This is weird? Anyone come across this?

[Faceplantfilms]

Just rebuilt a crank on a Honda CRF250 2007 and when it first starts up it has a loss of compression and blows oil out the exhaust. After that it runs fine. Anyone have this problem before?

[The Captain]

Did you check the compression ring end gap?

[Faceplantfilms]

Brand new piston and crank.

[csclocogato]

Just rebuilt a crank on a Honda CRF250 2007 and when it first starts up it has a loss of compression and blows oil out the exhaust. After that it runs fine. Anyone have this problem before?

sounds like you didnt use the "dry method" on the top end regarding the oil coming out?

Saturday was the first day on my new top/bottom end replacement, no wierd issues, Other that I forgot to tight two bolts on my shock linkage.

[Faceplantfilms]

sounds like you didnt use the "dry method" on the top end regarding the oil coming out?

Saturday was the first day on my new top/bottom end replacement, no wierd issues, Other that I forgot to tight two bolts on my shock linkage.

What do u mean dry method?

[The Captain]

Brand new piston and crank.

Which is why I asked if you checked the ring end gap. To me it sounds like this tolerance could be excessive which is why you see an issue when cold, but "fixes" itself when the engine warms up and the ring expands.

A messed up bore could do the same thing but your not providing enough info.

How did the jug look? Did you check it for out of spec? How was the X-hatch? Did you hone it? Did you deglaze it? How is the top end ie valve stem seals? etc etc

There are a lot of variables here, provide some more info.

[moto_x2005]

oil out the exhaust? so you mean it blows out blue smoke? does the oil level drop quick in the crank case? im starting to lean over to incorrect ring end gap, worn cylinder.. did you hone the cylinder? even installing the piston "wet- oil on rings/cylinder" it shouldnt smoke really bad on every start up (only first time)

dry rebuild is referring to putting an oil/atf/marvels mystery oil on the skirts, honing the cylinder, dry rings, cleaning the cylinder good and spraying a light coating of wd-40/atf on it, wipe off and rub "quick seat ring powder" on to the cylinder wall and install as normal otherwise