Nitro engine maintenance guide

[KouDy]

Hey everyone,
i tried to look for some informations but failed to find too much so i am bringing you photo guide to the nitro engine maintenance. I will be using my Redline .53 heli engine from my X50 Titan.

I needed to replace piston ring on the advice of experienced heli flier from the field so that is the main reason for me to create this guide.

I do not deal with bearings and crankshaft right now. I will eventually create guide for them too if piston ring fix didn't work to remove my problem, bearing are my next item on the agenda.

I will not go into how to remove engine from the heli, it's pretty obvious. If you are in doubts you can check the my X50 building guide here and try to reverse engineer some steps (it's 8+2 screws). If you fail anyway, drop me a PM and i will add more photos here.

Recommended spares to have : piston ring, nut that holds the fan on engine shaft

So let's get started. When you remove engine you will have something like this :


Remove the clutch first. Turn the engine and remove the backplate (4 screws from the bottom). This step will allow you to use crankshaft locking tool. I am using the one from the hobbyking. If you used red threadlock on the nut that holds the fan you may need to heat it (i use red and hairdrier does the job well) because it might get really tight. Use the locking tool to prevent crankshaft from turning. If you don't have the locking tool, remove the carburetor assembly, dial the slot on the crankshaft and put something inside so you lock the crankshaft. An old toothbrush or plastic chop stick (thicker end) do well. It's not ideal but you should be able to work with that. Then also remove the clutch fan and washer between fan and engine.

As next step remove the heatsink on the top of the engine. It's 6 fairly long screws that will likely be threadlocked so it might need some force. If you fly >15% nitro or in humid conditions there are chances you have paper thin washer between the heatsink and the engine, don't lose it!


As next you have to dial the crankshaft like on photo here :

You can see orange part there on the photo. That is sleeve between piston and crankcase of the engine. You should be able to stick your finger there and push it up (in direction where heatsink was mounted). It should come with not so much force but shouldn't go too light either.

Note the marks how they go. We will need these later. There is retainer pin on the crankcase, slot for retainer pin on the sleeve and arrow on top of the piston pointing at the pin/slot (direction is towards the main rotor when it's all mounted).

Now you have to pull the sleeve all the way out.

Dial the now loose piston all the way up (like before) and slide the conrod from the the crankshaft and take it out of the engine.


Piston disassembled looks like this :

There is shaft, locking spring, conrod and piston on the photo. You have to remove the locking spring, remove the shaft and then conrod is free. Spring is tricky to remove and consequently put back plus i didn't really find too much use in disassembling this so unless you have a good reason i'd say don't do it.

We got to the piston ring. You can see there is pin inside the groove on the piston :


The ring is made from easy to break material. You will want to use some pointy pincers to lightly push it away from groove and then in circle you can "seed" it on top of the piston. Do not use too much force or it will simply snap, it's quite fragile.

Piston ring closes the way it "hugs" the groove pin from both sides when it's slided into the sleeve. Make sure you will have the piston ring aligned later when you install everything back.
When you put it back it's just backward. Lie it on top of the piston and then put one end into the groove and with circular motion it should very easily seed by itself. Align the break in the ring with the pin in the grove.

Clean all the parts from the worst mess and we can start installing them back. Piston comes first. Conrod has a groove on one side. Groove side goes towards the main rotor of the heli when mounted. I am not sure what would happen if you put it backwards so don't mix it. You should be able to align arrow on the piston with retainer pin on the crankcase.

Now it's hard part, with piston dialed all the way to the top, you have to put sleeve into the crankcase and piston into the same sleeve. At the same time you need to watch for piston ring to close correctly around the pin in the groove on the piston (word of note here, the pin in the piston groove is NOT aligned with anything else! It's off to one side!). When all aligned it should looke like this :


Now you try to hold the piston up and slide the sleeve a bit down. I had problems here when crankcase was simply too small to accomodate the piston sleeve. If you run into same problem, you need to align like i described in the paragraph above. It will go inside at least a little. Then simply heat up the crankcase. I went to local car/moto repair shop and they let me use their heat gun (i don't have any). Then i was able to push it in almost all the way in. Few milimeters away. I used wood over the sleeve and gently hammered it down all the way until it was seeded.

