lol.....

not really as dramatic as the title says..... but the loss part does refer to lost power...and i personally find that sad...lol....

i want to talk a bit about the gateways for good air in and bad air out of our high performance thumpers... the poppet valve.... largely unchanged in its basic form since it's introduction over a century ago.....

when the valves are in their open position...intakes would be letting fresh fuel\air mix into the cylinder....exhausts would be letting the burnt charge out into the exhaust system....

the camshaft opens the valves....and the valvesprings have the difficult task of making sure the valve's motion faithfully follows the profile of the camshaft...without "floating" or launching the valve over the nose of the cam lobe...or letting the valve "bounce" off of its seat upon closing

when the valves are in their closed position...they are sitting tightly against their "seats".... which are steel or alloy rings that are prrssed into the aluminum head...and they need to be able to seal tightly against combustion pressures that can be as high as 1400psi....

the angle of the valve that mates to the seat...and the angle of the seat that froms the seal also...are both 45 degrees (although sometimes cut with a 1 degree difference) ....

and the valves themselves.... while actually the basis of our engines airflow operation...are also the biggest obstructions to the whole airflow path....very much so at low to mid lift levels...which you might expect when putting a big, largely flat barricade, right smack in front of the airflow....

which brings us to the next point..... valve angles and seat angles that are not the 45 degree sealing face surface.... what & why.....

all additional angles beyond the sealing angle are specifically to help the airflow get around the obstruction of the valve itself at low & mid lifts.... the multi angles of the seat can be something like 75...60...45....30...15...all helping aiflow do what it doesn't want to do...bend gracefully around an obstruction.....likewise, valves can and will employ mutiple angles to get flow around the backside...and sometimes to help flow get around the valve and into the exhaust port....

most of the 450 machines come with 3 angle valve seats....on the intakes, a 60 degree that works in conjunction with the back of the valve to form a guiding venturi to aid flow towards the 45 degree sealing cut...and a 30 degree angle to help flare the flow out into the cylinder after the 40 degree cut....

with the exhaust valves it works just the opposite.... 30 degree from the chamber side to help guide flow under the valve towards the 45 seat cut...and 60 degree after to work as a velocity enhancing venturi heading into the exhaust port....

now back to just the valves themselves....starting with steel valves like in the 04-05 TRX's....

for some reason (like cheap\ tight azz accountants perhaps).... the factories cheap out on the material they use on oem intake valves..... the exhaust valves need to be a higher grade of SS to handle the heat loads of the exhaust, so they can't cheap out there....but they use a lesser grade of steel on the intakes...and the intakes wear out many times faster than the exhaust valves, despite the heat loads the exhaust valves have to deal with.....

the ti valves can last a decent amount of time because their lessened mass hit the valve seats with less inertia\ force...and because the ti valves all have a hard outer coating.... which without the coating, titanium wouldn't be suitable as a valve material at all....way too soft and fast wearing.....so the ti valves last great UNTIL the outer coating has worn, usually from fine abrasive particles embedding in the seat...and once the outer hard coat is breached...the rest of the valve wears out like butter....

aftermarket valve mfgrs...like Kibblewhite....make both the intake and exhaust valves out of higher grade stainless steels...and as a result, they last many times longer than the oem stuff does....

now ...what happens when the intakes wear out...??

they do something known as "cupping".... the sealing face pounds itself wider on the surface of the seat (terrible for airflow since you are lengthening the path of tightest restriction)....and eventually the valve sort of pull itself up into the head and deforms itself to not only fit on the 45 degree seat, but extrudes itself into the port and forms an additional pseudo seal on the 60 degree seat surface.... which is HUGELY bad for airflow....

why??


because the 60 degree seat cut was originally supposed to work with the back of the valve as an airflow guiding venturi..... helping airflow negotiate the turn past the valve's 45 deg sealing surface at low to mid valve lifts..... but now the valve is actually pulled up into the head and deformed to sit on BOTH the 45 degree AND 60 degree seat surfaces...and instead of the 60 degree creating a nice funnel shape around the valve, it creates a torturous "stair step" like, flow stopping path that the airflow essentially stalls in until the valve opens a significant amount.....

in which case you are double screwing yourself on airflow...since the low lift happens twice per intake cycle (opening & closing), you have impeded flow for an extra long time....

you can tell that this is going on as you re-shim your valves with smaller and smaller shims...that is what tells you that your valve is being pulled farther & farther up into the port.....

some pics of beyond worn valves that have taken on the 60 degree shape...next to fresh\stock valves....

and also pics of the worn seat.... you should only have a shiney wear pattern on the outer 45 degree angle... NOT the 60 degree angle pulling up into the port...

fairly fresh oem valve on the left..... seriously worn valve on the right.....try to imagine the 60 degree cut & the back of the valve helping airflow get through the 45 seat on the left...then think that both the 45 and 60 surfaces on the right are close to the seat on the valve on the right...seriously disrupting airflow passage until higher lifts....

Click to view attachment

'nother angle

Click to view attachment

and a shot of the valve seat..... ideally, you should only have a small shiney contact area on the 45 degree angle.... .040" ~.060" wide

this shows a worn contact patch on a widened 45 degree angle AND a wide 60 Degree angle.... horrible for airflow..!!

just getting new valves and fresh seats cut would provide a nice power boost when things are worn like this......most dealerships or local automotive machine shops can provide such a service....

this wear isVERY common on 04-05 TRX's with a decent amount of time on them....

Click to view attachment

How many hours did that take to get that kind of wear?

it all depends on maintenance & riding conditions...... so it varies hugely from machine to machine....

this is an 05 machine with ~100 hours on it.... ridden in dusty conditions with a K&N filter.....

while we are on valves..like you said all the faces of the seat and valve have been 45 degrees.. but a few years ago when i worked at a honda dealership i found they had changed some of the seat and valves to 43 degrees.. had to buy a new cutter for them.. i wonder why they would change them ? if i rember right it was on a crf 230... seems like there was a few more i just can't rember off hand which models .. so anymore i have been really watching for this when i re-cut the seats for new valves..
and like you said there are alot of shops that can re-cut the seats... but.. like alot of things there is some place's better then others.. you have to know where on the valve to have it seat.. how wide.. a bad valve job is like a bad port job... there is power to be made or lost.. it all adds up...

true all of that corey^^^^^ i didn't know about the 43 degree stuff though...!

one big mistake i have seen made is with places that cut so deeply on the seats that you wont have a shim thin enough to get enough clearance....ouch...!!

on atypical stuff...... i have seen 45 degree on the seat and 46 degree on the seat....for sort of a 1 degree interference fit...lots of sealing pressure on a smaller area.....

Can I have those? I need a new razor.

lol...no sh!t tony....where there is supposed to be a ~.050" flat margin , it's now sharp enough to shave with!!

2 B pinned

hey i just took my valve out and they look just like that (the one on the right)