new to me motor that seems strange

[daniel_250r]

hey guys i got an atc 200s engine with a parts bike, the engine is in great shape on the out side, the bad is when i turn it over it has half the compression my 200s, what can i do other than buying a new piston for it. also it pushes air out of the breather hole on top of the crank case is this normal?

[tanks350x]

all internal combustion engines are obviously gonna build up some pressure, but not much if they're in good working condition. As far as the compression is concerned, It's probably just tired, It is 20+ years old

[oscarmayer]

sounds like the it's blowing past the rings. i'd say the top end is shot.

if you gotta redo the top end, i recommend getting a 200x cam and piston as replacements. they are cheaper than aftermarket stuff and will offer up some good power gains. but the top end is defenitally shot on that motor. (unless the timming is that bad outta wack so check to ensure it's in time correctly)

[daniel_250r]

thanks guy just what i figured the rings are worn, i had the head off now how to i remove the cam and timing chain to get at the piston?

[oscarmayer]

take the CDI assembly off. first take the shiny cover off.
next take the cam bolt off that golds the spark advance on and then remove the advance
next take the ring off that has the pickup on it (i believe it's 3 screws) then take ring off and make not where the pickup was last you coudl sue a marker if you want to mark where it was so it will be there agian upon assembly)
next undo the 3 8mm socketed head(or philip screw headed) bolts out and use a flathead to gently pry the cdi case off the head.

now u can see the cam with the 2 bolts that hold the cam gear to the cam. i found it easiest to use an impact to remvoe those 2 as the crank tends to want to move.
Now before you do take it iff, make certain your at TDC by alignign the circiel or "O" up to the notch in the top if the opening where cdi casing used to be.

now remove the 2 bolts and (use something with a 90* angle on it to make it easier, make one from an old wire hanger if ya want) pull the cam gear forward it will now slide down to the thin part of the shaft.

from here on out, it's the top bolts. there re 2 sets 1 is for the rocker cover the other is for the head itself. you have to undo the head studs to get the rocker cover off.

if you go to my sig, you shoudl find a link to my newly setup manual site. download the manual for your trike and use it to help give you details and info.

[oscarmayer]

i imagine the jug is probebly trash too. there is a guy on ebay that offers boring/honing and a complete top end rebuild for like $159 if your not in good with a local machine shop, then this is probebly one of your best bets. you send your jug to him and he does it and sends it back to you with a new piston set and all new top end gaskets. I've done lots of transactions with them. good honest guys.

good luck!

[cr480r]

, the bad is when i turn it over it has half the compression my 200s, what can i do other than buying a new piston for it.

Check the valves to make sure there is some lash... I have seen a XR200 lose a ton of compression due to this


also it pushes air out of the breather hole on top of the crank case is this normal?

Any single cylinder engine is going to "pump" a lil air..