How to install the big bore kit on a Kawasaki bn125 engine with original 125 con rod

By John Kjetil Lode, Norway (copyright 2013)

Parts needed:

1 cylinder block bn175
1 piston with rings bn175 and locking clips
1 reducing kit consist of 15mm piston bolt,2 bushings

Gaskets for cylinder base (2 pcs if you do not modify your bn125 cylinder head by increasing its diameter to 65mm) and for cylinder head bn175 type. You may also need to change the gasket of the flywheel cover/left engine cover.

Get a WORKSHOP MANUAL for Kawasaki Eliminator 125!

https://z-1-lookaside.fbsbx.com/file/Kawasaki-Eliminator-125.pdf?token=AWxkc7bELhEN8bCpOX_l2n_pNihwc_CNaV5tdNkxquuC9eTE1LR4WiE-TCS1Lh59xkDa3HCO6moojmLcPxskcYTuXVfgSpHMAdEmjonfZSV2wQZPPbNnY_Rszx4qWr0fsXTTiW9VDSKXt29g2DqjUCX_

Step-by-step instructions: Drain the oil from the engine by removing the large plug under the engine's crankcase.Clean the engine very well. No need to remove it from the frame.

Remove the exhaust pipe from the cylinder head. Remove the spark plug cap and the spark plug. Loosen the carburator intake manifold from the cylinder head by removing the 2 bolts. You don't need to remove the carburator,just let it remain detached from the head.

Remove the camchain tensioner that is situated at the rear of the cylinder block. You may also now remove the camsprocket cover on the left side of the engine (see photo to the left).

Remove now the camsprocket and just let the chain drop down into the lower parts of the engine.

Remove the front sprocket cover on the left side of the engine's rear part. 

Remove the oil feed pipe from the engine. It is made of metal,chromed,and goes from the left side of the engine,close to the driven sprocket,around the startmotor and up to the cylinder head.

Proceed by removing the seat and the petrol tank to get better access. The tank has an electrical contact that needs to be removed, and also the petrol hose and vacum rubber hose. Remove also the left engine cover that covers the generator/flywheel. Take care not to damage the stator inside,nor the wires and contact that leads from it to the frame. Scrape off the gasket residues using a knife or similar tool.

                   CYLINDER HEAD REMOVAL

Now you should loosen all the bolts on the top of the cylinder head. There are 4 large ones going all the way through the head and cylinder block and down into the crankcase. Then there are to smaller ones situated just below the opening to the camsprocket area, that binds the head to the cylinder block.

You are now ready to lift off the cylinder head. When removed, you can see the cylinder head gasket and 2 dowel pins in the larger holes for the bolts. Take good care of these dowel pins for the reassembly.

CYLINDER BLOCK REMOVAL

Now you can remove the cylinder block itself. Gently tap it upwards with a rubber hammer to loose it from the engine block (crankcase) and pull it off the piston.

Immediately cover the crankcase opening to avoid dirt and bits from falling into the inner heart of the engine.

You may remove the front chain guid (black plastic rod) for now,and drop the camchain down for the time being.

Then clean the surface where the cylinder block was in contact with the crankcase. Remove all residues of the cylinde base gaskets, so there will be no leaks with you new cylinder block.

125cc sylinder to the left,175cc sylinder to the right

PISTON REMOVAL

Now you need to remove the piston. Pry out one of the locking clips that secures the piston pin, and then press the pin out on that side. CRANKSHAFT CHECK

Carefully check the crankshaft's condition for wear. The connecting rod is the rod that the piston is fastened to, and is a part of the crankshaft assembly. If there is any slack up-down wise, you need to give your crankshaft assembly an overhaul, which implies a lot more work, and a new con-rod set. The good thing about it, is that you must then buy a bn175 con rod set, and that means the con-rod's upper hole matches perfectly the bn175 piston that your are going to use.

If the con-rod and crankshaft assembly appears to be in a good condition, you are now ready to fit the big bore set.

Installing piston rings

Start with installing the piston rings to the piston from the big bore set.

This is quite a complicated procedure,and should be undertaken by a professional mechanic. However, the system goes like this:

There are 5 rings inside the package. The 2 more solid rings are for the upper 2 grooves of the piston. They are marked,so you can see which one goes on top,and which one comes in the second groove. Check that each of these top rings fits perfectly and be pushed all the way in for their ends to meet with no big space. Then there is a third groove where the 2 thin rings called "oil ring rails" plus the funny looking oil-ring will come too.

