Its time for a top end rebuild.

[eprovenzano]

Its time for a new top end on my 99 250.  Not because its running poorly, but because its due..  Since my son has taken over the bike, I'm going to use the rebuild as a way to teach him how to properly maintain the equipment.  I recently popped off the head to make sure all is well, and the cylinder looks great. I could leave it alone for another riding season, but that's no fun...  I like to know when we go riding, that the equipment won't fail...  I hate riding with those who do not keep up the maintenance on their bikes.  It seems as though we spent the whole day making simple repairs that should have been done in their garage. Bike are machines, they can break, not a problem, but it just irritates me when its something that should have been taken care of before the bike was loaded onto the trailer is left to be fixed on the trail.

When I have her down, is there anything else I should be looking at?  Does anyone have recommendations for cleaning the power valves.  I will look at the crank etc., but I'm not planning on going into the bottom end for now.

 

[alan]

I think I would soak it in some carb cleaner for a week or so!

[Jeeks]

A couple tips:

Place a rag or cover with blue masking tape, the case after the jug is removed BEFORE you remove the piston.  Keep track of the circlips, you only have to remove one.  Install one new circlip on the new piston before any other assembly.

Spray gasket remover works very well on carbon deposits.  Just spray it on , when it's soaking, you can see all the splooge coming off.  Finish up with a can of brake clean. You can use a toothbrush to help too.

On a few motors I've worked on, I was able to install the piston in the jug before placing it on the case.  This eliminates trying to compress the ring(s) and holdong the jug at the same time. Just install the base gasket, line up the wrist pin, install the 2nd circlip and carefully push the jug on the case.

When the piston is off, very carefully pull up and down on the rod to check for play.  Side to side is ok, just not up and down.

When fitting the piston to the jug, I give the cylinder and piston a very light coat of engine oil.  This will help in with the initial break in. Also use motor oil on the wrist pin and bearing.

Be very careful not to gouge the case when removing the old gasket, if some pieces of gasket fall on the crank, use a vacuum.

[eprovenzano]

I just completed the top end.  When I pulled the cylinder, I could see where some blow by was starting to occur.  The cylinder was in great shape, the crank seemed tight, and all is well. After putting it back together, it fired on the 3rd kick.  The previous piston and rings were defintly at the end of their useful life.

Before I pulled the cylinder I was concerned about the exhaust valves, since the last rebuild I did (2 years ago) was on my vintage 74 Honda CR 250M. The exhaust valves were not a problem as I had anticipated.  The actuator arm disconnects when the cylinder is removed, and the valves did not have to be touched.  Other than dealing with the radiators, this basically is the same as on the old air cooled 2 smokers.

Thanks gcrim for your assistance.  As soon as the weather cooperates, I?ll get her broken in, and we'll be ready to ride again.

[eprovenzano]

Pic of the vintage Honda CR250M purchased new in 1974, sold in 2006. It was original, except for the pipe, carb, (I still has the originals) and back tire.  Everything else was original, right down to the torn grips, and the dry rotted front tire. If my back could take the lack of suspension, I'd still be on that bike.  It was a beast to ride.  You guys complain about starting the 500's this thing was not easy to kick over.

http://i18.photobucket.com/albums/b125/eprovenzano/74CR250M.jpg

Here's a pic of the current beast.  The one my son has claims is his.

http://i18.photobucket.com/albums/b125/eprovenzano/Kx250.jpg

[Hammer 4]

Re: hard to kick..Evere tried kicking a 73 Yamaha 500 MX..?  That was a Beast! BTW, very nice lookin kx..

[Jeeks]

I've been in the market for an early 70's MXer.  I may have zeroed in on one or two.

I can't wait to run circles around my buddies on a 35 yr old bike.

[gwcrim]

Man, that looks a lot like my old CR125.  It was a '75 model with red parts where yours are green.  I'd love to have one, but for what they bring dollar wise, you can buy a modern bike.  And they're more fun to ride.