TR4/4A Preignition

[KVH]

Caused mainly by timing too advanced? Or too retarded?

 

[Geo Hahn]

Too advanced. Also too low octane gas can be part of the problem.

 

[3798j]

Some more causes: https://www.hastingsmfg.com/ServiceTips/detonation_and_preignition.htm

 

[TR3driver]

As well as excessive oil burning and/or excessive combustion chamber deposits. But usually, retarding the spark will eliminate the problem, regardless of the cause. The TR3 owner's manual even mentions retarding the timing if the engine is "pinking".

 

[Geo Hahn]

I'll add that (IMO) brand of gas can be a factor. If I fill up the TR4 at Costco I need to get their premium but at Shell I can fill up with their regular and not get audible knock.