Using S90 heads in my 912 engine rebuild

[David Craigmyle]

So to summarise.
OK to use S90 heads.
Need the 22 degree big bore set.
Ok to use my 1969 912 case, crank, cam, rods, pushrods and rocker assemblies etc
I Need to drill a breather hole in the right hand head to accomodate the breather pipe to the oil filler. (Is this difficult)?
I am running twin webbers and the other pipe from the oil filler vents into the top of the air filter on the right hand carb.
912 tinware should fit with S90 heads.
Does that sound about right?

[Mike Horton]

"Also can I use the 912 rockers, push rods etc with the S90 heads. We plan to use a new cam, any suggestions on the best one for this set up.
Are there any issues with fitting the 912 tinware if I use S90 heads?"

Yes, as long as the rocker stands are the later aluminum version, rather than the early magnesium,

"We plan to use a new cam, any suggestions on the best one for this set up."

There is a world of information on cams, and their use, and like "which oil?", or "what C/R?", previously spoken to on this forum, and can be easily found by a search, I'll not go there. For my cruiser, and daily type use, I chose to stay with the stock S, SC, & early 912 cam,

"Are there any issues with fitting the 912 tinware if I use S90 heads?"

Only in your decision on whether to use the right side breather connection to the oil tower, or not, as in the "C" engines, which only use the top one, routed to the passenger's air filter, for the "suction through that carb.", to make the closed breather system work. For my current temporary needs, I've chosen to only use the top one, venting through the passengers side carb., as in the "C" cars. When I get my original 912 engine back in it, I'll need the other one, as delivered. With a new set of P/C, and fresh valve job, the breather gasses, after break in, should be low and the one vent tube, has proved adequate, in many "C" cars.

[Mike Horton]

" I was just trying for a brief description of the venting systems so folks wouldn't get too bored rehashing too much old stuff."

Craig, as always, you are wise. This detail, is one of the most mis-understood systems on these cars, and a most opportune chance, to discuss it. Thanks, for watching over us, we are always eager, to learn, from one of the masters...,

[Craig Richter]

Mike, to say you are over-the-top with praise would be a real understatement. Just a goofy kid (now old kid) that thought he knew a little more than most of the folks screwing up their 356's back in the 70's, when the cars had lost much of their value, but were still cool. This Forum and all it's contributors and authors are the real repositories of wisdom here. So let's keep enjoying these little beasties while they still let us!

[Dick Weiss]

David n& Mike,

The OEM 2-piece vertical side tin-ware are the same on the Solex-carbed S90/SC/912 engines; If using Weber manifolds,
they will need a little trimming to fit around their cast bases. The single piece tin-ware would need more trimming to fit.

The small hose-nipple on the 912 oil filler/breather is more of a wet oil return to the case as the 20/or 25mm vent hose is
directed to the right air filter. If a hole exists on the left (912) head, it can be plugged w/OEM parts listed in the parts book.

The S90 valve covers will NOT fit 912 heads due to the extra cast material around the long center manifold bolt to create
a blind hole to prevent leaks. (Never really seen) However, the 2-screw holes (on top of each head) for the vertical & horizontal
side plates around the manifold should've been blind-holed, but the screws need to be sealed for retainment--I use black RTV.

Dick

[David Craigmyle]

Thanks Dick
Are valve covers and rocker covers the same thing?
I assume the 912 valve covers will fit on the S90 heads?
The 2 screw holes are blind.
David

[Craig Richter]

The S90 valve (rocker) covers have an unusual breather elbow that interferes with a reinforcing tab on the later heads, like Dick said.