Too much vibration.

[Jay dee]

I think it was Fabian that ordered a “balanced crank” (or engine with balanced crank) and he sent it back because it vibrated so much. If you want something done right you have to do it yourself. The internet has been void of what I’m fixing to offer for free- a crank balancing program. No wonder dealers fail to properly balance a crank when all they have to go on is the old wives tales of how to.

How much would you charge to balance right. I got the new skyhawk it doesnt vibrate at all till i go over 30

 

[Deleted member 12676]

I live in South America. shipping costs are high.
Just do it yourself. it's not hard to do.

 

[FurryOnTheInside]

I would definitely be willing to try drilling into the crank edge to be able to try different amounts of weight removal and save dismantling the engine each time.. but I am going to have an atypical engine running at an atypically low rpm, and it is going to take me a long long time to get my engine running and start testing so I'm not an ideal guinea pig!

I definitely like your idea though and I think that duck tape and maybe a couple of small magnets or grease to trap the dust, and channel locks/ mole grips on the primary gear should be fine.

 

[WINDY CITY BOB]

When I am having a problem with nuts CONSTANTLY going loose I "JAM-NUT Them.
What is a jam nut?
Principle of a jam nut.
If you have an allthread stud that needs to be handled tighten (JAM) 2 nuts together on the stud to lock them in place. By doing thisyou can turn in the stud without damagimg the threads.

 

[WINDY CITY BOB]

You can use this jam-nut to keep your nuts from falling off if you have enough thread and an extra nut. You need 2 wrenches then just snug the 2nd nut up against the nut holding your part. This is very old you probably already knew about it.

 

[butre]

jam nuts work if you've got the clearance, but I often don't. in most cases I prefer safety wire.

 

[Deleted member 12676]

It figures out that if you drill an outside hole the same depth as the crank wheel is wide (close to 16mm) then you are within 3% of having the exact same result as drilling it from the side at 36mm from the crankshaft center. that's using the same diameter hole.

 

[Deleted member 12676]

I think I’ve straightened it out. I had some incorrect engine data and I now see that engine compression can’t be part of the formula if it’s to agree with real world results. For the following data set for a 69cc engine I see that the extra two holes need to be close to 9.8mm in diameter (use 3/8”)

69cc Grubee engine
connecting rod 80mm center to center (weight 65 grams)
piston/rings/bearing 91 grams
wrist pin 14 grams

If the connecting rod is 85mm then use a 10.5mm drill bit (13/32” #1G901 from grainger.com for $21)

 

[Deleted member 12676]

It's done. Probably my last great project for 2 strokes. I'm too old to be slaving over a computer all night long for weeks at a time. enjoy
http://www.dragonfly75.com/motorbike/crankbalance.html

 

[FurryOnTheInside]

This is fantastic. Great job, Jaguar!
*bows down*