Stainless vs titanium valves etc - is this BS?

[motorbyclist]

http://www.motoxparts.co.nz/motocross.php?page=41

they say OEM titanium valves break in half, and that the extra weight of stainless isn't too bad...

now knowing i can't lap titanium valves, and assuming mine are still stock titanium, i'm looking at oem vs aftermarket top end kits

anyone here know much about the product these people are trying to sell? can't make a decision through all the stereotypical marketing hype exaggerating benefits and downplaying the problems....



and while i'm at it - anyone know where a student could get a cheap top end kit and re-bore or re-sleeve?

i'm looking to do a rebuild on my yz400f this december, and seeing as it's been thrashed since at least 2006 when i bought it (only stopped the weekend rides this year due to uni, but still went nuts in the summer), without ever so much as being opened up, i plan on replacing everything in the top end.

seriously, previous owner had it 6 months without rebuild and i've had it for several hundred hours without more than oil/filter every 5 rides or so (20-30 hours) and air filter every ride, and only now (after sitting for a semester) am i bothering to rebuild, due to the cam chain urgently needing replacement and metal in the last filter:crazy:

and before anyone says i'm an idioit for leaving it this long, i know i am and won't be riding (much) til it's fixed - but this does go to say something for how reliable these bikes really are. she's still got the grunt, most of it's compression and no smoke or leaks :D

[no-coast-punk]

Those particular titanium valves do suck and I would replace them.

Titanium itself is a very brittle metal. Anytime you use a high heat joining method (such as a plasma arc) the union becomes more brittle than the base metal. Hence all the failures.

One piece titanium valves are the shit, but completely pointless for most riders.

The only time Ti really makes a difference is in situations where you are holding the throttle wide open for stupid long periods of time. Ti dissipates heat better than stainless and keeps valve springs alive under sustained high RPM situations.

[motorbyclist]

now knowing i can't lap titanium valves, and assuming mine are still stock titanium, i'm looking at oem vs aftermarket top end kits

so according to page 3-40 of my manual, you CAN infact lap these valves and there's even instructions on how to do it...

and i'm pretty sure that the stock was titanium

so what, is it some fancy alloy or is there some extra thick nitride(?) coating on the surface? maybe they reckon the aluminium head will wear rather than the valve?

[boostin]

The head will have valve seats in it that the valves seat on...

[motorbyclist]

well then wtf - can i or can't i re-use the old valves?

between manual or aftermarket marketing blurb i'm tempted to follow the manual

[boostin]

Yeah you can, well we do all the time. Usually you just reface the old valve and the seat, and then if you want to be all proper about it you can lap them in.

Edit - Although we don't usually deal with Ti valves, but im sure it is the same.

Edit edit - just read the link you posted...guess they say you can't reface them. Do they need refacing?

[motorbyclist]

well i won't know what needs to be done until i've opened it

right now i'm trying to plan the budget accordingly so i don't have a half finished engine kicking around the shed all summer accumulating dust while i could otherwise be riding the last life out of the cam chain...

[boostin]

Well I could do the valves for you, throw it back together and see if it lasts...(assuming they need doing)

Or just get the stainless ones and be sweet...

I guess you just have to weigh up the cost of new valves vs the trouble of taking it all apart again if the refaced ones dont work out.

[motorbyclist]

yeah when they finally give me a price i'll compare to the OEM ones and probably just replace them IF it won't cost too much

i've rebuilt a few motors before and always re-seat the valves 'seeing as i'm in there', but never had such difficulty with part availability nor titanium valves....

[Paulus]

I'm looking to buy a WR450 at the moment and so have been reading up a bit on thumpertalk. This is only what I have read on TT - I know nothing about this personally:

The WR400 had stainless valves not titanium - not sure if same applies to the YZ but the WR didn't get them till the 426. Maybe a magnet would help here.

In general the Yamaha Ti valves seem to be the longest lasting. Possibly a thicker Ti nitride coating??? They seem to hardly ever need reshimming (but there is always the odd horror story).

The new KLX450 has stainless valves but seems to have the same valvetrain inspection periods as all the Ti valved bikes.

In general the biggest cause of wear in Ti valves is dust getting past or through the air cleaner. Next biggest is lots of high RPMs then heat.

The WR250 motor is fairly similar to 1 cylinder of an R1 engine yet the valvetrain inspection interval is 1000km vs 32000km suggesting that dust and the WFO nature of the bike contribute quite a bit to wear (kind of hard to ride an R1 everywhere pinned).

Hope this helps in some way (and that too much of it isn't wrong).

[motorbyclist]

The WR400 had stainless valves not titanium - not sure if same applies to the YZ but the WR didn't get them till the 426. Maybe a magnet would help here.
.

good idea

cheers - i'll read the yz426 manual and see if it says NOT to lap the valves

[motorbyclist]

and it would appear that JE etc etc don't make pistons for my bike anymore

so i have to go OEM anyway.... lol

[Motoxparts]

Just let us know if you need any info about stainless steel vs stock valves

Valve base material
How they are manufactured
Micro hardness
Valve spring pressures open or seated stock and what you must use with a performance camshaft
Valve guide wear and wear limit
Valve rate angle
Valve seat weigh
Valve seat angle
Valve spring material and spring rate
How to prepare the cylinder head for new valves if you are getting you valves lapped by hand you are causing alot of damage lapping valves went out about 15 years ago
We have a machine that cuts a 3 valve seat the head machine cost over $80,000 just to do valve seats
Valve spring test which every shop should have it not just a spring that you throw back in your engine, and around another $280,000 worth of machinery just to make sure a engine job is done right

Yes there is alot about what goes on inside a engine that the guy putting your engine together would not no about most shop do not have a ball gauge micrometer to measure the piston to bore clearance let along a normally micrometer we have been machining high performance engine for more than 25 years

Stock Tituinm valves are made in two pieces than welded this is to keep the manufacturing cost down

www.motoxparts.co.nz