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Discussion Starter · #1 ·
Hello Gents.
I thought I start a new topic to separate the work done so far and work that will be done now.
this a continuation of this topic: https://www.125ccsportsbikes.com/forums/index.php?showtopic=99378&st=420

reason for a new build is the fact I have moved to Norway. the cheapest way to have the bike was to buy one "for parts" local and then bring all my stuff from home (Croatia / Serbia), but as Covid19 has started it is now put on hold.... but I can slowly gather the parts I know I want replaced.

I plan to keep my old engine, but I run in to a major issue. the availability of parts has decreased so much.
namely I am after inake manifold for a dellorto vhsb 34, so if anyone has it.. shoot :)

I plan to upgrade to VForce 4R reed cage

I thought of introducing the power jet to the VHSB 34 LD carb to help with tuning of it. https://www.jdscustoms.com/product/kan-power-jet-kit/


I need to Helicoil all of the threads in the block as they are really marginal...
and I need to fix the olf sprocket carier as I missed one "spot" so need to correct it (the adaptation of the rs250 wheels)

Wosner or Wiseco piston of a ktm sx200 (or exc 200) as it might be better than Asso werke (discused here https://www.125ccsportsbikes.com/forums/index.php?showtopic=147954) the goal is to have a piston weight less than 174g, as
It certainly would do any harm opening up the oil-ways would it. But I don't think extra lubrication for the bottom end is the only answer to longevity. Imo. the biggest issue is the extra weight of the piston compared to a 125
DesertGoon has measured some 56mm (std 125)

Wossner twin ring flat top = 137g
Wiseco single ring flat top = 129g
Asso W single ring flat top = 120g
Mitaka single ring flat top = 130g
Mitaka twin ring dome top = 124g
Rik Ring 56mm = 3g

Polini 64mm twin ring dome top = 174g
Polini Ring = 4g

the wrist pin is also heavier as well compared to the 125

I guess some weight could be taken out of the standard Asso Polini piston, but not enough to make that much noticeable difference I would have thought. The obvious part to modify would be the balancer shaft to counteract the extra piston weight, but by how much. I might have an A level in maths but that was a long time ago & I don't know how it could be calculated.lol.

If someone could do the math then we could be onto a winner

...
 
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Discussion Starter · #2 ·
how it started (once again)
IMG_20200723_183821 by Milos Balunovic, on Flickr

IMG_20200723_202937 by Milos Balunovic, on Flickr

IMG_20200723_203504 by Milos Balunovic, on Flickr

IMG_20200723_203510 by Milos Balunovic, on Flickr

IMG_20200723_203513 by Milos Balunovic, on Flickr

IMG_20200723_203525 by Milos Balunovic, on Flickr

exhaust in beautiful condition
IMG_20200723_202947 by Milos Balunovic, on Flickr

the original toolset (really unusefull but still

IMG_20200723_203027 by Milos Balunovic, on Flickr

also finnaly got an unbroken unrepaired front fairing
received_396579624652459 by Milos Balunovic, on Flickr
received_379679499666427 by Milos Balunovic, on Flickr
as both the one i got in titanium and my old one, and heaps other i see also miss the top part going around the windscreen
 

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The piston data.
alternative piston by Milos Balunovic, on Flickr
it will need shortening to fit properly. still trying to find some info on the actual weight. slightly higher pin to head distance is solved easily by a thicker gasket (metal)
 

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sadly the mitaka piston for the mentioned ktm 200 sx (exc) engine, piston is 195g or after cutting aprox 185g, ie worst than the polini / asso werke :( that will have to suffice me it seams. maybe do some machining on the Asso to loose a little bit of weight :)

ps: a lot of small details are brewing in the background, but on them when they are finished, or close to it :)
 

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Why a 200 cc piston, what cylinder do you have? An overbored Polini? I have no experience with those things, but a friend has his Mito MKI with a reworked Polini 165cc and after testing my standard MKII Lucky (73037, Mikuni 35, etc) he says mine is probably quicker than his. So are those big bore kits really worth it? I tend to think that a mono 250cc Hond CR engine or similar would do better if you want more power.
 

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Why a 200 cc piston, what cylinder do you have? An overbored Polini? I have no experience with those things, but a friend has his Mito MKI with a reworked Polini 165cc and after testing my standard MKII Lucky (73037, Mikuni 35, etc) he says mine is probably quicker than his. So are those big bore kits really worth it? I tend to think that a mono 250cc Hond CR engine or similar would do better if you want more power.
its a 73037 ported and bored to 64mm, done in a way to retain the original port map etc... the original polini cylinder is sh*tti porting. good torque low end but nothing spectacular or better up top.
the sx200 piston is same bore as polini, ie 64mm :) with simmilar crown height etc :)

I also obtained the weight of wosner piston which is 214g.. now comparing thatt to the list in above postst.. the polini piston (asso werke) is best choise.

