96 vfr750 cbr929 pistons???/

[v4vfrgixxer750]

hi guys ive been reading around and heard that the cbr929 pistons are a direct swap with my 96 vfr750 set, can anyone confirm this??

i know they are bigger so an overbore would be needed (just asked a company would be about £80) but other than that would there be anything else?

one last thing, what effects would this have on the engine good or bad?

i think i read that it makes it a vfr837 and that sounds good to me!

thanks for any help as im seriously interested in doing this

[V4 Rosso]

i know they are bigger so an overbore would be needed (just asked a company would be about £80) but other than that would there be anything else?

I doubt you can go this far with an overbore. You decide, here are some numbers:

929

VFR750

vfr800fi

The tables don't show compression height which is rather important too.

[mcrwt644]

V4, can you send me the links to the pages as I am at work and cannot view them...mcrwt644 at yahoo . com

I've been researching this a bit and it might be something I'm going to undertake. I've got a line on a complete engine for ~150 and if I can get 929 pistons, a good set of rings, and have ape bore it, it would run me about 500 with gaskets as I would do all other work in house (valve job, jetting etc)

I believe the ape website says the JE/Wiseco kits raise compression to 836cc 2.599" / 65MM bore, application; Street 10.25:1 K836 mods to be madeCylinder boring only price; 564.44

This is the street application, the race app raises compression to 12:5

Now, you go this route, do you go ahead and lighten and balance the crank??

[V4 Rosso]

I believe the ape website says the JE/Wiseco kits raise compression to 836cc 2.599" / 65MM bore, application; Street 10.25:1 K836 mods to be madeCylinder boring only price; 564.44

With compression height I meant the distance between the centre of the piston pin and the piston deck. If it is too large it will result in bend conrods (piston hits cylinder head), too low and you'll loose a lot of compression.

Now, you go this route, do you go ahead and lighten and balance the crank??

At least balance the cranck and have the conrods polished (increases strength).

[mcrwt644]

I believe the ape website says the JE/Wiseco kits raise compression to 836cc 2.599" / 65MM bore, application; Street 10.25:1 K836 mods to be madeCylinder boring only price; 564.44

With compression height I meant the distance between the centre of the piston pin and the piston deck. If it is too large it will result in bend conrods (piston hits cylinder head), too low and you'll loose a lot of compression.

Now, you go this route, do you go ahead and lighten and balance the crank??

At least balance the cranck and have the conrods polished (increases strength).

JE kit I'm presuming would fit flush, but I am not sure. I'm going to get a set of 929 pistons and pull this other engine apart and put the 929 pistons in. ....thinking now, that's gonna be REALLY hard with a 61.5mm bore....There isn't a ton of info on the web on this that I can find.

I'm taking my vfr by a local machine shop that said they might be able to do this today to see what they say.

If I undertake this? I'm probably going to go the 929 piston route, bore to 65mm, lighten and balance the crank , maybe have a 3 angle valve job done, possibly cams, jet kit and obviously a full exhaust. It'll take some time because this is NOT going to be cheap. It's very doable though, expeically with the availability of cbr parts.

I believe the hp gain was in the 40-45hp range?

[Veefer800Canuck]

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

[mcrwt644]

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

JE kits have the wrist pins etc, but yo ubring up a good point with the crank...that's why this is probably going to be a year long deal

[Guest]

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

JE kits have the wrist pins etc, but yo ubring up a good point with the crank...that's why this is probably going to be a year long deal

Just curious. Why is this route better than buying a ready made pistion kit?

[mcrwt644]

Hopefully the wrist pin diameter is the same, and the top of the pin hole to the piston crown is at least close, so the top of the piston isn't meeting the valves. Even so, you would need to dry fit the pistons, bolt the engine together, and rotate the assembly with modeling clay on the piston tops to confirm clearance at tdc with the valves operational too.

The piston weights would be your next worry, and you may need to lighten or weight the crank to suit.

JE kits have the wrist pins etc, but yo ubring up a good point with the crank...that's why this is probably going to be a year long deal

Just curious. Why is this route better than buying a ready made pistion kit?

I'm asking myself the same thing. I'm seeing 929 piston kits for like 1/6th the cost of a je kit, but that said, the je kit comes with new rings, wrist pins and circlips

[Chris71mach1]

I doubt you can go this far with an overbore. You decide, here are some numbers:

y'know rosso, you say that, but this is the typical size of the pistons in any 840cc overbore kit. I'm gonna start doing some research, cause he may just be onto something here....

[Chris71mach1]

just to put a little note on this thread...im about to absolutely lose my mind here, as I am looking at the same piston spec chart in the manual I have for the 86-87 VFR's, an already knowing beyond the shadow of a doubt that the 2nd gen VFR's used the same pistons for both the 700 and 750 motors (the extra displacement in the 750 bikes was accomplished via the crankshaft and connecting rods), and comparing these charts to each other, I am coming up with the following conclusions:

(1) these comparisons are being made under the assumption that the VFR750 piston spec chart is the one for the 96 model VFR

(2) all the numbers for the 2nd gen pistons match the #s for the 4th gen (96) pistons *exactly*

(3) the #'s in both the 2nd gen chart and the 4th gen chart also match the 929 pistons

(4) the wristpin measurements are listed in these charts, and they seem to match right on as well, implying that the VFR and CBR wristpins are the same, and there should be no problem mounting the 929 pistons on the VFR rods

(5) the only thing missing here is the total height measurement of the piston (ie center of the wristpin to the top of the piston). I would love to get this measurement, as this should be the determining factor in whether or not this will work.

