Oil burners and the dreaded #7 and #8

[Mudrig150 315]

Ah, #7 and #8. The head bolts above the exhaust port notorious for breaking off on oil burning engines. We've had 2 oil burner engines, one break off #7 and the other #8. I've seen a crap ton of engines break off #7 or #8. Not even that long ago someone made a thread about drilling out #7.

I know something changes in oil burning motors to cause #7 and #8 to break off, but what is it exactly? Different heat cycles? Rust? Carbon on the threads? Have any of you guys had an oil burner NOT break off #7 or #8?

Edited: Added the #8 head bolt to the description.

Edited November 26, 2019 by Mudrig150

[ebinmaine 71,991]

I can't say I've run into this personally but I've definitely heard of it before.

 

The one trick I can give you is to TIGHTEN the bolt a little bit first.

Loosen it. Tighten it. Loosen it. Tighten it. Loosen it.

 

That doesn't always work but it definitely helps.

[peter lena 9,194]

agree with ebinmaine  on the tightening procedure , another thing is that if you have a problem stud / bolt area  , you can remove it and dye nut it ,or use a tap to clean out the mounting stud point. think about what you are trying to do , also use never sieze  and a lubricant to recover your mounting point, pete

[pacer 3,177]

I've managed to get by with out breaking #7  ----- BUT! I've had 2 #8's break! Usually those bolts havent been disturbed for many, many years and that dont help.

 

Course, both of those are next to the exhaust valve and the intense heat that is produced there. Like Pete sez - on going back together I use a die to 'chase' the threads and really clean the bolts (wire brush of blast them) and a little dab of never seize.

[Burnerman 759]

The #7 bolt hole on the k181 on my sons tiller was actually drilled into the exhaust port. I could see the threads though the exhaust. It just skirted the port. I was able to spray penetrating oil in to help free it up. 
 There is so little material there and it gets very hot.