OK - I've hit a bit of a snag - need some input on my possible solution.

Got it all back together - plonked the GXV390 on and it fouled ( or rather it sat up on the gear box and rested on the front shield - way longer obviously than models of Honda engines available when this model slasher was first released.

Turning it around 180 I can either line up 2 holes but the engine is slightly off centre and to get it on centre I will need to drill 4 new holes. However this option puts a lot of weight to the rear and leaves the front very light ( 1.8Kg on the front wheel) - this could be counted by adding weight to the front - I will also have to remodel the connecting rod for the drive engage lever.

If I re-drill 4 new holes I can get the drive shaft centred and the load moved forward about 25mm.

Is there any reason NOT to mount the engine backwards. Should the drive shaft be dead centre?

This is front on with drive shaft centred

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This shows the rear overhang with drive shaft centred

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This is the alignment with 2 holes lined up - the engine is off centre to the left

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The two front hole right side. If I relocate to the closest to the spring the spring will be displaced slightly but still works tensioning the idler pulley

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The space between the engine and shield - if turned 180 the engine sits on the shield

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Just for interest the GXV340 is longer and the GXV160 is too under powered for the application.