Malossi 172

Hi everybody.


I´runing a MALOSSI 172 on T5. I am quite hapy with it but lately It starts when it´s cold at the first kick. Runs without problem but when I stop it (when "hot") I can´t start it again. Only after 15 or 20 minutes later it starts, and running again.

I´ve checked the spark it fires, I got gasoline (I´ve changed carb for other reasons but the problem it´s in the same way), and I can feel I loose some compression (I can kick quite easily).

I´ve changed piston rings, they only have 300km (Cilynder 7000km "working hard").

I´m thinking about compression can be my problem. I´ve seen piston A,B,C for the Malossi 172cc kit, but whats the difference?. Should be better change all (piston+cilynder) The cilynder looks in good conditions, There are no scrathes on it.

I´ll be very happy reciving suggestions.

King Regards.

Hi, thanks for your comment.

Not so far I split my motor to check a noise (Like a bearing noise), then i changed bearings and seals although the old ones looks to be in good conditions (the noise continue anyway).

So the clutch seal is new, that´s what you wana mean with " he clutch which is causing a loss in compression?".

I use to be quite carfully installing piston rings but anyway I´ll split it this weekend to chek this item. I also will check the cilynder head tightened torque I use about 18nw/m. It´s this right?

About the spark, yes I try it and when is hot no way to start it. The spark now I´m using it´s new (Just changed after the problems began) BOSCH W4CS Silber. I try with other ones but I get same answer.

I´ll tell you more about piston rings after weekend.

King regards.

Hello friends:

After a long wait , I opened the engine of my scooter.
Before doing so, I gave him a kick, and it started with the first kick. After a few seconds I stopped it.
When I opened the engine I was very surprised because all surfaces had too much oil. The oil could be eliminated easily with a rag.
Then I could see that the assembly of the piston rings is correct.
The crank seals are completely new as the crank itself.
The engine gasket are new, doubble and  thicker than original, I could read anywhere that it is recomended to avoid leaks.(But may be too much...?)
If oil is coming from the engine,I suppose that the clutch seal is the way with more posibilities. It's not?.

Any sugestion before split once again enginecases?

Hi, you mentioned too much oil inside the engine. I assume you're reffering to the crankshaft area of the motor. This area should be clean, a little 2T oil mix with gas should only be in the crank area. If its wet with tranny oil, then your clutch side oil seal is at fault. If oil seal is new, make sure you got the correct part for your motor. Some oil seals look similar but have small difference in diameter, which is critical to sealing the crank area from the tranny. You also mentioned you are using 2 gaskets for the case halves. One gasket is enough and a little silicone will do just fine. One more thing, if your bike is an autolube one, check the 2T pump for O-ring failure. 

Just my 2 cents. Hope it helps. 

Soory, I’ve  forgotten mention that It isn’t autolube.

The piston differences are minimal (A,B,C) and would not affect your compression.  Are you sure it's not the clutch which is causing a loss in compression?  Also, Malossi piston rings must be installed the right way up, they are chamferred to fit into the piston grooves.  Are you sure you have them the right way?  It would probably seize quite quickly if they were installed incorrectly but might be worth checking.  Have you tried changing the spark plug when it refuses to start?  Have you checked the torque settings on the cylinder head?  If they are not tightened enough the heat when the engine has been run for a while could cause enough expansion between head and barrel, enough for a loss in compression.

Did you have this problem before you changed the piston rings, or only after?

Not saying any of these is the answer, but could all be worth checking. 


Where i found oil was in the cililinder head, and cilynder top side.(After 10sec. running after one week stopped),only start testing as I told it starts 1st kick and then I stopped.

I don´t open engine case halves yet.

I check the spare I ordered. It's item Nr. 91012000 SIP. Do anybody know if this is suiteable with T5 (as the advice says), or any other better choice? 

Thank you very much. Regards.