Spark Plug Indexing for Yamaha F70

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
conch
Posts: 172
Joined: Sat Oct 17, 2015 8:43 am
Location: Florida Keys,Hawaii,Mississippi

Spark Plug Indexing for Yamaha F70

Postby conch » Fri Dec 01, 2017 8:32 am

Tell me more about spark plug indexing for a Yamaha F70.

[Separated from another thread in which boat performance with particular 70-HP engines was discussed--jimh]

flymo
Posts: 189
Joined: Thu Oct 22, 2015 2:58 pm

Re: Spark Plug Indexing for Yamaha F70

Postby flymo » Sun Dec 03, 2017 7:09 am

conch wrote:...tell me more about spark plug indexing...


Indexing the plugs is simply a matter of making sure the open side of the spark plug is pointed towards the valves, to let the spark ignite the fuel mixture more readily for more complete combustion. Practically speaking, the spark is exposed except where the side electrode itself is mounted. You just don't want to have this pointed towards the valves. To do this, you just put a piece of tape on the spark plug socket so you know how the plug is oriented, and then it's trial and error to swap the plugs around from one cylinder to another until you find the best orientations.

Hope that helps. As I said, it seemed to give me a little more get up and go, but I have not done a scientific comparison. But as mentioned, it's so easy to do when you're changing plugs, I figured why not?

Chuck, sorry for the delayed response. I don't get here to CW as much as I used to.--F

El Rollo
Posts: 87
Joined: Wed Sep 07, 2016 12:35 pm

Re: Spark Plug Indexing for Yamaha F70

Postby El Rollo » Sun Dec 03, 2017 10:41 am

How do you know the correct indexing position of the spark plug In terms of a clock hands, like 12-3-6-9?

I know there are four valves per cylinder on the Yamaha F70, so which position do you need to direct the plug?

I would assume you want the plug to point toward the intake valves.

Jefecinco
Posts: 1592
Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: SPORT 15: Yamaha 70 Two-stroke v. F70

Postby Jefecinco » Sun Dec 03, 2017 7:01 pm

El Rollo--the engine is a two stroke and has no valves. I believe indexed plugs should have the gap pointing toward the intake port or, in the case of a fuel injected engine, toward the injector for that cylinder.
Butch

flymo
Posts: 189
Joined: Thu Oct 22, 2015 2:58 pm

Re: Spark Plug Indexing for Yamaha F70

Postby flymo » Sun Dec 03, 2017 7:19 pm

Speaking to indexing plugs for the F70, which is not a direct--injected 4-stroke, you just want to point the open end of the plug toward the valves in general. The valves are at the top of the cylinder - that is, at the stern. So looking that the plug as you install it, ideally the electrode would be about 9 o'clock and the opening at 3. It does not need to be that exact - practically speaking, having the opening anywhere between 12 and 6 would be fine.

For a direct injection two-stroke, I would think the open end would want to point directly toward the injector. Didn't some of the FICHT motors require that?

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing

Postby jimh » Mon Dec 04, 2017 8:05 am

Usually a manufacturer of a SPARK-IGNITION engine will explain in the service manual the procedure to use to orient the spark plugs in each cylinder--if such a procedure is to be recommended or be necessary.

Many engines recommend indexing of the spark plug. For example, the Evinrude E-TEC engine recommends installing spark plugs with a specific orientation.

As noted, generally the goal of spark plug indexing is to have the spark plug ground electrode oriented so the open part of the plug, the part not shaded by the bent electrode, is oriented in a direction toward where the fuel-air mixture will be coming from. This gives the spark a clear path to the fuel-air mixture, making for better ignition of the fuel-air mixture in the cylinder.

In a classic two-stroke-power-cycle engine the fuel-air mixture enters the cylinder from ports in the cylinder wall; the mixture move upward in the cylinder as the piston rises.

In a two-stroke-power-cycle engine with direct fuel injection, like an Evinrude E-TEC, the fuel-air mixture is created by the spray of the injector nozzle which directs the fuel into a particular region of the combustion chamber. In some instances, there are protuberances in the combustion chamber that affect the path of the fuel-air spray. I believe in some cases they are position so the spray does not directly throw liquid fuel at the spark plug gap.

