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Stainless Exhaust Discolouring Time Rover V8
Irony - 24/7/14 at 07:47 AM

Started my engine for the first time recently and the exhausts get bloody hot! I ran it last night for maybe 10 minutes max and I can already start to see my nice new shiny stainless exhausts beginning to discolour! In fact I have been having ignition issues and two cylinders where not working properly and they haven't discoloured as much.

Is this normal??

BaileyPerformance - 24/7/14 at 07:56 AM

Did you sort out why it was idling rough? (Re your previous topics)

It is normal to get hot headers that will discolour, the temperature of the headers are directly effected by the ignition timing - retarded timing will increase temperature.

Also, incorrect valve clearances or lifter pre-load will cause hot headers as well as rough running.

Irony - 24/7/14 at 08:04 AM

quote:
Originally posted by BaileyPerformance
Did you sort out why it was idling rough? (Re your previous topics)

It is normal to get hot headers that will discolour, the temperature of the headers are directly effected by the ignition timing - retarded timing will increase temperature.

Also, incorrect valve clearances or lifter pre-load will cause hot headers as well as rough running.


I seem to have cured a lot of the problems thanks to yours and others advice. I think I had the timing out by 10 degrees and the normal ignition cable wrongly placed issue. I fabricated a new better VR sensor bracket and redid the timing at the toothed gear. I changed the ignition cables about and it runs a lot better now.

I was led to believe that the lifter preload is not that critical when using a standard cams. I have not done anything about it as it looks a bit of a pig to do.

40inches - 24/7/14 at 08:16 AM

My headers have turned brown, right to the silencer It polishes out easily enough, but I only bother with the exterior bits.

Irony - 24/7/14 at 08:18 AM

quote:
Originally posted by 40inches
My headers have turned brown, right to the silencer It polishes out easily enough, but I only bother with the exterior bits.


I was expecting it to happen eventually - maybe after the first proper run out. But after 10 minutes seems a bit quick.

40inches - 24/7/14 at 08:43 AM

quote:
Originally posted by Irony
quote:
Originally posted by 40inches
My headers have turned brown, right to the silencer It polishes out easily enough, but I only bother with the exterior bits.


I was expecting it to happen eventually - maybe after the first proper run out. But after 10 minutes seems a bit quick.


Mine turned brown almost immediately too. I was expecting them to turn blue lol

Andy S - 24/7/14 at 11:40 AM

Just Google steel temperature colour chart - colouring is temperature dependent not time. Putting a mirror polish finish makes it look better when it colours and holds off the oxides.

coyoteboy - 24/7/14 at 12:11 PM

From http://www.bssa.org.uk/topics.php?article=140

quote:


The table below represents the temper colours that are likely to form on stainless steel type 1.4301 (AISI 304) if heated in air.

THIS INFORMATION MUST BE USED WITH CARE WHEN INTREPETING THE HINT TINT COLOURS OBSERVED ON STAINLESS STEEL SURFACES AS THE HEATING CONDITIONS ARE NOT SPECIFIED.

Colour Formed Approx Temperature C
pale yellow 290
straw yellow 340
dark yellow 370
brown 390
purple brown 420
dark purple 450
blue 540
dark blue 600



My stainless downpipe has never gone past purple brown, but it is post-turbo.

[Edited on 24/7/14 by coyoteboy]

Irony - 24/7/14 at 01:03 PM

I can safely say they are pale yellow at the moment. I just didn't think it happened almost immediately.

BaileyPerformance - 24/7/14 at 05:50 PM

I was led to believe that the lifter preload is not that critical when using a standard cams. I have not done anything about it as it looks a bit of a pig to do.



If your running a stock cam, and the block and/or heads have not been machined heavily then you'll be fine.

If its a TVR engine they tend to machine alot off the heads to get the CR up and so install shims under each rocker post to bring pre-load back up. (without these shims you can get lifter jackup causing the valve to not completely close)

richardm6994 - 24/7/14 at 05:57 PM

Mine went pale yellow almost instantly but haven't got any worse since.
http://s1060.photobucket.com/user/richardm6994/media/photoshoot/Detail-06_zpsefc37299.jpg.html

[Edited on 24/7/14 by richardm6994]