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Engine basics => Engine set up tips => Topic started by: frank mccune on April 17, 2017, 05:37:05 PM

Title: OS .40S? Holes in cylinder liner and piston?
Post by: frank mccune on April 17, 2017, 05:37:05 PM

        Hello All:

        I was thinking about my OS .40S that has 6mm holes in the bypass side of the piston and matching 6mm holes in the cylinder liner.  What purpose do these holes serve? I have heard several theories but what are your thoughts about these holes? This engine is a fine stunt engine despite its old design.

                                                                                                     Tia,

                                                                                                      Frank Mc cune       

Title: Re: OS .40S? Holes in cylinder liner and piston?
Post by: Bill Johnson on April 17, 2017, 06:33:36 PM

Are the hole(s) in the piston are in the skirt? I believe those are transfer ports, Frank. I remember seeing them on mine.

Title: Re: OS .40S? Holes in cylinder liner and piston?
Post by: Brian Hampton on April 17, 2017, 07:10:18 PM

Many engines from that era had those holes (K&B, Enya etc) which helped clear the usually dead space under the piston into the transfer port but I think the best benefit was it helped lubricate the wrist pin area and kept the piston crown cooler because of the flow of cooler air.

Title: Re: OS .40S? Holes in cylinder liner and piston?
Post by: Lauri Malila on April 18, 2017, 09:51:25 AM

It's simply to improve breathing when piston is in bdc and piston skirt would otherwise hide the straight access of flow to bypass channel(s). And of course, keeping mixture moving through piston improves cooling and lubrication.
When taken a few steps further, piston ports also make the piston lighter. L

Title: Re: OS .40S? Holes in cylinder liner and piston?
Post by: frank mccune on April 19, 2017, 06:55:04 AM

     Hi Guys:

     
     That is what I thought.  I thought that it was a great idea but the extra steps involved would drive the price up a bit with the added consequences.

     I really like this engine for a stunt engine despite its ancient technology. Lol  It is a one flip starter, very smooth running and does the old 4-2-4 thing.  Yes, I know that I am living in the past but...

    Thanks for all of the prompt replies.

                                                                                                             Frank McCune