In a conventional four-stroke-power-cycle engine the fuel-air mixture enters the combustion chamber via the intake valves. Based on the design of the cylinder the mixture may be directed to flow in a particular orientation.

The usual method to perform spark plug indexing is to mark the outer body of the spark plug with a mark, then during installation, to reach the recommended torque setting for the plug with the plug in the desired orientation.

Due to inconsistencies and variations among spark plugs in their manufacture in the precise location of the electrode weld in relation to the threads, some spark plugs will be impossible to use. The spark plug will not be in a proper orientation when the torque limit is reached.

Typically the installation procedure will advise how much additional torque can be applied before the limit of rotation is reached. If the plug is still not in the proper position, that plug cannot be used. Modern spark plugs have crush-ring type sealing washers, so you cannot just move around a plug that has been tightened to its rated torque to other cylinders until you find a particular cylinder where that plug will index. Once you crush the washer, the plug cannot be re-used in most cases. For a typical six-cylinder engine, you might have to buy eight or ten spark plugs to get six that will index. With modern engines a spark plug can be a $20 item, so indexing plugs can be come a bit costly.

There is an extensive article on Wikipedia about spark plugs, and the topic of indexing is also discussed. See

https://en.wikipedia.org/wiki/Spark_plu ... park_plugs

Jefecinco
Posts: 1592
Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: Spark Plug Indexing for Yamaha F70

Postby Jefecinco » Mon Dec 04, 2017 9:10 am

Having incorrectly interpreted the title of the thread which sparked this new spark plug indexing thread I believed we were discussing some unusual Yamaha F70 two stroke engine. Thus my rather ignorant seeming post seen above for which I apologize. My previous 10 year ownership of an Evinrude FICHT engine was driving my comment.
Butch

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Mon Dec 04, 2017 10:47 am

It is also common in older two-stroke-power-cycle engines to use a so-called gapless spark plug, in which the center electrode is surrounded by a ring of ground conducting metal, and there is no particular gap distance that is set. With those spark plugs, there is no aspect of them that permits indexing or orientation, as they are completely symmetrical. Those plugs are often recommended in older engines, particularly in Mercury engines.

Also with spark plugs, perhaps a consideration more important than indexing is erosion of the electrode causing an increase in the distance of the spark plug gap. The erosion of the electrode is very common and can be quite rapid in older engines, particularly ones that use a very high voltage spark.

The spark plug gap distance affects the timing of the spark, as the electrical current jumps the spark gap when the voltage builds to a particular level sufficient to jump the air gap. If the gap widens as a result of electrode erosion, the spark timing may be affected as the arc occurs slightly later, assuming the spark voltage is dwelling upward as it is applied. As a result of delayed spark due to gap erosion, the engine running characteristics can be affected. An older two-stroke V6 engine I owned always let me know when the plug gap needed to be reset; the engine tended to hesitate on acceleration under load when the plug gaps eroded and the gap increased to more than the recommended distance.

Electrode erosion is reduced significantly in modern spark plugs by using very special metal for the electrode tip, usually the elements Iridium or Platinum. Spark plugs with these special electrode metal tips resist erosion much better than conventional part plugs with tips of normal metals, like steel or copper.

It is also common in modern engines that the ignition system generates the spark voltage from an inductive discharge instead of a capacitive discharge. The capacitive discharge gives a very intense but brief spark; inductive discharge (typically) gives a lower initial voltage for the spark but provides a much longer spark duration. Also, it is common in modern engines to create several spark discharges during one combustion cycle, which is done to insure there will be some ignition of the fuel-air mixture, including any remnant parts that did not ignite in the initial spark. The firing of the spark more than once per combustion cycle and the much longer duration of the spark both contribute to spark plug electrode erosion. For those reasons, you generally find engines using those spark methods will insist on using the much more expensive spark plugs made with exotic metal tips. Those plugs can cost $20 instead of the usual $4 for a common spark plug.

