Archive for the ‘Dirt Bike Repair’ Category

This 125 belongs to one of my regular customers.  Over the last year, I have installed a new clutch, trued wheels, replaced fork seals, re-packed the silencer, etc.  Recently the owner had accidentally put non-mixed fuel in the tank and ran it for a while.

The pictures show the galling of the piston and the cylinder.  This may have been caused by the non-mixed fuel.  I removed the seat, tank, exhaust,  and  radiators to access the cylinder.  I then removed the cylinder.  The crank has some minimal side-to-side play but has no vertical play, so we are going to send the cylinder off to Millennium Technologies for repair and also replace the piston, ring, and wristpin.

Update 3/8/12:  I finally added some more pics of the bike going back together.  I powder coated a few parts for some added bling.  The owner of the bike TJ Maher, went on to take a win at the WNC ag center that weekend.

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This 94 RM 125 had a serious problem of water getting into the oil.  I pulled the clutch cover and the transmission fluid in the gear box looked like pepto-bismol.  I assumed the water pump seal was to blame, and I was correct.  Once the seal was removed, it was evident it was leaking because the 2 bearings behind the seal were rusted and seized.  These bearings should never be in contact with water unless the seal is leaking.

With the installation of the new seal and bearings, the bike was ready to go.

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Here is a customers bike that has some clutch problems.  It started out as just some noise, but then developed into some more serious problems and even some breakage.  Upon inspection of the clutch basket, hub, and pressure plate, it was obvious that they all needed replacing.  If you have ever priced these clutch components, you know how expensive they can be.  Before bringing the bike to me, the customer had taken it to a local shop and received an estimate of approximately $1200.  I was able to replace all of the clutch assembly, and even upgrade the clutch basket to a forged wiseco basket for less than half of that estimate!

Look at the pics below and notice in the 3rd and 4th picture you can see the notches in the original basket.  When they wear this much, clutch engagement becomes rough and choppy.

The 5th and 6th pictures show the wear to the inner clutch hub.  This part also develops notches from the steel plates in the clutch stack.  There is also a very noticeable trough cut into the edge of the hub.  Compare it to the new hub in pic 7.

Images 8,9, and 10 show the wear on the old pressure plate compared to the new one.  Again, notice the trough cut into the outer edge.

In order to install any new aftermarket clutch basket such as hinson, barnett, wiseco, etc., you must remove the original primary gear and kick start gear and install them onto the new basket.  This can be slightly time consuming.  The original rivets must be drilled and removed, then the backing plate can be gently pried off.  The rubber cushions have to be re-used also, so pay attention to their orientation, it is easy to reverse them.  The kick start gear must be pressed off.  This can be done in a vice with a socket and a section of pipe.  To install this gear on the new basket, the simplest way is to put the gear in the freezer and the basket in the oven both for about 15-20 mins.  If you can do it fast enough, it will almost drop in.
Once you have the gears installed, and the backing plate screws are torqued to the proper specs with loc-tite, you can start putting it all back together.  New clutch friction plates must be soaked in oil prior to installation.  Refer to your manual for re-assembly if you forget where any parts go.

With the new clutch installed, it now engages smooth and there is no more noise.  The lever pull feels like a hydraulic clutch instead of a cable-operated one.

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A customer brought this bike in for repair because it is running terribly rich and fouling plugs.  I immediately assumed it was a carburetor issue, and I did find some clogged jets and orifices in the carb that did contribute to the rich condition, but soon found out it was something more than just the carb.  The amount of black goo coming out of this bike was more than I have ever seen on a 2 stroke.  So bad in fact that the rear tire looked like someone had sprayed it down with “wet-tire”.  Also, while testing the carb work I had done, the bike started smoking something fierce with the smoke being white and smelling like burning oil and not the typical blue premix smoke.  After doing some research on thumpertalk.com the symptoms lead me to believe it was a failing right-side crank seal.

Fortunately, for this repair you do not have to split the cases.  The clutch, water pump, primary gear and a few other misc. stuff must be removed, but nothing too complicated.  Of course, with this being a 24 yr. old bike, any disturbed gasket had to be replaced.

With the new seal installed, the problem is corrected.  There is still a lot of residual goo coming out of the pipe just from the old rich condition, but the bike does not foul plugs anymore and runs and idles the way it was meant to be.

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