E: Engine CR and ignition timing on a B series single

[Bill Thomas]

Strange, Just seen in my little book, Clevtrev said for a Twin, Head temp', 230 f, For the front, 220 f, For the rear. I wonder if just under the plug gives a high reading ?, Craig's numbers did seem a bit high to me
=160 c., Thinking we put bearings in at about 200 c, ?. Cheers Bill.

 

[timetraveller]

Bill. I think that the difference between the two temperatures is likely to be the difference between the temperature under the plug and the temperature some distance away, say near the tappet inspection cap. I do not know how Trev was obtaining the temperatures, thermal cameras, thermocouples or what. That might have made a difference as well. Bearing at 200 degrees C are in places which should never be as hot as the cylinder heads. If they were then I think you would be well on the way to an engine disaster.

 

[Bill Thomas]

I was thinking Valve seats etc, Long time since I did one, But I thought they were about 200 c when fitting ?.
Cheers Bill.

 

[timetraveller]

That's right but in that case the head is 200 deg C and the valve seat about 10 when it is put in. After that they are at about the same temperature so there is no temperature difference.

 

[craig]

Just to add some more information about my experience with TTO plug base temps -
My 47 Rapide runs about 333F, front or rear just cruising around, has been high as 353F.

My 1967 Norton P11 750 twin runs 380-405F on both plugs just cruising around with a TTO on each plug, and the plugs are not as clean as should be , so I have upped the plug heat range. No blued exhaust, but I have a temp concern due to my Vincent experience, and lack of TTO experience on parallel twins.