Evil Homer

Hi Bob
Went out to fly my D-Dust today, for some reason the engine would not start, ended up having to replace the plug, got the engine running, did a range check and which failed. Anyways decided to let the engine clear it throat a bit as it had not been run in a while.
This engine has done some milleage - couple of gallons but has not really been abused, mostly running 5 or 10%, normally castor/synthetic blend, always has run good.
Following the run, i pulled the plug and saw the coil had been hammered and twisted, figured bearings were or there way although they felt smooth.
Got home and stripped down the engine and i found the conrod had split at the base of the big end, any ideas what may have happened, there was no loose debris in the engine that i could find, piston crown has some pits, but these look quite old and are not under the detonation point. Prop is a 8.75x8 narrow blade pylon.

bob27s

My Feedback: (19)

Hey there.....

Thanks for writing.

Im not sure what happened there. A few gallons is nothing. These things run for years

The engine would blow plugs from a lean condition. Not from normal operation. The plugs should last quite a while, even under race conditiions.

Twisted-up plug comes from a very lean run or forigen object damage. (slighly bent or compressed coil is ok, as is one that has been moved aside a bit - that happens on the racing engines - but a seriously mangled one comes from something besides a normal hard run)

Pitting on the head means either repeated detonation (lean run/air bubbles) or it "ate" something causing the damage. Either one could cause the rod end to go. A broken rod end is pretty rare. It is the same rod used in the QM40 engine.

It is probably worth while sending the engine down to Dub and letting him give a serious once-over.

Bob

Evil Homer

Hey Bob
Thanks for the reply, were you at the Nationals with Dub over the weekend.
I will check what the costs are to send it over to the US, from here, seems strange this problem.
The plug is damaged internally, front of the coil is fine, just inside it has been mangled, looks like FOD, at the time the engine was running there was plenty of smoke coming out and a pretty good smear of oil across the plane.
Cheers
Steve

Evil Homer

Well engine is jetting its way across the Atlantic, wish I was....
Anyways just be back in the hands of Mr. Jett soon

bob27s

My Feedback: (19)

Steve,

Nope.... was not at the NATS this year ... had a wedding to attend, and my little boy's baptism. Maybe next year

It might be worth just ordering a piston/sleeve/head combionation and a new rod. Easy to install. Cheaper shipping. However, if the bearings are questionable, it is probably worth sending the whole thing over and letting Dub rebuild it from the bottom up.

Bob

Evil Homer

Hi Bob
I had thought about almost a complete rebuild since the parts are not that expensive considering. Still if there is some FOD in there or something else which i am missing I would prefer for it too be found.
Cheers
Steve