Warped Exhaust Manifold

[Mark Norton]

Hello all,
Helicoiled the usual stripped exhaust No 1 manifold stud and had the manifold skimmed which was very warped last March. All was O.K. untill recently the tell tail "whistle" of the exhaust manifold blowing returned.

I have taken the manifold off and it is again well and truly warped by 1/2 mm when laid on a flat surface. I will go for a second hand manifold this time as the engineers told me they had to skim off quite a lot last time.


Any tips on why it would go so soon would be most appreciated.

[Simon Jones]

If you're looking for a second hand manifold, try Kevin at Southern Bongos on 02389 733995 or 07860 612360 as he has several vans in for breaking at the moment. Mention Simon recommended him

[dandywarhol]

I took an old manifold gasket, drilled out the rivet and separated the layers. I then made up the gap by fitting gasket "shims" - worked for all the time I'd the bongo for and still fine 2 years later after i sold it to a neighbour.

I think you'll find any used manifold will be warped

[The Great Pretender]

Just a thought, try running a straight edge across the port outlets on the head.

[Northern Bongolow]

did you have the plastic undertray fitted during this time ??
did you have the tin heatshield fitted on the manifold ??
what engine oil are you using ??
how old is your stat and coolant, and which coolant do you use ??
and lastly do you drive at high speed and temps then turn it off quickly without letting it tick over and allowing the turbo to cool down, or the reverse, do you warm the engine before blasting off in a morning.

ive had one go myself, and repaired a few and am looking for a common thread.

i think myself that its something to do with cast iron and its properties when heated or overheated. when you weld it it has to be welded at lower temps or it makes it very brittle.
all those with coal/multifuel stoves will know that if you turn your stove into a forge with too much air it will distort the firegrate, and once it overheats/distorts it tends to go again at a lower temp next time until it fractures, but someone with more idea may know more .

[Mark Norton]

Many thanks for the replies,

Yes I have the plastic undertray, heat shield, fully synthetic oil, coolant changed in October.

It has been on 2 long trips fully loaded with the engine under load for long periods. The first time it was blowing badly was after a continuios 12+ hours of fast motorway driving accross Germany. After repair all was well untill struggling up some big long steep hills in Snowdonia, resulted in a slight blow which despite very carefull driving scince slowly got worse over the following 5 months.

Perhaps as suggested once the manifold warps it has lost it's internal strength making it more prone to going again, hence shimming with the old gasket would be more succesful than having the manifild skimmed? At least this time the studs are all O.K. I will check the block with a straight edge.

[Northern Bongolow]

thanks for the feedback, nothing odd there really. what grade of oil do you use please, and has it got a standard steel exhaust, or stainless, or modified.
my mrs's bongo did it,she has standard exhaust, and 5w 30 semi oil. the motor has quite low mileage too

[Mark Norton]

Standard genuine Mazda Exhaust fitted last year , I use Renault Approved Shell Fully Synthetic Diesel Engine Oil 5w/30. Quite High Milage on the Engine 242000 km. K&N Air Filter. Allan's blanking plates fitted to EGR.

I have another second hand manifold on it's way with the EGR pipe. I intend to cut and blank this where it comes out of the manifold as well as removing the big EGR valve and other pipe to the intake. Can't see the point in leaving the EGR system on the engine if it is never going to be reconnected and removing it will make things more accessable.

[lazyb5]

Not sure if this helps or not but... I work in an engineering plant. When we are machining large castings ie 1-3 tonnes we heat treat to remove any built up stresses before machining. I am told this prevents movement when the casting is in use. Maybe the skimming of the exhaust needs to be done after a heat treatment. If I remember we take our castings upto about 700 oC for a few hours.

[rapiddescent]

how far does the plastic cover go? mine seems to only cover the front part.

which made for a hooligan moment when listening for a problematic no1 with the passenger seat up (side window down) driving along a farm road at night in the dark and then went through a puddle which instantly steamed up the windows. don't ever ever do that. can't believe I was so stupid.

[wonkanoby]

its in 2 parts

front bits not that wide

rear is a huge lump goes to past rear of engine as i recall

[mikeonb4c]

thought I'd read that blanking the egr might result in higher exhaust temperatures. Any relevance?

[Simon Jones]

If the engine undertray is in two pieces then it's broken. Should be one piece like this one: http://www.ebay.co.uk/itm/Mazda-Bongo-F ... 43acbc6539

[dave_aber]

Shown as 2 bits on Lushprojects, Here

56-111A & 56-112G

[Simon Jones]

. In all my years of scrabbling around under Bongos, I've never seen one with a 2 part undertray. I feel I have missed out an all the extra covery goodness

Now you mention it, the one on ebay shows the extra section placed in the main tray. I want one now!