Problems with PAW .09
 

Hi gang,

I bought a used .09 R/C engine a while back, took it apart and cleaned it up a little (didn't need much). I finally got around to mounting it on a plane, and took it to the field last week. I was using an electric starter, and it spun up just fine, and was starting to fire, when I noticed fuel leaking out of the cylinder/muffler joint. When I looked closer, I found two of the three cylinder screws were broken, and the third was bent! They were fine when I took it apart earlier.

I have a lot of time on larger PAWs, so I have a fair understanding of how to run them, so what have I done wrong? Could it have been over-compressed? Does anybody know what size cylinder screws I need to look for?

Thanks!

Jeff

Sounds like you have damaged your engine by using the electric starter on it. You may well have had a "hydraulic lock" and then the weakest part/link will brake, i.e. the conrod or the cylinder screws....

Talk to PAW directly and they'll help you with spare parts. When the engine is repaired, then run it first without the muffler so that you can get used to how much prime and compression it needs. When primed correctly they are very user friendly and there is no need for an electric starter.

Honestly though, would two bolts, in good condition break and one bend from a hydrolock?

Sounds like they were compromised before the fact.

Think bolts were bad if hydrolock would have stripped threads out of crankcase and/or bent rod martin

Jeff,

the cylinder screws are 6 B.A. (aka British Associated).

Probably not a thread type readily available in Alaska.

Otherwise they're easy to get either from PAW or a Model Engineering materials source in the UK. Perhaps there's one that stocks them in Canada?

The stock PAW screws are relatively soft, probably deliberately so. They may do this so the screws will fail before you do any real damage to the engine.

Are the rod and crankpin ok?

Generally speaking it's usually safer to flick start a small diesel rather than using a starter.

I can't imagine a PAW so noisy that it actually needs a muffler, or is it your club that demands all engines muffled?

If you can run it without all the better.

I agree with the previously expressed views that you shouldn't go anywhere near a PAW 09 with an electric starter. The first PAW I bought was 2nd hand from a clutz with an electric starter, he ground about 1.5mm from the front housing. Apart from that though the engine starts and runs nicely.

Spend a bit of time getting to know what it likes and it'll start quickly every time.

I do like the muffler, it makes the engines very quiet and it keeps the oil away from the plane. But the muffler does make starting more difficult as one cannot simply prime the side of the piston. I guess one could easily add muffler primer tube, but I haven't tried that on PAW.

It is very easy to overprime the engines when priming through the carb as the crankcase tends fill up before you get fuel to the top on an upright mounted engine. Side mounted are easier, or simply hold the plane rotated 90° and turn the engine over, this way the fuel will reach the top (above the piston) more easily and there is less risk of overpriming. Turning by hand you will feel when the prime reaches the top and it is time to flip it for starting, or if you have over primed and need to empty that first.

'or if you have over primed and need to empty that first'

I just back off compression, and settle in for a nice long (minute or two) flicking session. Probably not 'best practice', but if time is not an issue it works for me.

You can usually learn to correctly intake-prime an upright engine by limiting the prime to a couple of drops down the intake. Most over-prime and end up with a flooded engine.

George

Getting back to the head bolts, it is possible to unevenly torque down the three bolts.

So perhaps this may have been a contributing factor too.

I was told to torque them down in stages , two finger tight, then whole hand grip lightly, then a final firm whole hand nip up.

Thanks everybody for the help!

A little more background may be in order. This engine was installed sideways in a Dynaflite Butterfly. I thought it would be safe to use the Sullivan Hornet starter which was made for 1/2A engines. This starter spun the engine quickly, but has very little torque. I only used the starter due to my being nervous about being alone at a field known to have brown bears in the area, wanted to get it running quickly! When I had it apart, I was very careful to torque the screws carefully in stages to avoid any unevenness.

The high speed of the Hornet starter will probably be enough to cause damage too.
It clearly sounds like a hydraulic lock combined with an electric starter to me...