So I was running my car and the buggy cut out and died. I tried restarting her but I noticed I lost compression and there was spray. I looked and saw a screw was missing from the cooling head. I took them all off to find this.

It looks unhealthy but was wondering what you guys think

Thanks

You really can't tell just by a picture like that. It sounds like the cylinder head was just loose so bolt it back on and make sure there are no compression leaks then try to run it again. A worn out engine runs strong when its cold then just loses all power when the temps come up because it loses compression from the sleeve expanding.

..

Your piston looks rather dark but other than that its fine, any regular buggy engine will fit even a MT will fit.

Your piston looks fine by looking at the color.

Take it out and see how far you can push it through. if it goes all the way like on my RG below it's toast.

A loose head and dark piston could be a sign of detonation. Assuming you didn't touch your mixture settings it would probably be a good idea to purge the fuel system and carb before trying to run the engine again. Also make sure that your exhaust system is sealed up good.

Detonation? What exactly does that mean?

Also - how would I drain the carb out?

Thanks

The extra fuel introduced into the combustion chamber increases compression by adding non-compressible matter; this also increases cylinder pressure during the combustion process, which may cause detonation. Detonation occurs when the fuel explodes instead of burning, and that can cause internal engine damage. a extra head shim will likely prevent

A combination of compression, heat and a catalytic reaction between the platinum in the glow-plug coil and the methanol in the fuel creates combustion in a nitro engine. Altering the heat range of your glow plug can alter the timing of the combustion process. Nitro engines don’t have an ignition system that can be used to advance or retard combustion timing, but a hotter plug that causes ignition a little earlier in the combustion process can have the same effect. “Advancing” the ignition timing can increase overall power output, especially at higher rpm. There are limits, however, and installing too hot a plug causes pre-ignition (detonation) and risks damaging your engine.

First of all - the piston should be dark and is not in itself a sign of detonation. It's a sign of 'good power'.

Now, if you have problems with detonation you will see that the piston has become pitted and the head will not be smooth. It will be kind of dull and somewhat rough.

Here's a close up shot that shows that I think it IS pitted. So likely this is not in good condition then?

So where does the "extra" fuel come from. Are you saying that's a bad thing to have extra fuel in there or that is just a matter of how these engines work. That there is extra fuel in there to aid compression, but with an extra hot plug more of it combusts, or detonates causing damage?

lastly - how does the shim help? By putting more space in and releasing some compression?

sorry for my questions I just like to understand thouroughly when I am informed of something new

Thanks

extra fuel probably running it rich,and yes you are correct about the shim

HEAD SHIMS

Engines are essentially air pumps. The engine takes air in, mixes it with fuel, and then the mixture is compressed and ignited. The additional pressure created by the burning fuel increases by a factor directly related to the amount of compression: increasing compression increases power output. But there are limits to the compression an engine tolerates. Too much causes the fuel mixture to combust too quickly, and that returns us to the same detonation scenario of an excessively hot glow plug.

The amount of compression is determined by the number and thickness of the shims (gaskets) between the cylinder head and the top of the piston sleeve. Well, it’s determined by many other factors, but the only one easily changed is the head clearance via head shims. More shims = less compression; less shims = more compression. Removing or replacing shims with thinner ones increases compression. Some engines have only one shim, so it isn’t advisable to run without a shim at all. Moderation is the key. Go slowly, and make small, not drastic, changes that will minimize the risk of damage to your engine. First and foremost, be sure the piston won’t hit the cylinder head if you remove a shim (or shims).

You can also change compression with glow plugs. Some manufacturers make a longer glow plug that protrudes slightly into the combustion chamber, effectively reducing the area in which the fuel mixture is compressed. This area is already small, and the little extra space occupied by a longer glow plug will raise compression. This is not the most desirable method, but it can be used on engines that have only one thin head shim. It’s unlikely that the longer plug will even come into contact with the piston, but just to be safe, check the head clearance before you install a long plug.





This chart indicates the direction in which you should adjust the fuel mixture when faced with changing weather and other conditions. It assumes the engine is currently well tuned. You could face any combination of conditions listed in the chart; knowing which way to go with the mixture adjustments is half the battle.
Higher air temperature Lean
Lower air temperature Rich
Higher humidity Lean
Lower humidity Rich
Higher barometric pressure Rich
Lower barometric pressure Lean
Higher altitude Lean
Lower altitude Rich
Higher nitro content Rich
Lower nitro content Lean
Higher oil content Lean
Lower oil content Rich
Hotter glow plug Rich
Colder glow plug Lean

thats the only way to do it read all about it yourself ,you are probobly the first guy i saw say that you must like reading like me right on bro feed the knowledge good work you are heading in the right direction into this hobby[8D]

It's still a bit hard to say from the picture but I'd say that still looks OK. The surface will not be perfectly smooth and it looks more like the dark residue is pitted not the piston itself. It could be borderline but I say just continue running it.
Can you post a pic of the head too?

Ok, so running rich with a hot plug will get the engine going hard but will likely cause detonation?

Thank you for all the info guys. I really apprecaite it.

Here is a pic of the head and also the last glow plug that was in there. The glow plug looks like the metal coil is actually broken off.