This is a bn125 piston with the rings installed

Install first this strange looking ring, called the oil ring expander,in the bottom piston ring groove. Then slide the other 2 small rings into the same groove,one over and one under the expander ring. Then install the rings of the upper 2 grooves. Take great care not to break the rings. If not treated correctly,they will break!

Positions of the openings of the different piston rings.

When all rings are finally on the piston, arrange the openings of the rings like this illustration shows: Upper ring (A)faces forward. Second ring's opening (B) faces backwards. Upper oil ring rail faces forward. Oil ring expander's opening faces backwards. Lowest oil ring rail faces thus forward. The details about the correct angles can be found in the workshop Manual page 132. Use a small pinpointed tool to arrange the rings like this,and be sure to check it before installing the cylinder block on the new piston.

FITTING THE BN175 PISTON ON TO A BN125 CONNECTION ROD

There is an important difference between the bn125 engine and the bn175 engine. All parts are the same,except for the diameter of the piston pin. The 125cc engine's piston pin is Ø15mm,and the BN175 pin is Ø16mm. To avoid having to change the whole con-rod with all the work and extra costs involved,I have developped a way to make a "cheating". However,I will stress that this cheating may not be very strong or stable over a long period of time,even if I have testimonies from people who ran the bike with this system for more than 3 year,and around 35000 kms without having any issues.

The best is of course to change the connecting rod to be from a BN175,and then there should be no worries concerning this matter.

My patent is as such: I take a 15mm piston bolt,and have 2 steel bushings from a workshop in Thailand that will be pushed into the 175 piston. The outer diameter of these bushings is 16mm,and on the inner side they have a hole of 15mm. The 15mm pin is cut so that there is room for both these 2 bushings,and the circlips to secure the pin not to be pushed out.

On the above picture I have fit the 15mm pin bolt inside the hole of the bn125 conrod,and then I show how the reducing bushings come on each side - only as an illustration. To actually fit the piston,you must place it over the conrod,and then insert the 15mm pin through one of the holes. Then push the bushings into the piston pin holes so the busings will enter over the ends of the 15mm pin. You may have to use some force to to this. If there is not space enough to introduce the clips to secure the pin,gently cut off a tiny bit of it to make it slightly shorter. When all is correct,you can fit the 2 circlips from the BN175 piston set. The 16mm piston pin from that set is of no use when you use this solution.

The arrow and EX symbol on the piston top shows the direction to put it: with the arrow and ex forward (ex=exhaust).

BEFORE FITTING THE BIG BORE CYLINDER BLOCK

I will recommend to bring the cylinder head to a machine shop so they can put it in a lathe and have the cumbustion chamber machined out from 55mm to 65mm in order for it to comply with the big piston. If that is not possible for your machine shop, then there is another suggestion: Have them modify the edge of the piston top itself so that it will fit nicely into the 125 cylinder head's combustion chamber. A third suggestion is to put 2 cylinder base gaskets under the cylinder block, thus raising the block slightly over the piston-top and make the necessary clearance between the piston and the head.

PUTTING THE CYLINDER ON THE ENGINE

Now, when you have chosen of these options, proceed. First, check that the surface of the crankcase is smooth, with no dirt nor any residues from old gasket. Then put the cylinder base gasket (or 2 of them if that is your solution). Install first the 2 dowel pins in the engine block on the right side of the crankcase opening. Have the surface of the cylinder's inside bore greased with engine oil. I would even apply a thick layer of gasket cement on the upper gasket before putting the cylinder on, to avoid leaks under the cylinder due to minor differences that might occur between the bn125 cylinder and the new bn175. Leaks may occur on the front left side of the cylinder bottom according to my experience. If you forget to put gasket cement, and that problem occurs when you start up the engine, you may use some 2 component compound with aluminium grains, and after having degreased the area, apply a lot of it around the whole cylinder bottom and let it harden well before you start the engine. Let the engine idle for some minutes so there is no strong pressure destroying the sealing cement while it is being hardened even more while the engine gets hot.
 

Now, when gasket(s) is in place,and also the 2 dowel pins, and the piston is properly secured on the conrod, push the piston rings with your fingers from each side of the engine, and while pressing them together firmly, gently slide the cylinder block over the piston and the rings. This might be a difficult job, but be careful so no damage is done to the rings!

Now is the time to pick up the camchain that has been down in the left side of the engine. Use a plastic strip or a steel wire and tie it around the chain, so it is easier to get it from the very top. Be also sure to install the chain guide in black color, if you removed it. The shorter one is fastened with a bolt to the crankcase, so it is the loose one you need to install in the correct manner.

Fit the cylinder head gasket - new one of course! for BN175 cylinder, and install the 2 dowel pins on the cylinder block's upper part. Then fit the cylinder head. Take care that all surfaces are smooth and clean. Fasten the bolts according to the workshop manual.

