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Old 10-10-2005, 09:20 AM   #2056
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while it idles good,the compression is good.
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Old 10-10-2005, 09:23 AM   #2057
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hi afm, zero pinch even when there cold? I've noticed most my motors when cold have a slight bit of pinch but when I pull the plug out straight after a run the piston and sleeve is only very slightly snug and pretty much free from pinch, I can keep rotating the flywheel while the engine is cooling and feel the slight bit of pinch come back as it cools.
I do sort of use pinch as a kind of guide to simply help me know where my engines are with respect to sleeve and piston wear, but like you say if you have good compression you have a good healthy engine, plain and simple.
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Old 10-10-2005, 09:28 AM   #2058
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Quote:
Originally Posted by dino.tw
while it idles good,the compression is good.
yeah, that is really the true test! if your engine has poor compression it will really struggle to idle, thats if you can even get it to start! 2-stroke engines are like pumps if they have very poor compression they wont be able to suck air through the carb on the induction stage, no air flow no fuel flow so no mixture to ignite so no go!
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Old 10-10-2005, 10:55 AM   #2059
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Quote:
Originally Posted by Hesky
hi afm, zero pinch even when there cold? I've noticed most my motors when cold have a slight bit of pinch but when I pull the plug out straight after a run the piston and sleeve is only very slightly snug and pretty much free from pinch, I can keep rotating the flywheel while the engine is cooling and feel the slight bit of pinch come back as it cools.
I do sort of use pinch as a kind of guide to simply help me know where my engines are with respect to sleeve and piston wear, but like you say if you have good compression you have a good healthy engine, plain and simple.
Do the oil-air bubble-hiss sound test when cold and you'll see what I mean, it's as you say, it is like a compressor. If it leaks....no compression.
Also as Dino says...no idle = poor compression = hard to tune = erratic functioning.

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Old 10-10-2005, 11:28 AM   #2060
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I'll try it out on an old kyosho engine i have that has lost compression, most the time when I've cleaned my motors up and oiled them I have a look through the exhaust port and slowly rotate the flywheel with my hand applying a constant pressure pushing the piston past the exhaust port a good distance hold it there and then let go if the piston bounces back no air is lost its just been compressed so i think it still has excellent compression, but if the piston sort of stays above the exhaust port the air has managed to force its way out. I guess this is similar to the oil bubble test.
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Old 10-10-2005, 01:57 PM   #2061
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You guys would of loved the D5 I've just retired. Turning it over you would feel compression starting to build. As you hit TDC compression is fully lost, then vacumme as you leave TDC. Damage was done from detonation - trying 0.2mm shim on 15% nitro. Engine has been like that for some time now, still ran ok (won an 1 hour enduro with it )

Moving to a D3R now though
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Old 10-10-2005, 02:26 PM   #2062
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I remember you saying a while back, if the detonation didnt score the piston and sleeve to much you should consider getting the sleeve resized by rayaracing or osrocket, I cant image it will ever run as well as it did new but the process is very cheap and you can at least keep it running and use it as a backup engine or somethin.
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Old 10-10-2005, 05:51 PM   #2063
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Quote:
Originally Posted by afm
Donít confuse compression with pinch. Sleeve Pinch is not that important contrary to popular belief. The question is how well does it seal as soon as the piston starts to close the exhaust port and if it holds compression after you roll it to top dead center.
Place a few drops of after run oil trough the top (removing plug), then place plug in place, then roll piston to top dead center and listen and look for air bubbles through exhaust port. If thereís none, then your engine still has compression, even if it has no pinch.
The fastest team motors we have, have zero pinch.

AFM
yes i know what compression and pinch is. and like i said it has less compression than my JP that has gone over 10 litres. My JP has no pinch.

the sts has gone about 2 litres now, i notice it still has pinch (i.e take off glow plug and rotate, it make small clicks over tdc) , but has very little compression....

i used to have a compression guague but lost it, and i dont think it would even put out 50psi.

i ran it with stock shims 0.4mm and 22.5%nitro using the RB/Rody team method (know as the cyril method on this forum)
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Old 10-10-2005, 06:23 PM   #2064
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Dino or Afm
I am going to be running dirt oval with a NTC3 what would be a good way to tune my d3r, i'm going to leave the settings where they are and see how it runs. I'm only asking because I have read where you change settings from small tracks to big tracks
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Old 10-10-2005, 06:39 PM   #2065
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Quote:
Originally Posted by qwerty
yes i know what compression and pinch is. and like i said it has less compression than my JP that has gone over 10 litres. My JP has no pinch.

the sts has gone about 2 litres now, i notice it still has pinch (i.e take off glow plug and rotate, it make small clicks over tdc) , but has very little compression....

i used to have a compression guague but lost it, and i dont think it would even put out 50psi.

