cause of fretting where the crankcase halves join

[RobertE]

Due to a prop strike I've had to have my IO 360A3B6 opened up.  It's got 800 hows since new.  They found some some fretting.  I know this is evidence of the case halves moving a bit between one another.  My question is, what likely caused this?  Is it entirely due to error at Lycoming or might my treatment of the engine somehow have produced this?

 

 

[N601RX]

It's somewhat common on IO 360's.  It is made worse if the through bolts are not a tight press fit into the case.  I overhauled my engine last year which had almost 2000hrs.  I dropped if off at DIVCO and had them redo the case.  They resurfaced the mating surfaces to get rid of the fretting and converted my case to use dowels to keep the case halves aligned.  The larger hollow dowel pins keep the 2 case halves aligned and the through bolts are just a slip fit.  The also added a o-ring pocket around each dowel so there is no possibility of oil leaks around the through bolts. 

 

The other possibility is using oversized through-bolts, but they are expensive.

[KSMooniac]

It is most definitely not operator error.  Hopefully yours isn't so bad that it can't be dealt with.  N601RX mentioned some great mods by DIVCO that are worth considering to prevent future problems due to the weakness in the original design.  I think it is more common in the -A1A variants, but that is just a guess on my part from anecdotal stories... or it could be that the typical -A1A engine has been in service many more years than our -A3B6D variants and they too can suffer the same malady.  

[320KPH]

Even my two stroke Yamaha bike  has dowels in the cases...

[KSMooniac]

Yep, and Yamaha doesn't have to answer to the FAA to make such a modification.      

[M016576]

Due to a prop strike I've had to have my IO 360A3B6 opened up.  It's got 800 hows since new.  They found some some fretting.  I know this is evidence of the case halves moving a bit between one another.  My question is, what likely caused this?  Is it entirely due to error at Lycoming or might my treatment of the engine somehow have produced this?

Not to hijack the thread, but out of curiosity: do you have the roller tappets in your engine? If so, how do they / the cam look?

[RobertE]

Not to hijack the thread, but out of curiosity: do you have the roller tappets in your engine? If so, how do they / the cam look?

No roller tappets, but one of the cam lobes is worn.

[Alan Fox]

I've never seen a a set of matched castings (case ,pump,etc ) that did not have a dowel setup ......I guess I havent been working on planes long enough....