Intake Manifold & AOS

[pfarah]

So last weekend, my wife and I decided to take a nice ride which turn out to be about 10 feet. The car started right up and immediately went to 950 rpm as usual but then in about 30 seconds, the engine dropped down to 500-600 rpm and began sputtering; acting like one of the spark plugs fouled. (I did remove each plug which were perfectly light brown). My wife lost interest so I ended up taking the car on to the highway to test. Unfortunately, the car still would not idle correctly even at operating temperature although she would run great above 1,500 rpm.

Anyway, I figured I would inspect the vacuum lines under the intake manifold since all the remaining hoses were replaced and in good shape. Also, it was a great time to clean up that area of the engine and replace the AOS seals (I think they're original).

Intake manifold removed:


AOS:


Just one of several cracked hoses:


AOS cleaned:


Intake manifolded blasted/cleaned:


Which leads me to a question; does the intake manifold to head mating surface need to be smooth to a semi-polished finish? The machine shop did a great job cleaning it but it appears that these surfaces were also bead blasted.Will the gaskets conform to the surface or should I take some 400-600 grit sand paper and polish them a bit? Thanks in advance!

[wildcat077]

No worries ... those gaskets are pretty thick , you'll be fine !

Cheers
Phil

[9FF]

What media did they use to blast it?

Man that’s risky. Seriously if it got inside just throw it away and get another.

[Stoneguy]

I agree with wildcat. Gasket thickness will take care of any blast finish as long as its still flat. I also suggest a silicone vacuum line kit. Change them all as long as you're in there.
AOS seals,...Good move. do the dipstick tube o ring too.
As far as the manifold,.....
I wouldn't get rid of it ,BUT, you need to wash it out and make absolutely sure there is no blast residue in there.
But then again, I don't think anyone needs to tell you that. Looks like you're pretty picky about your work and your cars!

Happy Motoring!!

[Stoneguy]

One more thing,
Looks like the vac line you are holding in picture is the line from the break booster.
Expensive hose ( Don't know why)
I just took the old one to local auto parts store and asked if I could go out back and look for a hose with a molded bend in it like that. Got one that worked. $15.00

[9FF]

Originally Posted by Stoneguy

...I wouldn't get rid of it ,BUT, you need to wash it out and make absolutely sure there is no blast residue in there...

My concerns are that the design of the inside of the intake makes it impossible to clean out completely and any specs of abrasive media in there will ruin your engine. I remember a while back a huge issue with extrude honing these intakes and the subsequent engine damage that was caused with media embedded in crevices that no amount of cleaning would shift.

... sorry but I just wouldn’t risk it, intakes are cheap and plentiful.

[Stoneguy]

9FF,
Point taken. Sounds like the voice of experience. Good info.
Thats why we have these forums. Info and exchange of ideas and experiences.

seal all openings before glass beading manifold so as to not get anything inside as a precaution.

Abrasives and cylinder walls are not a happy combination

[Stoneguy]

A slight turn of subject matter but would like input while we're on subject of the intake manifold.
I see people smoothing and polishing the intake manifold. It would seem to me that grinding the manifold smooth and polishing it would decrease the surface area of the part and reduce heat dissipation. Am I all wet, or is this plausible??? Just asking

[pfarah]

Thanks for the comments. The hose is the lower air regulator to "T" that goes to the J-Boot (only $25.00) and I typically use Porsche/OEM parts. As far as the intake, the machine shop that cleaned the intake manifold is a well-known engine rebuilder and assured me that the unit was completely run through their parts washing system/process.

[v2rocket_aka944]

Abrasive concerns come from issues on 928 manifolds and 951 intake extrude hone.

NA intake is very basic by comparison, much easier to clean since you can see the runners from the tb hole

[jjeffries]

Patrick, sorry I'd missed this. I'll be freshening those parts on my replacement engine-build up soon. Good job getting it all sorted.

John

[pfarah]

Thanks John. I haven't touched this part of the engine (since ownership) until now but glad I did. There were at least 1/2 dozen small issues that I discovered which I'm hoping will address this weird idling problem. One example identified was that the intake bolts were just beyond hand tight.

Also, I might as well replace the heater control valve while there's good access.

[Mike Goebel]

You can always send the intake out for ultrasonic cleaning. Not a bad idea since blast media was allowed inside!!!

Mike G.

[pfarah]

It was Mike, thanks.

[pfarah]

Injectors arrived yesterday so I had the opportunity to button everything up and take her for a nice 14 mile test run with no issues.

[ERAU944]

When I serviced the injectors on my '84 it made a huge difference! Glad to hear you're back up and running.

[pfarah]

Thanks... And on to the next project.

[jjeffries]

Patrick, I’m about to order all the consumables for that side of my engine, too. You’re looks magnificent.

John

[pfarah]

Thanks John. I wouldn't go that far; I would love to remove the engine and re-spray the entire engine bay but I don't thinks that's going to happen (yet). It appears that your car is coming along very nicely. When do you think you'll be up and driving?

[jjeffries]

No idea really, maybe this fall but more likely spring. Trying to be as clever as possible as to what I do and when I do it, mostly in terms of things I can do best while the engine is out, both to the engine and the engine bay. The rate at which I can throw money at parts is a prime factor; I aim to build it for reliable operation, so will do predictable stuff like new flywheel sensors but also send the PS rack for a reseal and will rebuild the front suspension while it’s out - I dropped the old engine complete with the subframe. Already purchased a new control arm for the right side ... original (date stamped!) was visibly tweaked. Will do rear shocks at the same time.New clutch, obviously. These are things that need to be done before it can be driven. I’m extremely fortunate to have maintained employment during these fraught times but there was still some degree of taking a haircut, so I’m spacing out the purchases. I do aim to get the aforementioned stuff done then register it, drive it some without the interior refresh I have planned, also get a bunch of paintless dent work done while access is best. It’ll also need tires ... I hope to acquire some 16” wheels for that ... building this with slight hotrod ethos .... stocks are just too weedy. Thanks for asking, John