djcwardog

I recently bought a beautiful 1968-69 low rise L-36 aluminum intake manifold to use on my '73 454 with the stock hood. It has four rivets but no heat shield on the bottom under the carb mounting area. I think the guy took the shield off to show the casting numbers, etc. under there (ebay auction). I have all the gaskets, choke parts, etc. needed to run this in my car. Do I need to find one of these shields and use it? If so, can I take off the one on my '73 cast iron manifold and use it? How to do that without ripping up either the shield or the aluminum manifold?

BlueL36

An advanced search in open and archived C3 forums using "carb gasket heat" gives you a bit of reading. I have the three gasket sandwich under my Q-jet that I got from Lars. The heat shield is about the same size as the composite gaskets. Here's a cut-and-paste from an archived thread from Lars:
_________________________

If you have the "smiley-faced" exhaust crossover forward of your primary throttle bores, you have to use the 3-piece gasket set, and installed sequence is of great importance. The high-temp composite gasket with the groove goes down first, followed by the stainless steel heat shield, and then a 4-hole gasket with the "bulge" on the driver's side goes down last with the carb on top.

Yes, I still have kits available. E-mail me for info at:
V8FastCars@msn.com

lars

dj -
I think you're talking about the riveted metal shield that's located on the bottom surface of the manifold - exposed to the lifter galley area. The purpose of this shield is to keep hot oil splash off the bottom of the manifiold. Since the manifold saturates to engine temperature upon warmup anyway, I doubt you will have any noticable effect due to the lack of the shield. The "rivets" are drivescrews that are hammered into the manifold. They are fairly soft steel, but they're harder than the aluminum, making drilling them out cleanly difficult at best. Once they have been drilled out and removed, you need to go to the next size larger (diameter) in order to get them to "grip" properly. The drivescrews are available from sources such as McMaster-Carr. But if it were me, I'd run the manifold without the splash shield for simplicity.

If, however, you're talking about carburetor gaskets and carb heat shields, disregard everything I said above...

RatRacer

Summit sells a sheet metal shield for this exact application. I removed my stock heat shield because it had a huge amout of crud built up underneath it. The Summit shield lays down in the lifter valley and protects the underside of the manifold from hot oil.

LemansBlue68

I think the shield was used to keep the oil from coming in contact with the hot exhaust cross-over passage that runs under the carb in an effort to prevent the oil from coking under there. According to my Chevy by the numbers book many of these manifolds were found to have been used in production without the shields. I would say you are probably OK without it. Also consider that the oils today are considerably better than they were back in the '60's and are much more temperature tolerant. That is also in your favor with respect to getting along without the shield. You need to be sure to use the 3 piece "gasket sandwich" between the carb and manifold, though. Lars has them available. They are very hard to find otherwise.

djcwardog

Lars,

You can see that I got a reply that mentions a Summit part made to fit this application - I wonder if it is a performance part or just a stock piece, search under what? I may try to run that down if I decide that I want the shield in there. Regarding carburetor gaskets, I think what I got from Dr Rebuild is only partially correct - only two thin pieces, one metal, the other a thin carb gasket. Therefore, I would like to order up your three-piece set. I'll send you an email with this text in there as well.

stingr69

If you block the exhaust crossover, the shield is not required.

You can use screws to attach a splash shield if you still need one. If the passage is still open you need a cover to prevent the cooked oil from building up then comming loose and dropping down into the engine.

-Mark.

lars

Most likely, reference is being made to the lifter galley oil splash shield, Summit part number MOR-25050. It is not a stock shield.

I believe you can also get a GM Performance Parts "Manifold Oil Shield" (do a search on it in Summit).

I'll get the gasket pak info out to you shortly.

Lars

RatRacer

Here's the shield I installed. It's the GM performance part.

http://www.gmpartsdirect.com/perform...CATID=611.html

lars

...available from Summit under part number
NAL-12555320

mvftw

Lars, does it pay to clean under the oil shield or just leave it alone?

