Differences between VFR 700 and 750's?

Maybe I should be starting this thread in a different (technical , garage?) forum. I want to know the difference between the Gen 2 700 and the Gen 2 750. Are they essentially the same motor, including cam profile, valve diameter's, conformation of the heads, etc? Can you use the same upper end gaskets on either or both? Is the difference only in the bore? Is there a difference in stroke? Do both engines share the same engine case, crank and rods?

What I have read thus far is that the 700cc engine was a compromise to tarif restrictions imposed by US on the import of 750 CC machines that might compete with the Harley Sportster of the same era (mid 80's). Is this true, whats the whole story about the 700?

If there is a 50 cc difference between the 700 and its bigger twin brother/sister, does the driver/owner get any advantage in gas mileage over its larger volume twin? Has anyone ever bothered to test it out or was gas too damn cheap back then for anyone to care?

As long as your at it what is the story about the overnight switch from cam chain to gear driven cams. I heard it was a design problem on the early v30 and v45 that spurred the race to change to a gear drive? Anyone up for telling that story. I've heard one or two 2nd gen drivers remark about teh gear drive. One member referred to it as a "teutonic fix" or an aspect of the bike's redesign that I assume was a tip of the hat to BMW or to German design in general. Why? And what advantage was it?

If you can answer these questions then I have a few dozen more on the back burner getting ready to boil. Any VFR historian's out there? I'd like to know the story behind the bull I'm about to straddle and ride. I hear it's pedigree was a V4 race bike (250, 400 cc class ??)? Any takers? The 5th and 6th gens are at each other's throats over something that started back in the late 70's or early 80's. What's the story? Does anyone here know? Or am I just a fatuous old fat man to ask? Where did "VFR" come from and what did it mean when it started out??

Like, why does VFR mean that it's a bad ass ride and the big cube "cruisers" need to move to the right side of the road when they hear one coming? How did it get that reputation? Was it all in the handling or was it also in top end speed?

P.S. I already read the Wiki article. It left out a lot of details regarding the redesign and why it was necessary. I'm particularly interested because I have one of them.

 

I have the Honda Service Manual for my '86 750 and the manual also covers the 700. I just checked it and both bikes have the same bore, but the 700 has a shorter stroke. The remaining engine and transmission specs appear to be the same. Visually, the only change I am aware of is that the instrument panels are different. You have a lot of great questions that I too would like to see answers for.

 

If Honda shortened the stroke, what then?

If the stroke is shorter on the 700 does that mean that the cylinders (barrels)on the two motors are different heights to accomodate the increased length of the 750's stroke? Is it correct to assume the two engines had different cranks with different throws? Did they have different rod lengths as well? Different pistons? Did Honda finagle a way to keep the cylinder height the same by changes in the piston design? Slipper vs skirted? Were the heads identical? Can you swap a 700 head onto a 750 or vice versa? Did the 750 have larger valves? Can you put the larger valve heads on a 700 without modification? Are the carburators the same on the 700 and 750 except for jetting? If the difference was in the stroke, did Honda have to build two different cam gear drive apparatus to adjust for the 750 having increased length from the crank CL to the cam CL compared to the 700? How long did these design differences exist before the 750 went back to chain drive? When did Honda go back to chain drive? Does a 90's 750 fit onto an 80's frame without modification? Is the later 750 non gear driven cam an improved hp/torque motor?

Sounds like the 700 motor was the same weight or maybe heavier than the 750 and down by 50 cc's. Are their external identifiable clues regarding what size motor a gen 2 or gen 1 frame with a VF motor has that tag it as a 700?

 

Different Carbs between the two. IIRC from reading my manual, the 750 wasn't sold with Cali air equipment, but all the 700s had it. This would have allowed the 700s to be sold everywhere, and the 750s outside of Cali.

Pick up a Honda Service Manual for the 2nd gen bikes, and you'll answer most of those questions yourself.

Further questions can be answered by using BikeBandit.com's parts fiche system, as you'll be able to get part numbers for all the stuff like cylinders, pistons, cranks, rods, etc, and compare if they match. A mis-match doesn't mean different necessarily, or why, but it can at least confirm shared parts.

