A50 - Air flow under rocker cover

[zidz]

Hi guys,

I am finishing my A50 top end rebuild and after fitting engine together I noticed that after kick I get air flow under rocker cover.

Am I right that air is comming from pushtod tunnel during downstroke and it is normal ?

I apologize for stupid questions I have experience only with two strokes so it supprised me little bit...

Thank you
Zdenek

[DAVE BRADY]

Hi Zdenek,

If you look down the pushrod tunnel you will see an opening that connects to the crankcase space so as the pistons go down air will get displaced.  With the rocker cover on there will be slight pressure build up until the pistons rise again.  At the same time the crankcase breather which is timed to the crank will operate to relieve excess pressure in the crank case.

Dave.

[zidz]

Hi Dave,

thank you for the reply.
I found it out when i have rocker cover mounted without nuts
I kick it and the cover was knocking so there was bit a panic what is wrong 😄😄😄

Thank you for the confirmation
Zdenek

[Allan G]

The cover should not be knocking, as Dave said there is a 3/8"-1/2" hole just below the centre bolt so air will come up but this won't cause any knocking.

Any air should reduce drastically when the engine is running as the crankcase runs at a negative pressure, ie it will breath out on the down stroke but the crank case becomes sealed when the rotary disc closes and the pistons ascend.

Any knocking could be the valve clipping the piston, a cam follower sticking then dropping suddenly  or a rocker catching the valve cover.

If the latter then removing the valve cover will get rid of the noise. Otherwise inspect the action of the rockers when turning over with the plugs out and see what you can see and hear then.

[DAVE BRADY]

Hi,

I think it was just the loose rocker cover moving as the engine was turned over.

Dave.