Hello again Davo, sorry for the delay but lots of things going on right now.
Scott is correct in that there is no right answer on how often to change bearings.
If your bearings dont feel rough or gritty and dont have excessive end or side play they should be good to go. However I have seen in a few cases with High Qualty traditional bearings and in many cases with the Ceramic bearings where once the motor was at temprature the bearings would bind even though when cold they felt fine (I would like to add that I would not install Ceramic bearings in my worst enemies motor.) They are without a doubt the worst thing since sliced bread in my opinion and the opinion some of my customers who learned the hard way.
Also a good way to tell its time to replace a set of bearings is when the motor goes lean for no apparent reason and you have exhausted all possible causes but not replaced bearing yet there is a good bet that once you do all will be fine again.
As Randy says to be safe change them yearly with the assumtion that you have had no catostaphic events within the motor such as broken rods and the like. In the case where you have had something in the motor break there could be particles in the bearings which at this point could be cleaned but better off replaced to be sure you wont have any FOD floating around inside to find its way to the piston and liner or perhaps damage the crank or the clearances that are critical to the performance of your motor.
I have also done as Randy states and ran my bearings multiple seasons which to be exact it was 3 seasons long, in Florida that is 36 months straight of racing just to test the quality and reliability of the merchandise I sell as top Quality. They held up to the test and I am back on my regular schedule of changing bearings in all my motors yearly over the holidays so that I am ready to go at the Winter Nationals each January. I will state that it is imperative that you clean out and store your motors properly to make such a feat possible. There are many different and great ways to accomplish this but the one I use and it works great for me is: I but Autozone brand spray lube $1.99 a can, plus some good ole everyday ATF (Automatic Transmission Fluid) of course I use Dexron beacause I am a Chevy man
. Drain all fuel out of the fuel tank, spray liberal amounts of spray lube through the carb and into the motor while turning it over with the starter flushing all traces of nitro out. Then through the plug hole I place the motor at BDC and squirt some ATF in then I turn the motor over by hand with my thumb over the plug hole to help build a slight amount of compression which distributes the ATF into the voids of the motor, after that I put the piston at the beginning of the compression phase (all ports closed) and fill the motor with ATF and then install the plug. Dont turn the motor over anymore so that the ATF will remain until you blow it out just before the next running session. WARNING be careful when you pick the boat up as the pipe may have some ATF in it that will turn your shirt all red and the wife will not be a happy camper :angry: LOL.
Hope this helps! Good Luck and Great Boating!
Ron Byrd
Race Craft Bearings & Hobby