Wednesday, January 8, 2020

Honda CL90-Learner bike

Ironically, my very first motorcycles was a 1967 CL90 Honda Scrambler and that was what was dropped off at the shop just before Christmas for “get running” repairs.
My customer is in his late teens and brought a scruffy CL77 last year for “get running” repairs that got much more complicated than expected. The CL90 project had been powdercoated, chromed up and cleaned up overall, but he never could get it running.

On the bench, I checked the basics and during a timing check could feel roughness in the engine as it was turned over towards TDC. I noticed that none of the four cylinderhead nuts had washers beneath them, including the copper washer used to keep the head from leaking oil. Rookies!

Tearing the top end off of a Honda 90 is about a 5-minute task, so I thought I would take a peek inside. Yikes! The camchain guide pin had been replaced with an 8mm bolt that pinched the roller at the edge, preventing it from rolling at all. The cylinder bore showed old water stains and pitting, plus the piston was showing being seized in about 3 places. Making this one run is going to be expensive and take more than a little time. I noticed that the spark advancer had 918 stamped on the edge, instead of 028. 918 is for an ATC 90 which only has about 25 degrees of spark advance vs. 45 for the CL90 engine. I had to round up a good used one from eBay sellers and that fixed that.

I dropped the engine out of the frame and saw an aftermarket coil and wiring mounted to the top of the engine. The coil wasn’t anchored on both ends because it was a generic part of the wrong dimensions. Plus he had left out the condenser! The wiring connection from the stator to the harness was connected in the wrong location which pulled the whole aftermarket harness downwards. This created a short connection to the headlight shell, which pulled on the wiring when the steering was turned to the left.

There were incorrect fasteners, loose wire connector crimps which came apart when pulled gently. Lots of rookie mistakes all around on the restoration effort. The rear wheel axle nut was just holding the axle in place, but the whole stub shaft for the rear hub was missing!

Quite a bit of time was expended in scraping off old gasket material from the head and cylinder. Whoever had been in there previously had used a cheap gasket kit that used thin green paper material which seems like a single-use material.

There was a lot of carbon build up in the combustion chamber, but the valve seats were not badly damaged from whatever water had gone through the motor in the past. I re-cut new seats and lapped the new valves in place. The cylinder was bored to 1mm over to clean up the bore and eventually it all came back together again.

Somehow the aftermarket ignition had been damaged and was non-functional. My friends at came up with a replacement switch for less than $10, plus gaskets and one of the valves.
The rest of the parts came from eBay sellers. I had guesstimated the whole bill at $500 before I got deeply into the project and with a discounted labor rate it still pushed close to $600. Funny how such a small bike, that sold for about $400 new, costs so much to repair now. Here’s what the total looked like:

$31.71 piston/rings
$12.97 tappet covers
$20.46 spark advancer
$18.94 sealing washers
$10.76 seal kit
$6.53 guide roller pin
$6 8mm guide pin washer
$21.54 cam chain roller
$6.47 8mm washer
$14.00 exhaust valve
$3 Float Bowl Gasket
$15 Intake Valve
$20 Engine Gasket Set
$8 Ignition Switch
$5.95 1qt oil
$5 gasoline
$5 valve stem seal
$40 cylinder boring
$30 Coil and condenser
$5 engine mount bolt/misc hardware
$286.33 parts

Teardown top end for evaluation
Remove engine for rebuild
Order parts (gasket, seals, spark advancer, camchain roller/pin, piston/rings, valves, ignition switch
Remove clutch cover for clutch inspection
Remove original gasket material from head, cylinder, and crankcase
Cut new valve seats/install new valves
Replace ignition components with the correct type
Reinstall wiring harness/repair wire connections/install new ignition switch
Inspect/adjust carburetor components
2 trips to the machine shop for cylinder boring 48 miles
Install new camchain roller/pin
Install new piston/rings
Assemble top end components
Install engine and adjust timing
Inspect and reassemble petcock components
Replace fuel lines
Check compression (150 psi)
Start engine and adjust carburetor
Total labor: 8 hrs. $320 discount rate

The bike fired up quickly and showed plenty of oil circulating in the top end. The compression check showed 150 psi. There’s lots more to do in finishing the rest of the bike, but I did “make it run” in the end.

Bill Silver “aka MrHonda”