Short-lived intake valves??

[F-16Guy]

I'm getting ready to rebuild a friend's '02 CRF450, and I've read a lot about the 450 engine eating intake valves. From what I understand, the intake valves are hard-coated, but the seats are so hard that they beat through the coating, and then it's over! To make it worse, the valves are shimmed instead of like the 400ex's nut/screw type, so your average rider would be less likely to adjust the valve clearance. I've heard a number of stories about people getting very few hours between valve jobs. I'm just wondering if this got remedied for the quad version? Something to keep your eye on, I guess.

[D Bergstrom]

All of the CRF's use titanium intake valves, while the TRX's use steel valves. The problem is with the titanium valves. From what I have found out from other sites, the ti valves are not hardend, but they have a hardend coating on them. When this coating wears off, the valve is "beat" in to the head, as the seats are alot harder then the ti valves. I had to replace the valves (only my intakes were bad, but I replaced intake and exhaust.) in my CRF after I had it for about 8 months. I have now had stainless steel valves in it for about a year and a half and the valve clearances have not changed since the intial break in. I think the TRX valves will be fine.

Doug

[911]

yea what he said;)

[fearthis_450r]

I wouldnt be too sure about that. I have talked to a lot of mechanics and they are saying its pretty much the same with the trx. I recently had mine in the honda shop to have them check over my cam installation and to adjust my valves. They said my valves were off pretty bad(which i already knew) and they said you should adjust your valves ever 100 hours or less. They said it was because of the rpms and it just beats the valves up into the head. You should really check your valves a LOT it is very important, if you just go on thinkin its ok then your gonna have one messed up quad after awhile.

[D Bergstrom]

I only said the valves should last longer then the CRF valves. The problem with the CRF valves are that they are Titanium. I check my valves about every 20 to 25 hours of ride time. (oil changes every 10 - 15 hours.) 100 hours is WAY to long in my opinion, much less 200 (I read your other post on checking valves.) You have to remember, this engine is based on a high performance motocross race engine, (slightly detuned for the TRX) it is not the same engine as in the 400ex that you could probably be a little lax with maintainance and be fine. But with good maintainance, I think it will run a long time. My CRF has been perfect since I went to steel intake valves, (I am sure I have had over 100 hours since then.) and the TRX should (hopefully) be the same.

Doug

[BSTURDIVANT]

Only 450's that give problems are those that eat dirt from dirty or K&N filters!!!

[450Racer]

well, i've put a little more than 100 hours (mostly raced on) on my TRX without looking at the valves. just last night Kyle Damon was nice enough to rebuild my motor for me and adjust the valves for the new cam. and they were WAY off, he said it shouldn't have ran half as good as it was. the exaust i beleive was around .28 mm for the correct clearance and mine was only .008! we're re-shimming it tonight though. lucky i didn't blow that dam thing right out the Big Gun :blah:

[outacontrol31]

i had my 450 since feb. of last year, i raced till around october almost on a weekly basis on a stock motor and cam, and in october it quit running instantly, almost as if i pulled the kill switch, it had shown no signs of power loss prior to it quitting on on, and tear down revealed trashed intake valves, so there is deffiniatly a problem with them, and they do wear out, now it was mostly my fault cause i forgot to get them adjusted, but now with new valve's and other things, i check them often, cause of the valve problems, but the intakes are a weak spot, atleast for me they were

[400exrider707]

Hondas are pretty well known in the bike world for eating the intake valves.

[walt miller]

the exhaust valve clearance is 0.28mm or 0.011 +or- 0.001. you where 0.002 out which means when you 4wheeler gets warm there could be 0 or less. this could leave a valve open which could make it run bad and burn valve or if it is open enough not run at all. valve can stretch from heat over time and seat can change by the valve shutting. that is why you check the valve clearance. at 0.002 out it should not be that bad unless you get it hot. there should be atleast 0.050 between the valve and piston at all times so it should not hit. think about it 0.002 is about half of a sheet of paper. just check you valves more often