Crankcase check valves on 2-stroke.

[holmen78]

I’m wondering if the crankcase check valves are supposed to let air in just one direction? I have 2 in my 90hp 2-stroke that lets air back and forth. What would the symptoms be on a motor with malfunctioning check valves?

Check valves marked with red in picture.

[robert graham]

I'm pretty sure those are oil circulation tubes that move oil from one area to another area in need of lubrication....

[rodbolt17]

look on the parts diagram. if it says nipple it is not a valve.
if it says valve it is.

[holmen78]

There are 4 checkvalves, a nipple in the other end of the hose. I guess I must change them out next season because 2 are not working. Need to remove power head to get the bottom one out.

I guess a malfunktioning check valve must affect the motors running somehow. My motor is hard to could start without throttle, runs for a second and then stalls. After 30 sek it runs normally at idle speed. Have cleaned the carbs, checked the ignition system and can’t figure why it would not start easily when cold without stalling.

[ausnoelm]

It's a carb 2 stroke, not many run "nice" when cold.

[99yam40]

I thought I posted this the other day, but it just showed up asking if I wanted to restore, so I did
you need to look up the part numbers and descriptions of each one you are looking at to make sure they are listed as check valves.
some connectors could be just nipples.

but as Robert mentioned, they are suppose to remover liquid gas/oil from the crankcase to keep it from building up.

yes check valves should only let things move in only one direction

I replace all 4 on my C40 when changing out the crank, only 2 were bad, but I figured if 2 are bad the other 2 are not far behind. Could have been wrong tho.

maybe lean sneezes destroy them

I do not think they affect the running that much tho.
maybe if there is a lot of liquid build up sitting in the bottom if some of the crank case sections it might affect the running

Change the ones you can get to.
is the one you cannot get to a bad one?

[holmen78]

Thanks for replying 40yam99. I read your posts from 2015 in an other forum. Great tips on how to remove them.

Unfortunately the one I can’t get to is bad. It seems it is connected from bottom crank shaft seal/bearing region.

Next thing is to bore the cylinders and buy new pistons and rings. My compression gauge shows 100psi on all cylinders. Don’t know how accurate my gauge is though. Had the cylinder head of last winter and cylinders were ok within wear limits.