Timing

Now, re-install the camsprocket and the camchain. There are marks both on the flywheel, on the crankcase, on the sprocket and on the cylinder head itself that are called TIMING MARKS. If these parts are not installed correctly, the valves will break and the engine will be destroyed. So you must check with the Workshop Manual. It is found online for free pdf download if you search for it.

Camshaft's position in the head when the piston is on the top

Position of camshaft sprocket when timing. Notice the position of the small mark on the sprocket in relation to the head top.

Timing marks on the flywheel in relation to the crankcase. The T mark on the magneto should be in this position.

But I can give you some hints:

When you think all is installed correctly (remember to use thread locking cement on the bolts securing the camsprocket), then turn the flywheel around with ur hands in the direction of the arrow on it. Be sure there is no spark plug in the cylinder head at this moment. If all seems to turn well, and there is no collisions between any parts (see to it that the piston also does not hit the head),then you must remember to install the camchain's automatic tensioner. Before fitting it, take a tiny flat screwdriver and screw it so that the pin of the tensioner is being forced backwards. Then keep it like that while you install the tensioner to it's place on the back of the cylinder block. Being sure that the camchain's timing is good will only be evident when you then use the screwdriver to activate the push-rod by turning it anti-clockwise. Now that the adjuster is pushing as it should on the black guide for the chain,you can again check all the alignment marks on the flywheel and the camsprocket. Rotate again the flywheel,and if all is well,you are almost done.

CARBURATOR AND MAIN JET FOR THE BIG BORE CYLINDER

In my experience,the big bore set works fine with the original main jet of the bn125. However,considering the great increase in the cylinder's volume,it may be smart to install a larger main jet. I tried - and also others - to use the standard main jet from bn175,but it seems to drown the combustion. On the Norwegian models from the late 1990's the standard jet is #110. I put a 117 jet with great result. If you want to use a large jet,you must balance and increase the air flow by removing parts of the airfiltering devices,put extra holes in that system,or use power-filter. I recommend you leave that to the experts.

SPROCKETS: Use 16T in the front,and 41-42T in the rear. Do NOT use the original set up for the BN125 as it will stress the engine!

The above information is provided for my customers who wish to buy the big bore set from me. Notice that all photos but one are my own,and I keep the copyright both to them and to the conversion secrets here.

IF YOU WANT TO BUY THIS KIT FROM ME, send me an email to 

john_lode@yahoo.no

Mange NYE deler til AC50!

NÅ må du slå til! Jeg har begrenset tilgang til omtrent komplette mopeder, fabrikknye, som har veldig mye til felles med AC50. I tillegg har jeg mange AC deler både fra egen produksjon og import fra rundt om i verden. For å kontakte meg, send epost til john_lode@yahoo.no   

Ikke send til den eposten som er oppgitt her på bloggen, da jeg sjelden eller aldri åpner den.

Komplette sykler i deler!

Fabrikkny 90cc motor - kun EN tilgjengelig

Fabrikkny ramme til de eldste AC-modellene

50cc sylindersett med 3 porter - full effekt versjon, med stempelsett

50cc sylindersett med 3 porter - full effekt versjon, med stempelsett

Bakskjerm til A100 - med huller for lyktefester

Klassiske blinklys - kopier av de originale

14mm forgasser til K50, passer sikkert på AC også...

Komplette framgafler

Nav- og hjuldeler

A100 bakgaffel - passer rett på AC50

komplette hjul, evt. oppbygging på gamle nav

Støtdempere (på bildet ser du A100 dempere)

90cc motor komplett med el-anlegg og eksospotte

Bygging av spilehjul til moped og lett mc

Jeg har i senere tid bygd 3 hjul til Suzuki AC50, og vil dele noen erfaringer og bilder.

1. Dette tar tid - masse tid
2. Du behøver et passende verktøy for å stramme spilene. Biltema selger et slikt sett, men de var for store til å passe til AC50 hjul-prosjektene mine. Jeg endte opp med å kjøpe en 5mm fastnøkkel hos en verktøys-forretning for proffe på Åsen i Stavanger (105,-kr).
3. Du trenger en jigg eller noe å sette hjulet opp i. Jeg har kjøpt et sånt verktøy i Asia. Du kan nok bruke en bak-gaffel med ganske stor suksess.

hjulbygger-verktøy fabrikknytt i esken

Jeg vil ikke røpe for mye om hjulbyggingens kunst her, både fordi jeg selv er ny i gamet, og ikke minst fordi dette er noe som kommer inn under det pedagogiske uttrykket LEARNING BY DOING.

