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Engine basics => Engine set up tips => Topic started by: John Craig on January 11, 2014, 04:57:04 AM
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From a friend I purchased a used OS 35S modified by Randy. My friend had very artfully ground the front portion of the head fins off with concrete. No problem, I would just replace that head with one of my un-marred heads from a well used & retired OS 35S. Surprise! Surprise! When I got the heads off they were two different animals. The newer ground down head extended noticeably deeper into the cylinder & had a more pronounced hemi shape.
Does anyone have experience swapping these heads. No biggie? Will the shallower one change the 4-2 break making it softer?
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From a friend I purchased a used OS 35S modified by Randy. My friend had very artfully ground the front portion of the head fins off with concrete. No problem, I would just replace that head with one of my un-marred heads from a well used & retired OS 35S. Surprise! Surprise! When I got the heads off they were two different animals. The newer ground down head extended noticeably deeper into the cylinder & had a more pronounced hemi shape.
Does anyone have experience swapping these heads. No biggie? Will the shallower one change the 4-2 break making it softer?
Hi John
It sounds like one of my Special Smith OS 35S engines, the head is a higher comp head with a better chamber, most of them also had either Bushed I Beam rods, or Hard vented rods , with special wrist pins with teflon pads, heat treated P/S and either blue , red, gold, anodized head, venturie and drive washers. Does that sound like yours?
You can use a stock head for it, but it will be just a tad down on the power output, so use a bump in nitro or prop pitch
Randy
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Thank you Randy,
The engine has no anodizing. I have seen one example of the engine you are talking about. From the outside the engine appears stock except for the ST needle assembly. I am not one to take apart an engine with out a specific need, so I do not know what is inside. I thought the head was modified by OS as the engine evolved over the years. You confirmed my suspicions about the power change. I am just a sport flier; so I will fly it as you & my friend have "customized" it. Thanks!