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 Post subject: crank web filling
PostPosted: Tue Aug 23, 2011 11:45 am 
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Location: Vienna, Austria
which material would you guys recommend for fillingn the crank webs, not only the 2 small balancing holes but the whole pockets around the pin? I wanna achieve a full circle web for increased crank pressure. Epoxy, nylon, alloy? It should be as light as possible but strong enough not to explode at 12000 RPM.


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PostPosted: Tue Aug 23, 2011 12:55 pm 
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A thin steel or aluminum sleeve pressed over the wheel to trap cork and epoxy. I've seen a picture on the www like this.


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PostPosted: Wed Aug 24, 2011 3:58 am 
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Location: Koege, Denmark
Hi,

What about welding thin sheet metal to the crank to make hollow fillings? It's made like that on my Puch 250 SGS (with factory crank). Strong, light and cheap ;-)

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PostPosted: Wed Aug 24, 2011 4:22 pm 
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Luther,
Quote:
A thin steel or aluminum sleeve pressed over the wheel to trap cork and epoxy. I've seen a picture on the www like this


That is what my engine guy has done in the past (20 years ago), but it requires modification of the crankcase due to the bigger crank web diameter, even though it is only 1 mm or so. Cost of machining time in Austria prohibits that solution.
The other problem is that the guy who will assemble and true the crank afterwards may destroy the sleeve with his copper hammer.

Our current best idea is to fabricate the inserts for the 2 pockets in the web from a kind of teflon (need to find right one) or epoxy mixed with glass fibres and bolt it on the web. Still searching for something better though. I searched for the pic you are referring to but with no success.

Twinsport,
Quote:
What about welding thin sheet metal to the crank to make hollow fillings? It's made like that on my Puch 250 SGS (with factory crank). Strong, light and cheap

for some reason I feel uncomfortable with welding on a crank.

Thanks a lot for your inputs, we will keep them in mind as plan B

regards

Wolfgang


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 Post subject:
PostPosted: Wed Aug 24, 2011 5:06 pm 
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Joined: Sun Nov 05, 2006 6:10 pm
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Location: Essex, England
I have an old two stroke tuning book somewhere
It discusses crank filling and used cork and araldite
Are your cranks disassembled ? would this make it easier ?

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PostPosted: Thu Aug 25, 2011 3:55 am 
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Dubsey,
yes I ordered them disassembled, they came from Gus last year.


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 Post subject:
PostPosted: Mon Jan 02, 2012 3:41 pm 
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My crank web fillings are completed, crank will be sent for assembly now. All 8 webs have this epoxy fillings, the inner webs have a thicker layer since the clearnace to the conrod is bigger.
This is an aerospace grade epoxy, resistant against oil, gas etc and heat up to 130°C

[img][img]http://img233.imageshack.us/img233/3822/crankfilling1.jpg[/img]

[/img]


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 Post subject:
PostPosted: Mon Jan 02, 2012 4:09 pm 
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Heat in the crankcase can exceed 130°C in some engine's .

I remember you saying you wont stress this engine, so you might not get to much heat into the crankcase, or was that a different engine?

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 Post subject:
PostPosted: Mon Jan 02, 2012 4:16 pm 
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No, this engine will be stressed indeed, we are aiming for much peak power, pure trackbike...although crankcase temp should not be more than 130° deg?? The gas temp will go up and down in sync with the pressure pulses each rotation, but the average temp should be much lower. I dont even expect 110°C, but I really dont know for sure

Our target is a power to weight ration of 1:1,2.
Not the world nowadays with the most recent superbikes, but for sure lots of fun!


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 Post subject:
PostPosted: Mon Jan 02, 2012 4:31 pm 
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:grin:

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Last edited by zomaardan on Wed Jan 04, 2012 10:55 am, edited 1 time in total.

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 Post subject:
PostPosted: Wed Jan 04, 2012 6:04 am 
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Hi Wolfgangh, I think you will have created some problems for the gas flows on both the intake & transfer cycles, this is what the cutaways are for. You may have lost a lot to gain a little.
Cheers,
Robert.

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 Post subject:
PostPosted: Wed Jan 04, 2012 10:53 am 
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Hi Robert,
this mod was done by an experienced fellow engine builder who raced all kind of 2-strokes. There is much more modifications to the crankcases done, including plugs on top where only the rods pass through with defined transfers etc.
I have seen similar web fillings on other 2-stroke racing engines as well.

I cant comment your statement since I dont understand enough, but I assume my engine guy knows why we are doing all this - and its a lot of work involved believe me.

He built similar RD500 engines in the 80´s and 90´s, with ca. 120 HP but without modern electronics like programmable ignition, etc.
Lets hope he is right.


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 Post subject:
PostPosted: Wed Jan 04, 2012 11:27 am 
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check the water inlet pipe and the reed cage:
Image

The inlet section of the lower cylinders in the upper crankcase has been removed and replaced with wider ones (billet). Not only the area is wider, also the angles of all 4 intake tracts are optimized.


Image


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 Post subject:
PostPosted: Thu Jan 05, 2012 10:33 pm 
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Nice work! :grin:


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