70 L46 Passenger side Exhaust Install (Heat Riser)

[Bill L.]

I looked through the AIM and did not see the exploded view for the passenger side heat riser and exhaust install. I was was looking at some of the diagrams on line from the vendors and some show a sleeve on the passenger side that fits down in the exhaust pipe that fastens against the donut.

My understanding starting from the exhaust manifold is as follows:

Exhaust Manifold
Gasket
Heat Riser
Donut (Sintered Iron)
Exhaust Pipe and flange.

Is there a sleeve anywhere on the passenger side?

Thanks,
Bill

[Joe L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

I looked through the AIM and did not see the exploded view for the passenger side heat riser and exhaust install. I was was looking at some of the diagrams on line from the vendors and some show a sleeve on the passenger side that fits down in the exhaust pipe that fastens against the donut.

My understanding starting from the exhaust manifold is as follows:

Exhaust Manifold
Gasket
Heat Riser
Donut (Sintered Iron)
Exhaust Pipe and flange.

Is there a sleeve anywhere on the passenger side?

Thanks,
Bill

Bill------


Yes, there is. It's called an EXTENSION rather than a sleeve. It fits into the exhaust pipe just as it does on the driver side. 1970 with L-46 which used 2" exhaust originally used extension GM #3890382. It's GM-discontinued but you can usually find a good replacement in a good auto parts store or from reproduction sources.

Note, however, that some replacement forward exhaust pipes have this extension "built-in" as part of the pipe assembly. In that case, no separate extension is required. No ORIGINAL 1970 exhaust pipes had the "built-in" extension, though.

[Bill L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Bill------


Yes, there is. It's called an EXTENSION rather than a sleeve. It fits into the exhaust pipe just as it does on the driver side. 1970 with L-46 which used 2" exhaust originally used extension GM #3890382. It's GM-discontinued but you can usually find a good replacement in a good auto parts store or from reproduction sources.

Note, however, that some replacement forward exhaust pipes have this extension "built-in" as part of the pipe assembly. In that case, no separate extension is required. No ORIGINAL 1970 exhaust pipes had the "built-in" extension, though.

Thank you Joe.

Did the factory install a gasket between the heat riser and exhaust manifold. Looks like at least some GM products just mated machined surfaces as mating surfaces for the heat riser.

If they used a gasket, did the factory use any kind of sealant?

Bill

[Joe L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Thank you Joe.

Did the factory install a gasket between the heat riser and exhaust manifold. Looks like at least some GM products just mated machined surfaces as mating surfaces for the heat riser.

If they used a gasket, did the factory use any kind of sealant?

Bill

Bill------


Yes, a gasket was used between the manifold and heat riser but no sealant was used in conjunction with this gasket. The gasket was originally GM #3732426 or, more likely, GM #3946828. The former was discontinued from SERVICE in May, 1969. The latter was discontinued in April, 1990 and replaced by GM #10159453 which was then discontinued in July, 1994 and replaced by GM #12522753. The latter remains available to this very day.

[Bill L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Bill------


Yes, a gasket was used between the manifold and heat riser but no sealant was used in conjunction with this gasket. The gasket was originally GM #3732426 or, more likely, GM #3946828. The former was discontinued from SERVICE in May, 1969. The latter was discontinued in April, 1990 and replaced by GM #10159453 which was then discontinued in July, 1994 and replaced by GM #12522753. The latter remains available to this very day.

Thank you Joe.

[Terry M.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Thank you Joe.

Did the factory install a gasket between the heat riser and exhaust manifold. Looks like at least some GM products just mated machined surfaces as mating surfaces for the heat riser.

If they used a gasket, did the factory use any kind of sealant?

Bill

Bill,
Take a look at the AIM pages. As Joe said, no sealant at the heat riser, but they did use a sealant at the pipe junction at the cross member clamp.

[Bill L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Bill,
Take a look at the AIM pages. As Joe said, no sealant at the heat riser, but they did use a sealant at the pipe junction at the cross member clamp.

Thanks Terry.

I had looked in the AIM and did note the sealant for the junction at the hanger by the trans. I did not find an exploded view showing the assembly details for the passenger side exhaust with heat riser. The page I found only shows the driver's side without the heat riser.

I found some old threads and combined with Joe's response I think I am good to go. I did discover that the ignition shield has to be installed just so to clear the heat riser weight. I also noticed that the replacement part number for the heat riser Joe mentioned in another post is stamped on the weight. The heat riser is also labeled "UP".

Bill

[Terry M.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Thanks Terry.

I had looked in the AIM and did note the sealant for the junction at the hanger by the trans. I did not find an exploded view showing the assembly details for the passenger side exhaust with heat riser. The page I found only shows the driver's side without the heat riser.

I found some old threads and combined with Joe's response I think I am good to go. I did discover that the ignition shield has to be installed just so to clear the heat riser weight. I also noticed that the replacement part number for the heat riser Joe mentioned in another post is stamped on the weight. The heat riser is also labeled "UP".

Bill

It is also important to install the heat riser with the weight properly oriented. I don't remember what that orientation is, however.

