OS 105hzr black gunk on head

[colemn615]

Hey everyone, after flying this weekend I noticed some black gunk coming out of the head. A little back story, I cross threaded my previous head and this is a new one. I have attached some pictures.

I run Coolpower 20%

On a side note wouldn't the gunk be coming out because the head wasn't down tight enough and wouldn't this lead to a decrease in power?

Last time I pulled the head in June as reference.
https://www.helifreak.com/attachment...1&d=1465141994

What it looks like now:
https://www.helifreak.com/picture.ph...ctureid=107479

https://www.helifreak.com/picture.ph...ctureid=107478

[smwht]

That looks an awful lot like a loose bolt to me. It'll rattle in the threads, and the resulting aluminum dust blends with the oil and gives you that paste.

If the head block is loose the engine will run very lean, but the top of the piston looks ok - I'd expect to see pretty obvious discoloration on the piston if the block was loose.

I'm gonna guess the bolt in that hole was a tad loose and the others were tight enough to keep it together.

[PowerDyne]

did you cross thread the plug? Or did you cross thread the head bolts? If you cross threaded the head bolts, did you re-tap the cross threaded hole and use a new bolt?

Typically the heads on OS engines aren't threaded, it's the block that is.

If you have a bolt that's not holding good torque it may be leaking a bit. This would reduce your compression and could cause lean running. It would also reduce power because you aren't getting the correct compression.

How is your ring? Your ring and sleeve will be a dead giveaway.



That rainbow pattern on the side of the sleeve indicates hot gasses are escaping the head at that point. Is that the screw hole that got cross threaded?

[colemn615]

I cross threaded the glow plug hole. That head has been replaced since. I looked down at it while it was all the way at it's lowest point and didn't see anything that looked out of place. The ring I have not checked. What I will say is that it has good compression.

On the second to last flight about 4 minutes in I heard the engine go a little lean so I came down and landed it. I richened up the mid and high needles by about 3 clicks. It leaned up a bit while transitioning between high and mid so I wasn't sure.

The next flight it started to go lean about 1 minute into the flight. I brought it down and this time when I put it into throttle hold the engine died on me.

I could not get it to start afterwards and that's when I noticed the black gunk.

I am a little nervous because the staining on the piston from the previous picture had the entire piston head stained. The new picture has some shiny parts on one side. I could be mistaken but usually when something is shiny like that there is a problem?

[PowerDyne]

Typically there should be relatively even amounts of varnishing on the piston crown. If it's uneven, that indicates that your head wasn't seated correctly. Check your ring. I would bet it's starting to go shiny if it was leaning out like that. That black/grey goop is probably filled with fine metal particles.

You need to disassemble the engine and check the ring and sleeve pronto.

[colemn615]

Well, I would expect the side of the piston that faces the exhaust to be darker then the opposite side. In this case it's shinier which is why I would agree with you that something else is going on.

[colemn615]

Well, I thought before I pulled everything out that I would post a picture from the exhaust port. The ring looks good to me from the side.

https://www.helifreak.com/picture.ph...ctureid=107481

[PowerDyne]

Yes, that doesn't look bad at all. Maybe you got lucky. Perhaps it's just a matter of getting the head tightened down evenly in a star pattern. Unless of course your head is warped. I find it unlikely, but you never know. It very well could be if there was a leak due to a loose bolt.

Though it doesn't look like the ring is totally fried, but I would still pull the piston to check just to be sure.

One thing I did notice, and it may just be camera angle, but the locating pin on the block appears to be a little misaligned with the notch in the sleeve in this photo. It also appears that your locator pin for the sleeve is pushed into the crankcase or possibly squashed. Hard to tell from the angle.



Again it might just be camera angle and flash shadowing playing an optical illusion, but if your sleeve has rotated out of alignment a little. Perhaps you might be getting some leaking between the sleeve and the inside bore of the crankcase that is venting out from under the head at the intake side?

[colemn615]

I will pull it and check. So if any of the ring is shiny I should replace right?

As far as it being aligned I will double check, the picture is at a slight angle.

[PowerDyne]

Originally Posted by colemn615

I will pull it and check. So if any of the ring is shiny I should replace right?

As far as it being aligned I will double check, the picture is at a slight angle.

Yes, replace the ring if it has bling.

Also take a close look at the locating pin on the pitson too. they can ear down and allow the ring to turn and possibly strike the ports in the sleeve and destroy your piston.

[colemn615]

Well, I opened it up last night. The ring is black all around, the sleeve doesn't appear to have any imperfections. It's all buttoned back up and in the heli again.