VFR 700 to 750 conversion

Ok Im gonna be suprised if I dont get a post that shows me a link to a previous post, I looked and didnt find one. So does anybody know what I would need to convert my 86' vfr 700 to a 750? or even easier maybe a lead on a 750 engine near North Carolina? thoughts, questions, Ridicule?

 

Is there a noticeable difference between the 700 and the 750?

 

I imagine so 10hp is quite a lot on a 500lbs machine. Plus my 700 is a cali model with all the emissions crap. I do like the consistent 65mpg though.

 

Thanks for starting this thread as I just made this conversion last week. Both my bike (VFR700F) and the new engine (VFR750F) came from 86's. It was a bolt in. Torque is noticeable with the long stroke engine. I kept everything else the same. Carbs, Ignition, pipes, gearing. The biggest deal was cleaning the 25 years of gunk off my frame.

I read somewhere that if both engines had the same brown side covers then there would be no issues.

I used a flat transmission jack to drop the motor. I didn't have to remove the radiator. Once dropped I raised the front wheel up on a block to allow enough room to slide the motor out.

My plan was to document these changes but my hands got too dirty and I didn't want to pick up my camera.


Here the old engine is out sitting on the jack. The radiator didn't need to get unbolted and the rear pipes stayed on the engine.


I've cleaned up the frame in the driveway. Gone are 50,000 miles of chain lube and various seepage.


I used a wire brush on the exhaust pipes. I have one cleaned up. They shined up pretty well. Like everything else not too much corrosion.

I have never been a mechanic but have always worked on my bikes.

 

Cool pics Camo.:thumbsup:

Got any more?

 

I didn't take anymore photos. My bike looks identical to what it did before. Well identical except for the small 748cc casting on the front cylinder. My gearing is 16/46, I'm not sure what stock is but my sprockets are in great shape.

Stosh monster, nice collection of bikes, when I got this VFR I was looking for a VTR1000 or RC51 before I bought this one. At least I don't have that much into it.

 

Thanks for the pics and the info, I assume the ignition system and carb worked fine on the swap? Where did you get the engine? Any idea on mileage on the 750? Torque is the biggest difference? Sorry for all the questions but your the first person I've talked to whose done the swap!

 

My old engine was pretty old with fairly low compression (70psi). I found the new engine here on VFRworld classified, Brad McDill. The new engine had just a few thousand miles on it. Keep your eyes open. Much cheaper than rebuilding. I had put a lot of effort on cosmetics and time into it over the past 6 weeks. The previous owner stopped by and couldn't believe the difference.

 

Awesome, I'll keep my eyes peeled. Although my 700 is in pretty good shape, and goes too. I will have to get a 750 one day.

 

How's she running after the motor swap? Any issues,leaky carbs,coolant leaks,chain alignment,etc?

Thanks Camo. RC51's are cool bikes but they're an absolute royal pain in the ass to work on. To be honest I don't think they were made to be disassembled.
Doing just about anything on them is like mining for gold,you have to dig the entire mountain off the top of it to get at that piece of gold,then once you get to the gold you have to pile the whole mountain back on top of it.
Even oil changes are a major pain since the oil fill plug is completely hidden behind the right fairing panel.
Trust me,working on my old '86 VFR700 was an absolute pleasure compared to working on my RC51.

My apologies for the thread jack VFRBafoonage.

 

Were all friends here stoshmonster.

 

More thread jackage. I'm suprised the RC51 is that bad to work on being a twin and all. Learn somethin' new every day!
I'd venture a guess that the KTM 950 Adventure I had 2 years ago is a bigger pain in the ass though. 3 hours to change the oil. I like to wrench, enjoy it quite a bit actually, but that was just stupid. It took me 8 hours to check the valves the first time and no adjustment was necessary. Of course it was a twin too, so I guess being a twin doesn't mean jack!

 

I am surprised by both comments on working on the twins. I am tempted to take the fairing off my bike permanently. My VFR 700 was not the most healthy running before, it would do 135 on the speedo. The new one revs quicker in any gear. My change was a good thing. You mentioned that the 750 had 10 more hp than the 700. It may. Probably an 800 has 10 more than a 750 and a 1000 has 20 more than a 800. It is all relative. Probably slipping in a VF1000 motor might be a cool ride.

At any rate changing engines just gave my old bike some new life for relatively cheap and fairly easy to do. Any more I value having a nice wide powerband.

I was surprised that I had no seepage or any alignment issues. Putting on the carbs was bitch as anyone can attest to. I lubed the boots with silicone oil and used wooden pry bars. The previous owner had a couple of the boots on upside down. They are directional.

 

Hey, I just ran across this thread, and I have something to add. I have an 87 700 with an 86 750 motor. It's a long-term unfinished project, so it's not running, but I started it back when lots more people were playing with early VFRs and info was easier to find. I have every confidence that the info I am passing along is correct.

Anyway, as Camo said, if you have an 86 motor and an 86 bike (magnesium-look golden tan sidecovers) it's plug'n'play.

If you have an 87 bike like mine, you need to install the ignition trigger (under the right sidecover) from your 87 motor into the 86 motor. Or you could install the entire wiring harness, ignition system and gauges from the 86 bike onto your 87. Whichever is easier... The 86 motor also has an ignition-related sensor on one cylinder head. You can ignore this, it is not needed with the 87 ignition system.

My 87 also has a CBR600F2 front end and a CBR600F3 rear wheel, plus a Penske shock. My GF bought the bike in ~94 and I bought it from her in ~96. I've also owned a 92 and a streetfighter 86, which is where I got my 750 motor.

HTH!
kevin

Oh, here are a few pics (the 92 isn't mine, but it's just like mine...):

 

From what I've read (and I'm not an expert on this), the engine internal differences were the crank, rods and pistons, and then of course the emissions equipment and carbs (as 750s weren't sold in california with cali emissions equipment).

 

I believe the pistons are the same. The 700 got longer rods to make up for the shorter stroke 'cuz rods are easier to redesign than pistons are.

 

I do have an 86' I will just continue to look for a donor engine. Thanks for the reply.

 

That's right. I remember this now from looking to see if there was a way to up compression to gain more power (requiring premium fuel, but that's not a big deal).