O-320 Connecting Rod Questions

[avq]

I am putting together the parts necessary to rebuild my O-320-A2A. I bought connecting rod bolts PN 78027 and nuts 74646 based on the thought that my connecting rods where PN 78030. I bought the 74646 nuts based on the narrow deck ?A2A parts list.

My first concern is that the nut 74646 is unlike most connecting rod nuts I?ve seen. It has about a ? in lip while the others I?ve seen have about a 1/16in lip. I put the two side by side below. You can somewhat makeout that the nut lips are different lengths.

From what I can discern from Lycoming SI-1106D that extra ?lip? is there because the 74646 nut is an ?older? style crimp bolt. It was later replaced with LW-12186 since Lycoming found crimping the bolt did not significantly decrease the likelihood of connecting rod failure.

My questions:
1)Is there any special procedure for crimping the connecting rod bolts or should I not worry about crimping them altogether?
2)How can I verify I indeed have connecting rods 78030? I was told this by AEA in Dallas but I cannot seem to make sense of the markings on the connecting rod.

Any help would be appreciated!!

[avq]

Jim,

I found this reference on the web. It refers to the 74646 nuts as "crimp lock."

http://www.lycoming.textron.com/util...Price-List.pdf

I was really surprised how expensive those rod bolts were. I will definitely be REALLY careful.

I also cannot find a reference to a 60313 part number in any Lycoming literature. I only get web hits for people selling the same connecting rod.

Anton

[rocketbob]

Do you have the latest overhaul manual? There is an appendix which contains the superceded part numbers and cross references old part numbers to the corresponding new ones. Sometimes its not very clear which parts are the latest. For example: on some 360's and most 540's, there are three different styles of magneto drive gears, but nowhere have I seen in writing what the latest is and what are the differences between the three even though one can see obvious differences. I suggest you call Lycoming to get the answer you need.

[JESSEAERO]

The 60313 is the casting # on the rods. The part number will be inked on the outside edge of the beam. There is a old SI1183 that tells you that you can convert the old style rods to the newer style that take the 78027 bolts by increasing the radius on the bolt holes. If you need a copy let me know and I can scan it and e-mail it to you. I would also buy the new style nuts to go with your bolts. They are like 3.41 each. Not bad compaired to the other style.

Thanks,
Jesse

[avq]

Thanks Jesse. If you can send me a copy that would be great. I will send you a PM with my email. SI1183 became inactive so I am not sure how to get it otherwise.

I am in the process of returning the older nuts now

[Russ McCutcheon]

Hi Anton,

Sounds like your getting this figured out but I thought I would let you know what I did when overhauling my Lycoming. I bought all my parts from Bart & Sue at Aerosport, since they build them they could answer all my questions and with a simple description from me they knew what I had and sent me the right parts for everything, dealing with people that know the products they sell & service is priceless.

[avq]

OK. So things are a lot more clear now after reading SI1183. Thanks Jesse for pointing that out.

60313 is a casting part number that referred to the old 61476 connecting rod that used the old 74667 connecting rod bolt. SI1183 required that all 61476 connecting rod assemblies were machined to accept the newer 78027 connecting rod bolt for higher torque loading. At this point the 61476 connecting rods became 78030.

This was definitely done to mine as it accept the 78027 bolts and it was recently overhauled but for some reason the new part number is not listed anywhere.

Thanks again to everyone for your help!

Anton