Re: IML: 69 heat riser revisited

I can put my own questions to rest finally on MY heat riser. Thank you Fred, Paul, Dave and others who have offered what they knew.

I went out to my '67 Imperial motor today. I believe mine is missing the spring mechanism, the anti-rattle spring, and who knows what else. Anyway, I have dual exhausts on my car, fired her up, and moved the heat riser in both directions & then checked at the passenger side tailpipe.

Definitely a noticeable difference - (looking at the manifold from the passenger's fender) with the heat riser turned clockwise / forward - a noticeable increase in sound and exhaust. Turned counterclockwise / towards the rear - a definite reduction in sound & exhaust.

To throw one last bit of info in there - I checked a Mopar exhaust manifold in my Mom's basement and the heat riser was mounted in front of the head pipe - not alongside it as is on my '67 440. Not sure if that has any significance, or if that was even a big block manifold - it was an arched "magnum" type manifold, though..

Anyway, my problem / question is solved, and it agrees with Dave's input. Perhaps Fred & Paul's '69s are different? Or who knows what manifold is actually on my '67?

Thanks again for everyone's input on this repeated question.

Dan Richardson

300L Family Heirloom

----- Original Message -----

From: Frederick Joslin

To: mailing-list@xxxxxxxxxxxxxxxx

Sent: Sunday, August 26, 2007 3:56 PM

Subject: IML: 69 heat riser revisited
There have been some questions about the heat riser valves.

On my 69 Lebaron I had locked the heat riser valve open because of a rattle.

I just did an experiment to check the function of this valve. Upon removing the hose clamp that I have to hold the valve open, the valve rotated clockwise about 100 degrees to rest against the stop.

I started the car and the valve began to bounce to about 10-15 degrees back from the stop in a counter clockwise direction. I could hear it rattling. As the engine warmed the RPM increased to probably about 1500 RPM, but the position of the valve did not really change. It was within a few degrees of being closed. As the engine warmed more and I kicked off the fast idle, the valve bounced less, but was still almost closed. I had my son get in the car and hit the gas. He had to give it quite a bit of gas (> 2000 RPM) and then the valve would open very quickly about 45 degrees. It would slam shut as soon as the engine slowed, again to within a few degrees of being closed. The slamming shut was accompanied by the rattle.

From this I conclude:

1) Rotation of the valve counter clockwise opens the valve. Clockwise rotation closes it.

2) The valve has just over 90 degrees of rotation.

3) The valve is very close to being closed at anything below about 1500 rpm or higher irrespective of engine temperature.

4) On my car the valve is open when the counter weight is at the top pointing forward and closed when the counter weight is to the front of the car pointing down or a little bit back.
Fred Joslin