(6) if all of these #s actually work out, v4vfrgixxer750 and Rosso may very well have accidentally found a MAJORLY money-saving alternative to buying JE's thousand dollar overbore kit, saving many VFR750 owners shittons of money on engine upgrade projects!!!!!

I've already found some very cheap sets of 929 pistons on eBay, and I'm dying to see somebody score a set just to complete the specs and measurements, and determine once and for all the answer to v4vfrgixxer750's question...

will the 929 pistons really work in the VFR750 motors as the coveted 840 overbore piston!!!???!!!???!!!???

[v4vfrgixxer750]

hmmm seems ive really started summin here lol , i reckon it needs to be found out once and for all with a definitive answer.

my question is this, i pretty much know the 929 piston could work even if it hits the cyclinder head / valves as you can get the piston head machined / grinded slightly to be shorter.

the bigger bore piston kit (837cc) is like £500!! before machine work so it will no doubt be cheaper going this route.

BUT what effect will it have on a vfr750? will it giv more hp / torque? less reliable? etc AND if you do the overbore will you NEED to work on the crank etc or can the rest of the engine be left alone within reason (can imagine jetting would be needed and minor tweeks)

what perks and pitfulls would this have in comparison to doing more engine work?

ive been adding up whats needed (this is based on just an overbore not other engine work) £70ish for 929 pistons, £80ish for overbore work, £70 ish for gasket set and would probably buy new piston rings as well just incase........... thats not a bad price to look at to get a vfr840

thankyou for everyone whos chimed in and helped out so far!

[Chris71mach1]

hmmm seems ive really started summin here lol , i reckon it needs to be found out once and for all with a definitive answer.

oh yes. this thread could potentially open up one hell of a can of worms.

my question is this, i pretty much know the 929 piston could work even if it hits the cyclinder head / valves as you can get the piston head machined / grinded slightly to be shorter.

the bigger bore piston kit (837cc) is like £500!! before machine work so it will no doubt be cheaper going this route.

you wouldnt want to deck the heads, cause that would bring the top of the combustion chamber CLOSER to the piston, and right now, the biggest concern I have is piston/valve clearance. this could best be determined by measuring the pistons from the center of the wristpin to the top of the piston (and comparing the measurements), and also measuring the depth of the valve reliefs on each piston, from the top of the piston deck to the bottom of the valve relief, as WELL as verifying valve relief placement on the piston, so to ensure it would not interfere with the valves when the valves are open and the piston at TDC.

BUT what effect will it have on a vfr750? will it giv more hp / torque? less reliable? etc AND if you do the overbore will you NEED to work on the crank etc or can the rest of the engine be left alone within reason (can imagine jetting would be needed and minor tweeks)

what perks and pitfulls would this have in comparison to doing more engine work?

you're kidding right? there's an old proverb in the performance world that dates back to the beginning of engine performance itself. it says "there's no replacement for displacement". I believe that when it comes to the bore and stroke of the cylinders being compared to the HP/TQ, the size of the bore tends to affect horsepower more, where the length of the stroke tends to affect torque more. (i may not be correct here, so anybody is welcome to chime in on this at your leisure). but increasing the displacement of your engine definitely will result in more overall power,

now one MORE thing I've noticed, is in comparing the VFR piston to the 929 piston, it's quite obvious that the 929 piston doesnt have nearly as much material on the piston skirt as the VFR piston does. this could actually yield an added advantage, as the 929 piston may in fact be lighter, which will result in a lighter overall rotating assembly weight, which has an end result of the engine being able to spin up faster (ie reach higher RPM's with less time and effort). theres nothing at ALL wrong with that!

ive been adding up whats needed (this is based on just an overbore not other engine work) £70ish for 929 pistons, £80ish for overbore work, £70 ish for gasket set and would probably buy new piston rings as well just incase........... thats not a bad price to look at to get a vfr840

one thing to look into here is to find out whether the cylinder bores would have to be sleeved to accomodate a 4mm overbore, cause lets be honest, +4mm is a pretty huge bore. (at least to me it would be, i'm used to seeing cage motors bored in much smaller incriments....that having been said, the 840 kit IS a set of 74mm pistons, so this has been done plenty of times before).

if you do decide to move forward with this project, PLEASE keep us all posted as to your progress and success!

[JZH]

I heard once that the legendary Tony Scott once built a RC30 engine stuffed with Fireblade pistons for someone to race on the Isle of Man. (Or it could have been an over-bored VFR750F engine in an RC30 chassis--I forget.) Anyway, it blew up.

But don't let that stop you! You could be the next Tony Scott...

