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Pederkr

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Black Piston
« am: 27 Juni 2019, 17:49:05 »

Started to strip down for my new crankshaft.
To my supprice the new piston whit 300 km on the clock, is very carbonatet but only at the intake side.
It's like at tick layer of nutela  :-\\
Whats the problem is it my carb ????

grüss

Peder



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Black Piston
« am: 27 Juni 2019, 17:49:05 »

Tino

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Re: Black Piston
« Antwort #1 am: 27 Juni 2019, 18:07:04 »

The fresh air cool down the piton at the intake site.
Temperature drops there to much for a proper burning of carbon.
About 400°C are required for burning carbon.
Sometimes a slug of 2 stroke oil will help to reduce burning temperature for carbon.
Bye Tino
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4Taktix

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Re: Black Piston
« Antwort #2 am: 27 Juni 2019, 18:21:12 »

Hi Peder,
I'd recommend to check your intake valve guide for wear. I doubt that fuel can create such a thick layer of coal within 300 km,
except you drove very very smooth and didn't rev it. It's more likely, that the intake-guide leaks a bit of oil. But however, I'd check it.
Besides that: Is your sparkplug the correct value ? I wonder about the other coal-spot near the center.
I'd unplug the plug and mark the direction on the Isolator, towards which the ground electrode points (the "open gap" )
Then plug it in again and check, to which direction it points. The ground electrode kind of "shields" the burn, similar to a shade.
Best would be, if the open end points to the center, +/- 30 degs. If it points to the outer brim, you can shim the plug or try another one.
Not sure, if plug-production is such, that the elektrode always points into the same direction in relation to the thread-start, but I don't think so.
Know what I mean ?

Cheers,
Sascha
« Letzte Änderung: 27 Juni 2019, 18:26:40 von 4Taktix »
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Pederkr

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Re: Black Piston
« Antwort #3 am: 27 Juni 2019, 19:55:11 »

Hi Sascha.

 have tried to run the engine with a normal range of revolutions. It is only a year ago that I got new valvet guides in the cylinder head, but you probably are right since the discoloration is also on the valve. The spark plug I drive with is a Blitz spark plug. Can't find the original Bosch 240W here in Denmark. If I cannot find a leak in the valve guide I will try with NGK BH 8.
I've separated the engine since the piston was from an Izetta, which means it's a millimeter too low on the side. The exhaust port is opposite and therefore the piston must be turned 180 degrees to fit. This means that the piston pin which is offset by 1.5 m / m is further moved to the wrong side. My crankshaft had a wrong connecting rod, so there was not 125 m / m between the bottom and the top center, which gave further lower compression. There were 3.2 m / m from the top of the cylinder to the edge of the piston.

Uhh I have enough to look at. Some one must change my status to meister scrauber :schrauber:
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Re: Black Piston
« Antwort #4 am: 27 Juni 2019, 20:13:10 »

Oh Dear, looks like you gotta have a lot of things to do. With lower compression the ignition woun't be as intense and hot as it should be.
You can take a Bosch W4AC or in your case a W5AC to replace the W240 T1.  They should be easier to get and equal the intended range of a W240 and more.
Advance your ignition timing as long as you drive with this low compression.
What do you intend long termed to get all these "flaws" corrected ?

Cheers,
Sascha
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Re: Black Piston
« Antwort #5 am: 27 Juni 2019, 20:21:17 »

Just a moment - if you say, you had to turn the Isetta-Piston 180 degs, then the arrow points to the rear, and the "coal" is in the exhaust-valve pocket.
I'm puzzled now, please shed some light on this.

Sascha
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Pederkr

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Re: Black Piston
« Antwort #6 am: 27 Juni 2019, 23:13:32 »

Exactly. Here is the picture of the old piston on the left and the Izetta piston on the right. The only way to recognize it is that from the center of the piston the pin and to the upper edge is only 31 m / m and that the seat of the exhaust  valvet is wrong in relation to the arrow.
I have made a mark "U"
I am in the process of changing the crankshaft to the big model with the right connecting rod in steel. Tomorrow I will bring my cylinder head to a barrel company and let him look at it. The piston whit the coal is a new KS piston i just bought for 300 km since

Peder
« Letzte Änderung: 27 Juni 2019, 23:16:03 von Pederkr »
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Re: Black Piston
« Antwort #7 am: 29 Juni 2019, 16:28:13 »

 Problems with the black deposits on the piston are due to poor compression and cold combustion of gasoline.

Have used a colour tune to see my combustion whit the new piston and cranck. Every ting looks fine.



Peder
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Black Head Question

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