I will also create a new head insert to retain the oricinal Corrected CR of 7.4:1 and uncorrected of 14.5:1, I had one low comp toroidal attempt but I want stock specs

PS: you have a time window to edit your post, after that the "edit" tab disapears.
 

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Discussion Starter · #8 ·
Cylinder and "old" head insert can be seen in this gallery, together with the proces of "conversion" from 56 to 64mm bore
https://www.flickr.com/gp/[email protected]/t6nL4i

cylinder:
IMG-20180425-WA0000 by Milos Balunovic, on Flickr

Cilinder head (with thoroidal inser)
20180609_125526 by Milos Balunovic, on Flickr

the old insert is 16.4cc with 40% Squish band area, giving a 11:1 uncorrected compression ratio and 5.7:1 Corrected Compression ratio

The new "design" will be a hemispheric 12.2cc volume and 44% squish band area. this way I will have two heads to play with.

I also "plan" to make a pipe for it and:
a little narrower power band, max at 12000cc could yield me 45hp and
wider power band, max at 11000 and 40hp
I could experiment with dual baffle (one would have to be perforated, the inner one) and that could be used to broaden the narrow power band of first (higher) hp version, which should make the power come in much much sooner, at an expense of little top end. (less than 5hp) (read further here https://buildandclick.com/html/dual_power.html)


OFC I know these numbers are just calculations, and I DONT anticipate to have such high numbers in real life, but for comparison of a design they do provide a god guide what works better or worse.
 

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I see, though the question remains if an engine swap wouldn't be better. One thing I know about those Polinis, they are crank bearing and connecting rod eaters, so with a 200 cc piston won't it be even harder on the bottom end? Admittingly one of my wet dreams always was a bigger piston in the Mito, but everything I have read about going that route seemed to cause problems.
 

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Discussion Starter · #10 ·
it will still have the lighter piston :) ie the polini one. not the 200
So the 200 piston was just an idea to replace the asso werke for a lighter one, but as I found out they are even heavier so I will stick with asso werke.

I have the tz350 "LONG" (brand) racing conrod, with upgraded bearing and solid wrist-pin (sold by PJME) which should help with that a bit :) https://www.pjme.co.uk/acatalog/Cagiva-Mito--Planet-Raptor-Supercity-Race-Con-Rod-Kit--3367.html#SID=252 which helps a little bit :)

The problem with polini kit is that you have to modify your head, the instructions are wrong, and even with "correct" one you would have way to high of a compression ratio (16 or 17:1 uncorrected) now that can run "of pipe" until the resonator/pipe starts working, but than it creates huge amount of pressure and knocks the engine out. those have huge bottom end torque which also destroys the bearings.

I had this engine for long time, and its been a 64mm bore all the time. ported the hell out of the polini cylinder but newer liked it as the transfer port ratios are so of compared to the original cylinder, which is the reason I went with the route of modifying the 73037 cylinder :)
66650E would have been even better option (since it is best with dome head piston) but its hard to find
 

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Awesome, that conrod looks sweet, might order one for the future even if I do not plan to overbore. Thanks for the link!


Yes I know my friend modified the head to reduce compression and running premix he has put many miles in the Mito succesfully. The Polini has actually lasted even more than the original cylinder, which seized due to oil starvation (Pump failure probably) and still runs nicely.

Nothing planned on the crank, is the current deemed good enough? I'll keep an eye on your build looks great
 

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Discussion Starter · #12 ·
Thanks :)

I would like to "rebalance" the crankshaft for the heavier piston/conrod combo. Its not excluded :)
The biggest problem for me is that the engine is in a corona restricted country :( so untill than I can only plan and gather stuff to be ready :)

By the way regarding a question of swapping a different engine. I was in negotiations for an ktm sx250 but he pulled out. That would be a sweet 45 rear wheel HP engine :(
Its still a possibility as I would really like that :) so if I stumble upon a complete 250 ktm (od CR or YZ or KX) engine i will snatch em. Tho they are uber rare on the market in a condition worth saving.
 

