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Old 06-10-2003, 04:51 PM   #1
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Angry SX12 Problems

I am having so many problems with my SX12 engine, I am getting EXTREMELY frustrated, I feel like throwing the damn engine through a window!

I'm breaking in the engine, i'm on my 6th tank. It will just randomly start when I try mabye one out of ten times, the car will run beautifully for about 3 minutes, then the engine will begin to idle extremely high even with the carb slide completely closed, mind you the engine does not shut off, it just idles extremely high regardless of my idle and low end needle settings. Of course I shut the engine off and check everything, and when I go to restart it the the engine just won't start nomatter what I do, however it eventually starts after like 30 minutes of trying everything, and I didn't even do anything special; it's like the damn engine has a mind of it's own and is out to get me! The engine will not start, I have tried numerous glowplugs and they are all fine, I have tried using different glow igniters, I have tried the pressure lock thing where you cover the exhaust pipe for 2 seconds and dry-start it like it says in the manual, I have tried every possible setting on the needles, and to no avail, THE ENGINE WILL NOT START! AHHHHHHHHHHHHH! This time the engine won't start at all, also the 12v powersource for my powerstart box is fine. I am running 30% nitro fuel, this is what my LHS reccomended.

This problem only started happening on the 5th tank or so throughout the break-in, before that it started up instantly and I never had any problem at all.

I've tried everything I can think of, nothing works.

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Old 06-10-2003, 05:02 PM   #2
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Do you need to shim the motor for running 30%?

Edit-
Im not sure but the strange idle could be due to an air leak.
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Old 06-10-2003, 05:03 PM   #3
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Quote:
Originally posted by Turbo9000
Do you need to shim the motor for running 30%?
I'm not sure what you mean, i'm just running the motor stock and my LHS told me 30% would be the best.
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Old 06-10-2003, 05:10 PM   #4
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Turbo9000 is correct. You need to add a head shim to run 30%. Without the head shim, the compression is too high. This causes a few problems including destroyed glow plugs, pre-detonation (which pits the top of the piston), and makes your engine run too hot. This may be why your engine is running crappy.

When you add a shim, check the engine internals for damage.

I just finished breaking in a shimmed SX12 3P MS Race Turbo with 25%, without any problems. I hate breaking in engines.....way too nerve wracking, expecially considering there is no single best way to do it.
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Old 06-10-2003, 05:11 PM   #5
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it means to put another shim under the head... cuz i think im right.. correct me if im not... but wit 30% theres a lot more compression i think and yah.. something like that... but it deff. means to but another shim under the head
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Old 06-10-2003, 05:17 PM   #6
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Quote:
Originally posted by chachi
Turbo9000 is correct. You need to add a head shim to run 30%. Without the head shim, the compression is too high. This causes a few problems including destroyed glow plugs, pre-detonation (which pits the top of the piston), and makes your engine run too hot. This may be why your engine is running crappy.

When you add a shim, check the engine internals for damage.

I just finished breaking in a shimmed SX12 3P MS Race Turbo with 25%, without any problems. I hate breaking in engines.....way too nerve wracking, expecially considering there is no single best way to do it.
Damn, I didn't know that, my LHS never told me when they reccomended 30%. What type of shim should I use and where exactly does it go? Is it just a glowplug shim and I use two instead of one?
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Old 06-10-2003, 05:25 PM   #7
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Whats the purpose of running 30% fuel when you have to add a shim? The extra power that is supposed to be gained is taken away by the compression reduction. Just curious what the advantages of running it when you add a shim cuz it doesn't make any sence to me.
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Old 06-10-2003, 05:25 PM   #8
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You need to get a head shim that is compatible with that motor. The one I bought was Novarossi. The shims come in different widths. I can't rememer what size I am using, but if you do a searh on the forums for 'head shim', the info is posted somewhere.

The shim (which is soft copper) goes between the button and the crankcase around the top of the sleeve. Take off the head and the button should stay fixed to it. Once you have the shim, and you have the head off, it will make sense.
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Old 06-10-2003, 05:38 PM   #9
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What is the highest percentage of fuel I can use without having to add a shim? 25%, 20%?

Also, I have an SX21 Evo5 MS that I have for my Serpent 950, can I safely run 30% in that without having to add a shim? I haven't even started up the engine yet.
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Old 06-10-2003, 05:46 PM   #10
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I don't think you need to add another shim, I run 30% in all of my Novas without adding an extra shim. It sounds like the low end needle may be too lean, try to richen the low end 1 turn and see what happens. You may need to adjust the idle set screw to compensate for the richer setting (open the carb).
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Old 06-10-2003, 05:52 PM   #11
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Grinder: Do you run a cooler glow plug?

Now I am confused...

I have heard that some people run high nitro (25-30%) in .12 engines without shims. However, most people seem to think you need to add the shim. I tried running 25% in my OS TR without a shim, and I killed 2 glow plugs in 2 runs, plus the top of the piston started to pit.
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Old 06-10-2003, 06:18 PM   #12
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Some might be able to get away with a higher nitro content with out shimming. I think its a matter of geography and atmospheric pressure.
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Old 06-10-2003, 08:04 PM   #13
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I believe there a lot of factors to be taken into consideration when talking about shimming and compression, etc.

1. Compression level pre-determined by the manufacture
2. The glowplug
3. The Nitro Percentage
4. Weather (Colder or Hotter Climate)
5. Geographical Location (higher or lower altitude - atmospheric air pressure)

But I dont think compression is Accord's problem. Even at worst case scenario a high compression level would cause the engine to stop running but I dont believe it will cause the idle revs to increase. Most likely, you have an airleak somewhere. Check your tank and fuel line for holes. Make sure that the carb is properly seated and that none of the o-rings are damaged either on the carb neck or the needles. Also check the seal on the front bearing.
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Old 06-10-2003, 08:22 PM   #14
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Quote:
Originally posted by modellor
I believe there a lot of factors to be taken into consideration when talking about shimming and compression, etc.

1. Compression level pre-determined by the manufacture
2. The glowplug
3. The Nitro Percentage
4. Weather (Colder or Hotter Climate)
5. Geographical Location (higher or lower altitude - atmospheric air pressure)

But I dont think compression is Accord's problem. Even at worst case scenario a high compression level would cause the engine to stop running but I dont believe it will cause the idle revs to increase. Most likely, you have an airleak somewhere. Check your tank and fuel line for holes. Make sure that the carb is properly seated and that none of the o-rings are damaged either on the carb neck or the needles. Also check the seal on the front bearing.
That's what i thought so, an air leak, when i response he posted on his engine problem on 705 forum.
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Old 06-10-2003, 08:55 PM   #15
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Quote:
But I dont think compression is Accord's problem. Even at worst case scenario a high compression level would cause the engine to stop running but I dont believe it will cause the idle revs to increase. Most likely, you have an airleak somewhere. Check your tank and fuel line for holes. Make sure that the carb is properly seated and that none of the o-rings are damaged either on the carb neck or the needles. Also check the seal on the front bearing.
Modellor,
I believe that Accord's motor and car is new so he shouldn't have any problems with a bad front bearing, o-rings or holes in the fuel line. HOWEVER, that is still a good idea to check them.


Accord,
Make sure that all the screws on the motor are tight and there!!
Nizee gave you a good hint to check your carb seal to the motor....make sure its all the way in and on tight. Nizee and modellor are correct about not having a compression problem it a air-leak problem and lean setting.
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