The Stovebolt Site Forums The Shop Area Engine Shop heat riser flap bi-metallic coil question.

I've completed the freeing up of my heat riser valve on my '56 235 engine, and now have the oil filter can and exhaust hooked back up. Last thing I need to do is install the bi-metallic spring to control it. I ordered the coil from classic parts, and didn't think much about it when it came in, but now that I'm looking at it, I need some advice. The old spring is rounded on the end that goes on the flap rod, but the new one has that end of the spring straightened for, I guess, a slot that is on some of those rods in different models. Here's a pic of what was on there compared to what I've got from CP. I'm not finding a slot on the rod on my engine. Should I bend the flat out of the way, or would that be a mistake? Thanks, Lee

How was the old one attached? There's no way it would work without being physically attached to the rod in a fixed position.

If you bend the new one, how is it going to work/attach to the rod?

I just looked at my truck and the axle on the valve definitely has a slot into which the center of the coil spring fits into. Did your old one break off in the slot? Did you re-install the valve in the right orientation?

The bimetal spring is brittle. Try to bend it and it will break. Use a thin cutoff wheel in a Dremel tool to cut a slot in the flap valve shaft if there's not one there already. The spring should be wound enough to overcome the counterweight on the other end of the shaft and hold the valve into position to route exhaust gas up and around the intake passage diring warmup. Heating the spring with a propane torch should allow the weight to move the valve to the "open" position- - - -same as what happens when the exhaust manifold comes up to normal running temperature.
Jerry

The heat riser shaft is slotted for the straight part in the center of the spring (the left spring in your pic) on a 216 at least. Don't know about the 235. Maybe the center of the spring on the right in your picture just slips on the shaft and is held there by friction (doesn't seem like a very good idea to me however.)

I was able to bend my replacement spring without it breaking. It needed adjustment to bear against the stationary rod. But it had the proper bend in the center. It's not really a spring, but a bimetallic (two metals with different thermal expansion characteristics) strip wound up so that it coils tighter or looser when heated. The one I got was the Jeep one that Jerry pointed me to.

Check the shaft closely. There was part of the spring broken off in it that I had to dig out. I'm seeing that the one on the right is the older spring and may also have that tab broken off.

Ok, just went out and re-checked it (with a light this time) and there is a slot in the rod, but I looks like the slot is only on the top of the rod?? I guess the tab on the old one broke off when i was removing it.

Used a mirror and there is no slot on the end of the rod, and none that I could see on the opposite side of where I'm seeing a slot. Seems to me that slot would have to be all the way through and all the way out the end to slide it in there. But it does have a slot. Sort of. I sprayed some PB Blaster on it in case it's just crudded up, but I also used my box knife edge on the end of the rod to see if I could scrape anything out of the way to expose a slot, but no luck. I'll go back out and wire brush it a bit. I may have to end up cutting a slot, but at least now I know there was one there, and my old spring is probably not in it's original condition. I'll report back.

The broken piece of the spring is most likely in the slot on the shaft. Try a piece of metal the same thickness of the spring and tap it with ( gently ) a hammer to push the old piece out .

I had to work on mine for a bit to get the piece out. Not the easiest place to get to with the manifold installed. I tried a small hacksaw blade, but didn't want to mess up the slot, so resorted to a small punch and hammer.

Got it. Apparently all the tapping I did on the rod to get the heat riser valve loose mashed the gap closed. I used a small straight screwdriver and opened it up with that a bit. Then I could see the slot on both sides and the end. The broken piece of the old spring was in the slot, and it came out after I widened it a tad. Slipped the new spring in and closed up the gap with my pliers. The spring was 1/4 to 1/2 turn to connect it on the pin. Now for the acid test. As in, what did I mess up somewhere else while doing this job? I'll let you know how it goes, but the good news is, the flap is free and the bi-metallic coil is on.

We used to test automatic choke coils and heat risers with a blast from a CO2 fire extinguisher. That -90 degree F. boost made them react in a hurry, no matter what the outside temperature or under hood temp might be.
Jerry

Glad you got it installed.
The bad news is probably that you installed the coil backwards. It's just an 80% chance of that.

Well, I installed it the way the pic in the manual has it. I think I took a good look at it when I took the old one off. After all these months of fiddling with it, I'm hoping it just fires right up, doesn't leak and doesn't get hot. Hoping all will turn out good. I'm ready to drive this truck again!

Good luck with “doesn’t leak”. You known what they say,”it stops leaking when your out of oil”!