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 Detonation

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mscutt

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Number of posts : 96
Registration date : 2011-10-21

PostSubject: Detonation   Thu Nov 10, 2011 11:45 am

Thought I'd post this in case there are some folk out there that have not seen detonation damage on a cylinder head.



Note that the main chamber is running cool and looks a little rich but the edge of the squish band has gone very light in colour where the detonation has occurred. With a small magnifying glass or a young pair of eyes you can see the aluminium is being eroded away. This is quite mild - if it goes on for long without siezing the head can start to look like a swiss cheese !

Mick
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john bass

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Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Good Pic Mick!   Thu Nov 10, 2011 11:05 pm

I posted a reply and it vanished...!? So here´s a second try...??

Congratulations! That is a really good picture of detonation Sticky Mick -- that is not happening at the piston crown centre as most times it does -- yet with the plug looking as if running lean-&-hot and the chamber looking black-&-rich ---

-- How do you explain that oddity?? What was the compression ratio??

I must learn how to send one picture at a time. As I said earlier -- it has been most embarrassing to think I have sent one -- call it a technical or respectable snap shot -- and have the recipient e-Mail or telephone in nasty manner to say all connections are broken since receiving such a collection....!!

No! I´d love to send a photo of Andy Boyle´s ABS piston with a hole in the piston crown -- just ERODED away as you say Mick -- not melted -- eroded away, atom by atom, as if spark-eroded...

I had my old 1927, 500cc Triumph at Cadwell & Brands still with hand-change so it was not really race-competitive but being a nutter I increased the compression-ratio to 9.5:1 and after a couple of laps it pinked like blazes and I pulled out... The piston looked OK but the head had similar evidence of detonation and then discovering methanol could be used I took an 1/8th" (3mill) drill to the main jet and it ran really well although it was running too rich, of course, but that is the important bit with using methanol -- is to always run rich....

Cheers!

Iza Nostal-Gia Hasbin.
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mscutt

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Number of posts : 96
Registration date : 2011-10-21

PostSubject: Re: Detonation   Fri Nov 11, 2011 5:47 am

The picture is from some time in 2002 so can only guess at compression ratio.

We don't go for extreme ratios - usually 12.5 to 13:1 geometric which will be around 7 to 7.5 from exhaust port closure.
Squish clearance would have been close to .040" and ignition timing about 2mm - sorry I can't be more precise but these are the usual settings we use.

Everything used to work fine on pump petrol until they got rid of the lead and started messing around with the mix and this is what happens if you don't get your compression ratio low enough or your ignition retarded enough.

Has anybody got some good guide line numbers for running on pump petrol ?


Mick
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john bass

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PostSubject: No!   Fri Nov 11, 2011 11:17 pm

No Mick I would not chance pump petrol.
You can never be sure ...

Way back in the early 50s when running a RE Bullet Scrambler I mixed pure Benzine with the only available Pool petrol at 50:50 and the Bullet compression ratio was 8.5:1.

C8H18 is the one petrol I know anything about and in the mid-nineties that still had 0.013g/L tetre-ethyl lead in it but if that has since been ruled out I´d not chance using it on anything over 8:1 (top of exhaust ...) cr.

Just recently there was a hue and cry about a petrol being sold at the pumps here in Germany with a fair percentage of bioethyline in it which the TüV here (MoT in Blighty) said was of `High Quality´ but someone said it burns out your valves and as is the wont of the Germans they stopped buying it. since you don´t have 4-stroking valves it´d be OK if its octane number is over 100?? Perhaps it si available in the UK now ....??

I´ll try and find out more unless Trevor can add anything....??

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john bass

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PostSubject: PS...   Fri Nov 11, 2011 11:40 pm

PS...
Just had a caller ... who knew about the bio-ethanol petrol scandal at the pumps here. There´s a Super Plus E5 which has 5% ethanol and a Super E10 Plus that has 10% ethanol available at the pumps. He reckons the latter is guaranteed >98octane but you´d probably only find that out for sure when your engine seizes -- which I think come down to buying a Premium-Super (or whatever the best is called) and mixing a higher octane fuel with it -- or....???

Shell and Aral are selling the above here -- in Germany -- so I reckon it must be avaialble in the UK.
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Derek

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PostSubject: Re: Detonation   Sat Nov 12, 2011 10:54 am

hi mick it would be interesting to know what material/grade of aluminium the head is made of, as some types especially no silicone and none copper content aluminium would be more prone to this at a much lower tempreturs than others.

AE 014 has a higher silicone and copper content than most and
AE009 this has higher silicone content - but a very small copper content, and very very similar to LM27 a piston material solid to a well known quality Italian Piston materials side/manufacturer Goetze.

however AE0014 was used for HIGH SPEED DIESEL PISTIONS AND TENDED TO BE MORE PRONE TO CRACKING AS USED ON PISTON OVER 210.Omm diameter.
out of interest i had the material fora few pistons chequed a YZ125 piston in 2002 my then place of work, Lucas aero space, who did a spectro with an electron beam Microscope, and cross scection and polish before etching and high res ex-ray photo;ed a plot, very interesting we also did a honda rs and cr pistons - completely different materials.

it was almost identical material to AE0014. VERY STRONG low silicon but a high copper content, so at higher temp stronger and would resist deternation much more, because of its copper content, so a higher melting point, as used in Gas ignition engines, converted from diesel compression ignition engines with a much reduced comp ratio's.

i think what I'm saying is the material in the cylinder head is important, and some can be made to avoid this.

regards Derek
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Derek

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PostSubject: Re: Detonation   Sat Nov 12, 2011 11:05 am

HI Mick on the cylinder head,

there are 4off blue grey squashed pieces look like blus tack, next to the studd holes ? what are these for?

regards Derek
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mscutt

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PostSubject: Re: Detonation   Sat Nov 12, 2011 11:08 am

Yes its Blu-tack !

I didnt have a digital camera in those days and put them on to avoid scratching the glass of my scanner

Mick
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Derek

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PostSubject: Re: Detonation   Sat Nov 12, 2011 11:12 am

what was the scanner for ?
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Ned

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PostSubject: Re: Detonation   Sat Nov 12, 2011 11:14 am

mscutt wrote:
Yes its Blu-tack !

I didnt have a digital camera in those days and put them on to avoid scratching the glass of my scanner

Mick

PMSL Laughing
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mscutt

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PostSubject: Re: Detonation   Sat Nov 12, 2011 11:17 am

It was just a normal A4 size page scanner connected to a computer

works just like a photocopier and puts a jpg file on your pc

as you can see it copies more than documents

Mick
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