converting vf700f into vf750f

[saf]

Does anyone here have any experience/knowledge about converting vf700f into vf750f? After looking at specks, my (perhaps naive) thinking is that replacing pistons, connecting rods and potentially the crank shaft should do the trick. Am I being too naive? Is there anything I am missing? Any comments/suggestions are welcome. Thanks.

[derstuka]

Welcome to the forum Saf. Where are you located?

I would have to say that finding a VFR750 motor to put in would be an easier route...I am sure you have thought of this though. Why do you want to do this?

[saf]

Thanks for your reply. I am located in RI.

Why I want to do this? Well, I'd like to keep my old bike (it's a 1985 and has a lot of sentimental value), but this bike is underpowered (IMO) and I am considering my options. Ideally I'd like to put 1000cc engine on it, however, I'm not sure how well it will fit (if at all). Besides I am yet to find a decent 1000cc engine for sale. I am planning on rebuilding my bike's original engine this winter and I thought this might be a good opportunity to get extra 7-8 Hp out of it by replacing pistons and crankshaft (hopefully I can get them on e-bay before winter). What do you think, will this work?

[JamieDaugherty]

The VF1000F engines will fit just fine. Make sure you get an exhaust too as those are different.

The VF750F engine is also a direct swap. That's probably an easier option than rebuilding the VF700F with the 750 internals. That's possible but difficult and expensive, it would be cheaper and more time effective to just get a VF750F engine, in my opinion.

[saf]

It's good to know that a 1000cc engine will fit into vf700f, I'll keep looking for one then.

As for the economics of the 700-750 conversion, I don't see yet how buying the entire engine is cheaper than replacing pistons and crank (assuming that this is all I need). If I find a used 750 engine it will be no less than $200 (likely more than that) plus ~$200-300 for shipping. I still will need to rebuild it (unless I find one in a very good condition which will run much more than $200). On the other hand, I could probably find pistons and crank for under $200 together plus ~$50 for shipping. I will be using my engine block and heads+cams that I know are in good condition. It's a lot of work but it's a fun project to do in winter...

[DANIMAL]

If you look at the specs of both engines you'll see that Honda just destroked the 750 by changing the Connecting rods. Just need to change the Rods. something about a tariff on imported 750cc bikes to protect some POS American Bike whose name is HARDLEY worth mentioning. So I won't....

[saf]

That's what I thought too but then I looked at the microfish for 700 and 750 and it looks like they have different cranks as well (at least part numbers are different).

[Sebspeed]

Originally Posted by DANIMAL

If you look at the specs of both engines you'll see that Honda just destroked the 750 by changing the Connecting rods. Just need to change the Rods. something about a tariff on imported 750cc bikes to protect some POS American Bike whose name is HARDLEY worth mentioning. So I won't....

The pistons are different also, there is more going on there than meets the eye!

The pistons of the 700 have more of a dome to them; according to Dave Dodge, building a 750 motor with the 700 cams will yield the best power from the 3/4 liter blocks.

[JamieDaugherty]

Originally Posted by saf

It's good to know that a 1000cc engine will fit into vf700f, I'll keep looking for one then....

Those can be tough to come by, there are a lot of people out there looking for VF1000 engines!

Originally Posted by saf

As for the economics of the 700-750 conversion, I don't see yet how buying the entire engine is cheaper than replacing pistons and crank (assuming that this is all I need). If I find a used 750 engine it will be no less than $200 (likely more than that) plus ~$200-300 for shipping. I still will need to rebuild it (unless I find one in a very good condition which will run much more than $200). On the other hand, I could probably find pistons and crank for under $200 together plus ~$50 for shipping. I will be using my engine block and heads+cams that I know are in good condition. It's a lot of work but it's a fun project to do in winter...

Engines on eBay are about $100 and shipping using BaxGlobal is $90-100. Here's a hint - many of the rebuild parts are discontinued from Honda. Even if you could get the parts, the bearings, gasket sets (that's over $100 right there) and other parts needed, not to mention the donor crank/rods/pistons would be a multiple of the used engine price. Don't bother with a rebuild, just throw it in and go!

I agree with your approach from the fun perspective, if that's what you are after than I'm behind you 100%.