Cylinder head and crankcase cover assy bolts

[busterthejetboater]

Hi All

I am in the process of re-building my 240EFI - taking muuuuch longer than anticipated due to time constraints. Just had a crankcase cover bolt snap on me while torqueing the 8 main bolts up. It did have all the indications of a failing bolt as she did not tighten up. There is also another one so I will be replacing all. Is this normal?

What are the general feelings regarding the qty 24 cylinder head bolts? I know the book recommends replacing these.

Thanks

 

[Dr Honda]

It's not normal for the bolts to fail on the Merc engines. AND... I reused my head bolts during my rebuild. The only bolts I would recommend replacing are the Rod bolts, since they are designed to stretch during assembly.


Now... the bolt you broke... it was one of the big ones that hold the 2 case halves together? If that's the one... I'm very surprised. They are big. OR... do you mean the threads pulled out of the aluminum case?

 

[busterthejetboater]

Hi Tony

Always nice to hear from you, and your assistance/knowledge is as always appreciated.

The bolt that snapped is one of the long ones (0.375-16 x 3.20 part # 10-66717). It snapped in the thread just after the shank. I measured the whole bolts after removing them (and the threaded bit left in the crankcase) and there are 3 bolts that are between 0,050" and 0,056" longer than the others.

I have used new rod bolts in my build. I have rebuilt the fuel pump and vapour separator. I am having the jet housing and ride plate grit blasted and will treat with alodine before paint application. I have a new 6 tine fixed grate, new impeller housing, new bearings, seals and gaskets.

This set back is not welcome as I was hoping to complete the engine today and start work on the jet pump next week.

NO worries, will get the bolts in and carry on.

 

[Dr Honda]

Those are 3/8" bolts (Close to 10mm). They shouldn't break unless you over torqued them. But, since you made the comment about "They never tightened"... I will assume they were damaged somehow already.


Sorry to hear about the issue. But since they are suspect... I would replace all of them.