Modifying Crank Pin SC 1.20  
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Modifying Crank Pin SC 1.20 - 6/17/2009 9:58 AM   
cutarug


 

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From: Melbourne, AUSTRALIA
Status: online 		I am converting a SC 1.20 to gas and because there is not enough material in the rod for a needle roller of 8 dia I am fitting a 6 dia bearing and pressing in a dowel pin into the counterweight as a crank pin.
My sticking point is how to press in the pin and make sure it is square to the crank shaft. Maybe some one has done this in the past and could reveal their secret method.
I would like to change to a needle roller and run 40:1 oil as my  ryobi's use 40:1 and plug fowling could be a problem at 20:1 with the plain bearing.
Although I have noticed the new Saito 20 runs 20:1 with spark ignition and bronze bush on big end!
I would be interested to know how long the plugs last or if the plug fowls up.


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RE: Modifying Crank Pin SC 1.20 - 6/17/2009 11:42 AM   
pe reivers



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Status: offline 		plug fouling is no problem, even at 15:1 mixes with mineral oils or castor or a mix of the two. Just do not run the engine slobbering rich, and you will be fine. Why not use the original crankpin?


< Message edited by pe reivers -- 6/17/2009 11:44 AM >

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RE: Modifying Crank Pin SC 1.20 - 6/17/2009 1:28 PM   
cutarug


 

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Status: online 		Thanks for the reply pe reivers, I am open to suggestions so if you think it would be fine with the bronze bush I will give it a go. A lot less work to do the conversion if I use the original bush.
Would 20:1 mineral oil be safe?
I noticed you said mineral or caster oil and not  a modern synthetic 2-stroke oil.
Is this because of cost or do the minerals burn with the combustion?



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RE: Modifying Crank Pin SC 1.20 - 6/17/2009 1:52 PM   
pe reivers



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Status: offline 		Not all synthetics mix well at ratios 10:1 to 20:1, hence the mineral or castor oil. Castrol R comes to mind as an excellent oil for your application. But if you can find a suitable high class synthetic  that mixes well, there is no reason not to use it.
I woild use 7% oil (15:1) for a plain bushed connecting rod gas engine.

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RE: Modifying Crank Pin SC 1.20 - 6/17/2009 2:36 PM   
w8ye



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Status: offline 		The connecting rod in a Saito FG-20 is not bronze bushed. It is just all aluminum


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RE: Modifying Crank Pin SC 1.20 - 6/17/2009 2:58 PM   
gkamysz


 

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Status: offline 		The amount of oil present in a model four stroke crankcase far exceeds the amount of oil in a two stroke engine.

If you put a pin into the counterweight, you will have a seriously out of balance engine. If you are going to go through with this modification, just replace the old pin with a new one. When you press parts the squareness of the hole and straightness of the pin determine the final squarness of the assembly. This is not something that can be done on a drill press with a drill bit.

This is the result. There are some other comments about oil ratio here.

http://www.rcuniverse.com/forum/m_8836757/tm.htm






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RE: Modifying Crank Pin SC 1.20 - 6/17/2009 3:04 PM   
w8ye



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Status: offline 		My FG-20 Saito Four strokes blow black oil that looks like old diesel truck crankcase oil, all over creation out the crankcase vent when they run. No doubt they are getting plenty of lube down there. There is smut mixed with the oil that makes it dark.


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