cagiva mito top end rebuild

beasty6

beasty6

beasty6

Soldato
Joined
22 Nov 2010
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Kettering
hey guys

i rebuilt my mito's top end yesterday and went to start it up first time this morning, it was turning over but now a clack noise has developed, it sounds like is coming from the cylinder :( have i broken a piston ring?

when i assembled the top end, i pushed the bike in gear to make sure if moved ok and it did, its started raining atm so i cant do nothing with it until it stops.

i really dont want to have to tear down the top end again

thanks
 
ive got a feeling one of the rings have got cought in one of the ports :( but surely once the rings are compressed into the piston and then seated into the cylinder, they should not be able to do that?
 
Could be a few things, if it's top end noise it maybe the small end bearing or piston slap. Did you try the piston in the bore without the rings. To check whether it needed a rebore? Two stroke engines are critical for this.

I had a ring break in a RD125LC and that engine wouldn't turn over/start, so at a guess I imagine it isn't that. But anything is possible. It looks like you're going to have to strip and investigate as potentially you'll create even bigger problems riding it like it.
 
nope, its the standard bore i believe, what causes piston slap? it sounded fine turning over, but now makes a noise while turning over.

im going to try put it in gear and moving it again, then test the spark plug, put some oil into the cylinder just to give it some more lubrication, then try again.

failing that ill just be in a bad mood and leave it for today lol
 
beasty6 said:
nope, its the standard bore i believe, what causes piston slap?
Click to expand...

A worn bore! The piston doesn't travel cleanly up and down the bore but rocks side to side as it travels 'slapping' the bore wall. Only a new over sized piston kit and rebore will cure this.

f15_25.gif
 
awww man! :( i just tried staring it, it started but something was catching and it cut out, it gains compression and then loses it again.

its to wet out atm to take the top end off

i got a OEM size piston, if this is the case then i will have to get a new cylinder :(
 
Don't forget a new piston to go with that new cylinder, as the one you have put in will most likely be wrecked now as well.
 
i have not rode the bike, since the new piston it started for about 1-2 secs.

i just looked up that the power valve can catch the piston, when closed, so ill have a look at that as well before i get a new cylinder
 
beasty6 said:
i got a OEM size piston,
Click to expand...

Did you make 100% sure the old piston was standard size as well? If it's been re-bored in the past then a standard piston will give horrendous piston slap.

Also did you check the the squish clearance when you assembled the engine? If your new piston has a different compression height or you used a thinner base gasket then the piston could be hitting the cylinder head.
 
just checked the piston, its not piston slap, everything is seated correctly BUT i now know what the problem is, the CTS power valve blade has somehow got itself poking into the cylinder slightly, so thats what the clacking was but i also now need another new piston and rings and probably a power valve as well :(
 
I thought you were letting a shop do it?

they will have all the right tools to check clearances ect,you wont tell by looking
 
i was until they said £60 an hour just for labor!

then i had to supply all parts, and he reckons 4 hours just for a top end rebuild!
 
Sorry forgot to mention, that's me taking just the engine to him, if it wasn't for this power valve blade, it would be running fine :(
 
whats the power valve like on those ive forgot

is it a metal plate that slides up and down infront of the exhaust port?
 
Yes it is, it is controlled with a little motor with wheels which is connected to the power valve with cables, i dont have a clue how to adjust it so I'll give mito mondo a call on Monday
 
you adjust the power valve blades from the servo end, the cables are like that of a bicycles you can turn out the adjuster and then wind down the locking nut to keep it in place.
 
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