Return to dirt = CR125

[tigertim20]

OK! some answers are here!
Took it down to a local cylinder specialist. he measured the bore for me and confirmed that yup, its still square, so no issues there at all.
he gave me all the measurements etc, and told me how much clearance the piston had etc etc.

Now the manual states that the bore size is 54mm. he reckons however, that the bore was actually a couple thou UNDER 54mm - which leads me to conclude that it is still a stock, unmolested bore.
To that end, I instructed him to give her a very gentle hone, and in turn, he recommended that I go up one size in piston. (from what searching I have done thus far, pistons are available for this bike in intervals of 0.01 from stock upwards.)

I pick it back up in a couple hours, and I can order a piston kit wednesday or later.

Now, my next question, piston kits. where do you guys recommend getting them from? I want the best price possible of course.

I noticed that some sellers offer a piston identical to the one thats come out, and others offer ones that are smaller, i.e. the distance from the top to the bottom of the piston itself is less than the stock one.
I assume that these are for a lower moving mass and equal higher rpm? or is it just a design difference? do these ones have any benefits/weaknesses over the taller pistons?

Keep in mind Im going to use this for occaisional fire break runs, and possibly the odd have a go day at moto-x. Im not intending to go hard out, so Longevity is more important to me than saving 3 grams of weight and getting an extr 0..6hp out of the thing.

[Crasherfromwayback]

so Longevity is more important to me than saving 3 grams of weight and getting an extr 0..6hp out of the thing.

Longevity and 125 two stroke motocross bikes doesn't go together sorry mate!

[noobi]

In the link I posted awhile back the're a few piston companies, with Wossner and Vertex being OEM piston supplies to many brands, around $195 or less, and the cheaper Namura piston brand being cheap and also an unknown quantity at this point, they haven't been around for very long. Any dealer can get those pistons, as long as they're in stock, within 2 days.
Then maybe $40-50 for a top end gasket set, if you went genuine, it depends what gaskets you want, a head and base gasket would probably only be $20 from Honda, but the aftermarket kit will come with every gasket and o ring for every part in the top end.
If that's still to expensive, then you can look overseas for whole top end kits on ebay or online sites.

[gwynfryn]

See if you can get a two ring piston.

[Crasherfromwayback]

See if you can get a two ring piston.

I wouldn't bother with a 125

[tigertim20]

Longevity and 125 two stroke motocross bikes doesn't go together sorry mate!

LOL I see your point, but I meant that Im not interested in getting the extra power and reducing reliability further.

Ive pulled to whole top end right apart, so i need all the little gaskets, including the exhaust gasket, and the ones for the HPP covers on both sides as well as the little ones on top of the HPP covers etc etc.

I could order from the USA but i dont want to wait for 3 weeks to get stuff

[ktm84mxc]

Glad to see you're going about this in a pragmatic process as you'll learn a lot making your new purchase all the more enjoyable in the long run, many take short cuts with dire results.
Wossner, Pro-X are fine choices you could find Honda have some pistons and gasket sets try Econohonda in Paeroa.
Twin ring pistons were normally fitted to Enduro\Trail bikes, they mellowed the power delivery [less snap].

[barty5]

LOL I see your point, but I meant that Im not interested in getting the extra power and reducing reliability further.

Ive pulled to whole top end right apart, so i need all the little gaskets, including the exhaust gasket, and the ones for the HPP covers on both sides as well as the little ones on top of the HPP covers etc etc.

I could order from the USA but i dont want to wait for 3 weeks to get stuff

we get stuff in from the states all the time normally only a week to 10 days try 454.co.nz they are in chchch so youll get in couple a days

[tigertim20]

thanks for the continuous feedback and advice people.
@ktm, yeah Its nice to have something that I can take some time with, its not as easy with a road bike that you need all the time. with this I can take my time and then go and enjoy it when its finished. It gives me something to do in the evening when Im bored but too lazy or tired to go do anything physical!!

I do have one other question. there is a flange bolted to the head, that the exhaust mounts onto. the bit that is bolted to the engine is the male half, and the exhaust is inserted over it when it is fitted to the bike.
The manual shows a ring thingy that goes between these two pieces, I guess just to make it air tight as the flange and exhaust are both metal.
I have some pics here...

this shows the flange bit Im talking about, and the exhaust. the ring thingy I think goes on the flange, and the exhaust is then pushed over the top of it.

The manual displays the exploded diagram and shows that there is a piece of something there, but doesnt name it, or show it in any detail.
I want to know what this piece is, and where I can get it. I am assuming its probably a rubber grommet or something, but its a bit hard to know what to order without the right name for it. I ebay searched exhaust gasket, but it just gave me results for the gasket that goes between the head, and the flange.
Here is a cropped picture from the manual that shows the ring thingy I need the name of.

[noobi]

I think its this

SEAL, EX. MANIFOLD
18359-KS7-000

Heres a good site for finding part numbers and sometimes o ring and bearing sizes.
http://www.mrcycles.com/fiche_select...1991&fveh=3231

[Tony.OK]

Have a look see on www.motoxparts.co.nz
They have the top end stuff for your bike, piston kit & top end gasket set for $150. Have got a few bits from them and being local if something ain't right its much easier to sort.
Don't seem to have the wossner piston for the 91 though, but for the 92. Not heard of the mitaka brand (and its only in stock bore size). They do show the catalogue for wossner and it has your bike in it.

[Crasherfromwayback]

Twin ring pistons were normally fitted to Enduro\Trail bikes, they mellowed the power delivery [less snap].

Bollocks.

The manual shows a ring thingy that goes between these two pieces, I guess just to make it air tight as the flange and exhaust are both metal.
]

I'm guessing high temp rubber 'o' rings. Two strokes hate exhaust leaks. It's really important you have the seal at the exhaust flange well sealed.

[tigertim20]

cheers for the help.

went to work this morning to hear that one of my workmates, young and fit, same age as me, dropped dead over the weekend out of the blue, so wasnt feeling like doing fuckall with the bike today, but tinkering usually gives me something to focus on.

So I tried to take the engine out, tried being the operative word. The bolt that goes through the rear of the engine/swingarm/frame is stuck pretty tight.
I tried putting the nut on and bashing it, tried heating it with a gas torch and bashing it, tried spraying chain oil down it, and leaving it for a while and bashing it, tried laying it on its side and repeating the above a few more times, but no go. I'm a bit concerned if i belt it any harder than I have been, that I will do some damage.

I dont have any penetrating lubricant handy, so i guess i will get a can of that tomorrow and see if that helps, buggered if i know what Ill do if it doesnt help though!!!

[unstuck]

Had that problem once or twice, usually I spray with crc and leave for a while then try turning the bolt with a decent powerbar and socket.

[noobi]

Are all the other engine mounts loose/out? They can radially load up the swingarm. If they are loose and still nothing, you need a bigger hammer.