TransFueler
Posts: 20
Joined: Wed Jul 26, 2017 12:19 am
Location: Monroe, WA

Re: Spark Plug Indexing for Yamaha F70

Postby TransFueler » Wed Dec 06, 2017 10:06 pm

There's only one legitimate way to tell if "indexing" provides any benefit: Dyno testing.

There is always a placebo effect when trying out any so-called performance mods. You simply want to feel a difference for the effort you made. However, it's well proven that the vast majority of mods do little if nothing to ACTUALLY increase power. We don't even bother to "index" the plugs in our two vintage race cars, which are far more highly tuned than your outboard motor.

So, "index" all you want, but unless you test for real horsepower on a dyno, you're probably simply wasting time...
1987 17 Super Sport Limited
2003 Johnson/Suzuki 90 Four Stroke EFI

Jefecinco
Posts: 1592
Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: Spark Plug Indexing for Yamaha F70

Postby Jefecinco » Thu Dec 07, 2017 10:06 am

As TransFueler commented indexing the spark plugs on a four stroke engine is a waste of time. For a two stroke DFI engine ( Mercury Optimax and Evinrude FICHT or E-TEC, the spark plugs should be indexed. Otherwise spark plug fouling and lower fuel economy may result. With early FICHT engines powerhead failure was sometimes blamed on operating with non-indexed spark plugs.
Butch

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: Spark Plug Indexing for Yamaha F70

Postby dtmackey » Thu Dec 07, 2017 3:54 pm

In modern day four-stroke-power-cycle [power]head designs, indexing should make no difference. And, as stated, any gains are probably placebo as previously mentioned.

On heavily modified engines you may see a gain, but every so slight and less than one percent--if that. Years ago I had the opportunity to use a dynamometer. Indexing and side gapping were tested with no perceivable difference. We ran countless runs on two-stroke and four-stroke-power-cycle engines of two-, three-, and four-cylinders with 1,200-cc displacement or less.

If Yamaha--or any engine company--could see any beneficial difference in engine operation, they would put it into their maintenance manuals.

D-

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Sat Dec 09, 2017 7:35 am

Evinrude DOES "put [spark plug indexing installation] into their maintenance manuals."

I am sure that Evinrude does not recommend use of spark plug indexing in their maintenance manuals for no good reason. I am sure they do it because in their testing and development of their engine they found that spark plug indexing was beneficial.

That someone else tested some other brands and types and sizes of engines and did not find a benefit occurring from spark plug indexing does not seem to me to be dispositive that no benefit is ever possible to be obtained from spark plug indexing, and particularly in the instance where the manufacturer explicitly requires it to be done. If the engine manufacturer recommends spark plug indexing, you should follow their recommendation. If the manufacturer makes no mention of spark plug indexing, then it is reasonable to infer that there won't be a benefit from spark plug indexing in those engines.

I do not see a particular imperative in the engine power cycle being two-stroke or four-stroke as the determining factor that permits spark plug indexing to have a benefit. Rather, I suspect that use of direct fuel injection into the combustion chamber is likely to be more influential. Modern four-stroke-power-cycle engines in automotive applications are now evolving to use direct-fuel-injection. I don't know if the manufacturers are recommending spark plug indexing, or not. Perhaps another factor is the design of the combustion chamber and the location of the spark plug.

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: Spark Plug Indexing for Yamaha F70

Postby dtmackey » Sun Dec 10, 2017 9:23 pm

jimh wrote:Evinrude DOES "put [spark plug indexing installation] into their maintenance manuals."


Yes, an Evinrude E-TEC [engine] does require indexing, as the Ficht engines did, as well, due to the direct-injection design. [Evinrude] want the open part of the plug gap facing the incoming charge of fuel, otherwise the motor does not run smoothly and can stumble. The technology of those motors is radically different than an [intake manifold] fuel injection four-stroke [outboard engines]. The [intake manifold fuel injection] system in four- stroke engines is not direct-injection, and therefore does not behave the same way with indexing.

