vibrations

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RADustin

New Member
#1
#1
I'm spinning my gx200 to ~6K with an ARC long rong, honda flat top, and ARC billet FW. Stock crank. ~11:1 comp on gas with +6 timing.

To anyone else running this combo or close, how would you describe the vibrations you feel?

My bike seems to vibrate harder(magnitude) than my harley. The frequency is much higher but the jolts are firmer.

I'd say the vibes start around 4K and carry all the way to valve float getting worse.

I do have knobby tires and am switching to streets soon. I assume this will help a bit but its far from "fun" to ride this thing when it puts my hands asleep within a few minutes.

Before I start messing with heavy bar ends to mask the problem, is anyone balancing these motors?

I have an adjustable horsemen clutch so if it vibes down low I don't care.

My machinist I use for all my cars says he can balance it, but he doesn't know the specs. Are these specs held confidential?

thanks.
 
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rmm727

Active Member
#2
#2
I curious how you're runing the ARC long rod with a Honda flattop. Unless you meant the +.010 or +.020 rod. The "real" long rods are for use with Wiseco or other pistons and are almost 1/2" longer than stock.
 
Stangrcr1

Stangrcr1

New Member
#5
#5
Hmmm. I was thinking of this issue for my upcoming build.

What is the weight difference of the modified rotating assembly compared to stock? Ie: stock rod/pin/piston/rings vs aftermarket rod/pin/bearing/piston/rings. If there is a large enough difference, it will vibrate badly.

Has anybody done a balance on the rotating assembly?

Also, what assembly weight was the flywheel machined for? Is it machined concentric with no counterweight?
 
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rmm727

Active Member
#6
#6
I would think the ARC rod is heavier than stock. The ARC flywheel is lighter than stock. How does advanced timing affect this? or doesn't it?
 
Stangrcr1

Stangrcr1

New Member
#7
#7
Ok, if the rod is heavier, and the balance of the flywheel is machined for the stock piston instead of a Honda piston, this could induce vibration.

Also, the lighter the flywheel, the more vibration will be felt as there is not as much mass to dampen the power stroke of the engine.
 
creia

creia

#8
#8
What type/brand frame is the engine mounted on? It very well could be that the "vibrations" you are experiencing is that the (now highly modified, higher HP, and higher rpm) engine is flexing the "stock" engine mounting plate which was designed for a much smaller and lower performance engine ( typically 3-5 HP). We experienced this on both of our DB-30's when we installed the (older) blue HF "Greyhound" and (newer) black HF "Predator" engines.:doah: I had an additional heavy gauge slotted mounting plate welded on top of the original Baja mounting plates and it made a HUGE improvement.:thumbsup:
Michael
 
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RADustin

New Member
#9
#9
this is just speculation.

dished piston -> flat top = heavier
stock rod -> longer billet rod= heavier
stock pin- stock pin= same
stock rings -> flat top rings- same

so the rotating assembly IMO is heavier modified. What does this mean on a single cylinder engine...??

I could believe the frame was flexing. I need to do more tests. and see if the vibration is speed or RPM related.
 
Stangrcr1

Stangrcr1

New Member
#10
#10
Heavier piston and rod without a corresponding increase in the counterweights in the crank = vibration. Add a lighter flywheel and the vibration becomes more pronounced.
 
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