Several of the older posts suggest there has been success with insuring with Carole Nash who I am currently insured with but when I rung them they refused blankly as the replacement engine was not a 'like for like' as it came from a generator not a motorcycle. The quotes bloke had heard of diesel conversions but their 'specials and customs' bloke said no. I did ask if they had called the underwriters on this and it would appear that they are going on the word of their specialist.
So who are you insured with and how did you phrase your conversion to them??
