SonexBuilders.net

Greetings...

Just getting my 2.1 engine back together after installing TIME-SERTS in all eight spark plug holes due to sub-standard machining of the spark plug holes. A known issue, apparently, Sonex said "yeah, when we switched over to Mofoco, there were using 'worn tooling', and produced some number of bad heads. The fact that Sonex kept this critical information to themselves is, IMHO, irresponsible. Oh well, what can you do? However, I'm feeling quite good about the inserts, they are definitely robust. I don't think I'll need to worry about any sort of plug thread issues for the life of this engine :)

Since I originally built up this engine, I have aquired Joe Norris' assembly DVD. My printed assembly manual says to use the aluminum spacer blocks between the head and the intake elbow, but the DVD clearly shows that no spacer is used. Which is it? Thanks1

Follow the manual. The video is a demonstration, the manual takes precedence.

If you re-watch the intro to the DVD, you'll hear me say that in any case where the DVD and the manual disagree, the manual is what you follow.

Now, having said that, the engine will run either way. However, with the MOFOCO heads the clearance between the intake elbow and the top rear spark plug is such that you may not be able to get a spark plug socket on the plug if you don't use the spacer. Now, that's OK if you don't mind removing the elbow whenever you want to pull that plug. But with the spacer in place you'll be able to put a socket on the plug and remove it without removing the elbow. Your choice.

Thanks, Joe, for that clarification. I'll be using the spacers.

What was your engine number? Just hung mine on the airframe for the first time and the spark plug threads look very worn and they have not had plugs threaded in them yet. Can you give more details on your spark plug issue? Thanks!

I'm not sure where the serial number is located, there are several numbers stamped in various locations on the cases, didn't notice any on the heads themselves. So I looked up my invoice from Sonex, no serial number there either (aside from my Sonex's #325). The engine kit shipped 2/2/15. Sonex should be able to tell you if your particular heads are poorly machined due to worn tooling at the Mofoco factory. Not sure what criteria they would use...

I have submitted an article for EAA's "Bits & Pieces" that will come out in a couple of weeks, a photo documentation of the TIME-SERT installation process. But the symptom was simply that the two plugs involved could not take any torque before spinning in their holes. As if the pilot hole was too large, and the subsequent tapping produced threads too shallow to grip the plug's threads. You could probably use a thread gauge (12x1.5mm) to measure the thread depth and predict that the threads would be insufficient.

jwd3ca wrote:I'm not sure where the serial number is located, there are several numbers stamped in various locations on the cases, didn't notice any on the heads themselves..

The serial number for the engine kit is stamped on the accessory plate.

Oh, of course, *knew* I saw it somewhere :) Serial # 0818