I have a TTS-built VFR837FP, which I definitely approve of, but if you're expecting huge power increases from that much additional displacement, well, don't. I expect a whole lot more from my A&A kitted RC46 (if I ever get it running...), but it also cost a lot more than a big bore!

If you're au fait with engine building and can get your hands on a couple of second-hand engines, you might be able to work out an OEM combination that would work. Honda does seem to like to use proven designs in more than one engine. The most interesting example I've found of this is that the V4 NC30 (and NC35) engines actually use the same exact pistons as the inline-4 NC29.

However, bear in mind that Honda VFR engine cases are notoriously difficult to over-bore accurately. I've heard of 750s and 400s that have been ruined by machine shops not familiar with the appropriate techniques. That "cheap" boring job may turn out to be anything but...

[FYI: Here's the old TTS big bore kit page--their current Web site is almost dead.]

[Oh, and another thing: Back in the day, only TTS and Dynamo Humm were selling VFR big bore piston kits. Both were made by JE, but to TTS' spec. Dynamo Humm in Canada actually had to buy the pistons from TTS, as JE (in California) would not sell them to Dynamo Humm directly. I don't know if TTS still has exclusive rights to those pistons or not. Dynamo Humm doesn't exist any more, but TTS apparently still does (even if mainly a Hyabusa supercharging shop now). Might be worth a call to JE/Wiseco?]

Ciao,

[mcrwt644]

I'm looking into having the crank lightened and balanced, the pistons with possible carilla rods, overbore, valve job, cams, jet kit and obviously a full exhaust. Any and all machine work would be done by ape out in California. They are a full service shop. Just check out their website.

I've been looking for 929 pistons etc on ebay and they can be had with rods, for ~10 bucks each. Probably need new rings, but that's another story. The pistons I believe are lighter like the previous poster stated. I've got an opportunity at a gen four engine for like 150-, and I'll order a 929 piston and check at least the piston height from the wristpin. If that matches up, we're in business.

I do not know if a sleeve is needed on the boring job. APE would be able to address that. APE charges ~$340 (if I am reading their site right) for a full bore job to match the pistons you provide (trust me you want to do this as one time I had an overbore done, I sent the smallest piston, only one, and regretted it)

Lightening the crank costs ~250. Get the bottom end and pistons done, and you can do a valve job at home, leave stock cams in, and have it jetted on a local dyno. I'm going to seriously consider it.

[V4 Rosso]

and you can do a valve job at home, leave stock cams in,

You can also have the cams reground for some more lift or fit VFR800 valves (and seats) which I think are about 1mm larger in diameter. The larger displacement engine has to be able to breath after all.

[mcrwt644]

Keep any and all suggestions coming

[Chris71mach1]

and you can do a valve job at home, leave stock cams in,

You can also have the cams reground for some more lift or fit VFR800 valves (and seats) which I think are about 1mm larger in diameter. The larger displacement engine has to be able to breath after all.

now this is a pretty good idea. i didnt know the VFR800 valves were only 1mm larger, which I think is an IDEAL size for a valve replacement. The questions here are, of course, whether the VFR800 valves are the same otherwise (ie the valve stem where theyd actually mount to the heads and vavle retainers, etc), and whether these oversized valves would interfere with the new 929 pistons.

as much as i hate to say it (only because of the involved expense), it sounds like this project would be best experimented on a donor engine from ebay. this way, youd still be riding your own bike during this motor build, and if anything did happen to go south, you're not jacking up the engine that you already depend on to run in your bike.

that being said, man i really hope you see some success with these ideas, cause you can bet your bottom dollar i'll be following suit with the super-viffer motor built on the cheap ;)

[mcrwt644]

That is exactly what I was thinking ^^

I've got a line on a gen 4 engine for about 150, and it runs, so that is where all 'experimentation' would take place

[Chris71mach1]

That is exactly what I was thinking ^^

I've got a line on a gen 4 engine for about 150, and it runs, so that is where all 'experimentation' would take place

wow, 150?! seriously?! dude thats WAY cheaper than id expect you to find a donor engine for a project like this. you should snatch that thing up, if for no other reason than to sell it and make a profit if you dont use it for the project rebuild!

[Chris71mach1]

I just found a page in the service manual for my bike that lists the specs and measurements of the valves in very similar detail to that of the charts that Rosso posted earlier in this thread on the pistons. If we can find the service manuals for the 4th gen VFR and the VFR800's, then that would help to compare the #s on the valves and determine whether it would be worth moving forward with that idea.

[tailgunn]

I have a 1/2 wrecked donor in my garage that I've been staring at and debating over for quite some time now...sounds like an interesting idea. Have a buddy that owns a motorcycle shop, bet I could talk his mechanic into helping out a bit.

[kgsmotorcycles]

[Chris71mach1]

does anybody have links for various VFR service manuals that can be downloaded in .pdf form? regarding this thread, I'm specifically looking for the manuals that would cover the gen 3-4 bikes, and the manual for the 5th gen 800fi bikes... (to start comparing #s and what not)

[V4 Rosso]

They are all right here in the files section. But if you're looking for valve dimensions, it's not in there.