I have had a quick search and have not seen this topic covered as yet. Recently, a gentleman in WA has made up a full jig setup to totally replace the rails on twin rail machines. While doing this, he has reported that the Kirby mowers have a higher crank output than Briggs-powered 45’s.
The difference is 3/32” which is suggested to be too great of a difference for the self aligning bearings to correct. He has suggested that if re-powering a Kirby machine with a Briggs, a 3/32” shim should be placed underneath the engine.
I found this quite interesting. These photos were supplied by him on Facebook and demonstrate the height difference well. the first photo is of a Briggs and shows that the output jig does not align with the hole in the chassis. The next photo shows perfect alignment with fitted to a Kirby.
Funnily enough, I have not rebuilt a machine with a Kirby on it, but this is certainly something to consider if users are planning to put a new Briggs on their rebuild.
