cowgod

Hey guys. My name's Dan. Not really sure if this belongs here or in the Beginner Heli forum. I've been reading the forums for the last week or two, and based mostly on what I've read here, I just bought my first heli yesterday, a Raptor 50. As I assembled it, I was actually surprised I was progressing so well without making any obvious mistakes. Apparently my subconscious decided I was feeling too smug, hehe. When it came time to tighten the nut on the crankshaft, I noted the part that says "Note: A piston lock (TTR 1166P) purchased from your dealer will make this a much easier task." I didn't have one, but I've jury-rigged solutions to this problem before with car engines:



So I figured I'd just figure out some way to keep the piston from moving. This seemed to do the trick wonderfully:



However, after I'd gotten the clutch shoe bolted to the engine and tried turning the crankshaft, I found that the piston is apparently made of a relatively soft metal (I was worried that might be the case), and even with the plastic wrapped around the screwdriver, I had managed to dent the piston:



And that dent flares out, which keeps the piston from going up into the cylinder past the exhaust port. Crap.

So what are my options? At worst, I could just buy another engine - looks like the PRO-50H(R) is around $130 online. Of course, if I'm going to buy another engine, I might want to consider other models available... I imagine I could order a replacement piston - I understand these engines aren't too difficult to disassemble and work on. But I wonder if maybe this one can be repaired? The dent is above the piston ring, so I imagine it doesn't need to make a perfect seal or anything. Maybe if I just file it down so it doesn't contact the cylinder wall, it'd be alright? I don't want to cut corners if there's any chance it will actually be less safe, but obviously I'd rather not waste the time and money to replace the piston or engine if it's not necessary. What do you guys suggest? Thanks.

Charlie

You can try filing it down. If you do, break it in on the bench just to make sure it's going to run right. If it was me, I would get a new piston, they are easy to change.

You should have just taken the backing plate of the motor and put the plastic handle of a toothbrush or a wooden cloths pin and put it in beside the crank so it can't spin.

w.pasman

The piston is of aluminium...
Chances are that you also bent the rod. Did you check it?
The ring is indeed the main seal. If it's a small dent you may be able to fix it. However irregularities may disturb the combustion, causing the engine to run unreliably. Probably better to replace the piston otherwise you may have big troubles tuning the engine (esp as you seem to be a beginner)..

Good luck.

basmntdweller

My Feedback: (9)

Pull the engine apart. If the piston ring is still free to move around the piston, remove the ring and carefully file down the bump that is raised. Put the ring back on and put the engine back together. It should be just fine. If the ring is stuck in the groove, get a new ring and piston. I am not sure on the TT 50 but I know the ring on the OS 50 has a real small pin in the ring groove that keeps the ring from rotating. Be sure to properly orient the ring gap to match up with the pin if it has one. I'd bet it does. They are there to keep the ends of the ring from getting caught on the edge of a port.
I use a nylon rod that fits in the bore of the crankshaft and I let the connecting rod lock up on the side of the nylon. You'd have to get really carried away tightening the nut to hurt anything this way. The nylon rod would break before anything else would.
Good Luck,,,Matt

Spaceman Spiff

My Feedback: (1)

doesn't look that bad to me, flip it over and see how it feels. If it still feels like a good engine, it probably is.

cowgod

Thanks for all the replies. Yes, I'm definitely a beginner when it comes to RC. I've got a nitro car, but I can never get it tuned right It's so foreign to me that engine internals are both cheap and easy to replace. I'm used to working on real cars, where opening up the engine is not nearly such a trivial endeavour.

Yeah, the damage didn't look that bad, until I took the engine to my LHS to see what he had to say. He said, "Hmm, I don't think there's a problem" and forced it with his hand, and now there's a nice long scratch down the piston:



I assume that means the cylinder sleeve is also damaged. It does seem to turn relatively freely now, but I imagine it wouldn't have very good compression and would be very hard to tune. I guess I'll just order a new sleeve and piston, unless you guys think that I should just try to run it as is.

Does anyone have any idea how long the parts might take to arrive? It's frustrating having to wait, because I went out to my local airfield today to actually see RC helis flying in real life (I'd seen videos but hadn't seen them in person before) and it only made me even more excited about finally starting the long and arduous process of learning to fly myself Oh well, I ordered a copy of Reflex XTR, so that will help pass the time once it arrives. Also, it will hopefully help to ensure that my first helicopter flight is not promptly followed by my second helicopter purchase.

Darksider

now you've turned it over afew times and it's free'd up a bit you've took the worst of the burr you made in the piston off and engine wear will do the rest for you, so just stick it in and fly it, your a learner so intially you'll be close to the ground anyway and an engine failure at this stage is not that big a problem, the blades will just slow gently and the heli will slowly drop to the ground, if it works out you've knackered it do yourself a favour and buy an OS 50 hyper, it's alot better engine than the TT50.

Gareth

cowgod

Hmm, well that's certainly the most appealing option (least work, time, and money required, and gets me in the air soonest). You're right, this engine will be spending a good portion of its life within a few feet of the ground, so unless it will have problems making compression, I guess it should be safe to run as is. And yeah, I've heard lots of good things about the OS 50, so I wouldn't mind an excuse to upgrade if this engine should fail Thanks for the advice.

