low compression

[roryntp]

hello all,
i have just aquired a crm 250, i believe it to be a mk2 because it is a 1991 model but it doesn't run because it has low compression. we measured it at 4.6 bar whereas it should be at 6.4 bar. another odd thing is that until you pull the clutch in, for the first few kicks, there is no compression whatsoever but then after a few kicks it compresses.
we're looking at taking it apart anyway so we can see the state of the barrel/piston/rings etc but just wondered if anyone knows if there is any common fault regarding 'mild' compression like this?
cheers!

[Jonorow]

the usual thng that causes low compression is worn out rings butif you say you get some compression back then this is down to the rings sticking in the grooves. Either waya strip down is in order. try lifting the barrel with outremoving the head (cheapr on gaskets)
Jon

[roryntp]

cheers jon. will have a look at the ring and barrel in particular when it's apart.

[roryntp]

top ring has gone and managed to force its way into the top of the piston which, in turn, has caused the piston to have a hairline crack from top to bottom causing the 'mild compression'. looks like a full strip is in order to see what else might have gone pop.

are leisure trail the best/cheapest/only place to get hold of gasket sets?

[roryntp]

yeah, next step is to have the head off and see just how bad the barrel is on the inside and then we'll find out if its had a rebore before too. i'm assuming LT are cheapest on pistons too? anywhere recommended for rebores?

[knackeredMk1]

LT aren't the cheapest for pistons but they can do the whole lot (piston, rebore, smallend etc....). But by the time you have messed around with postage hither & thither or petrol there is probaly not much in it ..................

[roryntp]

will have a look around first then just incase we have someone local.
cheers mate.

[boundy]

get your piston kit from honda, it works out the same price as the LT set but no postage, and if your frendly with the guys they can do it a bit cheaper

[Eddie Evans]

I've just had my barrel rebored by LT. They put the clearance in on the power valve and deburred the ports. Price was reasonable and the service excellent.
good luck