Vintage Dirt Bike Q & A

I am doing a complete rebuild on my '79 CR250 Engine. I plan on powder coating the cases, cylinder, head and
case covers. The ignition side cover has a caution warning not to remove the stator coils from the cover.

I'm assuming this is a precision alignment item and Honda doesn't want that screwed up by the careless owner.
Do any of you '79 gurus know any reason why I shouldn't remove the stator coils as long as I carefully punch
mark their correct location for reinstallation? I'm fairly certain that the powder curing process would ruin the
coils if they weren't removed.

Any help is greatly appreciated.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

Clearance between the coils' metal core plates and the rotor are the biggest concern as one doesn't want them to collide with the rotor's magnets. When replacing the coils I measure concentricity of the 140mm stator cover diameter in relationship to the curved machined area of the core plates. This can be done with a dial indicator using a lathe. If you don't have a lathe and do have a set of digital vernier calipers, you can use the depth gauge part of the caliper to measure equidistant relationship of approximately 29mm from the 140mm stator cover diameter to the coil core's machined surface. One should leave the coil screws semi-tightened to allow for adjustment with a vary small plastic mallet and light tapping and then tighten once accurate alignment is confirmed.
I haven't had any rotor collisions yet.

_________________
1978 CR250R
1979 CR250R
1980 CR250R
1980 ME360
1986 CR250R

On a related note, is there anyway to decode from the serial numbers on the stator coils which of the A-E ignitions they go to? I know the letter is stamped on the stator cover, but have come across mismatched flywheels/CDI's as against that stamp on parts bikes and wanted to get at whether they coils themselves match the identity marked on the cover.

Thanks for the info. After reading your post, I did as you recommended and also used a cylinder bore dial indicator to check the concentricity of the inside of the rotor and came up with 83mm with a runout of +/-.025mm. I checked the dimensions of the magnets using a caliper and came up with 82.5mm so the gap is pretty tight which explains the caution from Honda.

The rotor has quite a bit of rust so I am going to mask the magnets and media blast it with AO then paint it with a glyptal paint to seal it. I will scribe the magnet to mounting boss locations so they can be reinstalled to the exact same location (which I will verify with a caliper).

After removing all the rust and corrosion from everything I expect the ignition performance to be significantly improved.

As far as the part number match, check Service Honda's website. They have the Honda microfiche available which might answer some questions.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

I think I found the other reason Honda doesn't want you to remove the stator coils from the
ignition cover. I was test fitting everything prior to final assembly and as I was removing
the last screw it snapped off in the cover with no warning.

I have tried all of my normal broken screw removal tricks (slotting the screw, heat, penetrants)
it is really stuck. This is what happens when you use a cad plated steel bolt in an aluminum
casting whithout any prep (galvanization). I will have to take it to a machine shop to have
what's left of the screw removed.

The next problem is a replacement screw. Of course it is a special 4X20 mm with a sleeved
5mm shaft and large head that is not sold seperately. The only thing I can think of is to use a
5X20 mm screw (same size head and shaft) and have 4mm threads machined out of the last
10mm.

Anyone else out there contemplating removing the ignition components from the cover, my
advise is don't.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

While you have it at the machine shop have them make you a new screw

That's my plan. I have an extra 5X20 mm screw and the remaining mounting screw to use as
a pattern. The head size on the 5X20 is identical to the "special" screw I broke. If a machine
shop turned down just the threads, that would leave a 4.5mm smooth shaft just like the special.
Then by machining threads at 4mm diameter for the last 10mm of the shaft, you end up with an
exact copy of the "special".

The only reason I don't just thread a 4X20 mm screw into the cover is because of the very tight
tolerances associated with the coils and rotor. Without the smooth 4.5 mm sleeved section,
the stator coil could move far enough to foul the rotor.

This is turning out to be one of the bigger pain-in-the-butt mistakes I've made, almost as bad as
when I ripped apart that irreplaceable caged needle bearing in the case with a blind bearing
puller.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

I'd be glad to help. Please contact me through this site.

_________________
1978 CR250R
1979 CR250R
1980 CR250R
1980 ME360
1986 CR250R

Originally, the only reason that I removed the coils from one of my ignition covers was to machine an area for clearance so that I could run a Factory overweight rotor that I received with a retired 1980 CR250R Enduro bike in 1981 from American Honda. I had no problems with disassembly at that time however I had 27 years less metal oxidation on marginal strength screws to contend with, only a couple of years from manufacture. They weren't exactly Grade 8 strenghth. Don't dispair, we can get things going again.

_________________
1978 CR250R
1979 CR250R
1980 CR250R
1980 ME360
1986 CR250R

Update on the broken screw mess. I got the broken screw out of the ignition cover without any
damage to the cover. All I need now is a replacement screw. I talked to several of the local
machinist and was pretty much told that it wasn't possible to modify the 5X20 mm screw because
of the small size. They said it would be better to start with a "blank" and machine a new screw.

Before I go that route, I am going to place a "wanted" add to see if anyone has any extra screws
they want to sell. If that doesn't work, I'll have some screws made and also have a batch of star
lock washers fabricated for the clutch basket retaining nut since mine has been used way too many
times and it is no longer available from Honda.

On a better note, my engine cases are finally prepped and the motor is ready for assembly. Barring
any more "gotchas", I'm looking at three or four months before this one is complete.

The only big job I have left is the airbox restoration.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

Update on the update on the broken screw mess. Since I wasn't able to come up with a stock
replacement screw and I didn't want to spend a bunch on custom made screws, I decided to
make my own.

I started with an OE Honda 5x20 mm pan head and used a 4mm die and a T-handle philips head
to "machine" down the threads. Then I used the round cutouts on my vise to smooth and reduce
the threaded portion to 4.5mm. Below is a pic of the homemade custom.

The replacement screw is the exact same as the original in all dimensions. Total cost, $ .68

The best part is I was able to salvage my "E" ignition cover and remount the stator coils with
a little ingenuity and a lot of determination. Life is good once again.

dogger

[img][/img]

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R