Japanman

I mentioned in a post a while back about re-balancing norvel crankshafts- I have a 074 and two .061`s and while the .074 will rev to the moon as smooth as a turbine, the .061s start to vibrate like mad above 25k-
I know lots of you guys have had problems with the carbs comming loose from vibration- well i found recently that the problem is the crank just does not have enough removed from the pin side to balance the piston properly.

Actually I was surprised at how far I had to go to fix things- I thought that after I cut down a piston and lightened it as much as I could, it would have cured the vibration- but no- it made things a bit better, but by no means perfect.

compared to the piston modifications, the crank web mods made by far the bigger difference-

J.M

Japanman

O.K... and I nearly forgot... I found a good way to re-forge the indents that hold the pin in. With a lightened piston it is too thin to just bang away unsupported- so I made a little fork that fits in the piston and supports the piston from the inside- works a treat.
BTW.. i included a picture of a stock norvel .061 piston. Yep, they sure are heavy!

J.M

Dukester

My Feedback: (31)

Wow, looking at that I have only one thing to say...


SHOWOFF!

Seriously though, I'm always impressed by the stuff I see you do. How did you go about determing the proper balance and therefore the amount of material to remove from the crank?

BTW, those batts show up yet?

Duke

Japanman

Well, from what I understand there is a lot of varience in the balance ratios of various engines, and looking at the .074 it has a lot thicker web and therefore %balance offset so I just gave it a go- it could hardly get worse! I had a spare crank so if it all went wrong I`d still be safe anyway.

Yes they did- Thanks very much!

Stefan

bsindel

Japanman,

could you show some side by side pictures of the two cranks side by side so we could see what it looks like before and after metal is removed from the crankshaft.

Thanks
Bill S. (the other Bill)

Japanman

Bill, you got me just in time-

The crank pictured above is from Xanaphysts engine I did for him, so it is a bit prettier than my rough and ready experimental crank pictured here next to a stock crank (on the far left is a stock crank- compare it to the one above)

ptulmer

My Feedback: (5)

Dang, that's alot of metal to be missing. What are these mods worth in #'s. Nice work, but I'm going to stand back when you fire it off. (the entire nation of the USA and the pacific ocean aren't enough. I'm going to step back and wince....)

combatpigg

My Feedback: (3)

The old SUPER TIGRE .35s and TAIPAN .15s would occasionally break between the counterweight and the crank journal, sending the prop and crank snout on a free flight joy ride[X(]! I had it happen to a "helper", the junk cartwheeled up his arm and slapped him in the side of the face. After that, he always stood behind. I don't see where these mods would cause any failures, unless you drilled out the crank too. I bet those mods work very well. The stock amount of extra metal is pretty massive, and if you scaled up these parts, they would look like they came out of a 1930s tug boat engine! If you gain rpm and lose vibration it is a win/win deal. I am interested in finding out the net result of your work too[8D].

Japanman

PT- I am not to worried about it- most of the cranks strength comes from the thickness of the web- if you compare a norvel crankweb to a cox one you may think twice about firing up your cox!

C.P- sometimes I really wish I had a tacho- But I didn`t notice any great jump in rpms- but it runs SO much smoother[8D]

J.M

combatpigg

My Feedback: (3)

JM, before I had a tach, there was always one rule of thumb that told me if I had done anything to make more power from a TD: if you need to open the needle significantly after making a change, then that is good. Once you get an AME up into the 30K realm, then a mod like yours will improve glowplug life, radio equipment life, engine wear, eliminate fuel foaming, and get more power sent to the crankshaft instead of the mounting lugs too.