Any diagnosis based on this info?

Thanks again

well on the first pic i dont see a shim at all which might have coused to much compression and if the glow plug coil broke of then it was probobly running lean
this might help you out--------read the last 2 sentences
Reading” the glow plug is a tuning technique advanced by Ron Paris. It suggests that looking at the glow plug tells you something about how your engine is running. The element in a glow plug will turn gray in an engine that is close to the optimum fuel mixture. This method requires a new glow plug, as the element will eventually turn gray regardless of the needle settings; the length of time it takes to turn gray is the issue. Plugs that turn gray in just a tank or two of fuel (running at race pace, not diddling around) indicate a fuel mixture close to ideal—but also close to trouble. If the plug stays wet and shiny for a few tanks of fuel, you’re in the safe zone; a little rich but safe. When the plug wire gets distorted or broken, however, you’re in real trouble. It’s a sure sign that the mixture is way too lean, or that there is too much compression and the engine is detonating.

so basically reindeer was correct in the first place and deserves the thanks all i did is just supply more information [8D]

Thank you for the pictures of the plug. From that I can see that the plug is completely destroyed. How old is it?
A colder plug would be my first choice and if that doesn't work you should try an extra shim.

That plug is pretty old now and I have run it quite a bit.

I guess I have been running too hot though, eh? I figured I would run on the edge of risk and would learn for myself where the dropoff was.... looks like I did

Oh well, that's the fun of it eh.

There is a shim, I just took it off to wipe it down a bit... sorry for the confusion I created there.

So I was running to lean in general then - or is it possible a plug will look like that over time anyway if I use the same one over and over. If it's blown like that is the engine probably dead then?

Thanks for the help guys

The photos of the head and piston top definitely show signs of detonation. Pre-ignition might be a better description for whats happening in that engine, meaning its firing before it should. Excessive heat is what causes pre-ignition. Like some others have mentioned a colder plug would help, I like to use a McCoy MC-9. Make sure you keep the head shim in that came with the engine, a lot of guys will remove this to boost compression, but it also makes the engine run hotter. Higher nitro content in the fuel will also generate more heat and can just make pre-ignition worse. If your running 30% try 25%, that will help too. It is not so much a rich or lean issue. If your running it lean your shortening the life of the engine and blowing plugs, assuming everything else is set right, running lean by itself will not cause the pitting on the head and piston.

[quote]ORIGINAL: PAINLESS

. Higher nitro content in the fuel will also generate more heat and can just make pre-ignition worse. If your running 30% try 25%, that will help too.
quote mgtman
you are right but its comon logic to richen up when using higher nitro
Higher nitro content Rich
Lower nitro content Lean
Higher oil content Lean
Lower oil content Rich

Changing to a higher percentage of nitro fuel sounds like an easy method of developing more horsepower, but it isn’t always that simple. Without getting into all the particulars of nitro fuel, I’ll just say that there is a point where you can have too much nitro. Adding up to 10 percent more nitro than is typical produces more power, but you have to know how to adjust your engine to accommodate the extra nitro. Fuel-mixture settings need to be slightly richer when nitro content is increased. Also, you may have to increase head clearance by adding an extra head shim. The extra fuel introduced into the combustion chamber increases compression by adding non-compressible matter; this also increases cylinder pressure during the combustion process, which may cause detonation. Detonation occurs when the fuel explodes instead of burning, and that can cause internal engine damage. The extra head shim will likely prevent detonation when fuel with higher nitro content is used.

A final note about fuel: fuel with a lower oil content (for manufacturers that actually disclose the amount of oil in their fuels) should be run with a richer mixture setting. This doesn’t so much relate to performance as it does to the benefit of the engine. Conversely, fuels with higher oil content have the extra lubrication that allows a leaner mixture setting with less risk of engine damage. Fuels with a lower concentration of lubricant are intended for competition use by experienced engine tuners. These fuels will make marginally more power because the lubricant that’s removed is replaced with power-producing nitro and methanol. Evaluate your tuning ability honestly before you run out to buy fuel with a lower oil content.
http://www.*********.org/understanding_fuel.htm

The engine is not blown just because the plug is broken. Just puta new one in and run.

hey atleast he got some info right lol, it would be funny if it just needs a new plug, but its always good to read up on some precoutions [8D]

Mgtman,
I agree that you need to richen when increasing nitro, assuming the engine was tuned right in the first place. Adding more fuel and air per storke of the engine will still cause an increase in heat over a lower nitro fuel.
I have seen some pitting before but never as bad as in those photos. I wonder if something happened to cause it whether intentional or not by tdpastor. Either way something has changed with his setup and must be remedied or that engine will not last much longer.

The primary benefit of the oil in the fuel is lubrication, I'm sure everyone knows that, but the secondary benefit is removing heat from the combustion process, since it does not burn.

You think those pictures were bad!?
That was a very very mild case. I've seen big chunks of alu taken off in my marine engines due to detonation.

Anyway, hope he gets it going again. Just put in a new plug and fire it up.

Usually you see the pittng on the head or piston, seldom both. Seeing it on both make me think its pretty bad or has been happening for a long time.
I have put holes in motorcycle pistons but its usually from running too lean not detonation.