Notices
Engine Conversions Discuss all aspects of engine conversions in this forum

Modifying Crank Pin SC 1.20

Old 06-17-2009, 03:58 AM
  #1  
cutarug
Member
Thread Starter
 
cutarug's Avatar
 
Join Date: Jul 2006
Location: Melbourne, AUSTRALIA
Posts: 91
Likes: 0
Received 0 Likes on 0 Posts
Default Modifying Crank Pin SC 1.20

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.
Old 06-17-2009, 05:42 AM
  #2  
pe reivers
Senior Member
 
Join Date: Jan 2002
Location: Arcen, , NETHERLANDS
Posts: 6,571
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Modifying Crank Pin SC 1.20

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?
Old 06-17-2009, 07:28 AM
  #3  
cutarug
Member
Thread Starter
 
cutarug's Avatar
 
Join Date: Jul 2006
Location: Melbourne, AUSTRALIA
Posts: 91
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Modifying Crank Pin SC 1.20

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?

Old 06-17-2009, 07:52 AM
  #4  
pe reivers
Senior Member
 
Join Date: Jan 2002
Location: Arcen, , NETHERLANDS
Posts: 6,571
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Modifying Crank Pin SC 1.20

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.
Old 06-17-2009, 08:36 AM
  #5  
w8ye
My Feedback: (16)
 
w8ye's Avatar
 
Join Date: Dec 2001
Location: Shelby, OH
Posts: 37,567
Likes: 0
Received 1 Like on 1 Post
Default RE: Modifying Crank Pin SC 1.20

The connecting rod in a Saito FG-20 is not bronze bushed. It is just all aluminum
Old 06-17-2009, 08:58 AM
  #6  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Modifying Crank Pin SC 1.20

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




Old 06-17-2009, 09:04 AM
  #7  
w8ye
My Feedback: (16)
 
w8ye's Avatar
 
Join Date: Dec 2001
Location: Shelby, OH
Posts: 37,567
Likes: 0
Received 1 Like on 1 Post
Default RE: Modifying Crank Pin SC 1.20

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.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.