Jeg fant noe info på netter, som gav meg både nyttig men også feil info ang. disse hjulene ihvertfall.

Nav, bremseskjold og drevholder som passer til Suzuki AC50, A100 m.fl.

Man skal nok sette inn alle spilene først, etter mønster av et eksisterende hjul. Merk navet på begge sider med klokken 6, 9, 12 og 3 iht en urskive. Dermed kan du begynne å stramme spilene forsiktig på disse punktene først, en indre spile og en ytre spile.
Dette med indre og ytre spiler er viktig!
De indre regulerer felgringens avstand til navet, mens de ytre spilene balanserer felgen i sideretningene.

Nav, bremseskjold og drevholder som passer til Suzuki AC50, A100 m.fl.

Først skal man forsøke å få felgen til å unngå å hoppe for mye opp/ned (retning ut-inn i forhold til navet). Da må hjulet settes i en jigg, som vist på bildet, eller i en bakgaffel f.eks. og med kulelagere. Man må så lage til et system som måler felgens kast opp/ned og sidelengs.
På disse felgene har jeg funnet et greit system, mens på andre er det kanskje annerledes.

JUSTERE OPP/NED KAST I FELGEN

Felgring, nav og spiler

Når du  har spent hjulet opp (må ha hjullagere!), snurrer du det rundt til du finner det punktet der felgen hopper lengst utover (bort fra navet). Stopp det der, og finn de indre spilene som befinner seg i direkte motsatte ende av sirkelen (180 grader). Slakk spilene litt på den motsatte siden først, og stram så inn spilene like mye på den delen som hoppet lengst bort fra navet. Slik kan du gå fra punkt kl. 6 til kl. 12, deretter til pkt. kl. 9, og så til kl.3.
Spilene er som strenger på et piano eller en gitar. Når du slår på dem, lager de en lyd. Målet er at alle spilene til slutt skal ha samme frekvens/stramming.

De indre spilene stikkes gjennom først

JUSTERE SIDEVEIS KAST

Dette trikset er veldig nyttig på eksisterende felger også, og ikke minst på sykkelhjul!
Snurr hjulet rundt til du ser at det vrir seg litt mer til f.eks. høyre. Stopp det der. Finn den ytre spilen som er nærmest, og slakk den litt. Gå så til motsatt side, finn tilsvarende ytre spile, og stram den litt. Slik vil du etterhvert få en fin balanse i hjulet - men dette kan ta meget lang tid.

Bruk et eksisterende spilehjul som modell

Jeg merker navet som en klokke, slik at jeg kan stramme på kryss og tvers m/ referanser

Kulelagere må på plass, så kan man sette hjulet i balanserings-verktøyet

Justering sideveis og opp/ned

Ønsker du å kjøpe hjul, spiler, felgringer, nav etc kan du kontakte meg på:
john_lode@yahoo.no

så får jeg se hva jeg kan klare å få tak i.

Kawasaki Eliminator Big Bore Cylinder set

 

Big Bore cylinder for Kawasaki Eliminator 125

 

125cc versus 175cc

Need for more power and speed? I am the supplyer of this Big bore set.

Here you will hopefully find answers to your questions about the Big Bore set.

I have during the past 15 years (since 2001) worked with the Kawasaki Eliminator 125, and overhauled many engines of this model. I have found sources in Asia for cheap parts for these bikes, and one very interesting development I have made, is how to transform the BN125 engine into a 175 engine.
The engines themselves are quite identical, with only some minor differences.
The cylinder head of the 125cc is of course smaller in the cumbustion chamber (55mm diameter) as is also the diameter of the cylinder and piston for the 125cc version. The combustion chamber of the 125 can be machined out to obtain a diameter of 65mm, just like the diameter of the BN175 piston and cylinder, and head obviously has.
It is possible to put the 175 (174cc) cylinder block straight on to the BN125cc engine. It is a straight fit. The bores are different, but the stroke is the same, and so are the physical dimensions.

BN175 cylinder to the left, BN125 cylinder to the right

BN175 cylinder and piston

The problem is the size of the piston pins and the hole in the connection rod:
*15mm diameter in the BN125 engine
*16mm diameter in the BN175 engine

One way to overcome this challenge - the best, most durable but also most expensive - is to split the engine of the BN125 and either change the whole crank shaft assembly or bring it to a machine specialist and have the con rod exchanged with that of the BN175.  If your engine has internal damages anyway,this is the way to go.













If you can afford it, the best and safest result will always be to change the con rod or the crank shaft for worry-less use of the big cylinder.