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Discussion Starter · #13 ·
Since no produced exhaust fits the 64mm stroke well I decided to utilise a software and design it :)
45hp @11500 Duel by Milos Balunovic, on Flickr

Put a picture as reference and tried to model the pipe :D
1 by Milos Balunovic, on Flickr
2 by Milos Balunovic, on Flickr
3 by Milos Balunovic, on Flickr
5 by Milos Balunovic, on Flickr

than made drawing for cones :D
cones by Milos Balunovic, on Flickr

ready for laser cutting.
than had some spare time and wanted to play :D
so made a paper pipe hehe
IMG_20200916_093546 by Milos Balunovic, on Flickr
IMG_20200916_093558 by Milos Balunovic, on Flickr
IMG_20200916_093633 by Milos Balunovic, on Flickr
IMG_20200916_093640 by Milos Balunovic, on Flickr
IMG_20200916_093643 by Milos Balunovic, on Flickr
it missing the first "straight" pipe part, which will be a 45degre 1.5D bend

sadly I cannot test it as I still dont have my engine here :( but untill then its parts gathering and planing.

than finally fulfilled my old time wish :D the original one once sawed me from a tank slapper, so its well worth it. and this one is serviceable so will live for decades :)
IMG_20200917_195050 by Milos Balunovic, on Flickr

and a little unnecessary bling :D
IMG_20200907_215421 by Milos Balunovic, on Flickr

got some helicoids :D 1.5D and 2D length, although it doesn't makes sense as the 1.5D is 6mm long and 2D is 9mm long... these will be used to repair/replace all of the threads in the engine cases, as well all other M6 threads in aluminum (like steering damper mounts etc :)
IMG_20200909_115807 by Milos Balunovic, on Flickr

and than my long nemesis... the intake manifold... its impossible to source a vhsb manifold for a mito engine... so I will have to butcher this one. its for lambretas :D
plan is to make an intermediate plate that will perfectly mate the manifold to reed cage and also keep the distance as short as possible.
IMG_20200915_082046 by Milos Balunovic, on Flickr

IMG_20200917_195050 by Milos Balunovic, on Flickr
 

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That is truly awesome, good design job there Remy! One question though, why is the first part of the exhaust so wavy when seen from the top? (Sections 2-8) I guess because you don't want it to protrude too much forward and so had to compress that section into a tighter space?
 

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Discussion Starter · #15 ·
Since the pipe is longer design (total of 1030mm without the stinger) i wanted to cram as much as I can under the fairings :) I dont like the pipe sticking out, maybe except the exit cone :)
 

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Discussion Starter · #17 ·
That is a piece of crap my friend, but thanks for the help
the manifold should connect to the reed valve stuffier and not expand like on the picture.
 

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Discussion Starter · #18 · (Edited)
So much has happened but due to some priority its still not finished.

The red cage has been redisigned. It has been made on the principle of Boyesen rad valve. The only reed cage to have actually measurable gain in power unlike v-force that improves the feel only.

So the design aim is = constant cross section area from the carb to the reed petals. This aids in giving minimum volume (pre reed/crank) which should maximise flow speed and aid in more consistent carburation.
Also every change in speed is an energy loss (think how a free flow mufler works).

Inserts original vs mine
IMG_20210204_215330 by Milos Balunovic, on Flickr

IMG_20210204_215319 by Milos Balunovic, on Flickr

4 intermediate supports are removed as seen, as they are not needed when using Boyesen petals
IMG_20210210_144012 by Milos Balunovic, on Flickr
IMG_20210210_144016 by Milos Balunovic, on Flickr
IMG_20210316_204153 by Milos Balunovic, on Flickr
IMG_20210316_120501 by Milos Balunovic, on Flickr
IMG_20210316_204140 by Milos Balunovic, on Flickr

assembled with the inlet manifold
IMG_20210410_200155 by Milos Balunovic, on Flickr
 

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Discussion Starter · #19 · (Edited)
You can also see lovely wheel colour i have chosen :)
Sandblasted
Powder coat fluo yellow
Powder coat clear coat :)

IMG_20210203_091924 by Milos Balunovic, on Flickr
IMG_20210203_101823 by Milos Balunovic, on Flickr

modified RS250 sprocket carrier to fit the Cagiva.
IMG_20210322_181225 by Milos Balunovic, on Flickr
IMG_20210322_181911 by Milos Balunovic, on Flickr
used a piston ring to secure the inside of the bearing on sliding anywhere in the carrier...
IMG_20210322_153031 by Milos Balunovic, on Flickr
IMG_20210322_153052 by Milos Balunovic, on Flickr

had to use 2 bearings to create sufficient stiffness of the assembly so it doesn't "rock" on it self.
 

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Discussion Starter · #20 ·
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