Help Lapping Valves - ZXR250C

That's a beautiful thing, when I took an FZR250 cylinder head to the local performance engine builder, they had a Mira seat cutter.
Really nice piece of kit, it needed the pilot guide holder turned down on the lathe to fit into the exhaust valve throat, which they were willing to do no problems.

I then started researching the cost of the 3.5mm Mira pilot, ~200 euros IIRC and then the cost of cutters, about the same or more IIRC, that's going to add up really quickly considering that I intend to do two OEM heads and seats, then replace one set of seats and guides.

If your friend is interested in putting together a seat cutting tool to use on the mill, it's doable and not too expensive - the last clue is @gyro gearloose idea to secure a head using the cam housing.

 

the most important factor here, is the diameter of these valves and seats... as virtually no shop will have cutters this small. you may be lucky and have found that rare one?

i still havent found a mention in this thread of what the actual bike in question even IS... again, profile says ZXR250... can only assume... even your video descriptions mention nothing...

if theyre thinking its just a ninja 250, or something... sure, theyll say they can do it... thats what i bought my neway cutter for. iirc, 24mm valves. no dramas. a 200 dollar tool for four seats that took literally two minutes... thing is, it can still be used on a wide range of engines. but definitely not an an I4 250, without modifying it. and they only cut the main 45 degree angle. you need THREE of them! (cash registers dinging like mad in teh background...)

there was a ZZR250 as well... easily confused with "ZXR"... but definitely not the same engine! missing two cylinders, for starters... i believe it was the same engine as the gpz250? same deal. most shops can deal with it, no dramas.

finding 16-17mm valve seats, the shop in question may change their tune. suddenly it becomes... expensive. before they even start cutting.

linkin has stated that neways in his shop were too large for the mc22. as does their site.

apparently gen has tweaked a neway to do an mc22, or at least... one of the CBR variants...

both ruckusman and myself are looking into the QM "single blade" cutters, of course he seems to have got the more suitable blade...


i had a go at making my own cutters based on cheap and nasty multiblade cutters... after finding they didnt fit and the quality of chinese manufacturing was questionable. arbors far from specified size, and cutters all way too large anyway. they work much the same as the neway. by hand... push them in, slight pressure, give them a spin, done.

the one that i actually FINISHED... yeah, it worked ok. as i have the mill, im going to have a go at the single point QM, as it allows for consistency across all the seats. my guts still tells me to just make another set of hand cutters? now ive had a go, the second attempt will be vastly superior one has to practice...

the main issue in my case, FZR 3ln has 3.5mm valve stems...the ZXR very well may have 4.5mm stems. maybe even 5mm. i see theyre necked down in you pics. that REALLY simplifies things!

if your mate has access to a REAL tool and cutter grinder, thats the easiest option. custom arbor with the taper for the cutters, a thread above the taper to get the cutter back OFF, bunch of cutters with carbide blades brazed in, and yeah... sharpened properly.



just wont get every seat identical... close, but not identical.

 

i just saw the title, and thought for a second... wow, did i miss the obvious?

lol...

if he looks at the listing on aliexpress, and/or checks out my thread... this post specifically...
https://2fiftycc.com/index.php?threads/i-found-something-weird-3ln3.12002/page-3#post-151855

then the general outline of the tooling required is pretty easy. just a random "locking" taper, 1-2 degrees. morse #0 type thing. cut the arbor and cutter blanks with the same setting, it doesnt have to be anything specific. as long as its concentric. and you have a way to remove the cutter, hence the thread and nut.

yes, it is @Gen that used the neway cutters.

you know, i never got an answer to which slide and insert belongs to which cylinder? giggity. but i did work out to 99% assurance that the FZR and its dreaded chug is the valves... what a journey!

 

These guys sorted my valve seat / valve cut problem,,(cbr250r) after they (we) sourced a pilot, then ground it to the suitable diameter,,,they also had to rework their cutters (CNC machine used to perform the work)
Even the cylinder head surface they skimmed ,the finish was so fine, you could see your reflection in it
https://www.adelaidecylinderheads.com.au/

 

So $320 for all the seats cut because you're going to do it right, right?

New valves and springs, too.

 

Those prices for valves and springs are actually very reasonable compared to some prices that I have seen

 

Which valves more likely to wear depends on the engine. Some designs have problems, other's don't. On most/all of the 250 fours I've done (and any engine really), the exhaust valves always end up tighter than inlets over time, even though the exhausts have a higher clearance value, exhaust valves have to contend with heat transfer from the valve to the seat due to hot exhaust gases. Inlet valves have no such problems as they always have fresh air coming in and fuel to clean them (unless the engine is direct injected).

Of course, if you have a bad or no air filter, the inlet valves will get dirty and wear (along with your cylinder, pistons and rings).

If your exhaust valves still have sufficient margin after cleaning and cutting, I wouldn't replace them. That will come down to how much pitting they have and how much cutting it takes to have a good sealing surface. The inlets generally have less pitting.

Any valve that has insufficient margin after cutting will need to be replaced.

All the springs should be measured for free length and to see how bowed out they are. Specs are in the service manual. I ended up replacing all the springs on my ZXR when I did the top end.

I did clearances and timing chain/tensioner when I bought it, after 10,000km it needed clearances again and another tensioner. Tiny roller chain and very odd tensioner design.

 

Just thought I'd pass this one, I bought some diamond lapping paste - I had researched it previously and it was about ~$25 a tube from jewellery suppliers, so baulked at purchasing it.

I was searching for it again and came across this set
https://www.temu.com/au/12pcs-w0-5-...pping-compound-syringe-g-601099531728761.html

Too cheap to pass up, it's arrived though I am yet to test it out - it goes from equivalent of 320 grade right through to 10,000 grade

 

Too cheap to pass up IMO
The price of yours is much more reasonable than what I found previously, tubes at $25 each gave me pause for thought