Spark plug blew in half

[Rdavis0207]

Just had my plugs changed on the 08 sx230 and on of the new plugs blew in half the threads are still in motor but the head flew out. Any one ever seen or heard of this? Cause? I have a guy drilling the rest out just curious

 

[Rdavis0207]

Pics

 

[jmargo]

1. That does not appear to be a new plug.
2. Probably due to over torque.

 

[Cobra Jet Steering LLC]

use an EZ out to remove the rest of it

 

[marcham]

Who did the plug change? If not you, then I hope they are fixing it....

 

[Rdavis0207]

He is fixing it. It was new lol I took it for one ride and after about 15 minutes it threw and over heat code and started running rough so shut her down and that's what he found today. So if he over torqued it that can make it explode?

 

[marcham]

Either that or they are fake ngk plugs....

 

[mrcleanr6]

That is from over torquing the plugs. Seen it happen many times. Someone tightened the snot of that one

 

[Beachbummer]

There is a torque value for the plugs in the manual and it is obscenely low at only 9.4 Ft Lbs. It's not a lot.

Could be a defective plug from the box too, but that is quite rare.

EDIT: The info below is from the 2007 AR/SX230 HIGH OUTPUT Service Manual which has the MR-1 HO engine.

 

[jmargo]

Look at that porcelain and the metal. That looks old. New NGK plugs are a shiny gold/silver.

 

[tdonoughue]

Well, after combustion blowing out the plug, I would not expect nice clean shiny gold/silver any more. But I agree something doesn't look new about that.

On install, these are only supposed to be hand tight. If you are using a wrench you are probably torqueing too much. I have used a wrench, but when you feel the plug hit the block you need to stop immediately. Add a 1/4 turn and you are way over.

I have also heard of such a thing from undertorqueing the plugs. Gasses escape through the threads and will melt the boot (see the bottom of the boot in the photo) and separate the plug.

Either way: certainly a bad install job.

 

[Canuckjetboater]

Just had my plugs changed on the 08 sx230 and on of the new plugs blew in half the threads are still in motor but the head flew out. Any one ever seen or heard of this? Cause? I have a guy drilling the rest out just curious

@Rdavis0207 ..... thank you for the post. You have sure motivated me to do some serious fact checking. I assume there is a difference between the "regular" and supercharged heads but IMO not enough to explain the difference between the spark plug spec sheet that @Beachbummer posted and the Info I have from RIVA and Yamaha. The spec sheet for my 2020 supercharged 1.8 shows a gap of 0.8 to 0.9 for spark plugs - that difference I get but RIVA Racing and Yamaha HQ both said 18 foot pounds or 25Nm of torque for the plugs - now that IS a big difference from the posted spec sheet!

 

[Beachbummer]

Note that the sheet I provided is for the 230s HO engine, from the shop manual. The engine has a different design from the 1.8l engine in your 2020.

 

[Canuckjetboater]

Note that the sheet I provided is for the 230s HO engine, from the shop manual. The engine has a different design from the 1.8l engine in your 2020.

@Beachbummer .... yes, figured that and I can see the plug gap being slightly different but I have to wonder about the plug torque setting I was given as it seems to be too high when compared to yours even given that there should be a higher compression involved in the supercharged engine.

 

[Beachbummer]

@Canuckjetboater Sorry, I missed that!

I will say 18 Ft-Lbs is still a reasonably low number. I would not be surprised if that was appropriate for other engines. I was not very familiar with these troque settings until I got a torque wrench, and "wrench tight so it doesn't come of" that I would apply generally by hand before I had a wrench (and now still) feels more like 35 or 40ft-lbs. I know the number seems significantly higher, but 18Ft-Lbs is still a gentle force.

The 3/8 torque wrench doesn't even measure below 20. I have to put the adapter on the 1/4 wrench to go below 20ft-lbs.

 

[fatboyroy]

Id also check if there is water mixed with oil. increase pressure may pop out a spark plug? But I still think its the torque that did it. Change plug and mechanic lol

 

[zipper]

Was it on cylinder #3? It has been known for seizing plugs. I don't know why a new plug would break other than fake ngk's, they exist, or not installed properly.