getting info out of you is like pulling teeth.

Good luck and hope you find your fix.
 

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the crank is like,:rolleyes: a mile long.
Yeah, she's got some length but most harmonic problems associated with L6's wasn't related to the crank at all...........even on cranks with long arms.

I built a Chevy 292 back in the '90's for a local bracket racer. He was told max rpm was 6200. He ignored all that BS and shifted the glide at 7600.................for a few years.
 

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Yeah, she's got some length but most harmonic problems associated with L6's wasn't related to the crank at all...........even on cranks with long arms.

I built a Chevy 292 back in the '90's for a local bracket racer. He was told max rpm was 6200. He ignored all that BS and shifted the glide at 7600.................for a few years.
Well they do require a different balancing shceme vrs a traditional v8. could be the balance job is all wrong.
 
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