i ran it with stock shims 0.4mm and 22.5%nitro using the RB/Rody team method (know as the cyril method on this forum)
theres no fuel leaking between the head button and the crankcase is there? which would indicate a poor head button seal, I would have the head off and inspect for any scoring of the sleeve and piston, usually when you have pinch but poor compression it is due to a damaged piston and sleeve.
I'm just not sure what you consider barely existent to be, it really shouldn't idle well at all and you have manged to put an extra 1 and a half litres though it from the point you noticed the drop in compression by the sounds of it, so I can only assume it runs fine to.
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Old 10-10-2005, 07:07 PM   #2066
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Quote:
Originally Posted by qwerty
yes i know what compression and pinch is. and like i said it has less compression than my JP that has gone over 10 litres. My JP has no pinch.

the sts has gone about 2 litres now, i notice it still has pinch (i.e take off glow plug and rotate, it make small clicks over tdc) , but has very little compression....
Ok, but how do you arrive to the conclusion that it has little compression??
I just don't think that by feeling you can arrive to it.
If you had your compression gauge it would be a more technical way.
Have tou tried my method??
On the other hand one thing is to have less compression than engine X and another is to have NO compression at all.
If you are using 22.5 % Nitro I'd use 0.30mm shim, and then see how compression changes.

AFM
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Old 10-10-2005, 07:23 PM   #2067
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Quote:
Originally Posted by afm
Ok, but how do you arrive to the conclusion that it has little compression??
I just don't think that by feeling you can arrive to it.
If you had your compression gauge it would be a more technical way.
Have tou tried my method??
On the other hand one thing is to have less compression than engine X and another is to have NO compression at all.
If you are using 22.5 % Nitro I'd use 0.30mm shim, and then see how compression changes.

AFM

how do i arrive at conclusion of low compression? coz i have owned many new engines before and this is one of the lowest compression engines i have owned after run in (near complete run-in anyway)... and like i said i used to own a comp guage so i know roughly how many psi i would have from experience.

well from my experience these has lots less compression than RB and Novarossi.

and yes changing head shims obviosly increases compression, but head shims are there for other purposes and removing them is not a solution...

i'm not saying it has no compression, just has a lot less than other european engines i have owned, but like i said it still idles great.

anyway, my query (not a complaint) was on whether the sts is characterised by low compression similar to that of OS engines.
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Old 10-11-2005, 09:01 AM   #2068
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In our area the atmospheric pressure is always higher and we are close to sea level. Another reason is that most of local racers are using 30% nitro here. That is why our engine has more shims out of box. (except .28)
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Old 10-11-2005, 09:22 AM   #2069
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Hi,

Does anybody know the factory needle setting for the STS .12 Team engine? I just finished my break in (close to 20 tanks now...) for this engine and for some reason.... it's not fast... The powerband on this engine is rough... It feels almost like turbo lack (or shifting to 2 speed)... When you trigger the throttle there is no power at low & mid and all of a sudden... power come out and it's very hard to drive. I already lean out the low/high end too, temp at 240 so I don't think I am runing rich on either low or high end. Another problem is my carb seems to leak fuel cuz near the engine's carb area it's very wet... but I can't find the leak. Weird... Anyway, I will make sure all the screws on the engine are tighten then I will set all the needles back to the factory setting and start over. Thanks.
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Old 10-11-2005, 09:33 AM   #2070
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Quote:
Originally Posted by qwerty
how do i arrive at conclusion of low compression? coz i have owned many new engines before and this is one of the lowest compression engines i have owned after run in (near complete run-in anyway)... and like i said i used to own a comp guage so i know roughly how many psi i would have from experience.

well from my experience these has lots less compression than RB and Novarossi.

and yes changing head shims obviosly increases compression, but head shims are there for other purposes and removing them is not a solution...

i'm not saying it has no compression, just has a lot less than other european engines i have owned, but like i said it still idles great.

anyway, my query (not a complaint) was on whether the sts is characterised by low compression similar to that of OS engines.
Are you refering to compression ratio or to piston fitting. it is 2 different things.
I guess you are talking about piston fitting. Then let me try to explane you how it works. Piston material is designed to have lower expention rate then sleeve. So according to expention rate difference engines manufacturers are make sertain fitting. Some piston materials works better when they are pretty tight in sleeve, some when they are pretty loose-it is how good engine manufacturer-that he can make piston material will be pretty loose when motor is cold and it keeps slightly less tighteness when it got hot. Now how long piston will last is another thing-generaly speaking more Si in Al alloy longer it will last. I personaly preferd to have piston pretty loose when motor is cold, but in the mean time it doesn't loose a lot of tightening when motor got hot. It is ART of materials desings and it is biggest NITRO SECRET you can find in this world.
I never work with STS engines at all, so I can't give any coments on it. I just giving general info.
Edward
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