I got the loader off my 850 this weekend and ready to pull the engine for a rebuild. This is my first rebuild and I want to make sure I do it right. I'm going to take it to a machine shop and have them check the block and head and if everything is OK will have them install the sleeves. I will be doing the remainder of the work. I will be ordering the sleeves from this site. Looking at Part No. EAF6055D, I noticed that the OD is 4.10 and the 850 is not listed in the model no's. The 851 is listed. Looking at Part No. B3NN6055B, the OD is 4.098 and the 800 series is listed as the model no. I think the only difference is pressed or drop-in. I thought that the 172 engine was the same for the 850 and the 851 so why isn't the 850 listed in the model no's for Part No. EAF6055D. Since I am going to have the machine shop install the sleeves, can I go with Part No. EAF6055D even thought the 850 is not listed in the model no's?