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Typical failure of the GPZ305

Brakes: The GPZ305 is nowadays getting a bit long in the tooth so the brake-hose is mostly porous and cracky.

Pressure point is spongily, sometimes the brake-lever could be drawn up to the throttle-grip

  • Use steel-protected brake-hose from a supplier. Brake has an super exact pressure point after !

A very bad chapter of the GPZ305! This small piece has caused me a lot of trouble!

The push rod is likely to scratch and hangs therefore

Also the spring is weakening. At last after 60.000km it is so weak that it could not press the push rod enough to tension the chain sufficient

Look at these 3 spings: right side with 40.000km, middle with 60.000km and left side with 80.000km

Instead of hearing the camshaft chain ratteling (which is commonly assumed) a weak spring causes a high-tone hammering or clicking noise which sounds as if the valve has too much clearance or a camshaft bearing is dead.!

It sounds as if someon takes a lightweight hammer and hammers on the cylinder head (pling-cling)

You can do a quick'n dirty test by unscrewing a little bit the 2 bolts of the cmashaft-tensioner housing (roughly 3-5 turns). Then start teh engine and try to move a little back-and foreward, side- and up- and downwards and so on ("jiggle and waggle"). If suddenly the clicking dissapears for a short moment it is the camshaft-tensioner !

Unfortunately I do not know the length of a new and fresh spring

  • Polish push rod carefully that no scratches are visible
  • The spring could be tensioned with washer

Attention: By mounting the complete tensioner the spring respectively push rod must be fixed with the central screw. After mounting this screw has to be unscrewed to release the push rod. Thereby You can hear a "click" when the push rod jumps forward and everything seems alright. Unfortunately it is likely that the push rod hangs with its clip half the way at the inner cabinet flange.Nevertheless there is a soft tension on the camshaft chain, but it is not sufficient enough.

Loose the cabinet screws some turnings (ca. 3-4) and feel the strong backpressure of the spring by pressing the cabinet back. If there is no backpressure You have to repeat the whole procedure (unmounting, fixing the push rod , mounting)

Info: If the tension is too weak the chain doesn't begin to rattle, as expected. Instead the valves begin to hammer. It seems that if a valve is pushed by the cam lobe the "elasticity" of the weak tension of the cam chain let the cam delay first the closing of the valve and after it let the cam lobe snap foreward which makes the irritating noise !

Oil pump The cog wheel is made of Nylon. Therefore high revolutions with a cold engine and stringy oil can break teeth !

Attention: Behind the oil-pump there is a secondary filter which should be cleaned every time the clutch-cover is opened

Sprocket Some users reported problems with worn out tooth flanks on the transmission shaft and sprockets which wiggle and jiggle.

I myself have never made such an experience

Take care to mount the sprocket with the right side.to the front. It is not equal in size !
Sidestand-switch The sidestand switch also as the clutchlever-switch is very sensitive to water and corrosion.

If the bike doesn't want to start or igintion is often discontinued, esp. when riding over road holes it is likely the sidestand-contact

  • Use acid-free White Vaseline (from a pharmacy, no joke) to clean and protect the contacts. Don't use it economically. Remember: where vaseline is ther could be no water and corrosion. And acid-free vaseline is not interacting with electricity; that is also used on battery-contacts !
Tank Often it is rust inside, therefore the fuel tap doesn't work on "reserve" due it is gridblocked
  • In this case You can only clean it in an oldfashioned way: diemount everything from the tank, fill it quartely with brocken glass, chips or grid and Diesel (no gasoline). Shake it well for an hour (if You are Poppeye) or use a cement mixer (wrapping the tank into old rags and fix it well)
Fuel Gauge Is constructional defect .It is not linear at the slightes touch. Often the sensor is rotten You can do nothing :-(
  • If the fuel tap is open and after some time fuel began to drop out of the smaller drain tube at the bottom of the carb it is likely that the drain screw is rust. But first control the float level
  • Maybe the floater is leak and suffered from gasoline -> engine starting problems due to rich mixture
  • The GPZ305 is very sensitive to synchronisation of the carbs. A little out of sync and fuel consumption rises and on idle speed it began to shaking and bumping
  • If the drain screw is leaky I have simply sealed the outlet with a drop of liquid gasket inside the float chamber
  • Unmount the floater and blow-dry it with a hair-dryer. After some time, when the surface is already dry, You can see if there are wet cracks, pourring out some absorbed fuel. Maybe You can glue it with superglue
  • Carbs should be synchronised from time to time with a vacuum-gauge. It is be worth the money You spend for a vacuucm-gauge and conserves the engine
Drive belt Carefully look for indicies of waste.

First indication are pea-size "knobs" on the surface. In this state the kevlar canvas underneath is already wrenched !

If it is already frayed at the edge then it is no time to make an exchange before it is exchanged itself esp when You are just overtaking a big truck (ouch !)

  • If the belt is squeaking some drops of vegetable oil are an good aid. No joke, it helps really. Take a rug and use it economically.

Attention: Dont't use anything else especailly no silicone oil. It can weaken the intermediate layers.

See also here