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Discussion Starter #1 (Edited)
My engines are both worn out from last summers abuse so I decided to buy two brand new stock CAG engines (will see if they are 47 or 49cc when they get here) and I'm going to build one and mod the other one here is what I have

This crank and rod assembly it feels good I checked the wrist pin with my caliper both ways and it comes out to 14mm dead on that means it's not distorted or worn out and it's for a 10mm pin
IMG_20200503_143552271_1588554657964.jpg
IMG_20200503_143622913_1588554709689.jpg

For the piston I have one for a chainsaw I don't remember what chainsaw it's for but its 43.9674mm
IMG_20200503_165443475_1588554809236.jpg

The wrist pin is 10 mm (perfect)
IMG_20200503_165733177_1588554860525.jpg


With the bearing on the pin I get approximately 13.94 mm
IMG_20200503_170354728_1588554894778.jpg

So after I figure the oil film and expansion I'm right at .003mm clearance ( should be tight enough to hold together and still oil its self...


Now with the Piston hung on the connecting rod you have to check the side to side play of the bearing this is where many build's fail if the bearings rollers can stay in the center of the connecting rod it's good if not it has to be shimed
IMG_20200503_171726658_1588555055907.jpg

Now I have these special chromoly rings that goto the piston these rings are 1.5mm where regular Cagllari Daytona rings are 2mm eatch this gives me 1mm less ring contact surface making les friction the rings being made of the harder material is going to cost my engine longevity about in half (honestly who cares it's a pocket bike)
IMG_20200503_172628895_1588555546075.jpg

I have some regular steal ones as well you can tell the difference from the chromoly ones by the color of them thay must of came with the piston but I'm not useing them...
IMG_20200503_172746609_1588555131187.jpg

Then I have this head and dome it's the low compression dome ( well it's higher then stock ) ( my high compression dome is on my other engine - the one they don't make anymore) but I'm sick of tracking down race fuel every time I want to ride my pocket bike so I'm defentley useing this one so I can burn pump fuel.
IMG_20200503_173702627_1588555209357.jpg

There are a few problems the minor problem is during manufactureing the aluminum got distorted in a few small parts you can't see it in the picture but the mating surfaces will have to be sanded flat if it's going to stay sealed.

The major problem is the squish band angle doesn't match the Piston dome if it's assembled like this than it will cause detonation and my engine won't last past the break in period!!!
It's somewhat close so I think I'll be able to lap it in it's going to take some hours of laping but you know I have time thanks to covid-19
IMG_20200503_174617841_1588555271743.jpg


Then I have some other various odds and ends for the build lots of clutch springs an intake manifold for a pumper carburetor an aluminum starter pawl and of course a nitrous kit 馃槇
IMG_20200503_175208642_1588555304655.jpg

My next move is to de flash and de bure this piston and mod and lighten this wrist pin then start calculating the balance factor...
 

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Discussion Starter #3
I don't have my engines yet then I don't even know if they will be 47 or 49cc I'm hoping I will get lucky. If not I will have to order two from different places mic and pick the best one or order more I had a 44-5 cylinder that it fit perfectly in before but then i was stupid and used it now it's worn out.
 

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Kitty, can you tell from the pic what compression level that 2 piece head has? I suspect it's race gas territory because it's for a 44mm piston and only holds 3cc's. When you subtract the piston dome it'd be way up there. But that's just a guess.







Also in the pic you can see what I came up with for a 40mm piston. Again missing the piston dome but that holds 5.1cc's. On paper the compression ratio should be 8.3 to 1 from exhaust close ... and I don't plan on hunting for race gas either. :)



A Squish Band Velocity Calculator is what led me to the very wide squish band and why I needed that very small but deep combustion pocket to keep the CR down.. Whether this works in the real world remains to be seen.
 

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Discussion Starter #6
Kitty, can you tell from the pic what compression level that 2 piece head has? I suspect it's race gas territory because it's for a 44mm piston and only holds 3cc's. When you subtract the piston dome it'd be way up there. But that's just a guess.







Also in the pic you can see what I came up with for a 40mm piston. Again missing the piston dome but that holds 5.1cc's. On paper the compression ratio should be 8.3 to 1 from exhaust close ... and I don't plan on hunting for race gas either. <img src="http://www.pocketbikeplanet.com/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />



A Squish Band Velocity Calculator is what led me to the very wide squish band and why I needed that very small but deep combustion pocket to keep the CR down.. Whether this works in the real world remains to be seen.
Looks like the medium compershon one you still need to get the octane up to about 110 to run that

On your home made head all you have to worry about is if the squish band angle matches the shape of the piston top the squish band is what controls detonation. Then you can do a compershon test and see what your numbers are before you start it..
 

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Discussion Starter #8
I started reworking this piston mostly just removing casting flashing and rounding over the flat spots with my Dremel I know it looks a little rough but I plan on smoothing everything out with sandpaper and needle files
 

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Discussion Starter #9 (Edited)
Balance Factor

Time to calculate the balance factor

Weigh the connecting rod small end
IMG_20200506_210050563_1588905075265.jpg
19.10g

Weigh the total reciprocating Mass
( that's the piston, rings, wrist pin, wrist pin bearing and wrist pin keepers with the connecting rod end )
IMG_20200506_211138791_1588905322213.jpg
91.7g

now you have to make a balance stand out of anything that you happen to have available to you 馃槈 notice I just use some food boxes out of the pantry and a couple ballpoint pens taped to the top of them.

