Slightly loose exhaust valves? - Wrist Twisters
 
Thread Tools Display Modes
post #1 of 5 Old 03-04-2013, 04:08 PM Thread Starter
Le So Cal Troll
 
nd4spdbh's Avatar
 
Join Date: Sep 2009
Location: So Cal
Posts: 5,766
Rep Power: 1
 
Slightly loose exhaust valves?

OK first off this is NOT on the 919. this is on my CRF250X

its an 04, i ride 50/50 track and trail, i ride the piss out of it, it has a 250R cam (MUCH hotter) and do oil changes EXCESSIVLY. That stated its a magical bike even by the standards of an ex head honda moto race team mechanic. The bike probably has 500-700 hours on it.... and for a high strung race 4stroke dirbike motor thats ALOT. Intake shims are still STOCK from the factory, valves Stock from the factory... head, cylinder, piston stock from the factory.

Only thing not stock is a set of intake shims i put in 4 years ago as my exhaust valves were on the loose side. So i shimmed em back to spec. Spec is .28mm +- .03mm. Now i am back a little on the loose side (which is pretty much the opposite way the valves in these motors move, i swear magical) ...Currently i stand at .35mm.

So for you motor mechanics, is the extra looseness something to be worried about? should i shim back to within spec, or should i leave it, i have never really been too worried about loose exhausts as they due tend to heat up and expand... but .04 out of the .03 spec is getting a lil much no?

FYI the exhausts on the CRF250 motors are rocker actuated from a single forked roller rocker, so i attribute some of the extra slop to a combination of wearing of all the extra surfaces introduced by the rocker system. (VS straight shim n bucket to cam of the intakes)

nd4spdbh is offline  
Sponsored Links
Advertisement
 
post #2 of 5 Old 03-04-2013, 06:54 PM
Discen
 
Join Date: Aug 2008
Location: Alberta,Canada
Posts: 258
Rep Power: 1
 
If it were me I would shim them back into spec, and I'd buy the hot cams shim kit (as I did for my drz) it's nice to have all the sizes ready to go.

having said that though I'd be happier with them also on the loose side as you probably already know that tight valves suck. I assume the valves on those have the coating on them, and when it wears the valves start to tighten up so that's good that atleast they don't seem to be wearing.

My valves on my drz starting to wear down, I literally shimmed them every other ride (every 6 hrs of ride time) it was retarded. I'm surprised you got that many hrs without a rebuild, that's awesome

______________________________________
03 DRZ 400
05 VFR 800A
05 GSXR 1000
04 Honda 919
00 Honda Shadow ACE
Epicsoldier is offline  
post #3 of 5 Old 03-04-2013, 07:01 PM Thread Starter
Le So Cal Troll
 
nd4spdbh's Avatar
 
Join Date: Sep 2009
Location: So Cal
Posts: 5,766
Rep Power: 1
 
Quote:
Originally Posted by Epicsoldier View Post
If it were me I would shim them back into spec, and I'd buy the hot cams shim kit (as I did for my drz) it's nice to have all the sizes ready to go.

having said that though I'd be happier with them also on the loose side as you probably already know that tight valves suck. I assume the valves on those have the coating on them, and when it wears the valves start to tighten up so that's good that atleast they don't seem to be wearing.

My valves on my drz starting to wear down, I literally shimmed them every other ride (every 6 hrs of ride time) it was retarded. I'm surprised you got that many hrs without a rebuild, that's awesome
Like stated its a magical bike, i should have been on my 3rd top end by now. *knocks on wood*

I am going to stop by my buddies shop tomorrow n pick his brain along with his boss's and see what they say.

Truth be told the only concern i have is excess wear due to the slapping of parts together... but i really dont mind running em loose otherwise.

nd4spdbh is offline  
 
post #4 of 5 Old 03-04-2013, 09:20 PM
Community Moderator
 
g00gl3it's Avatar
 
Join Date: Jun 2009
Location: Idaho
Posts: 11,613
Rep Power: 1
  

Awards Showcase
Wrist Twisters Event Attendance Wrist Twisters Event Attendance Wrist Twisters Event Attendance 
Total Awards: 3

I thought I read something that the issue with those CRF's was the head material being too soft, so the valves were 'seating' to the point of leakage.??? I dunno. It's late.

2009 Aprilia Tuono - Ginger
2001 XR650R BRP (Big Red Pig)
2006 Honda 599 - Ex wrecked it :-D
2007 Honda CB900F (sold)
2006 Honda VTX 1300C (sold)
YouTube Channel
g00gl3it is offline  
post #5 of 5 Old 03-04-2013, 09:53 PM Thread Starter
Le So Cal Troll
 
nd4spdbh's Avatar
 
Join Date: Sep 2009
Location: So Cal
Posts: 5,766
Rep Power: 1
 
Quote:
Originally Posted by g00gl3it View Post
I thought I read something that the issue with those CRF's was the head material being too soft, so the valves were 'seating' to the point of leakage.??? I dunno. It's late.
There were LOTS of complaints about valves on the intial batch of CRF's (03 450s and especially 04 250R/X's) alot of this had to do with the riders. This was a transition period, everyone riding track prior to 03 was on a 2 stroke, they revved the hell out of them... the transition to 4stroke high revving bikes was a big improvement in performance numbers... but what the riders didnt realize was the different riding style was needed as you DIDNT need to rev the piss out of the 4strokes to get power... as they had power throughout the rev range. This led to many of the early race 4 strokes being over revved and banged on the revlimiter MUCH more than they should have.

Also, Oil changes.

Again this was a transition period... the 2smoke riders had never heard of oil changes, at most maybe transmission oil every season... but god for bid changing the oil in a motorcycle every track day thats ludicrous... unfortunately not. The honda CRF450/250's have a quart or LESS in the engine side of the case (7/10ths of a quart for the 250x) that VERY SMALL amount of oil gets chewed up real quick at high revs and due to the small skirts there is some oil consumption. This led to bikes running bad oil as well as many oil starved bikes which leads to failures of ALL kinds, especially in the head (cam shaft n rocker wear).

Pair ALL of this together and you get excessive wear on the components within the head, and excessive valve seat wear along with valve cupping.

This is why, and im sticking to it, i do AT MOST 50 miles of track riding, and 150ish miles of trail riding before changing oil in the engine side. And i keep a constant eye on oil level (ill go through half a dipstick in a 40 mile track day, and its been like that since day one). Im not saying that i dont bang on the rev limiter from time to time... just watch any of my dirt videos and i hit it quite often... but not like in the beginning of the 2 smoke guys where it was CONSTANT.

And yes they did slightly change valve seat materials i want to say around 06.

Typically the valves will wear at the seats and the valve will travel further into the head thus getting tighter on the clearances to the point of zeroing out which will leave the valve open causing leakage and often a burnt valve.


BACK ON TOPIC, i do not have a tightening valve problem... which is the magical part, and why im not really worried about the exhausts being loose, Ill probably end up re-shimming down to .30 (so .02 on the loose side) to get things back within spec... but more input welcome.

nd4spdbh is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Wrist Twisters forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome