Crankshaft Harmonics

Ken_Parkman · Post by **Ken_Parkman** » Thu Mar 10, 2005 11:49 pm

I'm doing a serious study of Crankshaft Harmonics and dampers as applied to my oddball AMC engines. It looks like I 'might' be able to get access to a nodal analyzer to do some vibration testing. But I need to know more about the different vibration orders in the crank. Read a few texts (deep deep stuff) and have what causes the orders figured out, but the math to calculate the criticality is beyond me. Apparently the criticality of these orders changes with number of cylinders and firing order, but I'm told practical experience is the third order is the most critical. Does anyone have tables for order criticality multipliers for a V8, and do they change with firing order?

Post by **ClassKing** » Fri Mar 11, 2005 3:13 am

Ken: Are you just trying to learn something or are you having problems?
Both?

Ken_Parkman · Post by **Ken_Parkman** » Fri Mar 11, 2005 10:40 pm

Both. Years ago I did have a crankshaft problem I fully blame on the damper. At this point I have tremendous respect for what destruction vibration can do, and blame vibration for many things. I've had a non technical problem the outfit I've gotten dampers from, and am going to go with ATI. That's made me want to really figure this out to see if I can make use of the tuning advantages of the ATI, and have permission to take stuff into work where we have a nodal analyzer. But trying to learn more has shown how complicated this really is, so I'm fishing for the order criticality tables that exist somewhere. The text's I've read tell me different orders have different multipliers depending on the engine configuration and firing order. I cannot check this on the analyzer, but if I knew which order was critical and the modes, which the analyzer can give me, then I could probably tune the damper on the analyzer. It would be really interesting to see if this matches up with practical experience. Or I might find it is too complicated and I'm wasting my time. Bottom line, want to learn as much as possible, then at least I've tried to make the right decision.

Wolfplace · Post by **Wolfplace** » Sat Mar 12, 2005 1:00 am

You might give JC at ATI a call.
This is what he does & he probably has a ton of information on his dampers under different operating conditions & applications.
You just might learn more with one phone call then 6 months in the "lab"

Ken_Parkman · Post by **Ken_Parkman** » Mon Mar 14, 2005 7:24 pm

Thanks Wolfplace. I've been talking to JC, he's been very helpful. ATI uses peak to peak displacement measurements, and JC has given me some suggestions on order criticality. I'm trying to approach this in a more fundamental direction by actually getting the natural frequencies. But I'm coming to the conclusion I might be wasting my time, the best plan probably is peak to peak directly on the engine (probably better on a chassis dyno) like ATI does.

Len · Post by **Len** » Mon Mar 14, 2005 7:31 pm

Hi Ken
Did you stuff that AMC in a metropolitan yet

Len

Ken_Parkman · Post by **Ken_Parkman** » Mon Mar 14, 2005 7:36 pm

Not yet Len - but believe it or not my father has a Met! That would be a fun ride, wouldn't it?