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Old 04-29-2010, 12:29 AM   #1
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Default Reading piston and combustion chamber

Hi there,

I am trying to learn how to "read" the parts of my engine after a run. Itīs a Nova Flash after two days racing at Lostallo. This particular track has an extremely long straight (7 sec full throttle). Question to the experts: If you look at the pictures, is there something I have to take care of before I run the engine next time on this track? The parts look a little bit different compared to when I checked them last time. Are those tiny spots signs of pre-detonation? I think the engine was not too lean, because I could hardly make 5mins. My friend told me to use a 8 plug instead of a 7, or put a 0,1mm shim more under the head.
Looking forward to hearing your thoughts!

Later, Stefan
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Last edited by fulcrum2; 04-29-2010 at 03:06 AM.
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Old 04-29-2010, 08:14 AM   #2
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Originally Posted by fulcrum2 View Post
Hi there,

I am trying to learn how to "read" the parts of my engine after a run. Itīs a Nova Flash after two days racing at Lostallo. This particular track has an extremely long straight (7 sec full throttle). Question to the experts: If you look at the pictures, is there something I have to take care of before I run the engine next time on this track? The parts look a little bit different compared to when I checked them last time. Are those tiny spots signs of pre-detonation? I think the engine was not too lean, because I could hardly make 5mins. My friend told me to use a 8 plug instead of a 7, or put a 0,1mm shim more under the head.
Looking forward to hearing your thoughts!

Later, Stefan
Your friend is correct
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Old 04-29-2010, 09:38 AM   #3
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Quote:
Originally Posted by fulcrum2 View Post
Hi there,

I am trying to learn how to "read" the parts of my engine after a run. Itīs a Nova Flash after two days racing at Lostallo. This particular track has an extremely long straight (7 sec full throttle). Question to the experts: If you look at the pictures, is there something I have to take care of before I run the engine next time on this track? The parts look a little bit different compared to when I checked them last time. Are those tiny spots signs of pre-detonation? I think the engine was not too lean, because I could hardly make 5mins. My friend told me to use a 8 plug instead of a 7, or put a 0,1mm shim more under the head.
Looking forward to hearing your thoughts!

Later, Stefan
We ran at Lostallo last year during the 1/8 worlds and we shimmed our engines to 0.90mm using ORION fuel (spec fuel during the worlds) engine ran perfect, no detonation whatsoever, using Ninja # 7 plug, it will only make a little more than 4 minutes per fuel tank, no body makes 5 minutes only Collari does, by the way Lostallo track is NICE !
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Old 04-29-2010, 10:09 AM   #4
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Thanks for you help guys, much appreciated!

@Team Kamikaze,

nice to hear that you liked the Lostallo track. It is one of the best rc circuits in Europe. On my list, a close second would be Fiorano in Italy. The have even flood lights and do night runs

You said that you shimmed your engines to 0.9mm. Is this total amount of shims (0.7mm is stock) or actual head gap? I assume the former...

You are right, almost no one makes 5mins when we talk about world championship performance. In my group, most guys ran 5 mins, but the times are 1.5 sec slower then worlds level.

I struggled to make 5 mins with the Flash engine and threw away 2 qualifying heats because of that. I tried to let the clutch engage earlier, but did not like the punch out of the slow 180 degree corners afterwards. Any tips on how to improve milage?

Thanks again, Stefan
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Old 04-30-2010, 01:13 AM   #5
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It's a total of 0.90mm head shims, you can try a 41022 Nova Rossi header, that will help make runtime, run a lower nitro content will also help make runtime, but if I were you, I would go for a splash then you can just drive all out as fast as you can, so are you talking about 22 or 23 second lap times?
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Old 04-30-2010, 02:28 AM   #6
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Thanks again for the clarification on the head shim situation. OK, the Nova 41022 is the non conical manifold. This would be kind of a last resort because it will have a huge impact on power...

Next time I will try the JP 2031 exhaust which I normally use when mileage becomes an issue. In my group most guys run Picco or Max engines and they have power and runtime with their normal (full power) exhaust systems. Novarossi engines (the 14.5mm crank types) still consume too much fuel
As we do 5mins heats you will not be in the top ten with a splash...

