'86 CR125 project bike - Engine rebuild

[navinmorpheus]

Hi Everyone!

I'm Navin from Sweden, I'm new to ATM and i joined the forum after I bought my first ever cross bike. Its a 1986 CR125 engine in a 1984 CR125 chassis. Bought it for dirt cheap and looking to mess around with the bike for a bit.
I might probably build a road racing or drag bike from it once its in good shape just for kicks :smirk:
I am a bit of a motorhead and i have a Clymer Manual so the future for the engine looks pretty bright

These are my observations for now :

As expected the RH outer case is heavily corroded and the previous owner has pasted the water pump cover all over with epoxy. The pump seems to run well but the tranny oil was milky. Need to fix that.

Are the radiators for this bike exclusively for it? or can i swap them with a newer sleek one from a 2011 125 4 stroke? I am not going to be doing hard riding and i hope the radiator doesn't have any thermostat or other essential components on it.

The ATAC system had been disconnected and there was no butterfly valve:shocked: No wonder the bike was lousy when i tried test riding it. Can i seal off the chamber and use it with the stock exhaust? And i'm planning to make a custom exhaust for a wide top range. So can i remove the ATAC manifold and connet a custom pipe directly? And i dont want to spend on a exhaust design software, so any help from you guys to design the chamber will be appreciated.

The carb seems to be OK but the slider has faint wear marks on it. I'll go for an upgrade once the engine is in full order. I'm doing away with the stock filter so i can change the intake manifold along with a new carb.. What are my choices for upgrade?

So as of now, The parts i need to buy are:
Piston kit
Full gasket kit
crank seals
crank bearings
front sprocket (14T)
NGK plugs
Clutch kit

Hope this will do for now and it starts running. I dont want to spend a great deal of money on this project. I'd like to know where i can get these parts in the US for an affordable price cause here in Sweden, the prices are insane! ($250 for a ProX piston)
Help and suggestions will be greatly appreciated!

[hunter77ah]

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good luck!

[moto_x_666]

Originally Posted by navinmorpheus

Hi Everyone!

I'm Navin from Sweden, I'm new to ATM and i joined the forum after I bought my first ever cross bike. Its a 1986 CR125 engine in a 1984 CR125 chassis. Bought it for dirt cheap and looking to mess around with the bike for a bit.
I might probably build a road racing or drag bike from it once its in good shape just for kicks :smirk:
I am a bit of a motorhead and i have a Clymer Manual so the future for the engine looks pretty bright

These are my observations for now :

As expected the RH outer case is heavily corroded and the previous owner has pasted the water pump cover all over with epoxy. The pump seems to run well but the tranny oil was milky. Need to fix that.

Are the radiators for this bike exclusively for it? or can i swap them with a newer sleek one from a 2011 125 4 stroke? I am not going to be doing hard riding and i hope the radiator doesn't have any thermostat or other essential components on it.

The ATAC system had been disconnected and there was no butterfly valve:shocked: No wonder the bike was lousy when i tried test riding it. Can i seal off the chamber and use it with the stock exhaust? And i'm planning to make a custom exhaust for a wide top range. So can i remove the ATAC manifold and connet a custom pipe directly? And i dont want to spend on a exhaust design software, so any help from you guys to design the chamber will be appreciated.

The carb seems to be OK but the slider has faint wear marks on it. I'll go for an upgrade once the engine is in full order. I'm doing away with the stock filter so i can change the intake manifold along with a new carb.. What are my choices for upgrade?

So as of now, The parts i need to buy are:
Piston kit
Full gasket kit
crank seals
crank bearings
front sprocket (14T)
NGK plugs
Clutch kit

Hope this will do for now and it starts running. I dont want to spend a great deal of money on this project. I'd like to know where i can get these parts in the US for an affordable price cause here in Sweden, the prices are insane! ($250 for a ProX piston)
Help and suggestions will be greatly appreciated!

well
i'll assume you already checked ebay
i'm not terribly familiar with the otherside of the pond...but you should be able to match the crank bearings at a bearing store...why a front sprocket and not a set with a new chain? i'm no expert but i think replacing just the front will cause premature wear on the new sprocket...
a full gasket set try bikebandit.com....or one of those oem parts places in the back of a dirtbike magazine....i have no idea the hit you'll take on shipping....
i'd be curious to see what you come up with for an exhaust....
good luck with it....thats quite the undertaking...i've a few projects on the go myself....lol....post pics

i checked ebay...all the parts your looking for are there...and there pretty darn cheap in my opinion.....good luck with the build

[FlashRed]

Hi Navin!

I'm starting a complete rebuit of a 86 cr 125 too. I'll post some pic of it on the next couple of days.

---------- Post added at 04:25 AM ---------- Previous post was at 02:47 AM ----------

There is two solution for your ATAC problem.

1- remove the expansion chamber from the ATAC system and put a metal plate to “emulate” a closed butterfly valve. The valve is actually closed when the engine is at Hi RPM. So this way you can make sure that you’re not using Hi end.
2- You can put a DG pipe instead of the original one. These pipes bypass the ATAC system. They come with a flange that allow to connect the pipe straight to the engine.

Hope it will help

[85cr125]

actually dg dosent mak that pipe any more but procircut dose i called both plaes because im working om a 85 cr 125
good luck

[FlashRed]

Really? That's wierd beacause it still on DG web site witch is actually a new website... Anyways... There is a buch of them on ebay.