From:Tom Wilcock
Subject:RE: Overheating Date:Sat Oct 24 06:01:06 2020
Response to:7404

I have a 1928 Deluxe. It has been rebuilt using new Ross pistons, new valve guides, new valves, a hot rebuilt Simms mag and a Zenith carb with the new idle mixture adjuster. The timing is correct,valve adjustments are right on. Idle mix is set according to Zenith instructions. I pressure tested each cylinder as I installed the valve plugs, with no leaks. The bike starts easily, idles smoothly and runs well going down the road. My problem is that it runs hot. After a quick 5 mile ride, the temp measured at the center bolt hole varies from 360 F to 411 F taken with an infrared thermometer. I welcome your advice.

With too heavy a grade of engine oil you do not get as much flow through your bearings and thus not taking heat away. More critical is with not enough flow through the bearings there is not much oil being flung to the cylinder walls and underside of the pistons taking heat away. I believe these engines depend on oil cooling as much as air cooling. The oil pan is an oil cooler.

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