I agree with you on the smaller engine sizes. Bill W. designed the K&B Sportster Series with four-bolt heads, and of course, the OS 46 AX has a four-bolt head. But I think that when you start talking 120 size engines, the span between bolts gets pretty large with five bolts. It is probably OK for normal running, but what happens during a lean run or two? In this situation, more head bolts would help by providing more clamping points to reduce head warpage.

I am not an engine historian, but I can't think of any two stroke model engines larger than 120 size that have less than six head bolts. OS's competitors in this engine class use six bolts. Why introduce a new product at a high price against strong competition and have any potential liabilities? I happen to think that OS has lost the good engineering common sense that they used to have when they were privately owned. Just look at the mess they made with the last two 70 four stroke engines they introduced.

I suppose that time will tell as to the durability of the five-bolt head arrangement.

Thanks for your reply,

Bruce