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crf 450 valves
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Posted by: yam 3---------------------
My friend has one of these beasts (unfortunate for him). His problem is that the valves tighten up after two weeks of riding. The valves are sinkiing onto the head. He has replaced the valves once before but to no avail. Has anyone else had this problem with the valves???? Please reply as he is really upset with such a fine ride. All of his intake parts are sealed including the top of the carb(seemed to leak he said????) Anyway he has no computer access so I told him I would askmy knowledgable friends at DRN!
Thanks in advance
Posted by: SFO---------------------
Try using these guys.
http://www.blackdiamondvalves.com/
The cr-f valve is still a custom for them but the demand is up and predict a cr-f valve being off the shelf soon.
BTW, even at the custom price it is still cheaper than the oem part.
Posted by: mike perry---------------------
A while back in this forum there were a series of posts about the problems some riders are having with the ti intakes running against the hard alloy intake seats. Somewhere in there I give a fairly lengthy description of what has been going on with these heads. (Mabe someone here can point you in the direction to read the past posts) Some folks are not having a problem, and others are barely getting the 15 hours Honda suggests for top end service and inspection. I have not yet discovered a common demoninator for the folks having the accelerated recession problem. (Ahh, make that the accelerated valve face recession problem. I have a mortgage and a teenager, those are common demoninators for many people experiencing the other type of recession!)
The demand for intake valves has been great enough to motivate us to do a couple of short runs of stainless intakes, and to design a spring kit with more pressure to handle the extra weight of the valve. (The kit will also handle the extra lift of the profiles that are being put on these cams by some of the after-market cam grinders.) The kit will also add some safety margin to your valve motion control. It has been suggested to me by a couple of very reputable builders that there is a problem with over-rev when down shifting and using the engine for braking. The rev limiter does not work in these situations.
So, the short story is that we are making standard size stainless intakes, and spring kits. Soon there will be oversize valves, and Ampco 45 valve guides available. MP
Posted by: Rich Rohrich---------------------
Here's the link to Mike's original posts on the CRF450 valve issues.
http://www.dirtrider.net/forums3/sh...eferrerid=16241
Mike - Can riders just swap out the valves and springs on a stock CRF cylinder head or do you recommend any specific seat work be done to accomodate the new valve material like lapping, or touching up the seat with carbide seat facers ?
Posted by: mike perry---------------------
Rich,
I know there are people out there who will just throw a set of valves in a head and take off. I am not an advocate of that approach.
Since the head has to come off the bike to make the swap, I would take it completely apart and have a look at everything. What's the cam look like, guide wear, bearing journals, etc. It's just silly not to take advantage of the opportunity while you have the head off.
I would touch up the seats, seat grinder, Serdi, whatever equipment you or your machine shop is comfortable with. I have some preferences as far as equipment, but that's somewhat subjective and I don't want to insult anyone who feels they have a proven method of performing a quality job.
As far as lapping is concerned, I have an opinion about that. When we are between rounds with the fuel car I will gind a seat and lap a valve. I'm rushed, and I have to try to make it work for 5 and a half seconds. I have over 300# of seat pressure to make the seal. It's gonna come apart again in 30 minutes. Often I'm trying to make diamonds out of goat turds at the track in 15 minutes, so I do stuff I wouldn't do elsewhere.
A motorcycle engine of the variety we're dealing with here is a somewhat different animal. Spring pressure is kept to a minimum to keep losses low, high rpm, small stems etc. Seat width unifomityand location on the valve face for sealing, loading, and some longevity is critical. I try to get everything just right so that I can put a very light covering of prussian blue on the valve with an acid brush, pop it on the seat one time and get a clear impression of the seat around the face of the valve. I will also vacum test the valve/seat seal without spring pressure to check its integrity. Occasionally I don't get the finish on the seat just right, and I feel the need to lap to get it right. In those cases I will take an old valve, face it, and use it to lightly lap the seat with a very fine lapping compound. I don't like forcing absasive into the seat and valve, or making a couple of grooves in my surfaces. especially titanium. (Although sometimes it seems impossible to get the chatter out of a titanium valve face)Also, the valve and seat expand differently under operating conditions. So, the two lapped surfaces that had 100% coverage at room temperature, do not have that same contact area at temperature.
All that being said, I do have some customers that request that I lap the pieces in. And, occasionally as I said I can't get the surface finish just right and I am forced to resort to lapping. In those cases I use the very fine lapping compund with light pressure. Remember this is after the seats and valves have been machined/ground and are very close to just right. It is not a situation where I'm taking an aluminum head in which the pressed in components (seats and guides) have probably moved around a little since it was 1st assembled, and trying to force the valve to make the seat round, or to correct the geometry between the guide and the seat.
Anyways, that's my approach to valve/seat reconditioning. Thanks for asking.
MP
Posted by: DerekM---------------------
I'm curious what is different in the Honda Ti-valve setup compared to the Yamaha, which hasn't (that I'm aware of) had this problem. Could a seat be produced that worked w/ the Honda valves?
Posted by: SFO---------------------
I believe this is covered in the earlier referenced thread.
Posted by: yam 3---------------------
Thanks guys I will pass all of this on!
Posted by: Rich Rohrich---------------------
Quote:
Originally posted by mike perry
Anyways, that's my approach to valve/seat reconditioning. Thanks for asking.
MP
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Mike - Thanks for taking the time to share the details with us. Having cut my teeth in the pre-Serdi era it's hard to break the lapping habit, but after seeing the beautiful work you guys did with the Serdi on my last 2 YZF heads I am a believer. :thumb:
Posted by: SFO---------------------
Archives anyone?
Posted by: Rich Rohrich---------------------
This and the original CRF valve thread will be put in the Technical Posts archives. :thumb:
Posted by: biglou---------------------
:thumb:
Posted by: motometal---------------------
when the valves "sink into the head", is this strictly seat wear, valve wear, or both? Sorry in advance if this is already covered.
Posted by: SFO---------------------
In the body of he thread there is reference to at least one other thread.
I believe we are dealing with valve face errosion here.
"Does anybody watch the movie?"
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