Join Date: Oct 2007
Location: Beacon Falls CT USA
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Rep Power: 8
I replaced a Hurth 50 with a zf 6. The H50 was the same spec as the zf5, so i think my experience may be of interest.
As you mention, the zf 6 is about an inch longer, so I did have my shaft shortened and rekeyed to keep the prop right where it was. I had the good fortune of having enough room aft of the engine, so that the longer unit did not represent a major structural issue. I did have to redrill the cable-mount plate to adapt to a new bolt configuration - you may or may not have this issue if you're going from a zf 5.
Detailed design specs are available on the website for zf - don't have it handy, but if i find it I'll post it here. These were helpful in resting my concerns on fit.
I will also post a reference of the vendor that sold me the replacement (new) zf6 - it was surprisingly close in price to a rebuild I was considering - something like $1,200/usd. I was also able to get $150 back on my H50 from a local deisel mechanic in CT.
The unit has been in all season without an issue. I'm thrilled with it - and with the fact that I didn't botch anything in the process (e.g. shaft alignment).