|
How it works: The stroke of a
CZ 125 is 58mm, and the stroke of a CZ 175 is 65mm, BUT the gudgeon pin hole
on the CZ 175 piston is 17mm lower down than on the CZ 125 piston.
This means that the piston comes up 2mm short at TDC and 4mm short at
BDC. The engine will run with this.
Fit
the 175 piston and rings onto the CZ 125 bottom end and fit the studs.
Now for the cylinder block: As
the piston runs 4mm high at BDC it means that it closes the ports off early.
Unless you use a reverse cone stone in a power drill to chamfer a 45
degree 4mm port lift on the exhaust port, the engine will ceiling in 1st
gear at 15 MPH (early). With the port
lifted it should do 19 MPH in 1st gear.
Fit
the cylinder block. Now the engine
will run with the CZ 175 head but compression will be lower than normal due
to the 2mm gap at TDC. It will still
start 1st or 2nd kick though.
I've
tried both, and the CZ 125 head gives a bigger hike in power output.
The engine is now 58mm x 58mm which equals 153cc in all.
The carburettor settings: I've
left the carburettor
as the bike came with but it should run with CZ 125 jets and
settings. If the throttle lags then
fit the 55 pilot jet. Main jet should
be an 88 but an 98 from a 175 would work also if a K&N or other high
flow filter system is fitted. I
always use the JIKOV carb instead of the useless AMAL item.
Also
make sure than the baffle in the silencer has the flat at the front and not
the rear. If the hole is at the front
the engine will not run properly.
As
CZ 175 parts seem to be more common than CZ 125 parts, this is a convenient
repair or upgrade to a CZ 125. A sort
of big bore kit.
By Andy Reid - Dorset
<<
Back to Technical Advice page
©
Chris Baddiley / JAWA CZ Owners Club of Great Britain and Ireland
Last
Updated: 17 June 2008 - Privacy
Policy - Terms & Conditions
- Email Us
|
(23KB)