My crank

[morbin]

Hi all,

here are some pics of my crank for a Polini 177. Inlet phase is about 110 nOt - 66 vOT.

I made this modification most of all for the blowback problem at low RPM and to optimize flow, now I'd like to know, will it work well? Any suggestion from you experts?

Any comment is wellcome!

Gruss

Matt

[freakmoped]

looks nice

you also did the 1pm thing ?

aaah was heisst wuchten gleichnochmal auf englisch...

[morbin]

looks nice

you also did the 1pm thing ?

aaah was heisst wuchten gleichnochmal auf englisch...

That's good to hear!

I'm not sure what you mean with 1pm thing...

is 1pm in the position of the green arrow?

[freakmoped]

i meant to weigh heavy the crankshaft

to about position of the big end bearing at 1pm

looking from the lima side

[Tec]

looks nice

you also did the 1pm thing ?

aaah was heisst wuchten gleichnochmal auf englisch...

Perhaps "balance" would describe it.

1pm thing means the stopping position of a well balanced crank when it`s laid with its ends on two blocks.

@freakmoped: Correct me if i am wrong

Regards

Tec

is 1pm in the position of the green arrow?

Yes, you`re right.

[morbin]

i meant to weigh heavy the crankshaft

to about position of the big end bearing at 1pm

looking from the lima side

I did something here...

[Green Bastard]

Mal zur hilfe Deutsch-Englisch übersetzer --> Übersetzungs Homepage

For to help german-english translator --> Translation homepage

Bearbeitet 7. Juli 2006 von Green Bastard

[morbin]

Mal zur hilfe Deutsch-Englisch übersetzer --> Übersetzungs Homepage

For to help german-english translator --> Translation homepage

Haha that's a nice piece of advice you Bastard!

Ok, so when standing on the edges my crank stands in 12.00 pm position...

So the right position on the edges will be this one?

Thanks all

[morbin]

By the way, should there be a weight on the pleuel when fine balancing?

Bearbeitet 10. Juli 2006 von morbin

[morbin]

Concerning the 1pm thing, do I have to add weight to the conrod when standing on the blocks?

[bigbene]

No you needn't-looks fine anyway, I'm sure you can assemble your engine.

Let us know about results and performance if you like.

[morbin]

Hi Bene,

thanks for replying.

I have already tried it on my Polini 177, final inlet was around 113-63, but lacked too much low end power for my taste. Then I had a slight heat seizure and put back on an original crank for the moment (inlet 113-42). Now low end power is definitely there but haven't tried it on high rpm.

I was asking again for my next crank, so is the way to fine balancing P125-P150-P177-P200 & more cranks always the same? No weight on the conrod at all?

Thanks,

ciao

Matt

[morbin]

up

[bigbene]

Yes, no weigth on the conrod-otherwise the results would be corrupt.

But how come you lack low end power now? Do you have heavy sprayback at the carb?

An optimized crank should, basically, give you more power no matter how many revs the engine does.

[morbin]

Yes, no weigth on the conrod-otherwise the results would be corrupt.

But how come you lack low end power now? Do you have heavy sprayback at the carb?

An optimized crank should, basically, give you more power no matter how many revs the engine does.

Right now I'm mounting the original crank and I'm doing ok with low end power even if I have blowback...

For me it was a problem when I had the crank from the pictures because of the too long inlet phase (and maybe not so optimized?). I ride very often in two and the city I live in has lots of down-uphills.

Even short-long stroke, drehschieber-reed-worb5 cranks should stand in the 1pm position?

[bigbene]

Yes they should- maybe you might want to have a look at the "rotary slide valve topic" http://www.germanscooterforum.de/index.php...c=76708&hl= , basically everything is discussed there in detail.

[bigbene]

Meine Webseite

Sorry link didn't work-how about this one?

[morbin]

Meine Webseite

Sorry link didn't work-how about this one?

I can't see it either...

Anyway I think you meant this one:

http://www.germanscooterforum.de/index.php?showtopic=76708

I'll have an hard time translating but I hope to come through it!

Thanks!

[MiNiKiN]

AFAIK a longer inlet timing might affect the low end power as you are changing the inlet resonance frequency, of course.

I do not agree with the statement not to use any "dummy weights" for the oscilating masses of the piston! There is a description on how-to (in german unfortunately) on THIS page! Basically they state to use a certain amount of nuts, which equal the balance factor (between 40 and 50% - matter of philosophy ) of the piston's oscilating masses.

I take of course no responsibility for my statements

Cheers

M

[morbin]

Maybe the GreenBastard, FreakMoped up there could untie the knot...

Thanks Minikin,

I read a bit and I believe what bigbene told last is correct, and the 1pm thing is all practical and if the crank stands in this position you can consider your crank balanced. The only thing you don't know is how much it is balanced...

And here comes the theory and if you want to do a better balancing you go with the weight at the pleuel and all the calculation stuff...

I hope I understood this stuff:

http://www.germanscooterwiki.de/index.php?...elwelle_wuchten