4 Fun & Challenging.Dirtfish | 07/05/2011 | See all Dirtfish's reviews (475)Top 100 Reviewer Top 100 DVD Reviewer Top 10 Books Reviewer Top 100 Toys Reviewer Haynes Build Your Own Combustion Engine is a working model kit which requires assembly. Putting this engine together is a lot of fun and very challenging.It took me about 5 hours to complete the engine. The instructions are quite good but a couple of the steps had no pictures and made things quite difficult at times.The assembly can be quite complicated and is very fiddly at times. This is not a kids toy and I feel young kids would find it incredibly difficult to complete the assembly.If you like difficult puzzles and model building kits then I would strongly recommend this. Its really fun and once completely the engine makes an interesting ornament.