 

Yes, I'm glad I read your reply before posting. I knew about the CA smog stuff. In addition, insurance rates jump substantially for bikes at or above
750CCs. I appologize in advance for the arrogance of this next statement. With California being such a HUGE part of the motorcycle market, of course they designed one just for us.:vanity:

 

I wanted someone to tell me the technical history

Yesterday I went to the Public library. I was looking for info on how BMW model numbering works. The BMW book was checked out but I stumbled onto a book covering Classic Honda's. The author starts with the late 40's (48-9) precursors of the Dream and the Honda 50' and 90' and then gets into the twins etc. He goes through the 750 fours and the Goldwings as well and near the end he describes the history of the VF engine and VF GP bikes of 81-2-3 and later. The author considers VF bikes classics or classics to be. He describes the problem with cam lubrication on the 83 VF 750's and the fact that it was fixed by 86 with the gear drive and other changes. He has a soft spot for the VF 500. He's not impressed with VF 1000's and he criticizes the VF 750 for having a 16 inch front wheel that he attributes a braking problem (lifting) while in a turn. The whole issue of the 700 is brought up more that once but he remarks that the power difference between the 700 and the 750 is ONLY 5 HP.

In thinking about this I considered that it's probable that the 700 and 750 carbs really only differ by the addition of vapor capture in the 700 version. Otherwise the differences will be limited to jetting, the two machines have interchangeable carburators.

The author gives some information about VFR's. His view is that the fastest 1/4 mile VFR was the 86-87 VFR 750. The third Gen 750 was changed for some reason related to emisson controls /or weighed more for some reason. This caused it to loose out to the earlier model in straight out 1/4 mile racing. He goes on to rate the 4th gen up through '99 and says it had the most attractive styling in red.

The author's last remark was about the VFR color change to Yellow. He seemed to prefer red.

The author had some criticism for the gen 2 VFR 700/750. He complains that the suspension on the 2nd gen needs to be made stiffer. He recommends a stiffer rear shock and heavier front shock springs/ or a change to CBR 600 front forks which require some machining.

But I did not want to tell you guys the history of the VFR I wanted someone with long experiece tricking VFR's out to give me some history.

 

Beg your pardon, but my 86 750 is a cali model with the canister and sticker under the seat saying blah blah blah meets or exceeds ca emissions....




I was bored so I added pics.........as far the soft front goes, I plan on sending my forks to Daugherty motorsports for the race-tech gold valve a stiffer spring upgrade and a works performance shock will cure the rear. All it takes is money.....

 

From reading the service manual, it implied the 700's carbs had far more emissions stuff than the 750.

 

Thats weird, maybe turning into a 700 from a 750 causes it to polute more.:unsure:

 

government mandated tarif on imported 750 cycles

The differences revolve around the tarif and not emissions. If you bought a 750 in the states you had to pay a federal tax penalty, but you got the faster ride. The alternative was to buy the cheaper 700, which looked the same and only performed slightly slower than the more expensive federally taxed model. So now, 23 years later I am asking what the difference between the two bikes was besides price and stroke. The guys with the money got the vfr's with "750" on their RWB paint jobs while those without it drove pearl white or medium blue machines that left off the "750". I was also told in this thread that the 750 had different instruments than the 700's.

My question is really a practical one. There were 2 years of 750 interceptors with the original oil starvation problem. This past month a guy near me has been trying to sell a "running" '83 VF 750. It was diagnosed as having chain tensioner noise by a mechanic. '83 was the first year of the VF with the warrantee problem. It is probable that the bike had been one which had never had the factory repair/ or the after market oil modification. What changes could have been made to repair it if it had galled or worn out its original head. Thus my questions at the beginning of the thread. Can you take a 700 head and put it on a damaged VF750 etc.

The guy who wrote the classic Honda buyers guide I referred to sees the VF models as collector's items. I could have picked up a decent looking '83 750 for @ $400. What was the score regarding swapping heads and the other parts to bring back one of these early model cycles with cam problems? No body was available with an answer? I lost the bike to someone who might have known, who drove it home for $300. If he did not know it's going to become a stripper and another classic is going to be lost to the road.
My son bought a VF 500. Is the same oil starvation a problem for his cycle? That is why I asked. Is anyone around who knows any answers. He would have had to turn a wrench on Honda's back in the 80's and have seen and heard what was happening in the back of honda dealerships in 1983-6.