Cummins harmonic balancer 2

[starspangled]

Hi guys,

I read of a fellow having success using the Cummins 6BT harmonic balancer with an adapter on a Cummins 4BT to solve vibration & balance problems. I'm no engineer so I though I'd check here whether that is a good idea, and if not, why not? Other alternative suggestions appreciated....thanks!

Starspangled

 

[starspangled]

Thanks, Fabrico, I've been considering just that. There is finally some competition in the aftermarket visous units so some are quite reasonably priced. It shouldn't take rocket science to adapt one, and if it does I can always ask here on this forum ha haha! Could solve all the problems.

I wish I could afford to have the rotating assembly balanced PLUS a fluid type damper. If I ever do rebuild it will be getting a bit of Mallory metal here and there, or maybe some QSB parts.

 

[GregLocock]

Well, before you waste your money, the TV damper does an entirely different thing to first order balance.

To me it sounds as though it is worth gettting your engine balanced before worrying about TVs.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[starspangled]

Thanks,Greg, and you may be right. Problem is I just can't afford that at this point. The conversion to 4BT included swapping out and upgrading the entire drivetrain, running gear/suspension, steering, brakes and rewiring from bumper to bumper etc. and that ate up the whole pie.

I located a new 4BT damper at a very reasonable price so I guess I'll try that first. Future plans include a balance job but for now I'll just have to hope this works. Some new rubber isolators may help also. I'll try to let you guys know how well the damper works for your future reference.

Thanks for all your helpful replies fellas!

Starspangled

 

[Tmoose]

I'd get a vibration analyst to measure the vibration at objectionable locations. If the frequency is 1X engine rpm then engine balance has something to offer.

If the worst frequency is 2X rpm (very likely with big 4s) then engine balancing (which only effects primary or 1X)won't do much.

Might be able to rig up a reed vibrometer to judge the problem frequency, or search other threads for using sound cards and free signal processing hardware to help with indentification.

 

[starspangled]

Thanks, Tmoose. I live up in the sticks so about the most hi-tech stuff around is the town's 2 traffic lights. I might be able to find those services down in the valley so I'll check next time I go. I'll look into the sound card/signal processing hardware and see what comes up. Thanks again.

 

[Tmoose]

One of the root causes of the secondary unbalance the rod length/stroke ratio. The other is reciprocating mass. If an engine had infinitely long connecting rods (or weightless pistons, etc) it would have no secondary vibration. A stroker motor is likely to have rods shorter or the same length as its little brother, with the result a "worse" RL ratio, and even more severe secondary vibration.

 

[starspangled]

Well thanks! I really like this 'little' engine at present displacement and have no complaints. For what all it can do as-is I can't see it being worth the resources to bother stroking it. Continually impressed with the power curve and MILEAGE! Hard to beat in many respects. Thanks!

 

[r2800]

An inline six cylinder engine is inherently balanced in both primary and secondary orders, as is a V12.Whereas an inline 4 cylinder engine is only balanced in its primaries, Hence a torsional vibration damper from one is not suitable for the other.
Careful attention to dynamic crankshaft balancing and mass matching of the pistons and connecting rods would certainly help.
If soft engine mounts are to be used then they should have sufficient hysterisis to prevent build up and radius arms should be used to reduce torque reaction.

 

[starspangled]

Thanks, r2800, for your reply. I believe I may have discovered the proper damper but need to check with Cummins for part number cross reference. There is an elastometric damper that is described as correct for both 4B and 6B, but of course that doesn't mean the seller fully understands the dynamics, which I'll leave to Cummins I guess.

At this point dynamic balancing is out of the question as it is a 56K engine and won't get torn apart for a long time. It may be that I just have to bite the bullet and get the pricey little fluid type damper, and also address isolator issues as you describe. I'd like to find a gel-rubber type isolator but there are some fitment problems there regarding frame and engine width interference.

Some have said that it may be an entirely different problem, that I just need to adjust the valves and possibly replace injectors or have them serviced. Didn't adjust valves yet but it's on the plate for this week. After that new injectors, and then more research on damper and mounts.

This water is deeper than I thought! Thanks again for your instruction and assistance. Bit by bit I'm learning more about these curious 4 cylinder diesels. In passing: how interesting to ponder a V12 diesel? Thanks!

Starspangled

 

[starspangled]

Hi all!

I started to go through the replies to click the button to thank people for their replies. I realize now that every single reply has valuable information and has contributed to my understanding. So, I stopped adding stars and just want to thank you ALL for your help! Every contribution is appreciated so thanks everyone and I appreciate the help.

Starspangled

 

[r2800]

A V12 diesel has a heavenly sound all of its own and is remarkably smooth a Rolls Royce Condor is a good example as is the Maybach.

 

[SomptingGuy]

And if you want to know what Armaggedon sounds like, stand on the platform of a provincial station as an Intercity 125 screams past.

 

[starspangled]

Oh, the fascinations in these mechanical things! I hope in my travels to hear at least one of each. I love the sound of a big aircraft radial, too. Funny how some engines are so impressive for the remarkable quiet of their subdued power while another thrills at it's peak power curve. I suppose it doesn't much matter which one when you're a hopeless gearhead and I confess, I am!

 

[r2800]

You are spot on there is nothing quite like all the seemingly disorganised clatter,rumble and racket of big capcity engines, aero engines have a romance all of their own Pratt & Whitney,Wright and Rolls Royce and all the others too.
The shrill howl of a Merlin at speed is without doubt one of the most fantastic sounds, I'm getting goose bumps as I write this.

 

[starspangled]

Yes! I once attended a race for Unlimited Hydroplanes and I don't think I've recovered yet 30 years later hah! That noise echoing off the waters is beyond description. Merlin's are truly a work of mechanical art with few others that even come close.