850 Experts -ONLY- Question. Pointed

lezesig1

lezesig1

expatriot
Hi All,

Don't let the title fool you nor do I mean to be demeaning...but I have a technical question here that runs pretty deep.

All invited to chime in. Thanks upfront.

Subject: Crankcase ventilation.

We know that the stub off from the rocker-arm cover feeds the port between the air cleaner and the carb throat to pull a vaccum and suck blowby from the engine.



Question: Where or what provisions are on the crankcase to introduce air into the motor ?



I think I know the answer....and it is not a very pretty one.....but feel free to chime in if you think you know the answer.


lezesig
'72 850Sp


FYI- This is all related to having to modify the newly offered alloy rocker arm cover to make it work on an 850. The vent stub needs modified as well as the air cleaner pan assembly introduction port. The alignment and diameters are all off. (But) I do have a 'fix'.
 
I like to think I know...

The vacuum port on the air cleaner housing only pulls the slightest vacuum, and the makeup air is not really needed, and is provided by the various levels of blowby that the engine produces. It's not a "hard" vacuum, mostly just a way to collect blow-by as needed.

If you have the stock carb setup, there's actually two modes of operation controlled by a throttle-actuated valve on the side of the carb. At idle the the crankcase vents to the air cleaner, above idle the fumes are routed through a passage on the carb if memory serves. At least that's how it was on my '72. Hope that helps!
 
As Greg stated, the air is introduced by the carburetor, is blown by the rings during combustion, pushed out of the engine by the pumping of the pistons and the amount of pressure from combustion.

The volume of air will be directly proportional to how worn your engine is or if you have a broken ring.
 
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Thanks

Hi Greg,

Good recollect of the theory and run from memory !

Kinda fuzzy in the corners but we'll let you by : ) It is a complex system to fully describe for sure.

That OEM arrangement has been discarded. The original was gummed up and rendered non functional years ago.....but still intact with all its electricals and plumbing.

That run is being......ah.....'simplified'.


What is the latest on the Scorp ?

out for now,
lezesig
72 850Sp
 
Thanks

kmead,

Good points. I solicited the info for figuring the valve cover vent.
Points to ponder for sure.

The blowby on this motor was negligible. I haven't broken it down yet but suspect to see some good bores and endgap.

What is the latest in your 850 adventure. Still gathering parts ??

out for now,
lezesig
'72 850Sp
 
Its been one of those springs (as in the season). My job periodically has me responsible for my companies permanent showroom redo in Chicago, the last two years I showed how well I can do it so they just wanted to see if I could do it a third time apparently... :(

I have barely opened the garage door, I am hoping to take a few days this week to get a start on some of the work. Likely with the steering column recall parts I found to start and then fiddle with the damnable starter. after that finish the alternator arrangement ( have a Ducellier one from an R5 70amp and a much smaller one from a Suzuki Swift 55amp).

No lack of things to do when you own 6 cars...

When I get started I will post up some pics. Many thanks for remembering and asking :)
 
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