Anzani Crankcase Venting

[rweber]

I would like to ask if somebody can give me a hint about the inner works of the crank case ventilation of the 3W Anzani.
I assume its simple, like the rest of the engine. I guess it hat to vent in both directions, so maybe there is only a piece of felt in it?

regards
Robert

 

[rklopp]

The crankcase vents on my Upshur twin riffs and on the Howell V2 are one-way check valves designed to exhale from the case but not inhale. The ones I made for the Upshur twin riffs were based on Howell's. His are built into the base of the fuel supply plumbing. I just made the vent part as I did not need his fuel supply aspects. The valve is based on a mylar disk loaded by gravity and negative pressure against a circular brass seat. There is some synthetic felt between the disk and the exit holes. The valves seem to work very well to keep the oil in.

 

[stevehuckss396]

On the 9 cylinder I'm working on the crankcase is vented through the front of the crankshaft. The front shaft is drilled a few inches deep and then cross drilled In an area that is inside the case. It's an open hole with no valve of any kind. Maybe yours is similar.

 

[Tim Wescott]

Wouldn't those little holes at the base of each cylinder sleeve tend to vent the crankcase a lot?

 

[rweber]

Thanks for your answers!

Wouldn't those little holes at the base of each cylinder sleeve tend to vent the crankcase a lot?

Well, thats a good point. I see, that at least one of the line of holes is uncovered almost all the time, about 280° crank. Only 40deg before and after BDC they are all closed. I agree, that the those 40 degres starting before BDC until BDC will not create much pressure. But Anzani apparently thought that it still need ventilation. For me it is more for the optics than for the function. But if I already install the valve, it should look (and possibly) work like the original.

 

[Jasonb]

The radial Anzani model just shows the vent with a plain small hole, couple of other engines I have done have also had a clear hole in the vent with no felt or screen.

 

[Tim Wescott]

Well, thats a good point. I see, that at least one of the line of holes is uncovered almost all the time, about 280° crank. Only 40deg before and after BDC they are all closed. I agree, that the those 40 degres starting before BDC until BDC will not create much pressure. But Anzani apparently thought that it still need ventilation. For me it is more for the optics than for the function. But if I already install the valve, it should look (and possibly) work like the original.

I'm pretty sure that the "fan" engine has a 180 degree crankshaft, so the pistons are timed 120 degrees apart. That would mean that the pistons aren't "pumping" the crankcase at all.

Which leaves me totally confused about why the designer felt that the crankcase needed to be so thoroughly vented -- unless those holes are there to provide fresh air induction at the bottom of the piston stroke, but they seem too far down for that. So again -- I'm confused.

 

[stevehuckss396]

If the rings leak a little the blow by will charge the crankcase and force oil out of every little crack. If its internal combustion you should vent your crankcase.

 

[rweber]

I'm pretty sure that the "fan" engine has a 180 degree crankshaft, so the pistons are timed 120 degrees apart. That would mean that the pistons aren't "pumping" the crankcase at all.

Nope, all 3 Cyl. Anzani fan engines have only one single crank pin!

Which leaves me totally confused about why the designer felt that the crankcase needed to be so thoroughly vented -- unless those holes are there to provide fresh air induction at the bottom of the piston stroke, but they seem too far down for that. So again -- I'm confused.

The purpose of the holes is to relieve temperature stress from the exhaust valves. The exhaust valve opens only when the top of the piston is at the middle of the top hole row and the most of the hot gases already left through them.

 

[Tim Wescott]

@rweber thank you!

I had thought that maybe those bitty holes were there for the exhaust stroke, but I couldn't think of why you'd want them -- making life easier for the exhaust valves makes sense.

Were those prone to backfiring? It seems to me that if you had some flame lingering outside the crankcase when the piston's at the bottom of the intake stroke it could be drawn in and ignite the mixture -- which would cause one heck of a backfire.