[Bill L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Hi Bill,
I've also wondered about the detail (or lack of) for the heat valve assembly.
My sense is that when the same parts are used on both the right and left sides of the car often only one side is shown or detailed.
In this case I think the drawing and "heat valve asm" note indicates that the parts used here (right side) are the same as the parts on the side detailed (the left side) EXCEPT for the addition of the heat valve…. thus, the flange, extension, and packing.
Since I've drawn for a living for so many years it's interesting for me to try to understand WHY the 'drawings', notes, and revisions, LOOK the way they do, and contain the information they do.,
Regards,
Alan

I, along with some other M-D members, spent a few hours this morning with a 70, bb, 4-speed, a/c, coupe.
It's a car that's been Flight Judged numerous time by different owners beginning in 1988, (I think). The new owner is going to have it Flight Judged to and hopes to go further with it.
A terrific car to have a leisurely look at.

HI Alan,

During one of your visits you mentioned that I should check the orientation on my heat riser. I think it was incorrect because at the time it was the only way the weight would clear the shielding and that position allowed easier access to the starter brace and shield. I spent the better part of an hour trying to get the shield properly oriented to allow full clear travel of the heat riser weight today. As a side note I discovered, while I was in the area, that my starter shield was not correct for a 70. The shield has been corrected with the kind assistance of another NCRS member. Killed two birds with one stone.

I always assumed that when the other side was not shown it mirrored the side shown as well. In this case there is a gasket with the heat riser that is not shown at all. Upon a little investigation, some chevrolet models just mated machined surfaces for the heat riser to manifold. In that case both sides would be the same except for the heat riser.

A 70 BB with A/C is certainly worth a casual glance

Kind Regards,

Bill

[Joe L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

HI Alan,

During one of your visits you mentioned that I should check the orientation on my heat riser. I think it was incorrect because at the time it was the only way the weight would clear the shielding and that position allowed easier access to the starter brace and shield. I spent the better part of an hour trying to get the shield properly oriented to allow full clear travel of the heat riser weight today. As a side note I discovered, while I was in the area, that my starter shield was not correct for a 70. The shield has been corrected with the kind assistance of another NCRS member. Killed two birds with one stone.

I always assumed that when the other side was not shown it mirrored the side shown as well. In this case there is a gasket with the heat riser that is not shown at all. Upon a little investigation, some chevrolet models just mated machined surfaces for the heat riser to manifold. In that case both sides would be the same except for the heat riser.

A 70 BB with A/C is certainly worth a casual glance

Kind Regards,

Bill

Bill------


The heat riser valve installation is shown in the AIM. It's in section 6. This section, of course, shows the configuration for the standard engine. However, with respect to the heat riser installation, the standard engine and L-46 are identical as to BOTH configuration and components.

[Bill L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Bill------


The heat riser valve installation is shown in the AIM. It's in section 6. This section, of course, shows the configuration for the standard engine. However, with respect to the heat riser installation, the standard engine and L-46 are identical as to BOTH configuration and components.

I will double check. Thank you Joe.

Bill

[Patrick H.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Probably too late to be useful, but a couple of notes from my experience. First, buy a couple of different brands of the triangular exhaust gaskets to try. One brand WILL fit a lot better than another. Second, it really helps if the mating surfaces of the manifold and heat riser are completely flat. A good machine shop can do that for you if needed. Exhaust leaks are a lot easier to prevent than fix.

[Bill L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Probably too late to be useful, but a couple of notes from my experience. First, buy a couple of different brands of the triangular exhaust gaskets to try. One brand WILL fit a lot better than another. Second, it really helps if the mating surfaces of the manifold and heat riser are completely flat. A good machine shop can do that for you if needed. Exhaust leaks are a lot easier to prevent than fix.

Thank you Patrick.

I would do exactly as you suggest if the exhaust manifold was not already bolted in place with all the shielding. The surfaces look very good. The gasket is from a VERY reputable corvette restorer who has gone through the exercise to find what works.

I had the exhaust bolted up and ran it for a bit before taking it apart to do some much needed work. There was a leak on the passenger side and when I took it apart there was no sleeve to keep the donut in alignment. You could see the black where the donut was leaking on the inboard side.

Bill

[Joe L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Thank you Patrick.

I would do exactly as you suggest if the exhaust manifold was not already bolted in place with all the shielding. The surfaces look very good. The gasket is from a VERY reputable corvette restorer who has gone through the exercise to find what works.

I had the exhaust bolted up and ran it for a bit before taking it apart to do some much needed work. There was a leak on the passenger side and when I took it apart there was no sleeve to keep the donut in alignment. You could see the black where the donut was leaking on the inboard side.

Bill

Bill------


The extensions are a MUST.

[Bill L.]

Re: 70 L46 Passenger side Exhaust Install (Heat Riser)

Bill------


The extensions are a MUST.

I have both sleeves now and they are a much higher quality than is provided by an otherwise excellent vendor.

They are a pretty snug fit and I had to tap them in place. Does that sound correct? How much of the sleeve should stick out above the donut?

Thanks,

Bill