Home Restoration Restoration topics Yamaha TZ350G maintenance 1#
Yamaha TZ350G maintenance 1#

You will remember that the TZ250J cylinders and pistons were heavily worn. So I got also anxious to know (I did not check it for a long time) what the condition would be of my faithful Yamaha TZ350G.

 

This operation is quite straightforward. After putting the machine on a stand the cooling fluid has to be drained. I always use regular car-type cooling fluid as this gives a totally clean engine all the time. With water you only get heavy calcium deposits. Start by removing the r.h. hose to the waterpump and the fluid can be caught in a clean tray. I filter it and re-use it! Next loosen the ventplug on the cylinderhead and the brass drainplug on the cylinder in order to drain the last fluid. Loosen the clamps on the hose from the cylinderhead to the radiator.

 

Yamaha TZ350G, waterpump
Yamaha TZ350G, waterpump

 


Remove the small hose that runs to the cylinder and unscrew the temperature gauge "feeler". Remove the 4 screws that hold the radiator to the frame (2 each side, 1 already removed here) and lift the radiator from the engine.

 

Yamaha TZ350G, radiator removal
Yamaha TZ350G, radiator removal

 


Loosen the carburetors from their clamps and induction manifolds and tie them with tie-wraps to the frame tubes. The exhausts should have been removed already earlier on, but it can be done now as well.

 

Yamaha TZ350G, carburetor tie-up
Yamaha TZ350G, carnuretor tie-up

 


Remove the cylinderhead by loosening the bolts in the normal criss-cross manner but now from the outside to the inside. The cylinder looks okay! And please look how clean it is in the cooling cavities.

 

Yamaha TZ350G, cylinder and o-rings
Yamaha TZ350G, cylinder and o-rings

 


The cylinderhead looks very, very good after 7 years of using this bike. I am either a good driver or a very slow one, or both! No detonation, no heavy deposits, nothing at all.

 

Yamaha TZ350G, cylinderhead condition
Yamaha TZ350G, cylinderhead condition

 


Removing the cylinder requires some extra work. On the left hand side the steering damper bracket has to be taken off.

 

Yamaha TZ350G, removal steering damper
Yamaha TZ350G, removal steering damper

 


And as there is very little space above the cylinder when you lift it carefully from the studbolts, it is easier to drop the engine by removing the 2 long bolts that fasten the engine to the frame.

 

Yamaha TZ350G, lower the engine
Yamaha TZ350G, lower the engine

 


Now we can measure the cylinderbores for wear. I measured everything with a proper gauge in the Yamaha workshop (forgot to take pictures), but this picture indicates that wear was considerable. A 0,25 mm feeler gauge slips easily through and maximum wear should be around 0,1 mm. Standard clearance is 0,040 - 0,045 mm.

 

Yamaha TZ350G, cylinder bore wear
Yamaha TZ350G, cylinder bore wear

 


I do not have a spare 3G3 6 port cylinder anymore, so the old one is put aside and can be re-chromed when money permits....! Fortunately I have a 1H4 cylinder (older type with 4 ports) but that is perfect today. I also use a pair of 1H4 pistons. They are not so good as the 3G3 ones but for my type of riding they will last a longtime I think. Here is the new "power-kit"!

 

Yamaha TZ350G, new cylinder/pistons/rings
Yamaha TZ350G, new cylinder/pistons/rings

 

 


New cylinderhead o-rings (the smaller ones) are still available, the large 3,0 mm O-ring I made myself. Needle bearings, pistonpin clips and other small parts are still available from your Yamaha dealer. (Also the 3G3 pistons and the rings).

 

Yamaha TZ350G, new parts
Yamaha TZ350G, new parts

 


The pistonrings have to be checked for clearance in the bore, but everything is new, so it is perfectly okay. (Push the ring into the bore with the top of the piston, about 2 cm deep).

 

Yamaha TZ350G, check piston ring
Yamaha TZ350G, check piston ring

 


Now the circlips can be fitted already on the inside of the pistons and the pistonrings can be carefully fitted as well (with a liberal amount of oil).

 

Yamaha TZ350G, piston assembly
Yamaha TZ350G, piston assembly

 


The pistonpin bearing is oiled as well and put in the small-end of the connecting rod.

 

Yamaha TZ350G, pistonpin bearing
Yamaha TZ350G, pistonpin bearing

 


The cylinderbase is greased lightly (the cylinderbasegasket was also lightly greased and already fitted). The carburetormanifold rubbers are attached already (also with some grease against leaking).

 

Yamaha TZ350G, cylinder preparation
Yamaha TZ350G, cylinder preparation

 


The pistons are now carefuly pushed into the cylinder and the whole assembly (cylinder + pistons) slides over the connecting rods. I always do it this way with the 350 as it is much safer. You never break the pistonrings! Just be careful to slide the pistons "square"into their bores, then you can push the pistonpins in very easily.

 

Yamaha TZ350G, cylinder/piston fitting
Yamaha TZ350G, cylinder/piston fitting

 


The pistonpinclips on the outside can now be fitted and the whole unit slides down easily.

 

Yamaha TZ350G, pistonpin clip fitting
Yamaha TZ350G, pistonpin clip fitting

 


Now the O-rings can be greased and placed in their cavities. Lightly grease the contact surfaces of the cylinderhead and do not forget to fit the 2 fitting bushes in the cylinder.

 

Yamaha TZ350G, top end preparation
Yamaha TZ350G, topend preparation

 


The O-ring in the cylinderhead is also greased and also here a light coat of grease is applied.

 

Yamaha TZ350G, cylinderhead preparation
Yamaha TZ350G, cylinderhead preparation

 


The cylinderhead can now be placed carefully over the cylinder and the bolts can be tightened a little.

 

Yamaha TZ350G, cylinderhead fitting
Yamaha TZ350G, cylinderhead fitting

 


Very precise torquening is required for the cylinderhead. The 8 mm bolts should have 20 nM and the 3 small 6 mm bolts 10 nM. Tightening is criss-cross from the inside to the outside, with the 6 mm bolt last.

 

Yamaha TZ350G, cylinderheadbolts torque
Yamaha TZ350G, cylinderheadbolts torque

 


The radiator can now be mounted again. It "hangs"more or less on the center down hose to the cylinderhead. Fit the 4 screws with the washers and bushes and tighten the relevant "Jubilee" clips on all the hoses.

 

Yamaha TZ350G, radiator fitting
Yamaha TZ350G, radiator fitting

 


The engine can now be lifted again on the front and the 2 long enginebolts can be fitted again (torque with 25 nM). Fit the rubber draintube to the cylinder and fasten the brass drainplug as well. Carburetors can be attached to their rubber manifolds and check that they are horizontal. Sparkplugs can be fitted as well (25 nM).

 

Yamaha TZ350G, r.h. side done!
Yamaha TZ350G, r.h. side done!

 


On the left hand side we only have to attach the temperature gauge "feeler". Use a new small O-ring with a bit of grease and do not overtighten. Also the small rubber tube to the bottom of the radiator is re-fitted again.

 

Yamaha TZ350G, l.h. side done!
Yamaha TZ350G, l.h. side done!

 


During filling the radiator you have to leave the vent screw on top of the manifold open. As soon as the liquid flows out of it, fasten the screw and fill the radiator up to the small baffle just under the overflowpipe (in the radiator).

 

Yamaha TZ350G, watercooling vent screw
Yamaha TZ350G, watercooling vent screw

 

 

 

 

 

 

 

 
 

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