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peck1937 09-11-2007 11:58 AM

Manifold problems- 1998 land yacht- 454 eng.
We have a 1998 Land Yacht motorhome with a 454 vortex engine which has continuous manifold and bolt problems, we continously crack manifolds and shear bolts. anyone have any info on this problem. Thanks.

CanoeStream 09-11-2007 01:00 PM

Howdy peck1937 -- Welcome to the Forums! I heard about this problem on The Vintage Airstream Podcast - Home, episode 51. It was said to be a common and repetitive problem. I think the solution offered was an aftermarket stainless steel manifold. I hope somebody sees your question and replies.

swebster 09-11-2007 01:21 PM

Welcome to the site. Manifolds on the gas 454 engines in a motorhome application can fail for a number of reasons, but it's mainly due to heat. Breaking bolts off however seems to be something larger.

A few questions just to get the baseline on your issue:

1. Is this on a P30/454 Gas Chassis?
2. Have you recently had any work done on the manifolds and what
3. What are you engine temps when operating?

Many of us have replaced the stock manifolds with headers to help remove the exhaust (and heat) from the engine bay and doghouse as quickly as possible. This has the added benefit of increase performance through better engine "breathing".

peck1937 09-11-2007 04:08 PM

Hi thanks for the quick response.
the answers to your questions is as follows.
1. P30 --454 gas chassis
2 No work has been preformed on it.
3. Temp runs between 160 - 170

GlenCoombe 09-13-2007 09:04 AM

Peck, headers would be the first place to go. They come with new bolts. I would not use the gaskets supplied with most. I've come to rely on doubling up on a pair of copper crush type gaskets for each side.

The small investment will pay you back with increased full mileage and power.

klattu 09-13-2007 12:39 PM

Crack Addiction
Had simular problem...
Exhaust cross over was flowing all, or most of the exhaust thru one side.
It would overheat that manifold causing a crack.
Streached so far, bolt holes would not line back up.
Never broke a bolt though.
Check for any restrictions on one side, or a stuck exhaust cross over valve, it is attached at end of manifold.

Avoid gaskets if possible, they only add to problems.
Make sure each surface is clean and flat.
Factory does not use gaskets there anymore.

Find out the heat problem, then you have many options.
GM even makes a few flex manifolds, and S/S mini headers.
The big advantage to the GM headers are they bolt on to each port individualy<sp...are not tied together until far away from head and down to collector. so they , like all headers, have room to flex.

scottanlily 09-17-2007 12:32 AM

Hello there ,Id recommend to go with the Doug thorely headers .they are the best on the market .heavy flanges and solid beefy construction .Don't go cheap on headers ,get the best and you will not regret it .One thing to think about regarding manifold problems ,make sure your coach is not running lean .The fuel filter is mounted on the frame rail underneath and should be serviced regularly .lean conditions and high manifold temps are a primary cause of cracking .Late vortec big block chevrolets did
indeed have the manifold bolts break ,specifically the heads of the fastener
or bolt pop off do to expansion of the manifold .you can have a shop check your fuel trim and o2 sensor readings with a scan tool to determine if your engine is running lean .Further ,you will want to purchase these little spark plug booties made of fiberglass ,extremely heat resistant and save your plug boots and the plugwire conductor core which gets burnt to a crisp inside the boot ,
and causes a misfire under load ,such as climbing a grade .you can get them at Kragen or summit racing or your local carquest auto parts .A must with headers or stock manifolds.

Scott of scottanlily

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