In the Swiss national championships the drivers are segregated into two groups depending on prior years performance. Top runners of group A were on worlds level (some of those drivers attended the worlds last year). Lap times were down to 19.9 on a sub perfect track (Rain til early afternoon). In that group we also talk about serious hp with Nova works engines and so on. Btw, the race was won with a Murnan power plant...

In my group you had to run consistently around 21.5 to be in front. I did some 21īs but not consisently enough. In this group most guys run out of the box engines with some modified MaxPower and Piccos.
Next time I will raise the head on my engine because I was doing well through the corners but lost on the straight. Some more revs would certainly help...

Thanks again and til next time!
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Old 05-04-2010, 03:09 AM   #7
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First off..... measure the thickness of that button with a good set of calipers. I'd then lap it with some vey fine emery on a piece of glass to get rid of the pitting. If left as is, that pitting will develop hot spots on the head and piston and increase your engine temps. When the pitting is gone, measure the thickness again. Subtract the difference and add appropriate shims to get back to your starting point. You'll probably only remove 0.1mm after lapping. That means your engine will always need 0.1mm more shimming than one that hasn't been touched.

Next, use a piece of 0.040" or thicker resin core solder (easier to compress than solid core) with the engine assembled. Make a small "L" shaped bend in it and insert it in the plug hole so it faces the area where the piston will compress it against the button. Turn the engine over ONCE and remove the solder. Measure where the piston has flattened the solder. Try to get the shim stack so you have 0.028"- 0.032" head clearance on the engine. On a stock 35+21 engine I normally have 0.8mm of shims (adding 0.10" to what it comes with) to get 0.030" head clearance with a Nova C7TGF plug running 20% Byrons. I have not seen any detonation running at sea level in FL in 90F+ temps with the engine @ ~260F after a good run.

I pull the plug after every run and inspect it with an eye loop. If it looks sanded or pitted- its gone. Slightly shiny and silver/tan is great if you're making good power. Dull silver/tan is good, but keep an eye on it as the weather changes. It takes a good 5-10 minutes of racing on a new plug to read it. Big races get a new plug before every main- usually replaced before "happy hour" so I can read it and check my tune.....I don't spend $500 to travel to end my main with an old nasty plug. If I ever "pop" a plug I set the engine aside to look at later- it usually needs a rod.

These things don't take care of themselves.... you have to keep on top of a ~$600 investment. A $9 plug is cheap compared to popping a plug element in your engine. 99% of the time if you lose an element you gouge the piston/sleeve. If you can find some Ninja/GRP plugs they will last at 300F+ if you happen to mis-tune for a race.

To me, a properly broken-in and maintained engine is worth more than a new one.....$25 in fuel plus hours of time count for a lot.
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Old 05-04-2010, 08:23 AM   #8
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Its no good lapping the head on a flat surface as the squish band is angled as its supposed to be approx 4degrees. You will end up with a flat squish band and have to remove a lot of material to get rid of the pitting because of the angle. Martin.
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Old 05-04-2010, 10:30 AM   #9
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Excellent advice guys. Thanks a lot, it is much appreciated.

cdelong: I have another head button from an engine which died early. To be sure, I will use that one and measure the head gap to be sure.
What do you think about my piston, will it run OK?
Talking about glow plugs - I will also inspect my plugs often and never sucked an element through the engine. But with the latest Novarossi TGF plugs it happened very often that the engine ran fine but the plug died after the run. So I tried to start the engine an hour later an it did not fire up. Old plug out (looking fine) new plug in, problem solved. This happened many times. Will try now Sirio plugs because GRP's are hard to find nowadays.

MartinH:
Could you please explain in detail what "squish band" means? Thanks a lot! Btw, you made a lot of very interesting postings recently...

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Old 05-04-2010, 11:36 AM   #10
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The squish band is the flat area that surrounds the combution bowl, This is the area that gets most of inbeded material due to detonation. If you check out a new one by holding something straight across the face of the head you will see this band is not flat but angled in towards the bowl usually around 4 degress. Martin.
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Old 05-04-2010, 12:11 PM   #11
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Thanks a lot for the clarification, Martin!
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