Seeking Edgeucation for 71-72 BBC crankcase/flame arrester assembly

[71CHEVYSHORTBED402]

I had the impression I had all the parts for crankcase/flame arrester assembly. Not saying I don't, but I came across the second image below, so not so sure.

The parts book lists an "arrester assembly, vent flame" (3993393) which is particular to all 71 BBC, and 72 BBC C-10. Can't say what that assembly includes, and there's nothing available on the web using the part number. I'd like to learn/confirm the make-up for the crankcase/flame arrester assembly. Couple of images, some questions too (numbered)..............Thanks!

[geezer#99]

It’s not a crankcase vent.
It’s an air supply into the motor used to mix with the fumes.
The rest I won’t speculate on except the older one seems to have a check valve that yours doesn’t.

[kwmech]

Whole thing is the crankcase breather assy, to see that the crankcase gets clean air. Screen is the arrestor. 2nd pic shows the 'saucer part' which contains the screen. Hose is special, has to be oil/fuel resistant.

Pic 1 is an aftermarket design

[71CHEVYSHORTBED402]

Originally Posted by geezer#99

It’s not a crankcase vent.
It’s an air supply into the motor used to mix with the fumes.
The rest I won’t speculate on except the older one seems to have a check valve that yours doesn’t.

Agree, missed-terminology. It pulls in air/and fuel vapor if not mistaken. The PCV valve "vents" and recycles the fuel/air leaked into the crankcase from the compression stroke.

Originally Posted by kwmech

Whole thing is the crankcase breather assy, to see that the crankcase gets clean air. Screen is the arrestor. 2nd pic shows the 'saucer part' which contains the screen. Hose is special, has to be oil/fuel resistant.

Pic 1 is an aftermarket design

Apparently the original steel tube didn't have a screen. I wonder if its the original tube. Is the tube to arrester a press fit or? Seems the screen would be.

Per the book are many variances in spark arresters. Seems to me an arrester is an arrester on a big block. You know if they look like these? Comes up under 3857476. More than a few available under that part #1, and they may be guessing https://www.ebay.com/itm/GM-NOS-1964...ox!89701!US!-1

I'll test my luck on the part's board for an original set-up. Thanks for the info.

[Steeveedee]

I'll have to go take a look at mine tomorrow, though it is a '70 C/20.

[geezer#99]

Originally Posted by 71CHEVYSHORTBED402

Agree, miss terminology. It pulls in air/fuel if not mistaken, and the PCV "vents" and recycles the fuel/air left behind from the compression stroke.

It supplies air only to mix with the fuel, oil and water vapours and be pulled out of the crankcase thru the pcv which uses manifold vacuum.

As far as the little screen goes, I’ve seen them right in the tube on the riser.

[71CHEVYSHORTBED402]

Originally Posted by geezer#99

It supplies air only to mix with the fuel, oil and water vapours and be pulled out of the crankcase thru the pcv which uses manifold vacuum.

As far as the little screen goes, I’ve seen them right in the tube on the riser.

I meant fuel vapor, but would have still been WRONG Thanks Geezer

Originally Posted by Steeveedee

I'll have to go take a look at mine tomorrow, though it is a '70 C/20.

That's going to be assembly 6262992....Looking forward to seeing a difference. Could have just been a change of vendor, just guessing. Strikes me an arrester is an arrester, BBC.