To get to the bolts you have to remove the flywheel. As I mentioned previously, the cowling could be frozen to the flywheel. I used a rubber mallet to tap around the cowling. I then screwed a 1/2 inch HT bolt in the flywheel and used this to apply some pressure using a bar. It took a bit of effort but the flywheel moved about 2 - 2.5 cm initially. I put plenty of CRC around the flywheel and, by moving it backward and forward, I had it turning freely in about 15 minutes. I am not saying this is the problem with your engine, but it's worth a look. Cheers, BigAl.