Re: Low Ash Oil?

Posted by Janicholson on June 10, 2006 at 16:38:20 from (66.173.50.116):

In Reply to: Low Ash Oil? posted by IaGary on June 10, 2006 at 07:21:46:

Coking is the buildup of carbon and ash deposits that are heated to less than carbon combustion temperatures. On engines prone to coking, the valves (usually intake, but not always) have excessive oil comming down the guide, This excess oil, and valves that run hot from engine design and placement of coolant passages in the head, combne to build up the deposits that cause the back side of the valve head to be insulated from incoming air/fuel and as a result they over heat, warp, or just burn an edge (margin). I have seen so much carbon on the back of the valve that the engine could not breath and was making maybe 15 HP total.
The way to repair them in my "book" is to use better valves with a slightly thicker margin than original, (even if some research and grinding are needed. Then I would use Perfect Circle style valve seals on the stems (they use a teflon ring in a special rubber umbrella that actually meters the oil into the guide. This assembly leaves less to chance. I would then run 15-40 oil (diesel) because it is capable of maintaining good 40 wt viscosity at operating temperature, while remaining thin enough at ambient temperature for good starting till winter sets in. Diesel oil is usually a low ash oil (as are a bunch of regular gas engine oils marketed today) Synthetic oils, are essentially ash free, and will not coke till the engine is already toast from no coolant or some other disaster. These findings are from a mechanics experience and education spanning 40 years. JimN

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