Set the crankshaft connecting rod set onto the stand then make a hook out of a paperclip hang it onto the wrist pin end hang random nuts and bolts and things onto the paper clip until you can turn the crankshaft and it will stay in its place in any position.
IMG_20200506_213606988_1588906103292.jpg

This is going to be your hung weight
IMG_20200506_213946181_1588906199249.jpg
12.18

Now what you do is is add the connecting rod weight to the hung weight
19.10 + 12.18 = 31.28
Now you take this number and devide it by the reciprocating mass
31.28 / 91.7 = .34111
Now move the decimal over two places for
34%

IMG_20200506_220023523_1588908914922.jpg

This is bad news for me the realistic goal would be 45% with 50% being optimal to achieve that Im probably going to have to take a lot out of the piston and the wrist pin and add some tungsten to the crankshaft counterweight then fine tune it on the flywheel but then I don't know I should be receiving my two new engines tomorrow maybe they will come with some parts that balance out better.
 

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Discussion Starter #11
I checked the balance on mine using the same method and came up with 43%! Beginner's luck ....
Right on you can add a peace of steal bolt to the flywheel if you want and your engine will be perfect 馃榿 for me it's going to take some work to balance my engine out so it doesn't shake all my power away...
 

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Discussion Starter #12 (Edited)
I just received my engines in the mail today here is the unboxing

Both engines came in a huge box IMG_20200508_144744972_1588974975153.jpg
IMG_20200508_144841650_1588975114360.jpg

The first engine I pull out is in a box and has a ton of packaging...
IMG_20200508_144921416_1588975260749.jpg
IMG_20200508_144935734_1588975297406.jpg

The second engine came in a different box and not so much pading none at all lol!
IMG_20200508_145139060_1588975446945.jpg

With both of these engines unpackaged and sitting side-by-side even though they were ordered from the same seller at the same time I can still see subtle differences right off I can see that.

One has a white pull start pully the other one has a pink one

The one with the white pully has a pink tube for the carbarator over flow looks like there is some kind of corrosion or rust inside the tube...

the one with the pink pull start pulley has a clear overflow tube on the carburetor. no rust or corrosion in the tube.

also the one with the white pulley has a thinner head gasket than the one with the pink pulley.

they both have different Chinese knock-off spark plugs as well

IMG_20200508_152333301_1588976730240.jpg

Both engines are 49cc and have 44-6 cylinders on them.

I opened up both carburetors right away because I'm curious they both look exactly the same the carburetor with the Pink tube on it surprisingly looks nice and clean and perfect inside...

the carburetor with the clear tube on the other hand has manufacturing debri inside the carburetor (for the people that buy a brand new carburetor and just bolt it on and then their bike runs good for about 2 minutes then starts having the same problem as there first carburetor this is the reason why Open the carburetor float when you first get it and clean it out before you use it!!! New bikes as well!!!)

IMG_20200508_153245190_1588978031920.jpg

I did pop The jug off of both engines but didn't find anything interesting except for the usual crap manufacturing!!!
IMG_20200508_161240478_1588979743381.jpg
 

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I'm sure glad you brought this balance issue up. I went back over my notes, which could also be called scribbles, and I can't figure out how I got 43%. I do get a little confused at times ....


My con rod weight is is within tenths of yours. Close enough for gov't work.


My piston, pin, bearing, and clips are way less at 64.7g, but it's a 40mm piston against a 44?


Hung weight is 5 grams or so higher at 17.1g. That would indicate the back of my crank is heavier than yours?


And when I plug those numbers in I get 56%! 56 and 43 do equal 99. I musta divided something backwards in there somewhere.


So now I'm thinking I need to lighten up the counterweights on the crank to reduce the hung weight. From what I've read here and there on the net the balance factor on a horizontal cylinder should always be 50% or less. Food for thought and more fun .... :)
 

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Discussion Starter #14 (Edited)
The issue is there is about 6 or more variations of crankshafts between the 47 and 49 cc

There's the full circle cranks that were intended to be used on the piston ported engines(I don't believe they're manufacturing them anymore because they throw the engine balance off so bad) (there is still plenty in abundance to be bought though)

Then you have the standard crank for both size engines 47 - 10mm pin and 49cc - 12mm pin

Then you have the HP crank for both engines with the different pin sizes 10/12mm

On top of there being some unicorn cranks out in the wild...

I'm trying to run that chainsaw piston obviously the reason why I want to run the chainsaw piston is because chainsaws are way more heavy duty than the pistons that The pocket bikes run and I whould be able to use Hot Saw parts like the chromoly rings and upgraded wrist pin bearing (this is going to be way better in the long run for running nitrous) Problem being the Hot Saw piston has a 10mm pin and they onley use 10mm pins on the 47cc engine meaning the counterbalance is actually designed for the 40 mm piston so I'm stuck right now I'm going to try to contact hot rods they make custom connecting rods for motorcycle applications and see if I can get a rod I can put on a 49cc HP crank and be closer to the 50% balance Factor if that is too expensive (and it probably will be) then I'll take as much off the Piston and wrist pin that I feel comfortable with drill holes and add tungsten into the crankshaft counterweight then add the rest on the flywheel and I will have it but man that's a lot of work!!!
 

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Discussion Starter #15
My fuel tank finally showed up after waiting a month and a half.

Time to get this badboy gen1 CAG back together

IMG_20200528_150504832_HDR_1590704079544.jpg

Unfortunately the hot saw piston being too heavy for the crank I have has put my project on hold until the winter time if I get a euro bike it will be an indefinite hold.
 
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