Info FZR250 valve seats

its also how i would support the head if i ever try skimming one. i always thought, whats the point of facing a bowed head if the end result when torqued down is the shafts/journals are now bowed? clamp by the journals, then face.

aaaand, if you get the pivot coincident with the convergence of the valve stems... no need to shift it over

that may be a bit TOO tricky.

that is, the two bars being ideally mounted on hefty end plates and pivoting around some sort of parallel centerline...

or just use one bar, and an adjustable stop. get the bar on center, square... and yeah, easy to flip the head over.

assuming the stems/guides are actually in line with the camshaft. which they should be. any offset to get buckets rotating should be axial.

 

Normally on a bucket and shim OHC setup, the stem centerline will coincide with the cam centerline.
The bucket bore centerline may not. An offset is one way of obtaining bucket rotation.

I've noted somewhere back a ways the comment that bucket OD is the limiting factor for cam lift. Yes and no.
No if you're prepared to cut entry and departure slots for cam lobe clearance front and back of the bucket bores.
This will give the room for a bigger lobe = higher lift. But the lobe must still first meet the bucket within the OD of the top face.
If it hits the edge first disaster follows.
This slot cutting was and is common on the big Z Kawasakis and the 2V GS Suzukis

I pulled down a couple of factory kitted GSXR1000 Suzukis a while back. They have small OD buckets - 22mm I think.
The kit cams have what looks like a finger coming off the peak of the lobe profile to reach down into the bucket cavity for the last extra bit of lift.
Compared to Yosh customer cams I think the additional lift is around .020in. They obviously think it's worth it.

 

No it was pretty cheap actually. The new profile was cut out of the existing one and the difference in base circle was accomodated with thicker shims.
The bigger problem will be finding a cam grinder with a profile library that goes down to that small a cam lift.
Kelford here in Christchurch have been going since the 1960's and have an enormous profile library as they've kept masters for everything they've done. I suspect the profile used was a copy of something they repaired.

 

Cam design has always been a can of worms. Old days it was calculate the lift/acceleration rate per degree of cam rotation.
And if you had enough background knowledge you could design a cam that went well - and didn't break the valvetrain
Now there are programmes available which can do it for you.
Around 50% of a cam grinder's business is repair work. If there's more than one lobe involved it made sense to do a master for the machine - and for your library.
Now they run a good lobe over a sensing/measuring device and they've got a digital copy. Which is good if you've got a CNC driven cam grinder.
I suspect that in the low lift/short duration cams for 250/4's any better profiles are going to come from the old style metal masters as pretty much everything on the market now is bigger/longer.
I'd be tempted to look for a small - maybe one man - outfit still doing it the old way.
I'll have a look through the detrius here post downsize/move and see if I can find the card from Kelfords.

 

i wonder how they would go with this cam i have that is about 5mm across at the widest?

lol. i once got obsessed with the OSFS26... RC bikes... for some reason 4stroke singles only sound good on little RC bikes, and the 2smokers actually sound annoying?

tracked down virtually every part for the "CX" or car version of it... including the cam. i am not disclosing what i paid for it...

and wow, for something that basically looks identical, it sure makes a huge difference to that redline! at that scale, (the raw powah of 4point2 cubic centimetres!!!) the variation in lift is probably only a thou or two. few degrees more duration...

always contemplated trying to grind one... contemplate being the key word. never even bothered measuring it. hidden away in a box somewhere...


anyway, usually the offset for buckets is axial, along the length of the camshaft.

judging by the witness marks on the shim... bucket and valve stem/guide is concentric. you can pop a bucket out, rotate it by any random degrees, and as long as the shim stayed "glued" in place... they slide straight back in again. its a pretty good sign its concentric...

will just be the cam lobes themselves that are slightly off center. i assume. its the only logical way to get the rotation.


i got the toolpost grinder now, not much more of a step to grinding a cam. more pitbike engine "sacrifices" to be made?

once upon a time i had a 7mm lift cam in a lifan 140, on a road registered pitbike. and it did 140km/h!
downhill... lol.

 

Taking a few thou off the base circle and hand blending it into the ramps was feasible when we were all racing singles.
If you dropped a valve you knew you'd got it wrong and started over.
Those two areas - first lift and the final drop onto the seat - are critical.
Too much acceleration and the rest of the lift curve has to take into account a spring that has been shocked and is probably surging.
Too fast a drop onto the seat and the valve will bounce.
It ain't easy.

 

some great info building in this thread.... of which about 50% ish i completely understand.
... what i do reakon is......
when gyro eventually fits a supercharger to a fzr250... we are gunna have to build a head to suit, maybe change the cam lobes???

 

JERK!

lol, the technical term for the instantaneous acceleration of the valve..


setting up on a lathe is challenging, and it will more than likely have to be shifted lengthwise for the travel, that poses an interesting challenge.

but as long as you got a nice "t-slotted" cross-slide, shouldnt be that big a deal. set of Vblocks and some good gauge blocks...

bastard!
thats simply a file.

dont talk to me of zeals... back when my R3 had its second warranty recall (clutch went at 7k) and wrote itself off at 17K (oil pump, supposedly "fixed" by dealership... not even 3 months!) i was rather anti-yamaha and passed up on a good one for next to nothing... and ive seen quite a few poking around in sydney... if i hadnt been given that 2kr... and i was dubious about it at the time...

main thing for real supercharging is "no overlap". docile cams are preferable. zeal is a nice starting point.

still waiting on the postie to bring me my packs of caption sucks?

i know i can lap valves in with the drill and a bit of tubing from the back, but it is so fiddly and annoyingly annoying. industrial "pneumatic manipulators" seems a far easier option... available in a wide variety of sizes, too

why is it, the things you sort of NEED from aliexpress take months and the things you shrug about and get on a whim turn up the next day?

 

Main thing for real supercharging is "no overlap"

Sorry, GG you've poked the bear. that's bullshit.
At high boost pressures an old way of describing it was as the "Fifth stroke" - the period where both valves were open and mixture flowed through to cool overhated valves. Modern thought is no overlap but there are still good reasons to have it.

I've been involved in several car and bike, air cooled and watercooled, blown projects. I've always gone for an overlap of around at least 30 degrees. The last one I did was a blown EX500 Kawasaki which gave around 130hp at the wheel on a rolling road. Straight Methanol, 15lb boost - and Megacycle's hottest roadrace cams. A lot of overlap. Boost gauge showed a flat 15lb from idle to 12,000 rpm. A lot of that was a very well designed 750cc displacement Roots type blower with low pumping losses. But the big overlap did not result in lost pressure.

For a 250 four I'd start with normal road cams on standard road lobe centers. No need at all to vary them.

 

more than likely its going to be stock cams if it ever even gets done, lol... theres the engine, theres the AMR300, theres the idea... and thats as far as its gotten

 

When my blown MC19 was converting $'s into broken parts, it began with stock cams, resulting in 8/10 lb boost
I then went to 250 Hornet cams (zero overlap) , the boost went to 15 lb boost, with no other changes
The difference in grunt was amazing