Heat Riser Valve Rattle

[Larry T.]

Is the rattling of the heat riser at idle just the nature of the beast? I have not removed mine to inspect it, but I understand there is an anti rattle spring. Can it be replaced with a stronger or newer spring to eliminate the rattle? Finally, should I just wire the heat riser open? My engine (L-72) heats up pretty fast, I can not imagine the heat riser makes a huge difference.

Thanks.

[Bill C.]

Re: Heat Riser Valve Rattle

Larry,

I put a NOS riser on my car, and it has the light rattle too. It is part of the assembly and I guess the cars had the rattle even back in the 60's and 70's.

I can say though, if you wire it open - it will freeze that way after a while.
I did this years back and after a summer of being wired up, I decide to unwire for the winter. That is when I realized it had frozen in the open position. I never could figure out why, just replaced it as part of the restoration.

It would be better if you purchased the riser/spacer that was used on the L88 cars. It fits in place and then you will not do any poitential damage to your working HR.

[Larry T.]

Re: Heat Riser Valve Rattle

It would be better if you purchased the riser/spacer that was used on the L88 cars. It fits in place and then you will not do any poitential damage to your working HR.

Thanks Bill,

I had thought of the spacer, but figured wiring would be easy to do and undo, but if it is going to freeze up that is no good. Any idea on the part number for the spacer?

Larry

[Bill C.]

Re: Heat Riser Valve Rattle

not sure of the GM part number but a repro is available. I saw one in my Paragon catolgue, ran about 45-50 $$.

If you need the GM number, I would IM Joe - I bet he knows.

[Lawrence M.]

Re: Heat Riser Valve Rattle

Thanks Bill,

I had thought of the spacer, but figured wiring would be easy to do and undo, but if it is going to freeze up that is no good. Any idea on the part number for the spacer?

Larry

Intead of using a spacer or wiriing the heat riser open, you can cut the butterfly out. This way it will appear correct, but should not rattle and you do not have to worry about it sticking closed. I did it on my small block and have had no problems. However I do not drive in cold weather.

Larry

[Stuart F.]

Re: Heat Riser Valve Rattle

I have the fuelie spacer to put into my 63 L-76. It is just the machined casting without the shaft hole bored and, of course, no butterfly. It is for the 2-1/2" pipes, but even before I install it, I prepared it by grinding out the flat areas to make a completely round opening. It is a minor restriction, I suppose, but I figured as long as I was committed to go w/o a heatriser butterfly, I might as well make it work as best I can. Just taking out the butterfly will not give you a completely unrestricted opening. I have wired them open in the past for a year at a time w/o any problem having it function properly afterwards. Guess it just depends on the unit and perhaps the climate. here in Florida, I can do w/o year round.

Stu Fox

[Joe L.]

Re: Heat Riser Valve Rattle

Thanks Bill,

I had thought of the spacer, but figured wiring would be easy to do and undo, but if it is going to freeze up that is no good. Any idea on the part number for the spacer?

Larry

Larry------


The GM spacer is long-since GM-discontinued. However, Paragon offers a near-perfect reproduction.

Eliminating the heat riser will make your right side muffler just about "immortal". With a heat riser, regular replacements of the right side are usually necessary.

One caution: eliminating the heat riser will make operation of a divorced-style choke (such as used for your application) problematic. The choke may not open fully or take a long time to open. However, you really don't need the choke, either.

[John H.]

Re: Heat Riser Valve Rattle

My engine (L-72) heats up pretty fast, I can not imagine the heat riser makes a huge difference.

Thanks.

Larry -

The heat riser has no effect on engine (coolant) warm-up; that's a function of the thermostat.

The heat riser does two things for an engine started from cold - it heats the well where the remote choke coil is located (opening the choke fairly rapidly), and heats the floor of the intake manifold plenum chamber, improving fuel atomization for better cold driveability until the manifold heats up. If you remove the heat riser or gut it, you'll need to disconnect the choke linkage to the thermo coil and wire it open.

[Jim D.]

Re: Heat Riser Valve Rattle

Larry -

If you remove the heat riser or gut it, you'll need to disconnect the choke linkage to the thermo coil and wire it open.

Unless your choke thermo coil gets its heat from the exhaust manifold and then it won't make any difference. I've always gutted the heat riser and there has never been any change in the choke operation.

[Joe L.]

Re: Heat Riser Valve Rattle

Unless your choke thermo coil gets its heat from the exhaust manifold and then it won't make any difference. I've always gutted the heat riser and there has never been any change in the choke operation.

Jim------


If the application uses a heat tube from the exhaust manifold then the choke operation will not be affected by eliminating the heat riser. However, no Corvette after 1965 used such a system. For 1966-1973, divorced chokes were used. These rely on exhaust heat being supplied to the intake manifold's choke stove. The heat riser forces the right side exhaust manifold heat to exit via the intake manifold cross-over. If the heat riser is eliminated some exhaust gas will still enter the cross-over. However, I have found that it takes a lot longer for the choke to open since there is a lot less heat in the cross-over.

[Jim D.]

Re: Heat Riser Valve Rattle

Jim------


If the application uses a heat tube from the exhaust manifold then the choke operation will not be affected by eliminating the heat riser.

My point, exactly.

[John H.]

Re: Heat Riser Valve Rattle

Unless your choke thermo coil gets its heat from the exhaust manifold and then it won't make any difference. I've always gutted the heat riser and there has never been any change in the choke operation.

Jim -

True for a pre-'66 car, but Terry's car is a '66, and uses a manifold-mounted external remote choke thermo.