Crankshaft assembly BN175

Con rod overhaul set BN175

 I have, however, developped a system that overcomes this challenge of piston pin differences, if the goal is to put a 175cc cylinder on a 125cc engine without too much hassle and time consuming labour. The set consists of a 15mm piston pin, that has been cut to fit into the bushings, and that there is left room enough to put the 2 circlips on either side of it.
The reducing bushings are made of steel, and have an inside of 15mm diameter, and an outside diameter of 16mm, which means it will be able to be used in the BN175 piston.


Now the cylinder head remains an issue. I have actually successfully installed the BN175 cylinder together with a BN125 head. The machine worked great, but from time to time there would be some ping sounds from the engine. It turned out that on idle rpm the piston would sometimes slightly hit the head. I had driven the engine for a few kms, but decided to open it and check. There were no damages of any significance in neither the piston nor in the cylinder head, but I could see some minor scratches. Therefore I took the cylinder head to a machine workshop, and the mechaninc opened the cumbustion chamber up to 65mm in a metal lathe. After that, no more worries.

BN175 head to the left, BN125 head to the right

I guess a cheap and fast way of resolving the issue, would be to put 2 cylinder base gaskets under the cylinder block, so the block would be raised just a few mm and thus avoiding the contact between the piston top and the cylinder head.





Yet another way to overcome the problem, may be to grind down the outer edge of the top of the piston.

In these 3 photos one can see a bn175 piston that has been modified by lowering the outer edge of the piston top, so it might fit into the bn125 cylinder head's cumbustion chamber.

(I have not yet tried to fit this piston on an engine though, so I have not reports about how it works.

WARNING: I do not guarantee the function of this solution with reducing bushings etc, as it is not a standard procedure. I only tried it on for a short while on a bike some years ago, and for the few days I had it, it worked perfectly. I have also sold this solution to other people, and I had very good feedbacks from one customer in Portugal, and another one in Italy. The Portuguese customer have used this system for a couple of years, and rode the bike more than 30 000 kms with my big bore set and reducing kit solution.

CARBURATOR adjustments.

The bikes I have worked with in Norway where I did this big bore cylinder thing, has turned out to work well with the original main jet in the carburetor. Main jet size of these bikes in my country is #105. No adjustments have been necessary. But on my last 2 projects I installed a #115 and the a #118 jet, and it sure added power to the bike. But this may vary with climate and different models, so I would recommedn to try out a slightly larger jet. The US models have size #125, so I suppose fitting a #135-140 jet may be a good solution for those bikes. However, if the main jet is too large, the engine will not work properly!
If you have a large main jet, you might try to put on a power filter, or even make some holes in the air filter boks to increase the air flow, but this may require some testing and failing before you find the perfect balance.


SPROCKETS

The BN125 has normally a 15T front sprocket and a 46T rear sprocket. This is very bad for the engine if you run the bike at high speeds. I would recommend anybody to try out with at least a 16T front sprocket, even if your engine is of stock version.

If you put the big bore cylinder, you should definately put the 42T rear sprocket, at least! You could even put a 41T rear sprocket with no hesitations.These days I can not find the 42T, only the 41T.

WHERE CAN I BUY THIS BIG BORE CYLINDER KIT?

I am the only one, as far as I know, that have this stuff for sale.
It is very hard to find those cylinders now, and they are quite costly, so be prepared to pay 350 usd to get a set from me. The set will include cylinder, piston, reducing set, 1 front sprocket 16T and gaskets for the cylinder and head: 2 cylinder base gaskets and of course a BN175 head gasket.

This is the gasket set for the top end, that comes in the package. Here with the front sprocket 16T, the reducing bushings on a 15mm pin bolt and the extra cylinder base gasket that helps lift the 125cc head clear off the piston

Shipping worldwide with air mail is included also in this price.

You can add to the order:
Sprocket rear 41T
Con rod overhaul kit
Valves
Camshaft
Rocker arms
Cylinder head bn175
Full engine gasket set with O-rings

Full engine gasket set with O-rings is an option you should go for. Add 10 usd more to your order, and it will come instead of the small top end gasket set

and many other items for your bike. However, this is NOT a serious, big business, just a hobby for me, so I may not have all parts available at all times.
Also, I may at times not be able to send the products quickly, as I often travel.

To get in touch with me, send an email to j o h n _ l o d e @ y a h o o . n o
(just remove the space between the letters, and you should be able to send the email to me.)

Note: I have not capacity to answer many emails about this issue, so please read the instructions here and also in my photobucket site, to find answers.

 http://s1134.photobucket.com/albums/m607/eliminator125/Big%20bore%20Cylinder%20kit/