912 ULS Spark Plugs

[jiott]

It was time (400 hrs) to change the Rotax/Bosch spark plugs in my 912uls engine, so I decided to change back to the NGK DCPR8E plugs that we used to use on all these engines. They cost $4.99 compared to $32+ each for the Rotax plugs-quite a savings. The NGK plugs fit just fine including the plug wire caps. My reason for going back to the NGK plugs was simply cost, but I received a pleasant bonus surprise. When I started the engine with the new NGK plugs it fired up noticeably faster than with the Rotax plugs. The engine also ran noticeably smoother than the Rotax plugs, both at idle and in flight. No other changes had been made to the engine like carb sync, fuel type, carb rebuild or cleaning, ignition changes, etc. I don't ever remember this kind of immediately noticeable difference when changing to new plugs-Rotax to Rotax, or NGK to NGK. This is the first time I have changed Rotax to NGK. I am of course pleased but don't know what to think or why this happened. Obviously the Rotax/Bosch plugs were at the end of their recommended life span, and the NGK plugs were brand new, so I guess you would expect at least some performance improvement. Its just the magnitude of the improvement that I had never noticed before on previous plug changes. I am now really sold on the superiority of NGK plugs and plan to stay with them, and not just because of the cost savings.

Possibly one reason for this difference is that the Rotax/Bosch plugs have no way to adjust the spark gap as they age, whereas the NGK has a conventional adjustable electrode gap which I always check and readjust at every 100 hr interval and replace with new plugs every 200 hrs (compared to 400 hrs for the Rotax plugs). Also, the Rotax plugs are duel gap, but the spark gaps are more buried in the head of the plug, whereas the NGK single gap is more exposed into the combustion area.

I know someone may ask so I will verify that the engine was running just fine (although somewhat rougher as I said) before I removed the Rotax plugs, runup ignition checks on A&B were all normal and good, egt's were all similar and normal, and the plugs all looked fine after I removed and inspected them. So I don't believe this difference was caused by one failing Rotax plug.

Just my recent experience I wanted to share, and wonder if anyone else has had an experience like this?

[bbs428]

Agreed!

I used NKG plugs in an earlier lifetime in all my dirt bikes.
They were definitely superior to other sparkplugs.

I have never used the Rotax/Bosch plugs due to cost, so I have nothing to add or compare but...
I do use the same NKG's plugs and clean/adjust them at 50hrs with the oil change. At 200hrs they are replaced with new.

I think everyone has to be comfortable in their maintenance practices, so run what plug/oil/filters etc. you like. Imho, the NKG's have a lot of airtime on them, so for me it's a "no-brainer" to use them.

[Dave S]

Jim,

Thank you for your thoughtful contribution.

My original ULS came with NGKs And I stuck with them exclusively after the rotax plugs came out. Easy to clean and an adjustable gap makes them very servicable. Price is a big plus on the NGKs but I like them mostly because they work well.

The new engine came with the rotax plugs, which are not worn out yet so I haven't had the experience of a swap to the NGKs on this engine.

You can bet NGKs are my choice for replacement.

Thanks for reporting your experience.