I'm not opposed to anyone that feels that indexing on a four-stroke engines makes the engine run better and say do what makes you feel good, I'm simply saying there is no dyno or manufacturers evidence to back up indexing in a motor that does not require it. If the manufacturer did see a benefit, you'd be sure it would be indexed from the factory and detailed in the maintenance procedures for the motor.

D-

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Sun Dec 10, 2017 9:53 pm

I think DT' and I are in agreement: if the engine manufacturer tells you that the spark plugs should be installed with indexing, you should follow that advice.

I do not agree with DT' that he has somehow proven that spark plug indexing is of no benefit in all engines because he says he tested some engines and found no benefit. In the absence of a direct recommendation from the manufacturer, I think spark plug indexing is like chicken soup: it might not help but it can't hurt.

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: Spark Plug Indexing for Yamaha F70

Postby dtmackey » Sun Dec 10, 2017 10:53 pm

Jim and I will disagree that indexing makes a difference, but in the absence of data (as an engineer), I cannot believe there is a difference and based on my experience with 4 stroke motors in a testing environment, not being able to link a benefit to indexing I will be biased to a position. Now, if someone had data or ran a Design of Experiments on this, then I may eat my words, but in the absence of data I'm a doubting Thomas.

Sorry, the engineer in me is six sigma data driven. ;-)

D-

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Mon Dec 11, 2017 8:25 am

I don't dispute the outcome of your tests. I don't think we really disagree. The engines you tested didn't benefit, but you agree that some engines do benefit. Me too.

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Mon Dec 11, 2017 9:46 am

DT' apparently tested only for improvement in horsepower as a result of spark plug indexing. There may be other benefits to occur with spark plug indexing that were not tested for in DT's experiments. Spark plug indexing could affect other elements of the engine performance, such as
    --better spark plug life,
    --better fuel economy,
    --lower exhaust gas emissions,
    --reduced plug fouling
    --smoother running
    --fewer misfires
My open mind about the experimental method keeps me skeptical of anecdotal reports. :-)

flymo
Posts: 189
Joined: Thu Oct 22, 2015 2:58 pm

Re: Spark Plug Indexing for Yamaha F70

Postby flymo » Tue Dec 12, 2017 9:25 am

I'd love to test my F70 on a dyno but only if the participants in the debate will foot the bill! But indexing is trivially easy and costs nothing so I am planning to continue to do it.

I do agree that plug orientation will be more critical in a direct injection motor - with indirect injection and particularly a 4-valve like the F70 the incoming air-fuel mixture is spread across a broad front so indexing likely makes less of a difference.

El Rollo
Posts: 87
Joined: Wed Sep 07, 2016 12:35 pm

Re: Spark Plug Indexing for Yamaha F70

Postby El Rollo » Tue Dec 12, 2017 12:11 pm

flymo wrote:I'd love to test my F70 on a dyno but only if the participants in the debate will foot the bill! But indexing is trivially easy and costs nothing so I am planning to continue to do it.

I do agree that plug orientation will be more critical in a direct injection motor - with indirect injection and particularly a 4-valve like the F70 the incoming air-fuel mixture is spread across a broad front so indexing likely makes less of a difference.



Do you use indexing washers, or do you just buy extra spark plugs to find the right orientation ?

And on your F70, what is the correct position for the electrode to be pointing when you index your spark plugs ? (12:00 -3:00 - 9:00)?
I haven't looked at a diagram for the the valve layout on the Yamaha F70 (exhaust/intake)

flymo
Posts: 189
Joined: Thu Oct 22, 2015 2:58 pm

Re: Spark Plug Indexing for Yamaha F70

Postby flymo » Tue Dec 12, 2017 6:05 pm

It's not that exact, or at least I wasn't - just point the open end toward the head and not the crankshaft. In practice, having the open end anywhere around 3 would be fine. I only bought 4 plugs. 2 lined up fine and the other 2 I had to swap between cylinders.

