New Spark Plug Rotax 912

by Pietro Rebuffini in 912iS Technical Questions 7 years ago

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Re: New Spark Plug Rotax 912

by Glen Marshman » 7 years ago

Glen Marshman

1 2 0

The plug pictured above looks like a masive electo plug commonly found in Lycoming and Continental engines. many builders have switched to auto plugs because these plugs can cost as much as $40.00 each!

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Re: New Spark Plug Rotax 912

by Glenn Dugger » 7 years ago

Glenn Dugger

4 20 3

Now that I've seen a picture, they look like the massive electrode style that I use in my IO-520.
And sadly, they cost as much too.

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Re: New Spark Plug Rotax 912

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.96k

Roger,

Yes and I agree we don't mix heat ranges or mfgs but I wondered if there was more to it. So it was a stupid question.

It is not a stupid question.
Rather than just saying, "It is just not what we do", you should know WHY it is what we don't do.

Consider that the engine has 4 cylinders and 8 plugs.
The 8 plugs are energized by only 4 coils.
The High Voltage sides of the coils do not have grounds.
Each end of the coils goes to two spark plugs.

This is a boxer style engine. The firing order is 1-4-2-3.
Cylinders 1+2 are at Top Dead Center when 3+4 are at the bottom. And Vice Versa.

When the coil fires the Plug In cylinder #1, the Plug on the other end of the coil wire in cylinder #2 fires at the same time.
When cylinder #1 is at the top of the compression stroke, #2 it at the top of the Exhaust stroke.
The spark in #1 lights off the fuel charge. The spark in #2 does nothing.
This is known as a "Waisted Spark Ignition". Very Common in engines without distributors.

It is important that the load seen on each end of the coil wires are the same.
Placing different plugs on each end of any one coil may cause misfires.
This is the reason WHY!

While it is technically possible to mix plugs in an engine, you will need to keep straight which two plugs fire as a pair.
It is highly NOT Recommended, as the risk of getting it wrong is just not worth the effort of tracing out the wiring to get it correct.

EX: Is the Mate of the Top Plug on Cylinder #1 the Top or Bottom Plug on Cylinder #2?
Are your Sure? ??? You get the idea!

Inquiring minds want to know!

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

Thank you said by: Scott Williams, Thomas Carlson

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Re: New Spark Plug Rotax 912

by Glenn Dugger » 7 years ago

Glenn Dugger

4 20 3

Excellent explanation.

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Re: New Spark Plug Rotax 912

by MARK JACKSON » 7 years ago

MARK JACKSON

12 332 11

It looks like we have got one heat range for every engine now, so was that a farce, and a very large gap which will put a lot of strain on the ignition system.

I can see more chance of HT leads rubbing on cylinder heads as they are now 90 degree plugs caps.

The standard NGK plug caps will fit the Bosch plugs perfectly ok.

I cannot see any advantage to this at all. Apart from Rotax falling out with NGK and securing a new deal with Bosch, what is the reasoning behind this change.

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