Hello all,


Well after sending off my plane to Hobbico about 4 weeks ago, I got the items back, well, after i had to call them and yell at them for forgetting half my items, and sending me the wrong plane "kit". Anyways, the plane had a mid-air collision, took it home and cleaned out the ening and it was running great after about 3 hours of working on it. I sent it back to Hobbico when they requested all the items I recovered from my mid-air, so, not wanting to leave anything out I sent the working engine back. Fast forward 4 weeks and I finished my Tower Trainer ARF and the engine is Knocking like no ones business. Sounds like wood planks in a bicycle spoke. Like I said the engine was running great when it left, now It sounds terrible, it starts up easy, just sounds horrible. Im not sure what the issue is, or if they even looked at the engine after charging me even though it was under warranty. Nothing is loose, everything is on just the way it should be but its still knocking. Any Ideas?


ed

Glow plug. I flew an engine so long (repeated flights) on an Avistar that I never checked the plug. Once while at the field and cruising over the field a fellow modeler remarked that it didn't sound right. I agreed and landed and found that the plug was all carboned up. What a difference a new plug can make. Easy to check. At least rule that out.

Tom,


Thanks for the input, I took the glow plug off lastnight and it did not look like the piston was hitting the bottom of it, nor does it have very many flights on it, maybe >1/2 gallon of fuel worth of flights. I just dont understand why it worked before I shipped it to them, and now it sounds terrible.

You try running it on a test stand so that you can eliminate the possibility of harmonic vibration from causing something like a loose wheel to make the knocking noise?

I do not have a stand, unfortunately. Im nearly 100% sure its not vibration, everything is cranked down pretty well. My dad is an engine mechanic and was in this hobby for many years, I put the phone down next to the engine and started it up, he said it sounded like the piston was hitting the bottome of the cylinder head, but there wasnt any visible damage on the glow plug, *sigh*

Could a head gasket been left out during an inspection or cleaning?

Thats actually what my dad said, however, three of the head screws are stripped, and im at a loss on how to get them off.

The cap head screws are stripped out? Or is the allen wrench you're using rounded? You can cut off an 1/8" with a cutoff wheel. Otherwise an Easy Out you can get from a hardware store will get them out. Best suggestion I can give you, get that engine into your dad's hands.

http://www3.towerhobbies.com/cgi-bin...?&I=LXJB36&P=Z

Trouble shooting via listening to an engine on the telephone is definately a new one on me It also stands virtually no chance of success. Find your local club and get that engine into the hands of someone with some experiance.

John

Thanks for the suggestions, Im pretty sure its the screws, but ill cut of the tip of the allen and see what happens, If the folks at the club cant fix it then I guess its going to get shipped off to my pops in Florida Thanks Again.

My dad just got off the phone with Hobbico (hes not easily prsuaded like me) and they admitted they did not fix the engine, even though they knew it had been in a crash, and that I had paid for it to be fixed. They must have taken it apart and not put it back correctly since they did admit they had in there notes what was wrong with it....Now i have to send this back to them and they'll take there time fixing it im sure.

Before you sent it back get it into the hands of your local clubs engine guy.

John

Yeah, Ill do that, there sending me out the return label today, but Ill try to get in touch with someone in my club that can help me. I'd rather not wait another 3 weeks for the engine to come back if i dont have to. Was hoping to get out this weekend and do some flying.

My .02 If the engine is that bad, send it back. I'd bet they send you a new one. They admitted that they screwed up (make sure you put that e-mail or a copy of the letter in the shipping box with the engine). I know it bites to be out of an engine for three weeks, but if someone at your club that does not the experience with the engine could screw it up even worst if they try to fix it. Unless I heard it, I couldn't tell you. You might take the back plate off and see if everything is still connected. It sounds to me like either a bearing has been spun or the connecting rod is bent. Sometimes just hangin out the field asking questions and observing is as good as flying.

Good Luck

Hi!
It sounds as you run the engine on too much nitro! Too much nitro (or to high compression) will produce a knocking sound.
Try 5%!!!

I usually run my Towers with 10-15% nitro and I have never heard any sound that sounds like "knocking".

I wonder if what you actually mean is a 4 stroke sound, which is typical if the engine is overly rich.

The implication that anything over 5% nitro content will cause problems is simply absurd.

There is a lot of specuation and very little info here only vague referrences to "yelling at hobbico" and shipping airplanes back, mid airs and crashs. Does Tower insure crash damage of their engines? seems unlikely.

I would want a lot more info before I made any more recommendations beyond leting someone local in his club who is experianced with engines look at it and then make a decision as to what he should do.

Calling hobby services up and yelling some more is not going to accomplish anything.

John