Anyone Ever Rebored/overbored A 5/6Th Gen

[CornerCarver]

Great job Phil!

Thanks for posting up the info.

[Mohawk]

Looking very good :) Did you check the piston valve/head clearances before removing the stock pistons ? Something I need to do, the 929 piston crown is .2mm higher than the VFR's. How long do you think it will take you to reassemble the motor ?

One thing, where did you get the cases bored, engine or engineering shop as I'm having trouble finding somewhere to do mine :(

[HighSideNZ]

Here are some shots of the underside of the 929 pistons after I attacked them.

When I removed metal from under the crown, it was more from the radius behind the oil ring and also to add a large radius above the gudgeon pin bosses. Basically undercutting the web similar to how a cast piston is cored, or a wiseco is machined. The bottom of the gudgeon bosses have a machined boss that stands proud and is used for balancing. I ground those down and blended them in to the rest of the boss.

I didn't check the valve pockets before I had the cases bored I'm going to do it now with plasticine as I need to check anyway. Looking for 2mm clearances all round.

I had the boring done by an automotive reconditioners who do a lot of race car engine building and had a good reputation.

Sorry, I missed one question. The 0.2mm difference in deck height shouldn't be a problem. When I dissembled the motor, I did notice that the existing crown was pretty much flush with the top of the liner. The gasket is reasonably thick, haven't measured it at present, but as I've opened the new gaskets up to suit the 74mm bore any increase will fit within that space.

I'll know more in a day or so as I'm going to trial assemble with plasticine on the crowns so I'll see how much clearance I have all over.

I'm still waiting on some parts, rings, bearings, pins etc. before I can do the final build.

I'll use the old bearings to do the trial build.

Cheers

Phil

[Mohawk]

Excellent work Phil & thanks for the info. I started modding the 929 pistons by removing the thin bottom of the skirts making them level with the flats on the bosses & was thinking of using 954 gudgeon pins, as they are shorter & have a wider inside diameter & are thus are 9grams lighter than 929 ones. I was going to use alloy rings to center the pin in the piston. It doesn't lose much piston support.

I just went & measured these parts distances & weights as follows;

Item------------929-----------954

Pin Weight, 52 --- 43 grams

Distance between Piston bearing bosses, 21mm --- 20mm

Piston Boss bearing length, 14mm --- 12mm (this is how much pin is in each boss bearing)

So the 954 pin will give 11.5mm of bearing surface in the boss each side of the piston. Strangely, this pin in a standard 929 piston is almost exactly the same weight as a standard VFR piston ! for obvious reasons you need to keep these centered hence the alloy rings mentioned above !

Bit late for you, but should help others if they follow along !

How are you modifying the head gaskets to fit ? as in what tools ?

[Switchblade]

Phil, any idea on how much money you have spent so far ?

[CornerCarver]

Phil, any idea on how much money you have spent so far ?

Boo....Hisss...Party Pooper...

[Mohawk]

Not sure about Phil, but this is not expensive if you spanner yourself. That said I've spent the following (UK pounds) so far in my research;-

£75 Spare engine (was cheaper than a set of cams, was from a heavily crashed bike, so lost right side case & a few bits)

£30 4 x 929 pistons complete (secondhand)

£22 4 x 954 pistons complete (secondhand ex race bike, bit worn)

£25 1 x VFR800Fi Top Crankcase (to research the MMC liners)

===================================================

Total £152, plus many hours reading. And I haven't even started yet. But by sharing the info, it has I hope helped Phil get on with it.

So if you just bought the 929 pistons & a full gasket set (circa £200 here) & do the spannering yourself, with a known good engine, so no need to replace bearing unless your found wear. then its more time & space to do it, plus paying for the boring of the cylinders. Total less than £500 (US$800ish)

Lets see how Phil's turns out on the dyno. Shall we start a sweepstake for the HP & Torque figures ????

So what will a VFR825 put out ?

Standard they put out around 95rwhp & about 54ft/lb torque, don't know what other mods Phil has in his, maybe he'll let us know before the guessing starts.

A basic CC/HP calc gives 8.22cc per HP, so in simple theory that should add 5HP, but that excludes torque. A simple torque calc says the CC increase should add 3ft/lb so 54 becomes 57, well my 57.5ft/lb motor kicks out 107HP. So increased compression will increase the torque more than the base calculation, I'd expect circa 59ft/lb, so at peak rpm (~10,500rpm) that should kick out around 110HP ! With some tuning & other parts could be higher :)

[HighSideNZ]

I used a trusty old die grinder with 25mm pferd drum sander sleeves to enlarge the head gaskets.

Did my old ones first, just to make sure it would work, and then laid the old over the new and scribed the circles to grind to.

Fitted them onto the case with the dowels and worked from there.

At this point in time I haven't costed it all up/out as I don't want to scare myself.

So far the most expensive part is getting the cams built up and profiled. Going to be close to $2k NZD to do this by itself.

