New guy GILERA SC125 help NEEDED



  • Hi folkes so my gilera Sc125 is 2008
    It has Covered 6100miles. Its used a yam dt125r engine. Change the top end turned it over Today For engine to sound like there gritty
    Nocking sound immeaditley turned it off. Train to work out if its the main bearings or big end?? Or some carbon thats fell off the power valve into the cyclinder.
    Any help or suggestions much NEEDED lol
    I thought these engines where tough



  • @gilerasc125 Did you drain the oil before or after the top end rebuild? If you did have you topped it back up? This may sound silly but it's an easy thing to forget and overlook. Also I would drain your engine oil and inspect it to see what it's like. If it's colour is very grey, then you may have some internal damage? If there are any metal fragments you will know if it's something major. This is a simple job which will give you some clues and may save you some time later on. And DTR engines are tough, but only if there well looked after. 😉



  • @NINJA hi pal thanks For reply
    Everythings brand new with the top end the Bike seen 5mins idling. Just doesnt sound right sounds like the piston is coming into contact with powervalve. All new gear oil and coolant.
    However the Bore is 57mm so it has been rebored.



  • @gilerasc125 at 57mm bore it could well be catching powervalve and/or head gasket. I'd whip the powervalve out and check for any witness marks.



  • @DTR-NSR thanks pal. Only discovered the fact it had a rebore when fitted a new top end. The garage i bought from told it was on orignal Bore 😂. The old piston was fully siezure marks to the front and rear. Yet the barrel was fine. On the orignal head gasket No apparence of damage and powervalve was working fine. Since the top end only ran For 5mins sounds like the piston is coming in contact with something.



  • Engines are tough, but if it's not built right then it's bound to go wrong. These engines don't just seize. I would want to know why the original piston was fully seized.

    If the oil pump was disconnected from the inlet manifold then it's likely that air got into the system and it will need bleeding (often overlooked).

    If the little end bearing was not replaced then this can sound like there is sand in the engine

    If the piston ring end gap was not measured and corrected, this can cause problems.

    If the incorrect piston size was selected then this can cause problems.

    If the powervalve was installed the wrong way, or was not setup properly, of not modified after a rebore, then that can cause problems.

    All of thee things have nothing to do with how strong the engine is, but ensuring it's been assembled correctly. In any event, it doesn't sound like it's been built properly if it's sounding rough.



  • @Calum hi pal the engine was built just like my other two strokes i have there fine.
    I am not a noob lol but just cant get to grips with whats going on only way of finding out is two tear it back down



  • @gilerasc125 I appreciate that, it's just that you've just joined, barely introduce yourself, ask for help, provide a really vague explanation and then are quick to slate the engine because it failed.

    The engine should be built to a spec, if it's built to that spec then it will be sweet as a nut. It's hard to diagnose the fault based off your description, I have no idea of your experience so have just posted a few things to get you started. If you were competent then I'd be surprised that you would need to ask such questions. The fact you asked them, led me to believe you needed some pointers.

    If I can help, I will. But you'll need to be more verbose in your description.

    Why did the engine fail? I would want to be looking there before I even contemplated starting it up again. At 6K miles, that's barely due a top end. Let alone having a rebuild and piston fully seized front and rear.

    I don't think I have it any more, but there was barely a scratch on my piston after the bike was stolen and thrashed with no oil. They are that reliable.

    So something doesn't sound right.



  • @gilerasc125 as regards to orignal piston
    The Bikes only done 6100 miles. Why would you need to Bore it out to 57mm in that time?
    In the space of two owners? These are pieces im trying to put together. The Bike has been derestriced. As For orignal piston siezure marks on front and rear looks mainly threw hear siezure so down to owner neglect running the Bike on No oil or cheap oil.



  • @Calum this is what im trying to put together callum. That a engine with such little milage
    Shoukd be sweet not in this state.



  • @gilerasc125 If the engine was scored badly it may have required an overbore.

    You really think the theives that stole my bike warmed it up before storming up the road on it. Yes it's not great for the engine, but they would withstand the punishment.

    So I would check to make sure the fueling hasn't been messed about with and the oil pump is not faulty. Check that the CDI is firing correctly, and not firing way too early.

    Also it's possible that the mileage is less than accurate, I.E. the speedo has spent a lot of time disconnected.

    MOT History check the vehicle to see if only a few miles pass year on year. That might indicate it's not been recorded accurately.

    I know my MOT for my DT says it's on 300 miles when in actuality it's done 20K



  • @Calum thanks man. Where you based pal?



  • @Calum ive fully Service history For this Bike confirming milage. Will put a video on it idling so people can get a Better idea



  • @gilerasc125 West Midlands.

    Something is definitely amiss. I've seen people on here get like 20K out the original piston. Someone claimed they have 40'000Km out of the original top end on here.



  • From experience it tends to be running too lean that kills two strokes. Though a 2 stroke makes more power the leaner it runs. At 57mm you often have to modify the power valve for clearance. And the head gasket will need opening up. When the barrel 1st seized they might have replaced it with a 'good' second hand barrel that had already been taken out a few sizes.



  • @DTR-NSR ![alt text))
    Taken power valve out now was all full of carbon cleaned up nice. There is a groove thats been cut into it as in machined. Got all the pics but want let me post them. Luckily piston and rings are good. When i was removing pv it had been pinned in the wrong direction





  • @NINJA thats like trying to speak mandarin 😂😂



  • @gilerasc125 Are you using your phone to access this forum??? As that will cause problems uploading pics. 😉



  • @NINJA yes 😎


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