at 85,000 miles my 08 RG 103 is getting tired and time for a rebuild

Is a 107" simply a rebore on my existing 103 cylinders, or special thin wall Nikasil cylinders to fit the existing cases?

 

As far as I know it's simply a rebore. Going any bigger requires the thin wall cylinders a la 110".

 

will a 110 fit my 103 cases

 

Yes, Harley makes 110" kits with the slim wall spigots specifically for the 103" engines . This is an upgrade I'm planning for this winter on my Dyna.

 

so how big can 103 cylinders be safely bored?

 

107" if you want to stick with your 103 cylinders, the HD 110" kit is made of special cylinders with hardened spigots

 

You can bore your OEM cylinders to 3.937"(107").
We were one of the very first shops in the country to start doing so back in 2007, going to 107", and we were boring the 88" to 98" in 2006.
Many folks scoffed at this, but time has shown otherwise.
Scott

 

I personally would go 107",the HD 110 kits havnt been proven yet and have had some problems in the short time they`ve been out

 

Stay away from nikasil. Great for a 2 stroke, not so for a 4 stroke.

 

The 110" kit, put together right, can be a runner. A dealer tech on another forum reports 80 kits, 110s and 117s, installed to date with only one having an issue.