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Old 10-29-2014, 05:27 AM
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Default Gokart MZ 250

as you know, old engine is dead so is time to get new one ..
So I did... I bought motorcycle engine 250 ccm, 20 HP, 5 speed gearbox..

Got it yesterday so only had time to quick check to see will it fit, looks like it will.

Probably gonna cut frame in half and make new back half, make it bit stronger than previous one cause engine is heavier and I saw few mistake in old one (too much flexing beneath @ss ) :p

Must change gear ratio too. Sprocket on engine is under cover so it is size limited. Origninal has 15 tooth, max possible is 19. On other hand , on axle cannot go with too small sprocket because limited by flange.

Also ordered 4pcs Flange Type Ball Bearings for spindles so gonna change that as well.

This engine do not have any rubber shockers so must figure that out to reduce vibrations and shifting and clutch as well..

Engine cost me 200 $ and have to wait to sell some parts before continuing work.

Hope to hit the road again at spring..

Few pics:

http://i.ebayimg.com/00/s/NTMzWDgwMA==/z/L~YAAOxy6MBSP6Hp/$T2eC16NHJHoFGlIh3C5VBSP6Ho7V-!~~60_57.JPG

http://pizdarije.medjica.com/gokartm...14/mz250_1.JPG

http://pizdarije.medjica.com/gokartm...14/mz250_2.JPG

http://pizdarije.medjica.com/gokartm...14/mz250_3.JPG

http://pizdarije.medjica.com/gokartm...4/mz250__4.JPG

http://pizdarije.medjica.com/gokartm...4/mz250__5.JPG

http://pizdarije.medjica.com/gokartm...4/mz250__6.JPG
Attached Thumbnails
$T2eC16NHJHoFGlIh3C5VBSP6Ho7V-!~~60_57.JPG   mz250_1.jpg  

mz250_2.jpg   mz250_3.jpg  

mz250__4.jpg   mz250__5.jpg  

mz250__6.jpg  
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Last edited by landuse; 11-25-2014 at 12:28 AM.
  #2  
Old 10-29-2014, 05:32 AM
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I am glad you found an engine so quickly. You will be on the road soon again
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  #3  
Old 10-29-2014, 08:17 AM
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Oh wow you are going to be going so fast when it's all said and done
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Old 10-29-2014, 09:11 AM
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Quote:
Originally Posted by gran_pann View Post
Oh wow you are going to be going so fast when it's all said and done
Especially if he puts those biggest looking slicks,sitting up on that shelf.
Karte, your shifting and clutch work can all be put on one convenient lever.... Grab lever and squeeze....Then shift...... . Easy.....
Instead of cutting the back off,I think I'd try to brace it up.......
Nice looking engine, BTW.....
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Old 10-29-2014, 10:23 AM
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I do not like how kart looks and act in back half...

After i bend it, I added L shaped profile to add streingt and it looks really bad...

Second, there would be too many scars of previos engine mounts...

And I think I made mistake by adding right2left instead front2back additional tubes...

For shifting and clutch I gonna to use that solution, but flappy pedal on wheel will be much cooler thing to do...

Also, if there is room, would like to use your idea Jim for starter...
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Old 10-29-2014, 10:59 AM
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Holy Molim..

Thats gonna be too much fun..

Good job on the replacement motor..
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  #7  
Old 10-30-2014, 02:26 AM
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HI guys. ..

Yesterday did some cutting and removing unnecessary pieces

http://pizdarije.medjica.com/gokartm.../MZ_250_18.JPG

So need your opinion , should be enough to reinforce chassis with three new tubes (marked red)?

http://pizdarije.medjica.com/gokartm..._15_edited.jpg

http://pizdarije.medjica.com/gokartm...0_9_edited.jpg

I really do not like this L shape ..

Some more sanding needed to remove old welds and mounts.

http://pizdarije.medjica.com/gokartm...4/MZ_250_7.JPG

Also need to bend exhaust pipe a little bit:

http://pizdarije.medjica.com/gokartm.../MZ_250_16.JPG

more pictures on LINK
Attached Thumbnails
MZ_250_18.jpg   MZ_250_15_edited.jpg  

MZ_250_9_edited.jpg   MZ_250_7.jpg  

MZ_250_16.jpg  
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Last edited by landuse; 11-25-2014 at 12:30 AM.
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Old 10-30-2014, 03:23 AM
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This is just 'my' opinion... 250cc w/ gears is an awfully large amount of torque/HP for a 'kart' vs a motor bike or a 'buggy'... but from my experiences... parallel bracing (like the design youre thinking) tends to not be as 'ridged' as triangular bracing, using the same amount of metal/length. Not saying there is anything wrong w/ your design (yea Im not too fond of the "L" shape either), but to be on the safe side I personally would do 'something' like the attachment. Bracing strengthens and stabilizes/increases rigidity... but did you also realize it is a transfer conduit of vibrations/shakes. The design I attached will/should strengthen and reinforce the frame for the engines torque, aswell as transfer vibrations towards the outer perimeter framework, vs inner framework... where your butt sits. And trust me... its very uncomfortable to ride a kart that'll numb you nether regions in a matter of afew mins.

I too am a stickler for appearance... and Ive found that black paint covers ALOTTA ...

Attached Thumbnails
MZ_250_9.jpg  
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  #9  
Old 10-30-2014, 07:07 AM
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huh, that gonna be stiff :p

I thought to remove this blue lines (tubes) , remove L shaped profile ( green) but left tubes instead and add this red ones.
Attached Thumbnails
MZ_250_10.jpg  
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  #10  
Old 11-03-2014, 05:21 AM
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So need help , someone to check my calculations ..

