Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

[Larry E.]

Working on my 66 L72 for next judging meet. My exhaust heat riser sticks closed at
times and play havoc with my exhaust system. Need a way to deactivate this item WITHOUT
taking everything apart and inserting a spacer or working on the flapper from the inside. Trying to make everything "Look" original
as possible. Upon researching this problem I have found two ways>

1) Wiring the flapper open

2) Cutting the spring from the flapper and letting the
weight of arm make the flapper stay open
P.S. Is there a way of "reworking" this spring as to have flapper stay open all the time??

Does anybody have any other ideas? If not which is better on the above? Or use both?

Thanks in advance>Larry P.S. Car is a Trailer Queen and stored for the Winter;not used in cold weather

[Brian M.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

I removed the flapper disk on the 67, it judged with NO issues. I have it wired open on the 66.

[Stephen L.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Wire it open. If you are worried about judging then remove the wire just prior to judging. As a trailer queen it would take a long time to rust in the wired position. I wouldn't cut the spring, as that would not be "reversible"........

[Duke W.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

When cold you should be able to easily close the valve manually. Try closing, opening it multiple times when cold, and verify that the valve is free prior to every cold start.

I recall GM sold some kind of "heat riser lubricant anti-seize" spray back in the day, but I don't know if they sell it anymore, and don't know of a commercial equivalent that you can buy at a parts store.

Duke

[Michael J.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

I wire mine open, and remove the wire for judging. Very simple, you can't really see it from the top.

[Duke W.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

I removed the flapper disk on the 67, it judged with NO issues. I have it wired open on the 66.

I can't recall if this is required in ops check, but I always checked the relative right/left exhaust flow immediately after the cold start. There should be noticeably less flow from the right exhaust pipe than the left.

Duke

[Michael J.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

I can't recall if this is required in ops check, but I always checked the relative right/left exhaust flow immediately after the cold start. There should be noticeably less flow from the right exhaust pipe than the left.

Duke

IIRC, this is not checked for Ops, but is an important part of PV. It is checked at cold start and then checked again after the drive.

[Larry E.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Duke>It will open manually but on occasion it gets stuck in the closed positions. Maybe the flaps are hitting something
on the inside wall of the unit. At any rate I will wire it open unless anybody has any better idea's. Has anybody tried
"reworking" the spring to suit our problem?? Larry

[Michael J.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

I have replaced 2 in each of my '65 and '67, and none of the new ones worked. I have heard you can replace the springs, but seeing as how the repo units are so bad, who knows if the spring would be good? Too much work compared to just wiring it open.

[Mike T.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Larry - Back when I first got my NOM 66 L72 Roadster, early on I checked the heat riser (stock exhaust manifolds) and when cold the weight was 'up' and of course the flapper was closed. Pushed down to overcome the spring and then let go and it came back up to the closed position...again, while cold. Figured we were 'good to go'. After a few shakedown miles, I noticed the carb would leak out some fuel after shutdown into the venturies. The temp, both by the dash gauge and IR gun, showed the engine to only be up around 185 or so, maybe 190 tops.
While trying to figure this out, I happened to see the heat riser weight was still 'up', even after the engine had achieved operating temps.
At that time, I pushed down in the weight but the spring brought it back up to the closed position. The movement was smooth, no binding or interference felt so I just assumed the spring had lost it's ability to relax and let the weight drop, opening the damper. This closed position was causing the exhaust gases to back up through head and across the intake manifold, heating it up and creating the fuel dribbling.
I wired it in the down/open position and it's been fine because I don't intend on taking it in for judging.

[Brian M.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Wouldn't that fall into the PV Category? Even then really?

[John F.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Take it off and soak it in EvapO rust for a couple of days. It worked wonders for me.

[Duke W.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Duke>It will open manually but on occasion it gets stuck in the closed positions. Maybe the flaps are hitting something
on the inside wall of the unit. At any rate I will wire it open unless anybody has any better idea's. Has anybody tried
"reworking" the spring to suit our problem?? Larry

The purpose of the heat riser is to quickly heat up the carburetor to enable quick fuel vaporization after a cold start in cold weather. Since most of us only drive our vintage Corvettes in mild to hot weather the heat riser is not that necessary, and even if wired open should allow decent "drive off" behavior after a cold start.

The heat riser also shortens RH muffler life since the low flow during warmup allows considerable water vapor condensation that will cause rapid corrosion and short trips are especially lethal to RH mufflers.

If you're not going through judging the most expedient thing is to use some stainless steel safety wire between the weight and an exhaust manifold stud to keep it full open all the time. Some remove the valve while retaining the shaft and spring or install a FI spacer, which is just a partially machined casting with no shaft, valve, and spring, but IMO it's not worth the effort to remove the exhaust pipe to do the above. Just wire it open.

Duke

[Larry E.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Here again> Got my answers from all of you that responded. Will wire it and go on to
the next project. THANK YOU ALL FOR RESPONDING>LARRY

[Patrick H.]

Re: Best/Easiest Way To Deacitivate C2(66) exhaust heat risers

Maybe the flaps are hitting something on the inside wall of the unit.

This happened to me recently. I had to grind down the exhaust insert until the valve opened routinely.