El Rollo
Posts: 87
Joined: Wed Sep 07, 2016 12:35 pm

Re: Spark Plug Indexing for Yamaha F70

Postby El Rollo » Tue Dec 12, 2017 6:41 pm

flymo wrote:It's not that exact, or at least I wasn't - just point the open end toward the head and not the crankshaft. In practice, having the open end anywhere around 3 would be fine. I only bought 4 plugs. 2 lined up fine and the other 2 I had to swap between cylinders.


Copy that. Thank you.
I will try it next time . . . can't hurt.

Jefecinco
Posts: 1592
Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: Spark Plug Indexing for Yamaha F70

Postby Jefecinco » Wed Dec 13, 2017 9:36 am

When I had an Evinrude FICHT (2 stroke DFI) engine I always bought a couple of extra spark plugs when replacing a set. I allowed myself a 45 degree angle meaning I required the spark plug gap to be no more 23 degrees from the fuel injector. On a couple of occasions I had to cheat a little bit on the high side of spark plug torque to make a spark plug "work". My engine was a 1999 model year 115 HP V4 and due to many powerhead failure reports I was more than a little paranoid about maintaining the engine exactly as recommended by Evinrude.
Butch

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: Spark Plug Indexing for Yamaha F70

Postby dtmackey » Fri Dec 15, 2017 9:40 am

There seems to be two paths in this thread: index for two-stroke engines (E-TEC and Ficht specifically); and index for four-stroke engines. Let me break these out so everyone can see where indexing is required and part of the manufacturer's maintenance procedures.

Before we start, here's a pic of a spark plug.
Image

Here is a pic of a Evinrude DI motor (2 Stroke). [The image below shows an E-TEC engine--jimh] As you can see the proximity of the spark plug and injector are quite close.
Image

Here's a pic of the inside of the head. Based on this pic, you can see that the injector sprays a pattern of gas into the chamber and the plug is strategically located so that you want as much unshielded center electrode as possible so you get a large contact area of ignitor to fuel as possible
Image

This is a cutaway of an E-TEC (sorry, this is a RAVE technology equipped Etec, but the relationship and principle is the same as a standard E-TEC). As you can see the fuel is sprayed directly at the plug and this is the sole reason for indexing. If you sprayed at the plug and it was obstructed by the side electrode it would disrupt the fuel pattern and cause uneven distribution (atomization) resulting in rough running and a host of other things, because of poor flame kernel growth that is not uniform in the combustion area. Remember, fuel is injected as a point as the piston is near the top of its stroke moments before spark is introduced.
Image


Now let's look at a Yamaha four-stroke head (pent head design) with a centrally located spark plug. The larger valve are the intake valve and on the other side of the plug are the exhaust. One would think that orienting the plugs open area toward the intake valve would be similar to the E-TEC, but it is not because the fuel is not direct injected into the cylinder, it is sprayed into the intake runner and drawn into the cylinder long before ignition.
Image
Image

Let me explain. The intake valve opens on the downward stroke of the piston drawing in the atomized fuel/mix which travels right by the plug and fills the entire cylinder as the picton travels down.
Image

Once piston is at the bottom most position, the intake valve closes.
Image

Then the piston starts to rise for the compression stroke, squeezing the air/gas mix so it is as close to 100% mixed and dispersed in the cylinder as squeezed by the rising piston. Valve orientation/position has no bearing since they are all closed.
Image

Since the fuel was injected into the intake, then drawn through the valves and thoroughly mixed during the downward (intake valve open) and upward stroke (intake valve closed) there is now no relationship to valve position to plug position (as the case in a directed injected motor) when ignition takes place.
Image

In this pick, in theory one might say the better plug index orientation would be positioning the open plug gap area 90 degrees from the valves so the spark has contact with a larger volume of air/fuel mix away from the valves than toward the valves. There's is no benefit to indexing the open spark plug gap toward intake or exhaust valve because there's no Direct Injection spray pattern directed at the plug and since the air/fuel mix took place much earlier in the process and mixed on the downward and upward stroke, there's no correlation to plug index position to intake valves.

Reach out to a Yamaha factory rep on indexing and his response will be "why?".

