You will have to replace the washer.

 

Heat risers...not that I've ever done it, but rumor has it guys used to load those puppies up with a roll of pennies(?), aluminum foil, metallic tampons, etc. to block the passages.

 

The half-circles go nowhere other than just about an inch "in". They are there to insulate the cylinder head from the intense heat from the heat riser passage, nothing more. Poke down in there with a screwdriver or a bit of stiff wire and you can see they don't go anywhere.

A small magnet will retrieve most anything that is small enough to disappear down there. For that matter, if you DO poke around with a small magnet, you'll be amazed at the haul of washers, cotter pins, small screws, carb linkage clips, etc. that have ended up there over the past 50 years....and each one was accompanied by the mechanic saying "Damnittttt!"

Bottom line: You are not screwed except for that vanished linkage clip that you needed to finish up your carb installation.

 

You're talking about the actual riser passage, not the insulating half-circle, correct?

 

I think he's talking about the half-circles.

 

Oh....okay. I guess to keep small stuff from disappearing? I didn't quite understand "roll of pennies, metallic tampons". Anyway....I think we've solved the half-circle issue.

 

My mistake, I didn't look long enough and thought he meant the risers, not the semi circles. Never heard of the rolls of pennies, aluminum foil to block off the heat risers ay? Well it's been done. I know this because I read about it here on FCBO somewhere.

 

I'll call on the roll of pennies in the riser passage. Wive's tale. I can't imagine all the problems that could cause, and without blocking much of searing exhaust flow. As for aluminum foil, that would last about 20 seconds at WOT.

I think most right-minded engine builders use a steel block-off at the intake/head surfaces. I certainly have done so for decades. Or use a manifold that doesn't have riser passages to the carb plenum.

 

Believe what you want, only relaying what I read

 

440 Valley pan with heat riser blocked off. Felpro 1215 is part number. I think old engines tend to run hot, so cooling the air/fuel mixture with a block off is a good idea. I'd rather take longer at warm up and have cooler air/fuel during normal operation.

Factory Manifold: In my opinion the half circles are not good as a heat release, because they release heat up toward where the air cleaner and fuel lines are. Hope the block off pan minimizes any heat issues. Heat needs to go out the exhaust pipes and radiator.

 

This seriously made me laugh out loud!

 

Older engines, if in correct tune and with a correct cooling system, are just as likely to run cooler than a modern engine that is trying to minimize emissions with a 200° 'normal' coolant temp. The heat riser passage is also there to keep the fuel atomized after it goes thru the carb; the venturis and vaporization of fuel will cool the intake charge considerably. Esp with a bigblock, which has an air-gap intake, and no hot cam oil hitting the intake (air serves an insulator). IMHO, I would not casually block one off on a near-stock engine. I have had 2 318s in my life ('68 and '81) that plugged the passage with carbon and both engines ran very poorly. Even upgrading them to a 195 T-stat did not solve it, and the LA has an oil-splashed intake manifold. Both ran normally after the passages were cleared.

If one is concerned with the faster vaporization/boiloff of modern fuel vaporlocking the carb when the engine is shut off, a carb insulator would be a good idea, because it will still allow the intake charge to atomize properly when it hits the intake.

FWIW - I tried a riser blockoff in my 68 Fury many years ago, got a *terrible* exhaust resonance around 2000rpm, it sounded like 3 cyls of misfire with no mufflers. Came and went like a lightswitch at 1 spot in the rpm range. I drove it like that for about 500 ft down the street, and went right back home to open the passage. The blocked passage moved the total exhaust system resonance frequency to where it matched the engine firing frequency at that rpm. I could've switched a muffler length or section of tubing size (the X-pipe would've equalized backpressure) to move the resonance frequency back outside operating rpm, but had no way to predict if it would've been sufficient.

Those passages hold exhaust gas and will be significantly warmer than the surrounding areas of the head, so that gap is to maintain an 'even' temperature gradient along the entire head, preventing the center 4 cyls from getting a warmer intake charge than the corner cylinders. Yes, that hot air will rise, but lesser of 2 evils?

Not to mention acorn hats and pieces of field corn.

 

@fury fan
Thanks for all the info.
This is what the engine looks like now. I already did the break in. I am going to see how it runs on the street soon. Then we'll know whether humid Virginia summers with temps in the mid 90s and heat indexes of 105 justify heat riser block off in a car that will mainly be driven during summer. Ben

 

Dammit - where's the emoji for salivation when you need it???
Gonna leave the air cleaner orange or go black wrinkle?

 

Nope. Not magnetic!

Besides....that sort of stuff is behind the glovebox!

 

Don't forget to install the vacuum advance hose.

 

Thanks! Leave it orange. It's been waiting 25 years to go on this car and it's staying the color wrapped the plastic around in the mid 90s. 1970 dual snorkel air cleaner hemi orange on hemi orange 440 in Alpine White 1970 Fury Convertible. (Original engine was 318 2bbl)

Hey Maniac. LOL. I'll unplug & reinstall after timing. My alternator - tested OK by Advance - crapped out in the middle of things. I've had decent luck with Duralast Gold from AutoZone, but the first one had stripped out strap bolt holes. Warranty replacement received late today. Looks much better and tested the threads at store with strap bolt and wrench. If everything works out, I'll time and tune later today. 3:19am now. Couldn't sleep. Need to try again. Ben