strulag

My Feedback: (-1)

This is crazy...At first I thought it was the lack of baffling in the cowl but then I took the cowl off and I got the same results. Right after the flight I measure the temp (with a Duratrax Flashpoint) and it goes out of the range of the temp gauge (over 428 degrees). This seems EXTREMLY HIGH. What can make the engine run so hot? I have no experience with gas engines so I just took some pics of the spark plug to get some opinions on mixture. I also took some of the piston as I read on a post that if the piston has pink marks then it's a sign of overheating. The pics are after I tried cleaning with a paper towel.

I was planning a whole day at the field tomorow but I am now worried. Should I not even run the engine anymore untill I figure something out? What could it be? Please help with this as it's my only flyable plane now

1st pic = no flashlight just camera flash
2nd pic = flashlight shining on plug

strulag

My Feedback: (-1)

Top, middle and bottom of piston. I also noticed that if I stick my finger in there I could move the piston back and forth a little bit (I could hear it clink back and forth)...is that normal?

Crusty

Ugh..top end looks fried, the plug is a nice colour, what was your fuel mix?, my first guess would be improper lubrication

strulag

My Feedback: (-1)

40:1 as reccomended by RC Showcase

H. Wayne S

My Feedback: (18)

I think you have a faulty Duratrax. 428 would melt the piston to the wall.

Flypaper 2

Plug is burning the right colour. Piston is showing normal varnish. Bum heat gauge too. See if you can borrow one. Where on the motor are you measuring it.? Oil mix is right. Go fly it.

OSilfa

My Feedback: (2)

i think that you need a new temperature gun!! your engine is good go and fly it.

OS

Crusty

strulag, the third picture shows what looks to me like chatter marks on the piston , caused by piston rock, if you can get hold of the specs get the piston/cylinder dia tolerances
checked, there will allways be a small amount of clearance but maybe yours is excessive, if this is so it will sound slightly clattery when running
I agree the temp gun must be out, but the amount of oil varnish that far down the piston looks, to me like it got hotter than it usually does
I guess run it and check with another sensor

Stiks

I think I remember reading somewhere that those guns can give dud readings if you don't aim it at a matt black surface. Has something to do with the shiny metal reflecting. Plus if it was that hot the motor would cut out.

BBW Walt

My Feedback: (11)

I use a Ray Tek Mini Temp. Its a good unit but it'll give readings all over the place. Its hard to find a reliable consistant area to get constant readings. Painted cylinders are worse. The marks you see are normal, the discoloration is normal and your plugs don't look all that bad. All the engines that I have seen in service that were overheating developed transition issues while at the extreme heat times. I agree with the majoity here your heat gun is playing games with you.. If your getting consistant runs from start to landings Go fly it..I have had some overheating issues and the engine let me know it wasn't happy. I took the battery out of my temp gun and put it in my volt meter. Battery's are a bigger issue to me that unreliable temp readings

Antique

My Feedback: (4)

There should be no brown buildup under the piston rings...They either never seated or are worn or stuck in the grooves..

BBW Walt

My Feedback: (11)

Just did an exhaust header on a blue head ZDZ80 for a friend, Exhaust port and piston looked exactly the same. Motor has about 6 gallons through it..Runs great

davewallace

My Feedback: (29)

Hi strulag,
Did you post this on the ZDZ support forum? They are the official experts this issue.

Dave

Diablo-RCU

My Feedback: (1)

The varnish on the piston looks normal, I don't think it's ring blowby. It usually comes from oil condensing on the hot piston skirt. You will see the same sort of deposits underneath the piston crown.

Antique

My Feedback: (4)

Could be...
Been looking at pistons every day for about 18 years, very few had brown deposits underneath....[8D]

RTK

My Feedback: (1)

Gotta be blow-by, how many gallons thru this engine?

One more thing, if you really want to know what your temp is put a thermo-couple under the plug and run a data logger.

rc bugman

My Feedback: (30)

Hi,

It has been my experience that ZDZ run hot (40's) and gum up the piston like the picture. ZDZ's are shy on fin area. My 3W's which I run harder than the ZDZ 's I had do not have brown deposits below the ring on the piston. More fin area and they run cooler even though I work them harder.

Listen to RCIGN. He knows his engines!!!!!

Elson

RTK

My Feedback: (1)

I'll second that !!!

rmh

Blow by?-- then why can this stain occur only on area aligned with the exhaust port?

Engines with ring seating perfectly-not stuck and not scored on piston or ring.

RTK

My Feedback: (1)

Hey Dick, not meaning to be argumentative (you know zdz's) but how can you tell it does not encompass the whole piston? In the first pic it looks like it might be going all the way around.
Would you not have to pull the jug to see for sure?
If the engine runs fine I would make sure my needles were set a tad rich (baffle it) and just keep flying. If I were ambitious and it was my engine I would clean it up first.

strulag

My Feedback: (-1)

Well guess what? Today I went and I flew it. STG was there with his temp gauge (exactly the same one I have) and it was a whole different story. Temps were 180s - 190s. I even did a bunch of hovering and 3D stuff to see if it will get hotter and it still came in around the same temps. I was VERY relieved and happy, but isn't 180-190 a little on the "too good to be true" side?

A couple of things I forgot to mention...After a very long flight I notice a slight delay in throttle response (is that a sign of overheating?) and also that when I put my finger in the exhaust port the piston moves back and forth noticeably with a clinking sound on each side. I also hear a similar clinking sound when I rotate the prop a bit. Does that mean anything? If it would help I can get it on a short video clip and post a link to it.

strulag

My Feedback: (-1)

What's blow-by? I have no clue how many gallons through the engine but I think it's at least a couple of years old. I also know that prev. owner had a piston change done to it a year ago.

Diablo-RCU

My Feedback: (1)

Blowby is when combusted gas expands and pushes it way past the ring and down the side of the piston when the ring doesn't make a very good seal against the cylinder wall and piston groove. It causes the piston to get very hot in that region and can cause the piston to expand and seize. If the piston ring is stuck in the ring land with carbon, you will get blowby in any engine. If the engine has good compression and good power, it's unlikely to have a stuck ring. When you start to notice the compression is soft, it's time to pull the cylinder and unstick the ring.

rmh

The 180/190 is typical of the engine run in an aerobatic setup-at decent fuel mix and good cooling. Iget this as a matter of course on ZDZ/DA etc., I have checked locally
The comment on inadequate fins was interesting -- in that DA has sent out some 150 size engines ---with almost half the fin area machined away
Properly setup they work fine -(seen em ).
The "loose piston" thing noted by finger in port is an odd one to me - never tried it but sounds like loose con rod -also odd as I never saw a ZDZ with one of these. Possible tho.
A loose skit fit will cause rocking tho I don'tthink you could feel this .
My own engines have some stain on skirts -no problems - My "hot rodded" 80 cranks the 26x12 ZM at 7400 in the air -so power is not down.
My 50 runs 8300 in the air on 22x8 Mejzlic - same stains --no looseness tho on either engine .
Unless you "smoke" these engines - they run well on and on -as they should.

Flypaper 2

There is always a certain amount of blowby . It's how the 4 stroke glow engines lube the bottom end.