If you are trying to squeeze every last benefit out of your 2 stroke or 4 stroke look at plug gap. There are several studies on flame kernel growth from various gaps on plugs with data to support. Gap to manufactures specs as they've tested to achieve the best performance characteristics.
Image

D-

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Fri Dec 15, 2017 12:54 pm

DT--thanks for the comprehensive remarks regarding direct-injection two-stroke compared to non-direct-injection four-stroke. There are now, at least in automobile engines, four-stroke-power-cycle valve engines with direct-injection. I suspect that your same remarks would apply to them: that is, the plug position probably needs to be indexed because of the direct spraying of fuel into the combustion chamber in those four-stroke engines. This suggests to me that the need for indexing is related more to direct-injection than it is related to the number of strokes in the combustion cycle.

Regarding the effect of spark gap on performance, I previously commented that I had observed the effect of spark gap erosion on engine performance, albeit not with any linked graphical representation of particular combustion chamber effects. I just noticed the engine ran better with the proper plug gap.

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Fri Dec 15, 2017 12:55 pm

DT--thanks for the comprehensive remarks regarding direct-injection two-stroke compared to non-direct-injection four-stroke. There are now, at least in automobile engines, four-stroke-power-cycle valve engines with direct-injection. I suspect that your same remarks would apply to them: that is, the plug position probably needs to be indexed because of the direct spraying of fuel into the combustion chamber in those four-stroke engines. This suggests to me that the need for indexing is related more to direct-injection than it is related to the number of strokes in the combustion cycle.

Also, I believe you can demonstrate graphically the same influences in the combustion chamber of a two-stroke engine without direct-injection as you did in the four-stroke non-direct-injection example. In a conventional two-stroke-power-cycle outboard engine without direct-injection, the fuel is already mixed with the air and comes into the combustion chamber from a port in the side wall of the cylinder; it is not sprayed directly into the combustion chamber as in an E-TEC engine.

Also, in the FICHT engines I believe that the cylinder head design evolved to includes a post called a spray deflector pin. I believe the purpose of that device is to deflect the injected mist of fuel in a way that prevents the spark plug gap from being wetted by it. That design has always been used in the E-TEC engines. The deflector pin prevents the injected fuel mist from coming into direct contact with the plug; this also prevents deposit build up on open part of the plug gap.

Your picture of a "DI" cylinder head does not seem to show the deflector pins. Perhaps it was a picture of an early production model FICHT. Your graphical representation of a RAVE snowmachine engine does not show a deflector pin. I don't know if the RAVE engines use them; perhaps the graphic artist omitted them for simplicity.

Regarding the effect of spark gap on performance, I previously commented: "Also with spark plugs, perhaps a consideration more important than indexing is erosion of the electrode causing an increase in the distance of the spark plug gap."

I have observed the effect of spark gap erosion on engine performance, albeit not with any linked graphical representation of particular combustion chamber effects. I just noticed the engine ran better with the proper plug gap, and with use and erosion of the plug gap problems began to occur in the engine running under heavy loads.

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: Spark Plug Indexing for Yamaha F70

Postby dtmackey » Fri Dec 15, 2017 3:44 pm

jimh wrote:Your picture of a "DI" cylinder head does not seem to show the deflector pins. Perhaps it was a picture of an early production model FICHT. Your graphical representation of a RAVE snowmachine engine does not show a deflector pin. I don't know if the RAVE engines use them; perhaps the graphic artist omitted them for simplicity.


In the DI head pic, the pins are hard to see due to carbon deposits.

Deflector pins are not used in the Rave models for snowmachines and I'd expect that technology to continue to migrate into marine world slowly as RAVE technology has been around for over 30 years and now just trickling into Evinrude motors.

D-

jimh
Posts: 11674
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Spark Plug Indexing for Yamaha F70

Postby jimh » Fri Dec 15, 2017 6:39 pm

dtmackey wrote:In the DI head pic, the pins are hard to see due to carbon deposits.


There may be irony in that situation. The deflector pins may accumulate carbon deposits that otherwise might have fouled the spark plug.