Engine Exhausting

[cherk]

Well , this is for the engine

 

knowledgeable. I've been tooling around with a flat 4 ( well known brand) engine for education reasons ; replaced exhaust valves ( hand lapped) into recut seats.

 

Compression "seems" much improved , on pull thru ( not leak down tested ,at this stage).

 

Here's the query, pulling through on the exhaust stroke the exhaust is sucking in prior to the actual exhaust ........as if the exhaust valve opens maybe 10 -15 degrees before the piston hits BDC. Is this typical or "normal" or is the timing of the cam misaligned??

 

The case has not been split as only the top end has been worked on.

 

 

[fly_tornado]

I doubt you wouldn't hear it if it was that far open

 

 

[jetboy]

For a well known brand its normal.

 

"exhaust valve opens 65 deg BBC."

 

For a Jabiru, probably not. they usually leak throughout.

 

 

[facthunter]

65 degrees before BDC us about normal for a "moderate" tune engine. When you seated the valves you could have applied a small amount of air pressure to each port in turn and observed bubbles with some kero or light oil to check the success of your valve seating. You can also check it with bearing blue or soot from a candle flame It's wise if the motor is being operated in an aircraft to ensure the valve guides are not worn excessively. as worn guides can cause valve stem failure. Nev