Again, I'm using second hand 929 pistons so they were $75 USD but I'm doing new bearings/rings/gudgeon pins and a full gasket kit whilst it is all down.

All the main expensive bits are second hand and the motor complete, in really good condition was $900 NZD.

I'm aiming for 120/125 rwhp when completed and I feel that is achievable.

Time will tell.

The 929 gudgeon pins are about 1g heavier than the VFR pins.

With some grinding inside the taper, I'm hoping to remove about 3-4g and that should offset the difference in ring set mass.

Bugger, wish I had of known about the 954 pins.

Would have saved a but of work.

Cheers

Phil

[spud786]

cast iron liners wear fast, I used to run cr250's naksil bore, no cylinder wear for years, cr500 (cast iron) would require rebore every 2 years, a very significant difference in bore wear.

[HighSideNZ]

These aren't cast iron they are MMC (Metal Matrix Composite) and believe me they don't wear.

Just hard to find someone to bore and hone them.

[HighSideNZ]

Women and family... Don't they understand a guys bike and the shed project come well up the priority list than moving a daughter out of home to her own place... LOL

Just got back on to subject.

Mohawk, well you are right regarding the piston deck height.

Wrapped an old VFR piston with insulation tape to fit the new bore and re-assembled No1 and No3 side by side.

Did some measuring and I need to do some machining on the piston crowns.

I'll post some marked up photos later but the guts of it is.

VFR piston

Between the pair of inlet valves the piston deck is 0.2mm below the liner top at TDC.

This is the same for the exhaust side as well.

Across the piston, inline with the pin, the deck is 0.7mm above the liner top at TDC and has a 2x45deg chamfer on the edge.

929 piston

The full area of the crown is 0.9mm above the liner top at TDC.

I will need to get 0.2mm taken off all over and then reduce the front and rear sections between the valves to the liner top or slightly lower.

As I said, I'll post some marked up photos as it is hard to explain in just words.

It's brought proceedings to a stop as I'll need to find someone to do the machining.

Damn, I wish I had a lathe and mill.

Phil

[Dutchy]

The daughter's bedroom can now be upgraded to bike spare part storeroom no? ;-)

[HighSideNZ]

Wife has dibs on it first so looks like I'm still relegated to the garage. LOL

[HighSideNZ]

OK, as promised, here are the marked up photos of the pistons with the relevant measurements.

VFR piston

929 piston

Sorry, you will probably need to download the images to easily read the comments.

Cheers

Phil

[HighSideNZ]

I've just drawn up the mods for the 929 pistons and the attached PDF file outlines them.

Shouldn't be too hard to get done but it is turning the overall crown, putting a 2 x 45 deg chamfer all over, and then milling the pads 1mm lower.

929 piston mods.pdf

Now to find someone to do the work.

[Mohawk]

Phil, have you tried it with an old head gasket & the head with some plasticene or plastigage, to check the old piston clearances ? Without bolting it down first, if the head lifts, then you know its too tight, if not then the gauge will tell what clearances are there.

I see you have had cams done. I had a set reprofiled for more duration which added 5HP. They are standard lift, which measured by the cam co was 8.2mm inlet & 8mm exhaust. I didn't get round to checking the piston valve clearance properly, but I did put one piece of electrical tape on a piston & put a head on with NO head gasket & the motor turned over. Then at TDC I turned both cams manually & they just contacted the tape, so I estimate about 1mm clearance at TDC.

Get with the grinder man to skim those piston, Bert Munro style ;)

Keep up the good work.

[HighSideNZ]

The old head gasket measures 0.96mm so I'd say a nominal 1mm is what they were designed at.

Can't see the piston clearing at that thickness and when you take rod stretch/bearing float in to account she is going to hit.

Nothing for it I think, but I'll plasticine it and see what is there now.

[HighSideNZ]

OK

Took to the pistons with my linisher and have pretty much got the clearances needed without much work.

Just going to plastigage the squish area now and make sure there is enough there.

One side benefit is that it's pulled another 2g off the piston mass and I now have a much better finished piston crown.

[HighSideNZ]

Here are some shots of the roughed out piston crowns after linishing then down and stepping the areas between the valve pockets.

I still need to finalise each of them individually as the "eye-micrometer" let me down a bit in the areas between the valve pockets.

It is time consuming as there is no way of measuring them than to assemble them back in to the block.

I'll add more shots once I've finished them off but I can't checks the final valve pocket clearances until I get the reprofiled cams back from the grinders, which looks like it may be a couple more weeks.

Cheers

Phil

[Mohawk]

Wow, looking good, Bert would be proud :)

Couple of Q's did you take a pressure reading off the cylinders before the strip down ? Just so you can compare the compression ratio ?

I take it from the cams comment that you don't have a spare set ? So can't check the standard clearances.

What spec have you gone to on the cams ? I did the following;-

VFR800 98-01 5th Gen cam timings all at 1mm lift are as follows;-

VFR800 STD

IN open 10BTDC Close 35ABDC Lift 8.2mm measured, Duration 225.