Tom454

I've been dealing with the splash shield since dirt was invented, since I media blast manifolds on a regular basis. The media gets hung up in the nasty. sticky, crusty "coked" oil under the shield. The stuff builds up and then starts to fall off in chunks.... dropping down into the oil pan and clogging up the oil pump screen. Can't speak for synthetic because I don't use the stuff, but current day dino oil still cokes up under the shield.

By using a pair of sharp (relatively new) wire cutters and a bucket full o' patience, you can pry the pins out of the intake. I've never even bothered trying to drill them.. they always pry out for me. On aluminum intakes, I'm scared poo-less that my drill might all of a sudden drive right through the bottom of the intake.

All pins are not the same diameter on different manifolds, and are not the same design. Some have spiral (screw type) flutes, some are just "swedged" or flattened in the middle to grab the metal, and some have "teeth". So when you pull them out, you have to adjust your "pulling strategy" to match the pin design.

After media blasting, I select a tap that will provide the necessary "bite" for SS machine screws, and I tap the intake with a bottoming tap for machine screws... usually 8-32 or 10-32. If the shield holes are too small for the new screws, I drill the holes to match the screws. I then re-attach the shield with machine screws using "medium" thread lock. Been doing it this way for years and never had issues.

On the debate whether it's needed or not... if the crossover passage is blocked, it seems logical that the shield would not be necessary.

Otherwise, the conditions that cause the gunk to build up under the shield will still be present without the shield, so I will assume that the oil will still "coke" (if that's the right term). Will the oil grow in layers or chunks? Fall off into the oil pan? I dunno. I always re-install the shield.

I just removed the intake of my own silverado 305 which was done as I described above. I use Valvoline #140 dino oil. The crud had reformed under the shield after 40K miles with the crossover functional. This time around, I'm blocking it off... so I must also make sure the heat riser defaults to "open", and stays open.

69monzaredbigblock

Just curious here.... how important is it to have this shield in place if the crossover ports are open and there is no heat riser? How hot does it really get under the carb without a heat riser to force the hot gasses to go through the crossover ports?

Tom454

That's a good question. How much (if any) will flow across with no heat riser?

We need some ambitious person to test the concept.... or the voice of someone who has already tried it.

Fevre

Just get an intake gasket set with blocked crossovers, I prefer sets where the gasket is not punched out as opposed the metal block plates that are installed

Simmo

Unless you live in Alaska you wont need the heat riser for the manifold. Aluminium is a very good conductor of heat and will warm up quickly. Iron is different. More power, more compression, less detonation are benefits of no heat riser. Slightly longer warm ups and in theory more engine wear are downside.

cardo0

I can only speak for sb manifolds but all i ever used was a gasket scraper to lift up the shield with rivit enough to pry it out with a screwdriver. I recall i wrestled with the first revit for 20 min then started the others with my Craftsman gasket scraper that looks like a flattened screwdriver and just popped the rest out. Works great on both cast iron intakes and aluminum.
Well oil does gets coked under that shield due to x-over heat even though there are drain holes for the oil to return. D. Vizard writes u can seal the tin on with hi-temp RTV if desired and also modify by tacking on more metal to the ends to cover full length of intake - again i'm taking sb manifolds. Both the iron and aluminum intake shields are same/interchangible - but again sb.
If u live in PA u gonn'a want that crossover open and choke working. I would use a sealed on heat shield to keep the oil from coking up and falling into the lifter valley/oil system. Find a boneyard iron donor intake for a shield, hey no NRCS judge gonn'a find out (i won't say a word ). Just my 2 pennys here and
good luck. cardo0

Tom454

That's the way I tried it at first also... ended up getting 3 out of 4 out no problem... the 4th shredded the shield, so I stopped doing it that way. The OEM shields are not sold separately. I was working on a 1962 T-Bird factory TriPower manifold, and was extremely pissed at myself for screwing up that shield.

If the pins are not too tight, you can just pry them up that way. If factory tolerances "stack up" (i.e.- fat pin/tight hole) and the pins are tight, you will mess up the shield... like I did.