I have a Snapper self propelled walk behind with a B/S 6.5 Quantum(I think). I think the compression is getting down a bit as it's hard to start. It takes up to 15+ pulls to get it running. I am considering repowering it with another B/S 6.5, but I see there's a difference in 6.5's available. One has OHV and iron bore while the others(cheaper) does not have OHV and it says "aluminum bore". Is that possible to have an aluminum bore? I thought they were all iron sleeves. These are the two that I'm considering......... Aluminum bore model(my existing one looks like this) http://www.smallenginesuppliers.com/shop/html/pages/products/briggs_vertical_shaft_engines4309.html Cast Iron bore: http://www.smallenginesuppliers.com/shop/html/pages/products/briggs_vertical_shaft_engines4321.html My existing motor looks like the aluminum bore motor, but I'm pretty sure it's a cast iron I/C motor. Is the new replacement just a throw away motor now?