EX open 35BBDC Close 10ATDC Lift 8mm measured, Duration 225.

RC45 STD for comparison

IN open 15BTDC Close 40ABDC Lift 8mm claimed, Duration 235.

EX open 45BBDC Close 10ATDC Lift 8mm claimed, Duration 235.

RC45 HRC Race cams

IN open 23BTDC Close 52ABDC Lift 9.5mm claimed, Duration 255.

EX open 50BBDC Close 20ATDC Lift 8.3mm claimed, Duration 250.

See here. http://www.vfrdiscussion.com/forum/index.php/topic/53905-rc45-vs-5th-gen-vfr-engine/

My Modified VFR800 ones

IN open 15BTDC Close 45ABDC Lift 8.2mm measured, Duration 240.

EX open 45BBDC Close 10ATDC Lift 8mm measured, Duration 235.

Looking good ;)

[CandyRedRC46]

Awesome info!!!

I can't wait for all this stuff to start coming together.

Mohawk I think the duration on the rc45 race cams is supposed to be 255 in and 250 ex.

[Switchblade]

Thanks , just curious

Not sure about Phil, but this is not expensive if you spanner yourself. That said I've spent the following (UK pounds) so far in my research;-

£75 Spare engine (was cheaper than a set of cams, was from a heavily crashed bike, so lost right side case & a few bits)

£30 4 x 929 pistons complete (secondhand)

£22 4 x 954 pistons complete (secondhand ex race bike, bit worn)

£25 1 x VFR800Fi Top Crankcase (to research the MMC liners)

===================================================

Total £152, plus many hours reading. And I haven't even started yet. But by sharing the info, it has I hope helped Phil get on with it.

So if you just bought the 929 pistons & a full gasket set (circa £200 here) & do the spannering yourself, with a known good engine, so no need to replace bearing unless your found wear. then its more time & space to do it, plus paying for the boring of the cylinders. Total less than £500 (US$800ish)

Lets see how Phil's turns out on the dyno. Shall we start a sweepstake for the HP & Torque figures ????

So what will a VFR825 put out ?

Standard they put out around 95rwhp & about 54ft/lb torque, don't know what other mods Phil has in his, maybe he'll let us know before the guessing starts.

A basic CC/HP calc gives 8.22cc per HP, so in simple theory that should add 5HP, but that excludes torque. A simple torque calc says the CC increase should add 3ft/lb so 54 becomes 57, well my 57.5ft/lb motor kicks out 107HP. So increased compression will increase the torque more than the base calculation, I'd expect circa 59ft/lb, so at peak rpm (~10,500rpm) that should kick out around 110HP ! With some tuning & other parts could be higher :)

I used a trusty old die grinder with 25mm pferd drum sander sleeves to enlarge the head gaskets.

Did my old ones first, just to make sure it would work, and then laid the old over the new and scribed the circles to grind to.

Fitted them onto the case with the dowels and worked from there.

At this point in time I haven't costed it all up/out as I don't want to scare myself.

So far the most expensive part is getting the cams built up and profiled. Going to be close to $2k NZD to do this by itself.

Again, I'm using second hand 929 pistons so they were $75 USD but I'm doing new bearings/rings/gudgeon pins and a full gasket kit whilst it is all down.

All the main expensive bits are second hand and the motor complete, in really good condition was $900 NZD.

I'm aiming for 120/125 rwhp when completed and I feel that is achievable.

Time will tell.

The 929 gudgeon pins are about 1g heavier than the VFR pins.

With some grinding inside the taper, I'm hoping to remove about 3-4g and that should offset the difference in ring set mass.

Bugger, wish I had of known about the 954 pins.

Would have saved a but of work.

Cheers

Phil

[CandyRedRC46]

Also I don't know if you guys are aware or not, but I have read that metal matrix liners are not compatible with forged pistons, the pistons will have to be coated with a compatible coating for example nikasil etc before use.

[Mohawk]

CR don't know where you got that info, but it's bogus, ALL Hondas since The RC45 have used mostly MMC liners, including the CBR9929/953 & the VFR800 (all models). It's NOT the means of manufacture, which are CAST =VFR800 or FORGED =CBR's, but the material the piston is made from, as in what alloy composition. The Honda Forged pistons for use in MMC liners are solid lube coated on the piston skirts to reduce friction during break in. As both VFR & CBR use MMC liners, then the pistons are compatible.

PS corrected the HRC cam durations, sorry pasted that in a hurry :(

[CandyRedRC46]

I got that info from Honda automotive research. The Honda k series block is aluminum with iron sleeves, forged aftermarket pistons are manufactured with no additional coatings needed. On the other hand, the Honda f22 from the s2000 has the mmc liners like our bikes, forged aftermarket pistons for those engines are supplied by fewer companies and more costly, as they require a secondary manufacturing process of the coating.

Now with that being said, if the 929 has mmc liners then it's pistons should be safe with our engines as well, but this would lead me to believe that the 929 pistons are coated to allow them to be forged with out damaging the liners.