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Thought I would start a new thread as per the title and start it off with the below: -

A 254XP, lean seized - I have cleaned the cylinder of aluminium transfer, lightly abraded the cylinder with wet and dry, fitted a new piston and pressure checked it...all OK. Unusual as it had seized on inlet and outlet piston sides.


Compression measures 145psi but expect this to go up once fueled and run - the cylinder has some light scores but will run and have decent power once done.






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hello spud looks like a good fix. when you pressure test do you gently pull up to tdc and see what holds, or do you pull over and try and read the max blip achieved? and what range would you find acceptable? cheers.


With a compression check you are testing the integrity of the rings, the piston and bore above the exhaust port - method is to pull the engine over around 6 times with a comp gauge in the plug hole.


PRESSURE checking is about checking all mating surfaces, carb boot if fitted, crank seals and decomp valve if fitted. The method is to plug the exhaust, the inlet and impulse and in my case, use a modded plug to pump the engine cavity (crank and cylinder) up to around 10psi and register if there is any leakage - a good engine will lose very little over a 15 minute period and a bad one will lose everything in seconds. The pump is via an external pump and has nothing to do with piston movement.


Two strokes rely on all air input being controlled 100% by the carb, any un metered air being pulled in isn't mixed with fuel and will potentially seize the engine due to weak mix.


Both tests are often confused and both are equally important in testing two strokes!

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Bought a 025 from My Nephew for £20 it had been in his container since it was stripped by a local agricultural plant dealer and condemed by them to the scrap bin because the piston was worn.

I bolted the exhaust back on, bought a new plug and drained the old fuel out that was 5 years old and she fired up after a few pulls.

After running fine for a minute or 2 it started belching out smoke from the clutch housing.


This is what I found was causing the trouble in the first place :001_rolleyes:

£15 later and she runs as sweet as a nut :001_smile:


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Spud, have you any pics of the pot?


I'd be interested to see what you see as a scored bore but still good to use.


Cheers, Pete.


Not of this pot but got this one from a 066 Magnum - http://arbtalk.co.uk/forum/members/spudulike-albums-stihl-066-picture3872-cylinder-cleaned.html


All looked good until the chrome bubbled where the seize had pulled off the chrome from the bore and the chemical got underneath it - first one I saw like that!


The bore came out clean apart from one score but wasnt in to the aluminium - best way to do it is clean it and put a new piston in and see what compression you get - got a MS880 up next and will post pics - just hope the cylinder is ok as there are no non OEM ones available:thumbdown:

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