| Yamaha TZ250J maintenance 2# |
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My Yamaha TZ250J finally needed an overhaul. The engine had been used for several seasons without any trouble. This is my "shopping list" for the overhaul of the TZ250J engine: 93210-62323 o-ring 2 Cylinders and pistons are not available. All the other parts can be ordered from Yamaha and others (Renthal sprockets) Parts are neatly laid-out on the workbench
Yamaha TZ250J parts for re-conditioning
After fitting the new rear sprocket (Renthal) the rear wheel can be put into the frame loosely. Fresh grease on the shaft (I also fitted new wheel bearings, they were very rough....!). The rear brake caliper stay has been cleaned, looks better.
Yamaha TZ250J rear discbrake
And a "fresh" sprocket also looks better. (Front sprocket is also renewed of course)
Yamaha TZ250J rear sprocket
Before putting the pistonring around the piston, be sure that the "N" mark is upward ! You can see the "N" on the upper left hand end of the ring
Yamaha TZ250J 240 type pistonring
After that check the pistonring clearance in the cylinder. Push the ring with the piston about 2 cm deep into the cylinder, then measure the gap. (TZ250J about 0,4 mm)
Yamaha TZ250J pistonring clearance
Many people forget it, but it is very important to check the pistonpin clip. The HOOK on the clip bends upwards as you can see here. Always fit the clip with the hook turned to the outside of the piston. Otherwise the pistonpin might scuff against the clip and destroy it. Show you later how you can see it clearly.
Yamaha TZ250J pistonpin clip
Now we can fit the clips to the inward side of both pistons. When this it is forgotten it is difficult to put them in later as there is little space between the cylinders. And do not forget the fit the clips with the hook directing to the outside ! Fit the pistonrings too and use a liberal coat of oil with all these small operations. 
Yamaha TZ250J 4A0 type pistons
The cylinder base gaskets get a thin coat of LM grease and can be put into position.
Yamaha TZ250J cylinder base gasket
The pistons can now be placed over the connecting rods and with the new needle roller bearings and pistonpins they fit perfectly. Now the last 2 pistonpin clips can be put into the pistons. When done properly, you can see on the small shadow that the hook turns slightly to the outside, it is a perfect fit now.
Yamaha TZ250J pistonpin clip position
The left-hand cylinder can be be placed over the corresponding piston easily. Just compress the pistonring to the rear of the piston, where the pin is situated and it will slide in place.
Yamaha TZ250J l.h. cylinder fitting
Now we do the same with the right-hand cylinder, but here we have to check as well that the YPVS connectors grip smoothly into each other. Before doing this, both YPVS valves should be completely open.
Yamah TZ250J r.h. cylinder fitting
The connectors are in place and everything works smoothly.
Yamaha TZ250J YPVS connectors
Now the cylinderbase nuts can be tightened. As there is no space to use a torque-wrench, it is better to use a short 12 mm ring spanner and tighten all nuts from the same angle with the same hand/arm in order to get possible equal tightening. That is why I also left the intake manifolds off, there is a little bit more space now to "wrench"!
Yamah TZ250J cylinderbolts tightening
Two of the fitting pins remained in the old right hand cylinder so 2 new pins have to be inserted with a small ball-ended hammer.
Yamaha TZ250J cylinderhead fitting pins
Now the new cylinderhead o-rings can be laid into their respective grooves. Use a light coat of LM grease on the o-rings. You can see that they are a little "greasy"!
Yamaha TZ250J cylinderhead o-rings
Before forgetting it, we now have to fit the 2 cylinder coolant bleed screws. Use new copper seals/washers and grease them properly. Do not overtighten.
Yamaha TZ250J cylinder drain bolt
The old cylinderheads are cleaned with paint thinners and look like new.
Yamaha TZ250J cleaned-up cylinderhead
When the cylinderheads are put onto the cylinder you can see that because we used new o-rings, there is a clearance of about 0,7 mm before tightening the bolts.
Yamaha TZ250J cylinderhead o-ring clearance
The 8 mm bolts can now be torqued down properly in small steps (cross-wise) up to 20 nM (2.0 kgM).
Yamaha TZ250J cylinderheadbolts torque
Now the rubber intake manifolds can be attached to the cylinders and the carburetors can be mounted. Use a straight level to align the floatchambers so that the carburetors are nicely in line.
Yamaha TZ250J carburetor level
After mounting these 2 hoses first to the radiator you can "hang" the assembly more or less on the cylinderheads. After that you fit the radiator with the 4 bolts. I always use a little rubberspray on the ends of the hoses in order to keep them supple. Do not overtighten the clamps!
Yamaha TZ250J waterhoses
On the waterpumpside of the bike we have the large hose from the bottom of the radiator to the pump and the "pump" hose to the cylinderheads.
Yamaha TZ250J waterhoses
The exhausts can now be fitted but as you can see the springs are in a bad condition. The hooks are partly worn through and they need to be replaced.
Yamaha TZ250J worn exhaustsprings
Fortunately these springs are still available (partnumber 90507-20035) and they should be fitted as is shown here. The inner spring runs from the higher hole on the cylinder here to the inner metal strip on the exhaust. The outer metal strip is welded slightly lower on the exhaust and corresponds with the lower hole in the cylinder.
Yamaha TZ250J new exhaustsprings fitted
Before fitting the r.h. exhaust make sure that the Yamaha YPVS system works well. For this picture I had to make acrobatic movements with my old neck, hit my head (of course), but anyway you can see clearly the YPVS valve and the piston!
Yamaha TZ250J YPVS valve
As we are sure now, the connecting rod from the centrifugal adjuster can be connected to the YPVS arm. The arm/needle is positioned correctly.
Yamaha TZ250J YPVS control rod
A new drive sprocket is fitted, together with a new lock washer (always use a new one on any bike!)
The clutch was also jerky and slipped sometimes, although I had fitted new friction plates and springs. It turned out that the adjusting screw (part 4# from left) was a too tight fit within the push rod (part 3 from left). Please note that the adjusting screw has 1 small o-ring and the push rod 2 o-rings!
After all the parts were cleaned out and re-fitted a new clutch nut and lock washer was used to fasten the unit again on the transmission shaft. After further assembly the clutch now works perfectly.
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