Differences Between the CRF/XR80 and the CRF/XR100
by Gman (from Thumpertalk)
Engine on the exterior are almost identical.
Yes you can bolt the XR 100 engine into a XR 80 and visa versa
The XR 80 carburetor is a 20mm and the XR100 is 22mm. This also affects the carburetor air box boot. You will need to replace the air boot form the model engine that you replacing.
You will also need to change the counter shaft sprocket form model engine you are replacing. The XR 80 uses a #420 chain and the XR 100 use a #428 chain.
For example: Bolt a XR 100 engine and carburetor into a XR 80. Swap the air boot form the XR100 air box on to the XR80 air box. Swap the counter shaft from the XR 80 engine on to the XR 100 engine.
List of differences and compatibility between the XR 80 and XR 100 Engines
a. Yes the engines strokes are the same a 45mm. But engine similarities are few, and far between.
b. You Can NOT bolt the XR 100 top end on the XR 80 for a budget big bore kit (at least with out major modifications)
c. The XR 80 use a shorter 91mm connecting rod with a 13mm wrist pin, versa a 97mm connecting rod with a 14mm wrist pin for the XR 100
d. The XR 80 cylinder is has a 86mm jug height and the XR100 is 98mm
e. The XR 80 cylinder stud are also shorter than the XR 100
f. The XR 80 cylinders oil passage way is not in the same location as the XR 100
g. The crank and crank bearings are also different
h. The XR 80 use a 14 t camshaft sprocket and the XR 100 uses a 15t sprocket
i. The cylinder heads are also different, however the XR 80 head can be use on the XR 100 with the XR 100 cams sprocket and vise versa. (The XR 80 cylinder head has smaller intake and exhaust runners. Also a slightly small combustion chamber) the do share the same 22mm intake and 20.5mm exhaust valves.
j. The XR 80 uses a three plate clutch, the XR 100 is four plates (clutch assembly will interchange between models)
k. The transmit ion ratios are also different The XR 80 is the preferred trans ratios
l. The transmition gears will interchange between models
m. Exterior engine cases will interchange (ignition and clutch covers)
n. Inner engine cases will not interchange.
o. The XR 80 uses a 2 bolt stator backing plate and the XR 100 use a 3 bolt backing plate
p. Stators and flywheels with inter change (small change in woodruff keys/slots)
q. Wiring, coil, and CDI will also inter change.
r. Kick starts and shifters will interchange
1. Listing of chassis differences and compatibility between models XR80/XR100.
a. Frames are identical between the XR 80 and the XR 100
b. The XR 100 swing arm is 1” longer than the XR 80
c. The XR 80 14/16” wheels will bolt on the XR 100
d. The XR 100 19/16”wheel will bolt on the XR80 However, the 100s 1” longer swing arm will needed to be use for this swap.
e. The 2001-2003 XRs and the CRFs 2004 to present bodywork will NOT bolt on to the 2000 and prior XRs with out fabricating appropriate brackets for mounting. Some Exhaust pipe interference with the new style body work
f. Suspension will also interchange between models. The XR 80 fork are shorter that the XR 100.
Both your bikes are 1990 they have point ingintions
CDI CONVERSION FOR POINTS ENGINES
1. Yes you can convert the points engines to a modern CDI ignition
a. You will need a complete system form a late model bike and specific to the model bike your converting XR 80 or the XR100
b. Stator (not model specific)
c. Flywheel (specific to model, can be modified)
d. Stator backing plate (specific to model)
g. Wiring harness
h. Spark plug
i. You will also need to fabricate some brackets for mount the Coil and CDI box