How to Read Spark Plugs???

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Richard Wisniewski
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Joined: Fri May 02, 2008 9:32 pm
Location: FL

How to Read Spark Plugs???

#1 Post by Richard Wisniewski »

To All,

Is there a way to read the Spark Plugs from my Engine?
I am going to do a valve job and I have disassembled the top of the engine and removed the plugs (Bosch Platinum WR7BR). The engine is a 1600 super with Solex 40PII Carbs.
All four of the plugs had a lot of BLACK deposits one had a slight touch of oil.

What is causing this? Is it Valve guides or is it a fuel problem?

Any help is appreciated.

Thank you,
Rich Wisniewski
1960 356B Roadster
No. 87284
Member # 2275
Rich Wisniewski

Michael Cass
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Posts: 133
Joined: Fri Apr 11, 2008 5:06 am
Location: Sydney Australia

#2 Post by Michael Cass »

Hi Rich

This could be caused by any number of things. I have found that when I have had black deposits on my plugs the engine produces less power and sometimes develops a miss due to fouling of the electrode. The ideal colour I have found to be a grey colour which I have been able to achieve by fitting a hotter plug. Better power and no more fouling.

Also you should consider fitting new points, dizzy cap and rotor and condenser as a friend of mine had these same problems and that fixed his problem.

Cheers Michael.
59 Porsche 356A Coupe
59 VW Kombi
60 VW kombi x2
61 VW Karmann Ghia Coupe
92 BMW E30 325i Convertible (at least it's German)
02 Toyota Townace SBV ( aka. The Unspeakable)

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John Lewenauer
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#3 Post by John Lewenauer »

Google, read spark plugs. Lots of articles.
1964 356 C Coupe, Togo/Fawn, Chassis 126634
Enjoy some pictures of my Togo 356 at:
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Ron LaDow
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How to Read Spark Plugs???

#4 Post by Ron LaDow »

"Google, read spark plugs. Lots of articles."

I haven't googled it, but like a lot of things, it will take effort and study to come to reliable conclusions. Specifically, once lead was purged from gas, we got better gas, but more difficulty in 'reading plugs'. You'll also need to maintain a certain load, throttle opening and RPM for some period of time (like 30 seconds) and then 'clean cutting' (flip into neutral and immediately cut the ignition) to get any reliable data. Letting the engine idle for any period of time before pulling and reading the plugs means you're reading idle conditions; almost always 'rich' in aircooled engines. And the plug type makes a drastic difference (I have no idea how to read platinum plugs).
I'd suggest a tune (yet again) and a leak down test; both will likely give you better information to make choices.
Thanks,
Ron LaDow

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Ron LaDow
www.precisionmatters.biz

Michael Eker

How to Read Spark Plugs???

#5 Post by Michael Eker »

See:

http://www.boschautoparts.co.uk/pcPlug10_8.html

My 356C suffered from poor starting and the occasional fouled plug.

I think this was due to lack of use and short trips, the egine was not getting hot enough to

burn oil and carbon off the plugs.

I fitted Iridium plugs in an attempt to cure this and it worked, I don't know why but it did.

See: http://www.spark-plugs.co.uk/pages/tech ... _plugs.htm

They are expensive but the manufacturers claim a service life of 120,000 miles.

meker

Cliff Murray

#6 Post by Cliff Murray »

Ron is correct, a leak down test is much more accurate than reading plugs. Your machinist will tell you the condition of your guides and valve stems. Air cooled engines rely heavily on these for valve cooling so when in doubt, throw them out. If your machinist knows air cooled engines, he will know what to do. If not, tell him to hold his work to the highest standard. No knurling or short cuts! While you have it apart, you should look at the cylinders for any obvious problems. The oily cylinder(plug) should correspond to a worn guide or bad ring seal. If you find the guide bad, the ring seal is more likely to be ok. Next time, do a leak down before you disassemble the engine. Good luck.

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