2 Stroke Engine help please

jack_p92 · Two Stroke Sniffer Joined: 10 Apr 2011 Karma :

I was out today on my bike, DT125, and it just decided to bog down and cut out. After a fair bit of hard riding (flat out mostly for a while) Pulled the clutch in straight away as i thought it it might have seized up.

Checked, fuel was okay, choke wasn't stuck or anything, took the spark plug out which was fine. Put my finger over the spark plug hole and turned it over, but it didn't even blow my finger off (not much compression i guess).
Put the plug back (new plug) in and tried starting it, but nothing, it just kept backfiring, sounded like a dog barking out the exhaust... Rolling Eyes

A guy in a porche pulled up (none of the bikers that went past stopped tho Shocked

) and offered to help, he said it sounded like the reed valve might have snapped?

Ive taken the head off and there doesn't seem to be any scoring marks down the barrel, cant get the bastard barrel off tho as one of the nuts is starting to round off.

Anyone got any ideas?
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DT125 Supermoto

steven_191 · Nearly there... Joined: 31 May 2009 Karma :

there should be compression even if the reed valve has snapped.

check your piston rings and head to barrel seal. worst case there may be a crack or hole in the metal somewhere causing a leak.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Reed valve shouldn't affect compression seriously, unless it has broken up and gone into the barrel, scoring it.

If compression is low it suggests the barrel is toast (which you have already discounted), the rings are broken, the head is cracked or the head gasket had gone.

All the best

Keith
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cb1rocket · World Chat Champion Joined: 30 Jan 2010 Karma :

no scoring? if so your probably need a good honing and new rings which you may get away with. Otherwise a rebore and new piston

jack_p92 · Two Stroke Sniffer Joined: 10 Apr 2011 Karma :

finally got the rounded nut off and the barrel off. had to cut the stud coming out the bottom end so i dont no what im going to do about that now.
But anyway... realised the top ring has snapped in two right in front of the exhaust port, also some of the piston has shatterd off, knowing my luck its gone into the bottom end Thumbs Down

but hopefully its come out the exhaust port, not sure how to tell without engine out and splitting the casing?
Theres some slight scores above the exhaust port on the barrel so i'm off to see what they say at the bike shop tomorrow if a re bore is in need.

Will take pics tomorrow of the battered piston.
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DT125 Supermoto

steven_191 · Nearly there... Joined: 31 May 2009 Karma :

best bet is to remove the engine and split the cases but that then means spending more on replacing parts like main bearings etc.

i had my powervalve fall into the cylinder and the piston chewed it to tiny bits. i got the engine out and hung it up and just flushed it out with a few litres of petrol until id gotten about everything out. these were tiny ally shards though.

if you have big lumps of piston and or ring then it may not work. especially if the bits are lodged in the bearings. also this may damage the seals. probably not worth the risk. if your capable, i would order some new bearings and seals and a seal kit. have it all out and do it properly unless you need it.

a tip for making sure you have all your piston ring is to take all the bits you have and lay it all down on the table and make every bit line up. If you have a gap then your missing a bit. its either a case of find it, or hope its been blown out.