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HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › OS .91 HZ --Still ok to run?
01-19-2010 06:33 PM  8 years agoPost 1
natew

rrApprentice

Brattleboro,VT USA

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Hey guys,
I have had this engine since about this time last year and this past fall had to replace the rear bearing...I have always run this rich and due to the bearing I guess had a lean run. Anyway I replaced both bearings and looking at the piston I noticed this really fine pitting. On the head too. I can feel it with my finger that its somewhat raised also, not just pitts but like dings of little bits of metal. It's not terrible damage, but I called OS to get their oppinion to see if I should replace it and the guy on the phone told me to run it but he said his boss told me to replace it for warranty reasons. I guess what I want to know is no matter if it was rust from the bearing that got in there and dinged it up or if you get a spec of junk in the cylinder from replacing the plug or some crap from the fuel is this amount of wear acceptible or is it something to worry about? I guess I have never compared a normally worn piston to anything so I am looking for some insight. Tell me what you think, I'd appreciate it.
Nate-

Trex 700, Trex 500, Trex 450 Pro

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01-19-2010 06:56 PM  8 years agoPost 2
rexxigpilot

rrProfessor

Florida

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Nate, the pitting does not look too severe. The real question is how do the cylinder wall and ring look? If you have deep scratching of the wall and/or damaged rings, they need to be replaced for the engine to make good power and run smoothly. If they are OK, run the engine as is.

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01-19-2010 07:27 PM  8 years agoPost 3
natew

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Brattleboro,VT USA

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The cylinder wall has no damage to it at all and forgot to mention that the ring is new. Do you suppose that rust from the bearing did this or something of that sort? and also is this fairly common damage from it?
Thanks for your quick responce.
Nate

Trex 700, Trex 500, Trex 450 Pro

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01-19-2010 07:31 PM  8 years agoPost 4
natew

rrApprentice

Brattleboro,VT USA

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Forgot to ask if there is any risk of further damage from just normal opperation? Will the heat/compression just keep making those pitts worse or will it have no effect until something else starts bouncing around in there?

Trex 700, Trex 500, Trex 450 Pro

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01-19-2010 09:46 PM  8 years agoPost 5
CoronaL

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Winnebago IL

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you should be fine
could be pitting from lean runs too

Randy!!! I am the liquor

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01-19-2010 10:04 PM  8 years agoPost 6
airdodger

rrElite Veteran

Johnston USA

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I can't tell if any parts were floating around but if you saw none I am in agreement it looks lean. It may have been detonating so richen up or add a head shim.

Chris

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01-19-2010 10:37 PM  8 years agoPost 7
natew

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Brattleboro,VT USA

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Yeah I did have a lean run...I'm kinda on the fence about adding the other shim. The engine always ran great, I've been thinking about trying some Rotor Rage, not that that would solve any problems but going to give it a shot I heard it runs alot better and cleaner than any other fuel. Been running CY Wildcat and like it but a lot of oil. Hopefully all will be well they sure aint givin parts away for this engine

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01-19-2010 11:16 PM  8 years agoPost 8
Pulento

rrVeteran

CHILE

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Looks like a bit of detonation. I ran CY30 on my HZ and had to shim the engine due low altitude, after shimming it ran really smooth on CY30.

On CP30 I didn't need the extra shim.

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01-20-2010 01:59 PM  8 years agoPost 9
supertigre

rrApprentice

Castle Rock, Colorado

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Yep, that looks like pitting from detonation. The tell-tale sign is that it is only in the squish area. The design of the engine is causing this because the squish area SHOULD be cooling that particular area to prevent detonation. Putting in thicker head shims to run higher nitro defeats that purpose.

Paul Mcintosh
Owner-CRCustom.com - custom vinyl lettering, banners, signs

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01-20-2010 02:09 PM  8 years agoPost 10
natew

rrApprentice

Brattleboro,VT USA

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I guess I'm not clear with what you just said...would it be wise to run both shims? or just the one 0.02mm for 30% I have in there now?

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01-20-2010 04:30 PM  8 years agoPost 11
jschenck

rrProfessor

La Vista, NE.

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my thought is this look like damage from shrapnel coming from the bearing that was going bad. I'd think that a lean run would have shown some heat damage on the exhaust side of the piston and some discoloration - don't see either of those. If the ring is fine I'd probably just clean it up, see if you can knock any of the particles off the piston and head and fly it. If the engine doesn't work out you really haven't lost much at this point. I agree the parts costs for the HZ are very high. I had to buy a new piston, $60, I broke it - ouch

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01-20-2010 05:39 PM  8 years agoPost 12
natew

rrApprentice

Brattleboro,VT USA

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Thanks Guys,
I think I'm gonna run it as is. The piston being $60 and the head another $75 if I was really gonna worry about it I'd replace them both, which I would do...I wouldn't leave the head like that and just get a new piston. I'll drop the motor on occasion--maybe. but I'll pay attention to it during flight and hope it stays running well. I just plain hate the thought of a 400.00 engine being less than perfect, but I guess so goes it...maybe with some tax $ I'll replace it for a piece of mind. I know the talk of detonation sure would hate for that to be an issue, I've been thinking of running another fuel with a lower viscosity maybe the CY 30 is a little to dense I really dont want to add another shim so maybe a different fuel like CP or Rotor Rage would be an improvement or a safer bet for this engine. But by the way the shards of metal are sticking up off the piston and head I could only imagine this being caused by something bouncing around in there.

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