sounds odd!!! check cambelt first and try rotating by hand, then do the basics, compression test etc etc
rebuilding them is a PITA, generally don't bother, get a second hand engine and wang it in
that's cheap TBH, 182 engines are going for £800+ at the moment which is silly
http://cgi.ebay.co.uk/Renault-Sport...arts_Vehicles_CarParts_SM&hash=item3f01d82a35
Ebay link, but posted here.......
How much would you be thinking for a 172 engine, with average (say 70k) and service history?
Do you have contacts that you use for engine swaps Fred?