Dan

w.pasman

Mmm now it looks like the scratch is going deep through the piston ring too. I would not run the engine with such a ring. Also to damage it this way there must be a damage on the liner set. This is more serious because the liner is special treated steel. Replacing both liner and piston will be more expensive. May I suggest that you get the engine apart and properly assess the situation before going on...
Why did this shop guy FORCE the engine? You're probably further away from a repair than it was before...

Wlouigene

My Feedback: (66)

Checkout what happen to my brand new OS 50 Hyper only 3 tanks of fuel I’m still breaking the engine, it running so rich I can barely hover it. The fuel that I used it cool power 15 low nitro.

cowgod

Well, today I ordered a new piston, ring, and sleeve. Comes out to $59 total, half the cost of a new engine, but I didn't like the idea of running it as it is. How hard is it to replace these in a ringed engine? Are there any websites that describe the process? I've done some searching but haven't come up with anything. Will I need a special tool to install the piston ring, like you do with cars? Thanks.

Wlouigene

My Feedback: (66)

It easy, here a [link=http://www.traxxas.com/support/howto/trx_trouble_enginerebuild.htm]link [/link] to check it out, it not for heli engine but it the same principal

Darksider

thats nasty Wlouigene, didn't happen to use a piston lock tool that goes in through the glow plug hole did you??

Gareth

w.pasman

Check my web pages

[link=http://graphics.tudelft.nl/~wouter/helipage/tips/openengine/openengine.html]http://graphics.tudelft.nl/~wouter/helipage/tips/openengine/openengine.html[/link]

BTW I now have an oven to heat up the block. 175C to get the stuff out, 150C or lower to get the new bearings in. If the bearings are still OK, for the liner set I dont even have to heat up the block, it slides in and out without effort.

w.pasman

May I comment on the link given by Wlouigene
Never use metal tools and don't hammer on the engine with anything hard (eg hard plastic)....

Wlouigene

My Feedback: (66)

I used the crankshaft clamp tool to hold the piston in place

-pkh-

My Feedback: (2)

I didn't use any kind of piston lock at all on my 50. You don't want the fan screwed down too tight against the front engine bearing, just snug. You do want to torque the crankshaft nut down very tightly against the fan, though. To do this, I just use a thick rag and hold the fan tightly while I torque down the nut. Just be sure to use some blue Loctite and you'll be set. Now, if you want to get the fan off of the shaft after the Loctite has set... you'll probably will need some sort of piston lock! RaptorTechnique recommends a crank lock...
http://www.raptortechnique.com/manua...-50_page13.htm

emosolo

Good Day,

It has been a while since I have made any comments, but here is my two cents....

I have had two engines and managed to create the burr as described in the first entry. The streak across the length of the piston didnt change my engine performance at all, not on either of the engines that it happened on. I have had over a 150 flights on the same engines and piston and rings without any engine failure.

I however do keep an I on it...

Regards
Emosolo

A150L

I'd also vote for using the engine as is. You aren't going to see a major engine failure from a scored piston / sleeve. the very worst that could happen is lower top end power due to slightly lower compression. Since you are a beginner, you will not need anywhere near the power that engine is capable of for some time.

Your first few weeks are going to be spent learning to reliably hover at 1/2 stick and 30 to 40% throttle anyway. Run it as it is. IMHO.

hitman45

Same thing happen to me, when I stuck a allan key in the exhaust port to lock the piston from moving...and dented the piston. And I was crapping myself because my piston didnt want to travel up the top because the dint was stopping it from travelling up. So I took the risk and forced it (like the guy did to your engine at the hobby shop) and now my engine still runs great.
I didnt really noticed a change in compression, but yeah still runs good.

By the way this was my car engine. But similar type of stories.

cowgod

Well, the parts arrived today and I replaced them (everyone was right, that was simple and took like 20 minutes). It sounds like I could have just left it as is - oh well, I guess I'll just keep these scored parts on hand as emergency spares for the future. For now, the engine is back together and in the heli. Now I just have to see if I can get the servos adjusted etc. in time to go flying on Saturday. Thanks for everyone's advice. It's very reassuring to hear answers from a whole bunch of different people, especially when it's advice that goes against what I'd considered conventional wisdom.

WhtBronco

I don't use anything to lock the piston either. Not even a rag on the fan. I just grabbed hold of it and tightened the nut, using locktight of course. My hands, however, more course than most. I can sand drywall for hours bare handed no problem.

Wlouigene

My Feedback: (66)

OS came through for me; they sent me a brand new engine

Buck Rogers

dude i had a problem simular to your one when i first got my rapter when it came time to put the kooling fan on the engine it was a verry tight fit so how i got it on was...got 2 small parts bags frome the kit rolld them up tight enuf to fit into the exausc port so the piston could not go up and turn the motor over then screw the fan on the crank shaft..i only yousd plastic bags because i did not want to put somthing hard on top of the piston incase it damiged it.

joe..i feel like jackson mississippi

RevGadget

I got lucky and read in a forum to removed the backplate and use a toothbrush or plastic screw driver handle to hold the piston rod. If you don't know, its best to do a search for it or ask. Someonoe may disagree, but there are no stupid/dumb questions when it comes to this hobby.