I have been looking at a used engine with mechanical advance ignition. I've never had one before only magneto or electronic advance. When you go quickly from idle to full throttle isn't the spark advanced before the RPM's are high enough to match? This seems like you would have pre-ignition problems. Is there something I'm not taking into consideration?

Yes, don't slam the throttle open. Roll it on and there should be no problem. Also, never flip the prop with the throttle above idle (choke on or off) and the ignition turned on - it will bite you.

Not a real problem on most engines.

Many run with fixed timing at near full advance all the time. I know several that just removed the advance and set it to the max setting; just so they don't have to mess with the linkage.

The retarted timing reduces the idle torque vibration. I have seen mechanical advance work better than electronic because it advances earlier then revs up faster.

If you fix the timing at full advance how do you hand start the engine? Wouldn't it kick back? Any engine I've seen with fixed timing is not at optimal timing for full throttle.

Maybe you haven't seen enough engines with fixed timing [8D] 28 degrees BTDC is optimal timing for full throttle on almost all engines..There is only one company selling engines that are not timed this way, and by now maybe they changed...
Myself and C&H have been re timing these engines and increasing rpm by 6 to 800 by using 28 degrees....
Hand starting a fixed timed engine is not difficult, just get a big leather glove and flip it like you mean it....Been doing it for 20 or more years....
All my G26 conversions are fixed at 28..I can't tell any difference between that and one with syncro spark....I HAVE tested them both ways...

I would be concerned far more over the age and general condition of the engine than with its spark advance design. Both mechanical and auto advance ignitions work very well and reliably.

All the engines I have ever owned have been mechanical advance and it works great.

If the age & condition were an issue I would not have considered it. The reason for the question is that I never had one before. Any way I've decided not to go with it. I'm going to purchase a new engine. The cost difference between new and used is not enough to cut corners now. I do not understand why used gas engines bring close to new price.

Because used gas engines don't wear out, except for piston rings, easily replaceable..a good used engine runs as well or better than a new one....The fastest G62 in our USRA racing series is about 6 years old.....It's been crashed and straightened more than once, just keeps getting looser and better..Like a fine wine [8D]
The championship Zenoah twin is a 2 or 3 year old GT74, faster than all the new GT 80s...

ronk1, I for one would be willing to pay more for a well broken in (used) gas engine - that I know the history on - than a brand new one that I had to put "gallons" of fuel thru hoping it was not involved in a crash before it got to max performance.

Dang, did I just type that, hope the next guy I buy a used gas motor from doesn't read this.

Ed M.

RGIGN1, Please don't take this the wrong but wouldn't a "more modern" engine work better for racing? Less weight, more power etc. It seems like they are preferred for acrobatics. Just curious

While I am not responding for rcign, you will get more power out of a good used engine than a new one. (at least until the new one is broken in) most people go with the new ones because of weight. The older engines usually weigh more unless they have been modified by someone who knows what they are doing. (rcign)

A G62 from rcign is as strong as some of the newer 50 and 60 cc engines and about the same weight. While I am not an expert, the piston and cylinder is about the same for most of the engines, the crank and case may be different.

Racing and aerobatics are two different animals. The Zenoah motors are designed for high rpm - take a look at their published power/rpm curves. Most aerobatic motors are designed to be propped around 6500 rpm (for 70-100cc motors). Zenoahs develop their best power + 9,000 rpm. If you want to use a Zenoah for aerobatics - use a smaller prop and let it wind up.

GEISTWARE---- Ditto!

I seemed to remember there are some classes of racing that REQUIRED all planes to have a G-62. I thing they were all AT-6's IIRC.

A more modern engine would be lighter, but a scale plane would need the weight anyway (and often more.)

The T6 class requires a stock G62, the other classes vary..
Unlimited class is just that, anything goes, engine must not weigh more than 14 lbs..We use Herbrandson 289cc twin drone engines, 9000 rpm,Aerrow 200 twins,10,000 rpm, Husky 8.8 and 11.6 twins, 10,000 rpm,ZDZ twins, and maybe a few others..All were derived from chainsaws except the ZDZ..The formula one and biplane classes have a limit of 80cc, so the engines used are Q75, Husky 4.4, Zenoah twins, and sometimes a Stihl or something else in that size..The engine of choice in this class is the Zenoah twin..No limit to these except 80cc...they turn around 11,500 rpm in the air...We tune these on the ground with a 15-8 prop to turn 11,000 and simulate the carb mixture conditions in the air....Props are all carbon fiber, fuel is methanol and nitro in varying percentages..We ran the Herbrandson twins with no nitro..
Note that there are no "modern" engines in the bunch, with the exception of the ZDZ...
Dave Johnson tried a 3W 120 about ten years ago, not successful...
There isn't enough money in racing engines to get a manufacturer to build a dedicated race engine, so we just get along with our old underpowered outdated chain saw conversions and go 230 mph The Herbrandson 289 makes around 32 hp with no tuned pipes..

My Brison 3.2 is a very nice engine and it has a mechanical advance... Easy to start, very good power, and reliable. What more could I ask?

does anybody run one of those beautiful, red airhobbies racing twins??[:'(]


dave

Nope.We only use what works...I have seen exactly 3 Air Hobbies engines, 2 were 4.2 and one was a twin..the first 4.2 was assembled too tightly to run.I had to bore the rear bearing bore deeper in the case to free up the crank..The second 4.2 was made with the back bearing bore .015 lower in the case than the front one, then someone ground the rear part of the crank smaller so the case would fit together..It ran, but the rear part of the crank was loose in the inner race of the bearing..It's still in the drawer in my shop, never to run again..I'll use the only good parts, the Sachs cylinder/piston and the Walbro carb, on something with a useable crankcase and a crank that hasn't been destroyed by grinding the rear shaft too small to fit the whole bearing race..
The twin did run after I changed the ignition to one that worked properly and refit some of the clearances in the engine....None of these engines were sent back to Air Hobbies..I figure if they can't get it right the first time there's no way they could do it later..There's a twin here in Flagstaff that doesn't run either, I haven't seen that one yet...

I bought a used Brison 3.2 w/ mechanical advance from a fellow here on RCU. It's the best engine purchase I have ever made! That thing runs as good as anything you will come across.