This has probably been covered to death, but needs must, I have a SOC 2 litre sierra and just a couple of weeks ago fitted some new plugs, since then it has occasionally been a pain to start, the recommended plugs in the Haynes book are Champion RF7YC these are what was in the car and now have NGK APR6FS plugs from my local motor factor my question is are these a suitable alternative, or is there a cross reference web site which I could use
Rich
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the ngk are the best plug you cab fit. I would check that you have the right plug gaps (in case they have been dropped , and the condition of the leads, especially since you have recently pulled them off as that is the likely time for failure.
mrcheerful
Yes I can see your point and I know that NGK are good plugs but I am concerned that they not the right ones? Rich
I can't answer your specific question, but I would certainly recommend NGK plugs rather than Champion. NGK's quality control seems to be much better than Champion's. So, if they are a suitable replacement, you've got better plugs. Mike.
The right ones are the ones that fit and are gapped correctly.
"Rich" wrote
is there a cross reference web site which I could
The book recommends Champion, the owners club recommend Bosch or NGK.
Here's the best place to ask about Sierras
That's great thanks all
Rich
sorry I should have said that ap6fs are right.
mrcheerful
Yes, thanks
Rich
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Really? Wonder why I managed to melt a set of plugs some time ago then.
Thanks for all the posts on plugs. what good points and bad points are there to altering the hotness of a plug, so say if it is suppose to be a 6 and you go for a colder one what will happen and what will happen if you go the other way ? Can someone explain it if possible.
Rich
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If you fit a plug to an engine running colder than the plug is designed for, it will oil up in the case of a two-stroke engine, or otherwise fail to fully overcome the resistance of whatever crap is accumulated on it in order to fire. If you fit a plug to an engine running hotter than the plug is designed for, it can cause the crown of a piston to overheat and begin to melt at the point nearest to the plug. It looks like it's been nibbled by mice.
Go on, ask me how I know :-((
In the case of your everyday cooking engine it's not that critical, but for racing etc it's vital.
Steve
Go on then how do you know!!
Rich
The message from "Rich" contains these words:
Colder plugs are more likely to get fouled. Hotter plugs can melt if you take it too far - the ends just frizzle away.
As others have said, too cold a plug will lead to fouling and misfiring. Deposits, including carbon and metallic residues from oil detergents, will remain on the plug's internal insulator and provide an alternative (leakage) path to ground for energy that should be in the spark.
So you need to run the plugs hot enough to burn these deposits off.
But too hot, and that heat can itself ignite the fuel-air mixture before the plug sparks, causing detonation (pinking) and possible engine failure.
So it's safer to go too cold than too hot.
Bosch catalogs typically have good pictures of what a used plug should look like. I quickly found the following PDF:
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