This will test my memory, I think there were nuts inside the bearers, with access holes from under the engine that you could get a thin greasy arm into. Access holes had big nylon plugs and there was one near each engine mount. Long time since I looked so I hope I am right.
My SO30 has nuts inside the bearers, accessed as Sitara has described with the plastic disks on the front end of the bearers.
A tapped plate like you you suggest would be easier to maintain. You need a long bar and a good quality socket for the back ones, though if they are turning, you can turn them from the top to line them up with the socket points. You can’t swing the bar much!
Thanks very much for your prompt replies, I can't tell you how relieved I am to hear that there are access points under the bearers. I had visions of cutting bolts and mixing epoxy to repair the fixing.
Thanks again and I'll report back next week when I get back to the boat.
You Mentioning the exhaust elbow which maybe made in stainless is leaking this is a common problem and can be wielded or replaced , worth doing there could be a metal gasket for the elbow to replace available from a yanmar dealer ..
Rob, Rene, you are correct, access is via holes under the mounts sealed by plastic disks. I managed to tighten the bolt on the rear engine mount by using a ratchet spanner on the nut under the bearer. This was fed in through the access hole for the front mount and tightened from the top.
Access to the nut nearest the stern is more difficult and Rene's suggestion of a long bar with a socket should work but it is not an easy option.
John, thanks for the feedback on the exhaust elbow, that was indeed the problem. It happened a couple of years ago and I did get the elbow rewelded and it has held up well. It was while I was checking on the weld that I noticed the rust which I am workiing on now.
I took a couple of pictures but I don't intend to post them as the access points are obvious once you know what to look for. But if anyone does want to see them just let me know and I'll post.