Heat Riser Valve Question

[Rob M.]

When moving the hear riser valve manually on a '66 327/300, how much movement should there be in a normally operating valve? Trying to determine if it's sticking or not opening fully. I hope the question makes sense.

Thanks in advance

[Joe L.]

Re: Heat Riser Valve Question

When moving the hear riser valve manually on a '66 327/300, how much movement should there be in a normally operating valve? Trying to determine if it's sticking or not opening fully. I hope the question makes sense.

Thanks in advance

Rob-----


It should move from stop-to-stop. My recollection is that this amounts to ABOUT 45 degrees of rotation.

[Duke W.]

Re: Heat Riser Valve Question

It's like a carburetor butterfly - about 90 degrees from full open to full closed. Fully closed I think the counterweight points to the right and "down" full open, but I'm not sure. I replaced that POS with a FI spacer.

Duke

[Jack H.]

Re: Heat Riser Valve Question

In my opinion, using an FI spacer tube is a waste of money...

You can achive the same results by pulling a failed original heat riser valve, cutting the straps attaching the butterfly valve to the center post with a cutoff wheel, removing the butterfly altogether and simply re-installing the now 'gutless' heat riser valve.

You've effectively made a spacer that looks from the outside identical to a working/functional heat riser valve and you spent nothing...

[Joe L.]

Re: Heat Riser Valve Question

In my opinion, using an FI spacer tube is a waste of money...

You can achive the same results by pulling a failed original heat riser valve, cutting the straps attaching the butterfly valve to the center post with a cutoff wheel, removing the butterfly altogether and simply re-installing the now 'gutless' heat riser valve.

You've effectively made a spacer that looks from the outside identical to a working/functional heat riser valve and you spent nothing...

Jack-----


Yes, but it still "rattles" that way. However, one can easily make a cheap spacer out of a heat riser valve. Just remove all the guts, including the shaft. Then, drill and tap the shaft holes on either side for 1/8" NPT internal hex pipe plugs.

[Rob M.]

Re: Heat Riser Valve Question

As I live in a warm climate (San Diego) that might just be the trick - thanks for the tip Jack and Joe.

As far as movement goes . . . I can move the lever down somewhere between 30 and 45 deg. It certainly doesn't go 90.

It seems as though every time I go to fix one thing I find three more to add to the list!

[Gerard F.]

Re: Heat Riser Valve Question

Rob,

On my 67 S/B, the heat riser valve does move 90 degrees, or slightly less, between stops.

On a cold engine, the weight in a full closed position is about 30 degrees above horizontal. As the engine warms up, the coil spring moves the weight to approximately a horizontal position, about a third open.

With an offset butterfly shaft, gas pressure on accelleration and cruise opens it up to the full position, with the weight in about a 60 degree position below horizontal.

If you are worried about it causing heating problems on a cruise, just wire it open with the weight in the down position. That's what I did for my Tahoe trip.

However, for the convention road trip, I just worked it back and forth a few times and sprayed it with Tri-Flow (like wd40 with teflon) to get rid of the sqweak. Worked out just fine for the 900 mile trip to San Jose, and I passed my Ops.

If you are going for judging, a judge can tell whether the heat riser is working properly. On a cold start, the overnight condensation first comes out the driver side exhaust, then shifts to the passenger side as the heat riser opens.

So, if you are going to go for future judging with your car, don't modify it, just clean it up, repair or replace it, or wire it open for cruising.

[Timothy B.]

Re: Heat Riser Valve Question

I think with a 300 HP car and cast manifold the heat riser valve is important. The more heat below the throttle plates to vaporize the fuel the better the combustion so this valve keeps the cast manifold hot.

On my 67, 300 HP the hot slots are also open under the carburetor. I have run the car with no perculation problems. The gasoline in the carburetor keeps the housing from getting hot and so far no problems with shut down.

I have said this before but I think the 1/2" of caked oil on the bottom of the intake manifold held heat and baked the cast. The car seems to cool faster but that may be me.

[Jack H.]

Re: Heat Riser Valve Question

Dead nuts on, Jerry! If you want no deductions OR you want to pass a PV test, the use of a 'gutted' heat riser valve won't 'get it'...

I only suggest this approach for those who want to drive/use their cars without having to worry about the heat riser sticking and want to avoid the $80 or so cost involved with buying the FI spacer...

[Roy B.]

Re: Heat Riser Valve Question

The anti-raddle item for a 1955 V8 Corvette only I have in my 55.

[Joe R.]

Re: Heat Riser Valve Question

Hi Rob:

A range of 30-45 degrees is too small. As Joe Lucia pointed out, the counterweight should move from stop to stop, which is about 90 degrees.

At one time I had a problem on my 67 SB where the blade of the valve would hit the flange of the exhaust pipe, preventing the valve from fully opening. I think the cause was a poorly aligned aftermarket pipe. I fixed it temporarily by grinding a bit off the edge of the valve blade to eliminate the interference.

If you are really getting only 30-45 degrees of rotation, you should find the cause and fix it. Chances are that the valve is not able to fully open, which will cause your intake manifold to continue to heat even after the engine is warmed up.

[Stuart F.]

Re: Heat Riser Valve Question

Still, you have to admit that if you are determined to run just a spacer, then the proper way to prepare it is to grind out the flats to make a full round opening. As purchased, they come as a partially machined heat riser valve with the same opening for exhaust, but no shaft holes. That's what I've done for mine, but I don't feel the need or the energy to replace it yet.

Stu Fox

[Rob M.]

Re: Heat Riser Valve Question

Thanks to everyone for the information. I have a new one on order to hopefully solve the problem. I do plan on having the car judged again, so this will be just one of the many things to fix or replace to improve the car's score. I also drive the car and love every minute of it!