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2 stroke trouble

Posted by Expat Stu User icon on August 24, 2026, 3:08 pm

When last I parked my Ossa 250 is was running ok. I needed to replace the primary chain as it was very worn. This morning I received the clutch tool to lock it and undo the center nut in the clutch basket. The tool is supposed to "rest" on the crank, but the engine wont turn. Spark plug is removed, the clutch centre turns ok, the outer turns until the chain goes tight, but the crank wont turn.

Please has anyone an idea what may be happening?

UPDATE

Posted by Expat Stu User icon on August 24, 2026, 4:13 pm, in reply to "2 stroke trouble"

I put some penetrating oil and 2 stroke mix down the plug hole and got it to rotate. Hopefully there will be a video here. Is this noise normal?
https://docs.google.com/videos/d/1Rtyhnl7DKlPMwcBGij1kbxujUrRGDEzhbP1Ie6cGdVc/play?usp=sharing

Re: UPDATE

Posted by Andy C User icon on August 24, 2026, 5:37 pm, in reply to " UPDATE"

Sorry Stu I cant view as I don't have a Google account.

How long was it parked up?

If it would not turn without removing the plug it could have become hydrolocked by fuel, if the float is not seating properly.

When you kick it over with no plug are there any signs of fuel coming up into the cylinder? If there is do not try and start otherwise it will probably lock and bend the con rod.

If not hydrolocked it must have had a partial seizure, so you probably need to at least pop the head off and take a look. By taking the head off you could also check for excess fuel by kicking it over.

Just a few thoughts.

Who needs a signature anyway......

Andy C

Posted by Expat Stu User icon on August 25, 2026, 7:52 am, in reply to "Re: UPDATE"

thanks Andy, it was parked about three weeks. It makes a "clonk" sound as it goes over TDC...If I spin it fast the sound goes away.

Re: Andy C

Posted by Andy C User icon on August 25, 2026, 12:36 pm, in reply to " Andy C"

Cant really offer any advice on that one, never had a 2t makes a clonk going over TDC.

Who needs a signature anyway......

Re: Andy C

Posted by geoff the bonnie User icon on August 25, 2026, 2:10 pm, in reply to "Re: Andy C"

A small end seized might clonk at TDC as the piston would hit the side of the bore.
It does not seem possible to seize up when just parked though

Re: Andy C

Posted by the old one User icon on August 25, 2026, 3:19 pm, in reply to "Re: Andy C"

2 stroke has ports in sides of barrel , they also have piston rings , sometimes rings try the great escape

Re: Andy C

Posted by Andy C User icon on August 26, 2026, 7:09 am, in reply to "Re: Andy C"

I think Stu might have to pull the top end off and check to see if small end or big end has movement.

A clonk it more likely to be the big end, never had a 2t with a blown big end.

Dosent take long to pop the top end off, worth it for peace of mind.

Who needs a signature anyway......

Re: Andy C

Posted by Expat Stu User icon on August 26, 2026, 5:16 pm, in reply to "Re: Andy C"

Engine in bits

Re: Andy C

Posted by Expat Stu User icon on August 26, 2026, 5:19 pm, in reply to "Re: Andy C"

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