Now put back the heatsink (don't forget to high % nitro/high humidity washer if you use it) with it's 6 screws. Tighten them in star pattern so you don't warp anything. Then it's fan with washer, nut. Backplate and clutch and you are done.

Bearings maintenance will maybe come soon. Bear with me...

[zattan22]

Bro,
You do not need to remove the clutches and fan.

Sometimes, the piston sleeve is just too tight to pull out. Use a small cable tie, insert into the holes in the sleeve and turn your engine to use your piston to push the sleeve out.

[KouDy]

You don't need to remove them unless you want to run maintenance on the bearings. I have still that point on my agenda for future. Just didn't have time to do that now.

[omarb]

Hi, please advise how did you remove the fan/hub assembly? I have tries heating and tapping the crank on the threaded end etc, it just wont budge, the clutch, prop nut, etc came of easy enough just the fan is stuck on there.

[omarb]

Oops... Never see date of the posts... Sorry for the thread necro...

[Rob43]

In this thread, he indicated to use a crankshaft locking tool to hold the crank/connecting rod so you can use a wrench on the locking nut on the fan hub. It can be VERY difficult to break it free.

In case you might not be familiar...here's a link to such a tool. Might be best if you can match up the right tool for your engine. I have one like this one, and it doesn't fit very well.

LINK


He mentioned using heat to help loosen the nut if threadlock was used. A soldering iron tip, or micro size torch could be used for this purpose.

I have found this can be a problem area on the X50. Attempting to start a hydrolocked engine is a sure fire way to loosening the nut and fan hub when not wanted, LOL! Without threadlocker, this is sure to happen eventually. The result is if it loosens up, it will unthread itself when the heli spools down and spread the frame apart. Can cause a complete tear down to re-tighten the hub and nut.

[omarb]

OK... Problem solved, I put the crank case in a vice and used some elbow grease, the prop nut was not the issue it was loose. Tell me how do you tell when the piston, ring and liner need changing?

[Rob43]

liner: scratches, scoring
ring: scoring, shiny bare metal appearance
piston: damage to the crown

[omarb]

Hi Rob,

Thanks for the replies, really appreciate it. I have attached pics of my piston and liner, let me know what you think. The liner looks good, not sure bout the piston and ring.

[Rob43]

Sorry I didn't catch your reply sooner!

Can't tell 100% on your liner as there's only one pic. Looks good from the one pic I see.

The piston crown looks suspicious. Are those pitted areas on the piston crown? If there is pitting, I'd probably replace it. I would suspect it was from predetonation at some point. It didn't blow through, but might have if run that way longer. I am no expert, though. You might post this in the engines forum and see who else could comment.

Best wishes!

[Andy from Sandy]

Looking at the staining on the side of the piston it looks like you have had blow by which means the ring isn't sealing properly.

The crown of the piston looks burnt as if at some point it has run quite hot.

The problem is that to change the ring but keep the liner you need to hone the liner to allow the ring to seat. The coating on the liner is very hard. It will take something like a brake slave cylinder hone to do the job properly.

See if you can find any threads on glaze busting or honing.

[omarb]

Thanks for the help, I can see the liner is stuck to the piston, the crown is discolored but still smooth and the liner is smooth, was reading up on the honing and from I understand I can do it gently with high grit sand paper. Also do u think I should replace the piston? Is the staining on the side of the piston a problem?

[Andy from Sandy]

The staining down the side is not a problem. A new ring seated properly is all that is needed.

If you are sure the crown is smooth and not pitted then carry on using it. Check carefully the pin in the groove that stops the ring from turning. If that looks worn hen you will need a new piston.

You could probably clean it all up using a plastic scouring pad.