On net found few different specs for MZ 250 bike and its tyre size ..

Anyway, there is calculations for gearing:

For tyre size 89/100 r16 , tyre circumference is cca 184 cm
For tyre size 89/100 r18 , circumference is cca 200 cm

My tyres are 25 cm in diameter and circumference is cca 80cm

With bike top speed of 130 km /h or 36,1 m/s and 16'' tyre, wheel on bike is spinning on 1177 revs and for 18'' tyre 1080 revs.

Also found that bike has 19/48 sprocket ratios or 0,39.

Adding that ratio to calculated wheel revs, I have gearbox output spinning on
2864 (16'') or 2769 (18'').

Now, I have on axle 28 tooth sprocket, so I thought to put 20 tooth sprocket on gearbox to have 100 km/h on 2864 rpm or 97 km/h on 2769 rpm .

As sprocket on gearbox is in closed case, and if won't fit inside, will try with 18 tooth sprocket , wich give me top speed of 87-90km/h.


So just need your thoughts and calculations check.
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Old 11-03-2014, 07:39 AM
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http://pizdarije.medjica.com/gokartm...4/mz250_18.JPG
http://pizdarije.medjica.com/gokartm...4/mz250_19.JPG
http://pizdarije.medjica.com/gokartm...4/mz250_20.JPG
http://pizdarije.medjica.com/gokartm...4/mz250_21.JPG
Attached Thumbnails
mz250_18.jpg   mz250_19.jpg  

mz250_20.jpg   mz250_21.jpg  

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Last edited by landuse; 11-25-2014 at 12:32 AM.
  #12  
Old 11-24-2014, 02:40 AM
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so, not so much progress lately ..

when try to put sprocket on axle, find out that hole is 0,5mm too big ..

so only do engine mounts with rubber absorbers as I can not use original ones (I do not have it :p)

the big one is from the bus and small ones are from lawn mower

http://pizdarije.medjica.com/gokartm...4/DSC_1195.jpg

http://pizdarije.medjica.com/gokartm...4/DSC_1199.jpg

http://pizdarije.medjica.com/gokartm...4/DSC_1201.jpg

http://pizdarije.medjica.com/gokartm...4/DSC_1203.jpg

http://pizdarije.medjica.com/gokartm...4/DSC_1202.jpg

http://pizdarije.medjica.com/gokartm...4/DSC_1154.JPG

so I thinking to maybe add one more absorber to rear mount..
Attached Thumbnails
DSC_1195.jpg   DSC_1199.jpg  

DSC_1201.jpg   DSC_1203.jpg  

DSC_1202.jpg   DSC_1154.jpg  

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Last edited by landuse; 11-25-2014 at 12:34 AM.
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Old 01-12-2015, 12:47 AM
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after almost two months , finally some work...

not much, just engine mount...
Attached Thumbnails
DSC_0028.jpg   DSC_0029.jpg  

DSC_0031.jpg   DSC_0032.jpg  

DSC_0033.jpg   DSC_0035.jpg  

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  #14  
Old 03-09-2015, 02:17 AM
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finaly some progress ...

I decided to cut frame to the half and gonna build new rear end...





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Old 03-09-2015, 02:41 AM
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I am glad you got back to this build. I look forward to seeing it finished
  #16  
Old 05-04-2015, 01:11 AM
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not much but ..
Attached Thumbnails
DSC_2121.jpg   DSC_2122.jpg  

DSC_2124.jpg   DSC_2128.jpg  

DSC_2126.jpg  
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Old 11-10-2015, 02:03 PM
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finally restarted this ..

welded frame back together, abandoned idea to use rubber absorbers on engine mount, kept only one ..

anyway, few pics:
Attached Thumbnails
20151110_102342.jpg   20151110_102347.jpg  

20151110_102355.jpg   20151110_102416.jpg  

20151110_113602.jpg   20151110_113653.jpg  

20151110_114931.jpg   20151110_114941.jpg  

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Old 11-11-2015, 10:47 AM
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today's progress:
- exhaust pipe cuted and welded to make turn tighter
- exhaust support
- fuel tank support
- brake cylinder support
- seat support ..

I am trying to use as much is possible old parts so some solutions are not the best...

few pics below...
Attached Thumbnails
1.jpg   2.jpg  

3.jpg   4.jpg  

5.jpg   6.jpg  

7.jpg   8.jpg  

9.jpg  
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Old 11-12-2015, 02:51 PM
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for today:

- finished engine mounts and made them a bit stronger

- holders for brake cables

- started on gear shift linkage ....

please do not write so much, I do not have time to read all
Attached Thumbnails
20151112_112441.jpg   20151112_112449.jpg  

20151112_112509.jpg   20151112_112724.jpg  

20151112_112941.jpg   20151112_123330.jpg  

20151112_123348.jpg   20151112_123429.jpg  

IMG-20151112.jpg  
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  #20  
Old 11-16-2015, 01:17 AM
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not much progress over weekend..

finished shifting linkage and clutch...

few ideas , few prototypes and maybe I just buy clutch lever ...

also , there is idea for kick start , as I don't think is safe to start engine by putting leg in middle of frame ...

anyway, few pics below...
Attached Thumbnails
20151113_123604.jpg   20151113_123615.jpg  

20151113_123634.jpg   20151113_155614.jpg  

20151114_130956.jpg   20151114_131010.jpg  

20151114_131019.jpg   start.jpg  

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