273 4 bbl intake-plate riveted underside of manifold

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Bob Jasinski

Bob Jasinski

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Removed my 4 bbl intake manifold as part of rebuild teardown. Looking at intake turned over, there is a riveted plate under where the carb mounts. One of the rivets has been replaced with a bolt. What function does this plate serve? How do you remove it for bead blasting, obviously the bolt can be removed but the one rivet is still in place. If I bead blast it, I'm concerned glass beads will remain trapped under it. Suggestions?
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Remove and discard traps junk under it I had to scrape bout 3/4 in of crud off manifold It's supposed to keep heat from under manifold
The rivit will come out with some prying
 
The rivets twist out. It's a heat riser passageway. Exhaust goes through the passage when the geat riser valve is closed and the engine is warming up. The area is usually filled with carbon.
 
Thanks Bwdart and Toolmanmike. So, Mike, on your 273 rebuild, it looked to me like you kept the plate in place when you reinstalled the manifold, yes? Will it help the engine warm up faster? What does b.c. mean?
 
Bob Jasinski said:
Thanks Bwdart and Toolmanmike. So, Mike, on your 273 rebuild, it looked to me like you kept the plate in place when you reinstalled the manifold, yes? Will it help the engine warm up faster? What does b.c. mean?
Click to expand...
Lol. Bc was a typo. Yes, I removed the cover, cleaned the passage and reinstalled the cover. Yes my heat riser valve works and it does help with cold drivability.
 
As mention, they have a slight twist to their splines and will back out of you carefully use a small, sharp cold chisel on them. Tap the chisel lightly under the head of the rivet. work your way around and it will usually start to come out. It's there to keep hot oil from splashing up and hitting that hot exhaust crossover passageway. The old engine oils we had back then would burn and coke up on the manifold. This plate would (supposedly) keep that coke from building up and falling off into the lifter cavity. Good quality modern oils won't coke under normal temps, so, use it or not. I won't make much, if any, any difference.
 
Cudamark et al, I was able to remove the rivet and pull the plate off. Full of crud so I cleaned it up. I don't see it having any affect on the choke as the gasses only channel through the manifold, not under it. The explanation of engine oil hitting the underside of the manifold and burning off (coking up) makes a lot of sense. I was not aware modern oils don't have that problem, very good info, thanks. This engine is filthy inside, other than the manifold being off once, I don't think its ever been apart. It looks like the car was just driven for years without the oil being changed. The heat channel for the choke is completely blocked, and the PCV valve was stuck on the valve cover so tight I had to pry it off, it was completely plugged.
 
Yeah, I've chiseled many a carbon deposit out of intake crossovers. I even had a few I had to have hot tanked to get it out. I don't think I even know someone with a hot tank anymore. They're pretty expensive to run with today's EPA hazardous waste requirements and associated permit costs. Usually they'll clean up with a small long chisel or screw driver and a little patience.
 
IMHO the plate is to keep oil from coming into direct contact with the exhaust crossover and burning the oil etc.

I would keep it. Tap the holes, use locktite
 
No one can guarantee that synthetics will always be used!

No reason NOT to use it!
 
I finally got the exhaust chamber in the intake cleaned of the extensive carbon build up. My blast cabinet had a hard time with the build up, so I took it out and started chiseling it out, and there was more soft goop in the middle of the chamber so I kept chipping away and running fluid through it in the parts washer, its now pretty clean. I noted that the intake area under the shield showed no carbon build up, yes there was goop between the shield and the underside of the intake, but no coking. Chrysler engineers put it there for a reason, and since I want to stay faithful to the original design, I'll tap and bolt the shield back in place and it will be serviceable when/if the manifold gets pulled next. Kind of a belt and suspenders approach, I can run synthetic or dino oil and don't need to be concerned.
 
as a side note on the sandblasting good point>
I sand blasted a pair of valve covers, restored and painted them and they came out beautiful.
...I thought about the sand that may have been caught or hidden in the baffles and then was afraid to sell them so they got scrapped.
 
I too was concerned about blasting my valve covers in the cabinet, so I bought a Harbor Freight soda blaster and used it on the valve covers. The soda just rinses away with water.
 
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