Vintage Dirt Bike Q & A

I haven't performed the leak down test, too much turkey and too much football during Thanksgiving... I did take the side case off, and the interior of the case was wet with the strong odor of gas... mmmm, seal gone bad... anyway, I've decided to fix it correctly. I know need to freshen up the top end, and while its down, I should replace the crank oil seals. I believe one can be replaced without splitting the cases, and one requires the cases to be split. My question is, is this something a garage mechanic can do with basic tools, or should I find someone to rebuilt it for me? I can turn a wrench, and I do know I need to get a proper manual before I begin disassembly. I believe the seals/gaskets are readily available. I'm just not sure if this is something I can tackle, or if its something I should have someone with more knowledge, and proper tools rebuild for me.

Any thoughts.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

About the only tool I think you can't do w/o is an impact driver. They are pretty cheap, $12-$20 at a hardware or auto parts store. I've seen videos of bikes being put together and they actually are driving the screws home with impact drivers which is why you can't get them off w/o one.

The real nice to 'have or borrow' because you may only need it once are an impact wrench and torque wrench. Impact wrench can remove nuts on rotating parts like the clutch basket so you don't have to jam a screw driver in the gears. I've seen an electric impact wrench forsale at Kragen's for ~$50.

I've only seen the Haynes manual and it is good'nuff.

I got my 1979 CR250R bottom-end rebuilt - complete with oil seals - by Racers Toy Store, but you can do it yourself. You will need an impact driver to get the OEM screws out, an clutch-holdng tool, a rotor extractor, and a crankcase splitter. You get the first from Pep Boys and the others from Motion Pro or similar. With the piston off I use an old wristpin, bearing and two blocks of wood to lock the crank to get the primary drive off. Crude, but effective. You can use a little local heat to get the seals out and make it easier to tap the news ones in. Use a large socket and go real easy and don't let anything touch the lips that will bear on the crankshaft. Whoever takes the motor apart, it is false economy not to have the main bearings and bottom-end checked out and replaced if necessary. Good luck!

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

I was getting ready to tear the bike down, but I thought I'd do a proper leak down test first. And of course, it would not hold air... Upon further review, I noticed 2 bolts were missing at the bottom of the exhaust flange. Air was pouring out in this area... mmmm I installed new bolts, and redid the test. My air gauge was broken, but it held air. When I removed the unit I built to put in the air, there was no question, she's holding air...

I pulled the head, and after a lot of friendly persuasion, the cylinder was free, and the piston was removed. After careful inspection the portion of the piston which melted, was the area net to the exhaust port... mmmm Could this be due to the missing bolts allowing air to enter, lean it out, or not allowing the hot gas to leave the engine... At this point I think the two missing bolts were the cause of the failure.

Now for the effect, the cylinder wall was coated with the remains of the melted piston. I was able to peel away the remains of the piston form the cylinder. After picking away the material, the cylinder is perfect, there isn't even a scratch. I'm still going to send it out to bored 1st over, and with a new piston kit, we will be riding again. (When it gets a little warmer, itÌs snowing today).

Progress has been made.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

It lives....

I finally got around to repairing the old Elsie. My son plays high school baseball, weather permitting, so we've been playing 6 -7 games per week. So the Elsie sat waiting for me to get back to her.

Over the winter, I had the cylinder-bored 2x over. Purchased new piston, rings, wrist pin, wrist pin bearing, clips, new gaskets, etc, all from Vintage Ellsinore. I spent the spent the past few days cleaning everything up, removing the old 31 year old gaskets, basically getting ready to put her back together. (The last time the cylinder was of this bike was 25 years ago, I replaced the rings, and so it was due for a good cleaning.)

I started the rebuild. I drilled the piston as per instructions, installed the piston, and associated hardware. Reinstalled the cylinder, and the head. Bolted on the carb, then the fuel tank. I then thought before I go too far, lets see if she will start. I kicked her over 2 times, realized the on/off was set to off. Flipped her on, kicked 2 more times, and she fired right up... She purred like a new bike. I ran her long enough to see if I had an air leak, nothing, she runs like she's new... IT IS ALIVE.....

I'm taking her out on a little test run tomorrow to break her in, and then I'll get a chance to show my son the way we did it back in the day...

All kidding aside, I appreciate everyone's help. This bike holds a lot of good memories for me. Every time I think about maybe selling her and getting something from this decade, I can’t help but think that she is so unique. I get more stares and questions every time someone see’s the bike… And not to mention, it’s a lot easier to work on then the bikes of today.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

Just a final note on the rebuild. We took the bike to the trails to give her a once over. After putting around a field for about an hour, we took a long trail ride to where there are some pretty good hill climbs. I watched as my son on his YZ125, and his friend on his KX125 talk about how tough the hills were... Now these were nice hills with a short takeoff, and obstacles, trees, rocks, ruts, etc. I said OK, it’s my turn. After a few runs to get the feel of the hills, I was able to use the exposed tree roots as jumps, and then thunder up the remainder of the hill. To say the least the boys were impressed.

All in all the bike preformed without a hitch. Yes, I did foul a plug, but considering the amount of penetrating oil I used on the cylinder walls prior to inserting the piston, well... Plus it was not a new plug. I was saving it for my son's bike. I'd say really only one time did I really get a chance to completely open her up and let her rip.... That was on the way back to the bike trailer, on an old dirt road. Let just say she can still move.

Eric

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

Very cool that this all worked out for you! Can't wait until my 5 year old is big enough to enjoy riding with me.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF