...Still fighting with my manifold leak. Stethascope tells me its rear bottom of right bank manifold, plus a little at the donut.....

Vowing never to have to drill-out a broken stud again, I'm sending it to the local Workhorse shop to R&R, including having it milled.....

...I could have sworn I read somewhere where a Chevy/GM document alluded to grinding out some of the web stock to reduce future warping. One Workhorse mechanic says it's urban legend, the other says he's heard of it, but can't locate official GM paperwork.....Any help?

Also, posts all over the web discuss the need or non-need of an exhaust gasket - some suggest that a properly milled & flat manifold with high-temp RTV is sufficient, and that gasketing actually interferes with proper heat transfer.
(Maybe it's year/model sensitive - this is '78 carb'd.) Your thoughts?.........

I've routed a ram air duct from the grille to the right side...hopefully, this will help in the future......

I haven't dealt with 454's that much, but I do have an opinion (keep in mind it's worth what the price is: nothing) on manifolds and gaskets in general.

First, the idea of a "gasketless" interface helping heat transfer is bogus - the high-temp RTV would insulate anyway, not to mention heat transfer of cast iron is crummy, and manifolds don't have a task of dissipating heat - just carrying it away in the exhaust gas.

Secondly, a perfectly flat machined pair of surfaces are unlikely to remain that way for long considering the number of bolts and the locations. That technique might work for certain headers, but cast iron is very rigid. That's without considering what it would take to machine the block and manifolds...

Thirdly, if the nuts were tightened enough to prevent leaks at operating temp, the studs would be stressed and eventually elongated, and you'd again have a leak when cold or at operating temps...or both.

My vote is to do the usual straightedge check on the block and the manifolds (even new ones), install new studs where needed, and see what the concensus recommendation is for an aftermarket gasket , as it appears the OEM one's don't last.

A final note - make sure the tech uses a torque wrench and the recommended sequence when tightening the nuts...

"but can't locate official GM paperwork"

Hey!: this is GM; if it's official the paperwork is locatable - many places. It is an urban legend.

"as it appears the OEM one's don't last."

I do (did) have some experience with small-and-big block Chevys. The motorhomes actually have LESS heat problems than some early autos, esp Corvettes. This is a '78, for goodness sake - 28 years old.
Otherwise, R is right on everything.
My suggestion: use the OEM gaskets on the (resurfaced) factory manifolds; improve airflow as is practical; KEEP THE OIL LEVEL ALL THE WAY UP (low oil is a prime heat-generator); keep the exterior block walls clean. A look at these manifolds will show they are free-flowing: almost a straight line back to the exhaust flange. Also: ensure your exhaust is un-blocked and free-flowing. Good Luck.

I only worked on a handful of 454s (2 I remember in 'vettes - how did they get that thing in there, anyway?) - but not exhaust manifolds.

Anyway, one technique to avoid heat stress is that when the engine's been working hard (like on an Interstate) and you come off to refuel, let 'er idle for a couple of minutes to cool down before shutting down. I do this routinely in my Barth, not just for that, but to allow the turbo to cool so's I don't cook the oil in its galleries...

Chevy motor homes come without a gasket. Chevy recommends a graphite paste on the faying surfaces. The graphite hardens to a slate-like film allowing the manifold to expand and contract while still conducting heat. The manifold expands as much as 1/8 inch. They also recommend drilling the bolt holes 1/32 oversize to allow for expansion without breaking the end studs. My observation is that it is usually the right rear stud that breaks. Torque is center bolts to 20 ft lbs and a little less farther out.

Chevrolet says milling a used manifold is better than buying a new one, as the old one is seasoned and will be less likely to warp again if a gasket is not used to impair heat transfer.

My own experience with a number of 396s, 427s 454s and two 502s indicates Chevrolet's advice is good. I also spot face the bolt holes and use hardened Unbrako washers under the bolt heads to allow expansion.

I also cut slots, but can't remember if I saw it in a Chevy manual or not. I first learned it from John Geraghty in the sixties on a 396 or 427, I think. He walks on water. It has worked for me and many others, though.

All that makes sense - especially drilling the end bolt holes oversize...one wonders, where can the graphite paste be bought?

BTW, I also remember the cut-slots recommendation, but I can't recall where I saw otheard it either...but it was supposed to relieve stresses.

On my 1973 I installed a set of Thornley headers and just used the "well I'm sure it was not a fancy copper one" standard gasket. I picked up a set of stainless bolts from summit (it's that whole "sparklie" thing) and things bolted up nicely.

The heads were BAD and I did nothing except scrape them and hit the worst of the rust pockets with some emery cloth. The "stock" gaskets and the red sealer appear to work great with the Thornley headers.

So based on my approach I suggest installing Thornley headers.

Timothy


Oh yea having said all this I still have an exaust leak somwhere in the heads, intake manfold area. I plan to pull the intake manifold next and see what is what. Now I am told there is exaust that runs through the intake maniford, this makes little sense to me but it is rusty and ugly so I'm going to pull it and do a little learning.

Any thoughts are appreciated.

I'm with you on the Thorleys, Timothy....Billh's past postings over the years has got me convinced that's the way to go....
But that'll be an off-season lay-up project, along with the whole exhaust system,

For right now, I'd like to get through the next 4-5 months and 3-4k miles in a cost-effective way.

No studs are broke or loose...looks to me like the gasket blew out at the bottom rear...maybe from warping...maybe not.....

At 24', my 454 seems to loaf...never have seen an inkling of high temps on a hard pull, always perform a cool-down idle, fan cuts in when it should, etc. This will be the second R&R in 28 years & 75k miles...maybe that's acceptable.

Lee:

You do have a point, things have lasted quite a while on your coach.

For what it is worth my stock manifolds leaked in the same place as yours. Heck as I recall they had rusted (burned maybe) to the point they would not seal.

The red RTV stuff looks to be holding, about 1000 miles on the headers so it may be a way to go.

The headers were less work to get on than remounting the stock set up. I put it back to get some measurements and that consumed more time that putting the headers on.

I think we have about the same Barth, they call mine a 25 footer and like you the 454 does not work very hard.

Good luck:

Timothy

John Geraghty does not merely walk on water. He freezes it with a look, & drives on it.

quote:

Originally posted by Rusty:
...one wonders, where can the graphite paste be bought?

Chevy says it is "key graphite base" and can be obtained from "any plumbing shop". I got some flange lube from out boiler mechanic at work. He said it was what I wanted. On our turbine engines, we used Molykote G paste on the faying surfaces. They got plenty hot and it did the job.

That was a while back. I now use Thorleys.

quote:

Originally posted by timnlana:
I still have an exaust leak somwhere in the heads, intake manfold area. I plan to pull the intake manifold next and see what is what. Now I am told there is exaust that runs through the intake maniford, this makes little sense to me but it is rusty and ugly so I'm going to pull it and do a little learning.

Any thoughts are appreciated.

Yeah, there is an exhaust passage across the intake manifold from one side to the other. It aids in warm-up and helps you pass smog. Is your heat riser valve free? If it is not, the intake manifold is hot all the time, which is not good. Since you are going to remove the intake, how about putting on an Edelbrock Performer? They work well in concert with the Thorleys.

quote:

Originally posted by timnlana:
Now I am told there is exaust that runs through the intake maniford, this makes little sense to me...

Any thoughts are appreciated.

Look at your EGR valve. Look at the intake manifold gaskets. If you don't have an EGR valve look at the blockoff plate.

EGR Valve: Exhaust Gas Recirculation Valve

Exhaust gas recirculation is an Nitrogen Oxide and Nitrogen Dioxide (NOx) reduction technique used in most gasoline engines.

EGR works by recirculating a portion of the engine's exhaust gas back into the engine cylinders. Mixing the incoming air with recirculated exhaust gas dilutes the mix with inert gas, lowering the peak combustion temperatures. Because NOx formation progresses much faster at high temperatures, the EGR valve serves to limit this generation of NOx. NOx is formed due to the presence of oxygen and high intake air temperatures.

In a typical engine, 5% - 15% of the exhaust gas is routed back to the intake. The maximum quantity is limited by the requirement of the mixture to sustain a contiguous flame front during the combustion event; excessive EGR in an engine can cause misfires and partial burns. Although the EGR valve does measurably slow combustion, this can largely by compensated for by advancing spark timing.

Contrary to popular belief, an EGR system actually increases engine efficiency.

The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses.

Lowered peak combustion temperatures not only reduces NOx formation, it also reduces the loss of thermal energy to combustion chamber surfaces, leaving more available for conversion to mechanical work during the expansion stroke.

The lower peak temperatures result in more of the released energy remaining as sensible energy near TDC, rather than being bound up (early in the expansion stroke) in the combustion products.

EGR is typically not employed at high loads because it would reduce peak power output, and it is not employed at idle, low-speed, or zero load because it would cause unstable combustion, resulting in rough idle. (EGR Valve stuck/rusted open)

EGR is achieved by piping a route from the exhaust port of the head to the inlet manifold. On Chevy motors this is done via an exhaust port built into the intake manifold. An EGR Valve in the intake regulates and times the gas (exhaust) flow. Early Chevy EGR systems used manifold vacuum as the input to an on/off EGR valve after it ran thru a coolant temperature controlled valve usually mounted in the thermostat housing.

Does a 73 have EGR?

quote:

Originally posted by bill h:
Does a 73 have EGR?

Looking at the Edelbrock site it shows EGR from 72 to 89 for there intake.

www.edelbrock.com But without looking I'm only guessing here. Maybe, maybe not.

Bill N.Y.