Vintage Dirt Bike Q & A

Just finishing up the motor for my '79 CR250 resto. I have been taking pics along the way
for my build book. Thought you would enjoy seeing the "evolution". The final picture is
a test assembly, there are no gaskets installed except for the center case and obviously
the stator coils are not installed in the ignition cover. The exterior of the motor is coated
with a special Tahitian red and Tiger Drylac matte clear powder. The inside is painted with
glyptal engine paint custom mixed by PPG to Tahitian red.

dogger

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_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

You shore got a purty motor!

Very nicely done!

Nice!

Thanks guys.

Except for all the headaches associated with the color match, this resto has gone much smoother
than my '73. I have finished the forks and shocks and have everything needed to lace my wheels.
Once I powder coat the frame and swingarm, I'll have a roller soon after.

The last big project is going to be the airbox restoration. The plastic on mine is pretty rough so
I am going to use a new (to me) process to restore it and restore the original graining. The metal
parts (mounting plates, stiffners and strap mounts) need to be restored and cad plated and
reinstalled using solid, cad plated flat head rivets - just like Honda used. Should be a real learning
experience.

I'll post some more pics as soon as I get the "roller" completed.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

thats some great engine detail! do you have any numbers as to the powder colors. so this could be done by other powder coaters. allso should the bearings be removed from the cases? i'am just starting on a 79 cr125, should get the crank back next week. i will replace all the bearings. but the one in question is the small needle bearing on the clutch arm, i have heared it is unavaible. mine is in good condition and i would hate to damage it trying to remove it. so my question is. will the heat from the powder coating oven damage the bearing if its in the case? and agin that engine is awsome jd

First of all, thanks.

I recommend you remove all bearings from any component you will be media blasting.
I checked, and all the bearings for your application are still available from Honda.
Check out this link http://www.cmsnl.com

If you plan to powder coat your cases, the best way to get the surface prepped for
powder is with media blasting in my opinion. I use glass bead on aluminum and
aluminum oxide for steel. Even if you are carefull and really mask the area around
that bearing, some how some of it always gets through and it would be next to
impossible to clean that crud out of a blind mounted sleeved needle bearing. You
would be looking at a possible bearing failure which would really suck after all your
hard work.

What has worked best for me has been to heat one case at a time in an oven (no
torch) to 250 - 300 degrees then flip it over and bang the case on a 2X4 until the
bearings fall out. If they don't all fall out, I reheat it a little hotter or a little longer
and try again. I use heat again to install the bearings only this time, I put the new
bearings in the freezer while I heat the case. Hot cases and cold bearings, works
like a champ.

The secret recipe for the Tahitian Red powder per pound is 3 oz of Powder Express
Soda Red and 13 oz of Tiger Drylac RAL 3020.

Make sure you out gas your components to cook off all the oil that has been absorbed
in the castings over the years. I use 350 degrees for one hour for this followed by an
acetone wipe down once the casting has cooled to room temperature. If you don't
get a clean wipe down (your white cloth gets dirty), put the casting back in the oven
and do it again. Repeat until the white cloth stays clean. If you don't do this step,
the oil will bubble up during the curing phase of your powder coat job and ruin the
finish.

Finally, let the freshly coated components cool to room temp and hit them with Tiger
Drylac Matte Clear powder for the correct finish.

Hope this helps and good luck with your resto.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

thanks for the tip on the bearing, and all of the other excellent information. it's going to be very helpfull. jd

Dogger, can you share your airbox resto method with me?
My airbox isn't the best, but I'm not sure how to clean it up correctly.

Thanks
Dale

_________________
Dale E White
1980 CR250R
2002 R1

Be glad to. It is rather lengthy, so bare with me.

My airbox was in comparatively good shape in that it didn’t have any holes or cracks in the plastic.
Superficially though, the plastic was scratched and gouged and the hardware corroded.

I started by removing all the hardware by grinding off the pop and flat head rivets. Be careful here
because the heat build in the rivet from grinding will melt the surrounding plastic. So be patient and
go slow. I wired brushed and polished the hardware to prep it for cad plating with gold chromate.
I purchased replacement cad plated flat head rivets from http://www.rapidrivet.com

The plastic got a thorough bath and degreasing with a plastic specific cleaner called Scuff Magic.
The airbox is formed out of polypropolene (pp) plastic which requires substrate specific chemicals
to restore. The next step is to clean any remaining residue or oils with Super Clean Plastic Cleaner.

The box is now prepped for repair work. I scuffed the surface with 180 grit paper on a DA sander.
Prep the areas that need repair with 1060FP adhesion promoter then fill the scratches and cuts with
2000-T flex filler which is well suited for pp. Now go over the repaired areas with 80 grit on a sanding
block (profiling) then hit the box again with the DA using 180, 240 and 320 sandpaper. Blow off the
box with compressed air.

Now you are ready to add texture and color. Spray the box with 1050 Plastic Magic adhesion promoter
to prep the pp to accept the texture. If you have a spray gun, use a 1.5 tip to apply the 3800-4 Flex
Tex (practice on some cardboard squares to get the desired results first). If you don’t have a spray gun,
you can use a Prevail sprayer (an aerosol cartridge on a reusable bottle) available at many home supply
stores. Once dry, lightly rub with a medium scuff pad to remove any dry spray.

Finish the job by spraying the box with 3300-A Flexible bumper finish in satin black.

Once you have the hardware plated, dip the hook ends of the cover retaining brackets in black plasti-dip
to recoat, then install the hardware using pop and solid rivets.

All the chemicals I have listed are available from Urethane Supply Company http://www.urethanesupply.com
a good source for supplies and information.

If your hardware is in good shape, you can simply mask it and concentrate on the plastic.

Total time involved in the plastic resto is approx. 4 hours, total cost of job specific supplies approx. $100.

I will post some before, during and after pics of the resto as soon as I get a chance.

If you have any question, let me know.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R