JVCycles - 1972 Honda SL350 Restoration Project


The Honda SL350 (Motosport 350) was the bike to have while I was growing up in the foothills of Northern California.  Only a few were lucky enough to have one.  I think we call these bikes "dual sport” today, but the concept is the same; A bike that’s easy to ride on the street and fun to ride off road.  Are there better dirt bikes?   Yep…  Are there better street bikes?  Yep… But the SL350 is a great all around bike that will not leave you stranded, I hope!

This particular SL350 started live at Spinetti’s Honda in Jackson CA.  It belonged to a friends Father and was then traded to another friend.  Once I heard that my friend was going to sell her, I couldn’t pass up the opportunity to own probably the most significant Honda motorcycle of the 1970’s for  adventure riding.  I rode the bike for about a year before starting the rebuild.  I think this rebuild will be a “custom” one.  The goal of this rebuild is to make the bike as good if not better than it was new, but not being concerned with it’s “concourse” value.  This bike will be ridden not shown, except for that parking lot gathering of new riders that have never seen an SL350 or those of us that are reminded of our youth when we see one.

Tear Down

To start I removed the seat, fuel tank and engine.  The rear engines mounts were all broken.  I’m not sure why this was the case, maybe the vibrations.  These bike do vibrate…a lot!   

The engine mounts were all repaired and the process of stripping the paint From the frame begins.  But first, the engine...

I wanted to repair the shifter spindle and the kick start spindle.  The shifter spindle was welded to the shift lever, which was a common fix for these bikes.  However, not a good one!  Once welded, removing the cases is impossible.  I was able to find NOS spindles on ebay.  Be careful, as the SL350 used different kick start spindles than did the other members of the family (CB350 and CL350).   Not all sellers know this. 

Since the engine has to be completely dismantled this would be a good time to clean and paint the cases.  The paint I use if Harley Davidson Silver high temperature paint (part # 98660-78) and happens to be very pricey (part # 98660-78) at $16 per rattle can.   First I removed the head, then cylinder block and the pistons.  Before separating the cases I cleaned the cylinders and heads with Castrol’s Super Clean and a Scotch Bright green cleaning pad.  This should clean and scuff the aluminum enough for paint.  I didn’t have the special socket required to remove the oil filter, so I left it attached to the crank shaft.  With the cases separated I was able to remove the transmission gears and shafts from the lower engine case. 

Once the case was empty I cleaned it inside and out.  After the case was dried I put it in the BBQ and heated it to 350 degrees.  I find if you put a pan under the case or aluminum part, it heats very evenly.  While still hot I spayed the paint on the case and let it dry in the sun.  Some people put on a second coat of paint, but I like to keep the paint very thin so that heat dissipation is not effected

 The engine covers were sanded, starting with 400 grit, then 600, and finally 1000 grit wet dry sand paper.  I finished them with fine steel wool (#000).  For this rebuild, I will not be polishing the covers.  Once done the covers were washed with dish soap and painted with 500 degree clear engine paint. 

 Back to the frame...  I removed everything from the frame and broke out the steel wire “cup” brush for the grinder.  I find it works best if you spray the entire frame with paint remover, let it sit for 30 minutes, and then start wire brushing.  After all the paint has been removed and you’re left with a naked steel frame, I like to wash 

it with dish soap and a Scotts brite pad.  This removes all the grease and oil and give the frame a final sanding before paint.  I blow the frame dry with compressed air and immediately give it a coat of primer.  Once the primer is dry I apply Rustoleum Aluminum paint followed by the Rustoleum Chrystal  Clear paint.  The clear seems to “gray” the shinny aluminum paint, making the finished product very close to the original Honda silver frame paint.




I’m over the hump now.  I’m starting to assemble the bike today.  I should have a rolling frame by end of day.  I start by attaching the triple clamp to the frame, making sure to clean and lubricate the bearing with high quality grease.  Next the fork tubes can be attached, followed by the front wheel, headlight and handlebars.  I can now attach the swing arm and shocks to the frame. 

The wheel is next, but before it can be added it has to be cleaned.  It should really be disassembled and the spokes and rims replaced.  But since this will not be a show bike, they will be cleaned with steel wool and assembled for now.  The front and rear fender are original and the paint is good enough to save it.  There are some scratches but most of the paint is in great shape.  I’ll put them on for now.  The wire harness can now be strapped into place.  It cleaned up nicely with a rag and Simple Green.  The clutch cable and the front brake cable were in sad shape visually but looked functionally OK.  I decided rather than look for new cables, I would apply shrink tubing over the top of the cables.  They won’t be gray, but the black shrink tubing looks pretty good!  Last major part to clean and paint is the battery box.  I removed all the rubber without destroying them, cleaned and sanded the parts and re-installed the rubber parts.


Today I started to assemble the engine!  The upper engine case engine is the base to install the crank shaft and transmission into.  I installed a new kick start spindle and shifter shaft in the lower case.   Once all the gears, shafts and shifting forks were in their correct location I used Hondabond to seal the top and lower case together.  
 With the engine all complete and back in the frame, the ol Sl350 is ready for fine adjustments and a new battery.  Warning... If the battery doesn't put out 12 volts, get a new one.  I tried to use the old battery after keeping it charged with a Battery Tender while doing the restoration, but experienced some very strange problems.  The bike would start, but would not increase the RPM at all.  It seemed like the timing was off, but it was dead on.  Once I replaced the battery with a new one, it ran great!  Speaking of timing, before starting the bike I timed the ignition with a volt meter.  You could use a 12 volt light, but I prefer the meter.  Once the battery was replaced and the engine was warm I timed it again with a timing light.  You'll lose a little oil, but not much. 
As you can see, the bike is all together and looks pretty good!  I kept the original paint on the tank and fenders, but the side covers will eventually need to be painted. 
I'll have to paint all the blue if I can't match the side covers to the tank and fenders.  You'll notice "cracks" in the side covers.  I used clear PVC cleaner and glue, like you would use on a PVC sprinkler system, to repair the side covers.  So far so good!  I've only had to re-glue one crack that wasn't strong enough.  The seat will also need to be redone, but for now it's good enough to hit the trails around Tahoe!  Only a few more good days before winter shows up.
This is probably my favorite bike!