Main Bearing/Dowel Pin Alignment

[Steve Pierce]

I recently tore down an O-320 out of a Pacer for a prop strike inspection. Engine had about 500 hrs. since a major overhaul so it was in pretty good shape. Upon inspecting what came out I found that the alignment holes in the front main bearings were not aligned with the dowels pins in the crankcase.

These are the two dowel pins in the left crankcase half.[attachment=7:1vs71frv]100_2821 (Medium).JPG[/attachment:1vs71frv]

One main bearing half properly aligned. [attachment=5:1vs71frv]100_2822 (Medium).JPG[/attachment:1vs71frv]

Main bearing shell misaligned as installed by engine assembler.[attachment=6:1vs71frv]100_2825 (Medium).JPG[/attachment:1vs71frv]

The result to the back half of the bearing shell. [attachment=4:1vs71frv]100_2826 (Medium).JPG[/attachment:1vs71frv]

Marking the bearing shells that are split 90 degrees to the crankcase split line.[attachment=3:1vs71frv]100_2831 (Medium).JPG[/attachment:1vs71frv]

Two marked bearing shell halves.[attachment=2:1vs71frv]100_2832 (Medium).JPG[/attachment:1vs71frv]

This is what it looks like if the bearing is installed misaligned.[attachment=1:1vs71frv]100_2834 (Medium).JPG[/attachment:1vs71frv]

Bearings installed with two alignment marks to help when installing the crankshaft with the bearings installed.[attachment=0:1vs71frv]100_2839 (Medium).JPG[/attachment:1vs71frv]

Hope this helps someone not make the same mistake the previous engine builder made.

[JoeB]

I wonder what surprises my engine has in store for me...

BTW - Nice details and photos! You always do provide the best technical information (and website links)! When the engine was assembled incorrectly like this, wouldn't the case halves have a slight gap there since the bearing wasn't properly seated? I'd expect that the crankshaft turning torque was a little bit high for a few hours too!

[Steve Pierce]

Yes, I am sure it was a little tight right there. There was a little more wear right there on that bearing and you could see a sort of shadow on the case half where it wasn't seated as tight. I call all these airplane projects snowballs. There is always more to do than you expect. ;)

[Bultaco Jim]

Amazing! That it went 500 hrs, I mean. I hope you can call the installer on the carpet, Steve. Who knows how many he installed like that.

[Hillbilly]

Amazing! That it went 500 hrs, I mean. I hope you can call the installer on the carpet, Steve. Who knows how many he installed like that.


Ahh dont worry Jim that guy only built two engines...that one and YOURS...giggle

[Steve Pierce]

There was a guy that was building engines for experimentals. He forgot to put the lock tab on the crank gear and the RV landed without damage in a field. Come to find out the guy forgot it on his own engine and it cost him his life.

[Bultaco Jim]

Ahh dont worry Jim that guy only built two engines...that one and YOURS...giggle
I am pretty close to 500 hrs..........

[stevesaircraft(Bri)]

The only time I had one move out of alignment it froze up the shaft as soon as I started to tighten the case at all.
Personally, I have always felt it was poor design on Lycomings part because of that potential of bearing misalighnment. Anyone ready to go after the mechanic that assembled it, ought to try to put one together first. I am still surprised it turned at all.

Steve

[JoeB]

...a bit off topic but years ago I worked at a British car restoration shop. I was walking by another guy in the shop assembling and engine, at first glance I figured he was driving cam bearings in place, but upon closer inspection saw that was a wiggle stick at the other end of his ball peen hammer! I made a 'comment' to the boss about checking out the new guy hammering the camshaft into the block but he kinda shrugged it off. Guess I was wrong to say anything about his methods... :lol:
They both spent about an hour with a breaker bar and a reeeeeaaaaallllly long pipe trying to get the installed engine to turn over, but they did eventually get it running. (I still don't know how he adjusted the valves?)
That material he peeled off those bearing should come out of the engine on the first oil change, right???

[Hillbilly]

The only time I had one move out of alignment it froze up the shaft as soon as I started to tighten the case at all.
Personally, I have always felt it was poor design on Lycomings part because of that potential of bearing misalighnment. Anyone ready to go after the mechanic that assembled it, ought to try to put one together first. I am still surprised it turned at all.

Steve


Me too.

[Bultaco Jim]

I have. Completely stone-age stuff.

[Curly]

I once worked with a kiwi ag. pilot - his motto was "If you can't fix it with a hammer and screwdriver - get a bigger hammer and a bigger screwdriver".

And he was true to his word - we got stuck on a job way out in the donga and needed to change a cylinder (gypsy major engine). Not having the correct spanner in the toolbox he undid the cylinder nuts with a screwdriver and hammer - one flat at a time! :o

(And Tim - if your up there reading this while sipping a scotch and soda, you are still the most gifted and natural pilot I ever had the pleasure of flying with!)