351 kit with stock head
#11
03-21-2010 | 09:27 PM
Senior Member
1st Gear Member
Joined: Jun 2008
Posts: 539
From: Saco, Maine
And watch out if you use any gasket stripper when removing the old base gasket. I used mine a little too liberally and it took the paint off my beautiful perfect engine. Now I have some missing paint just underneath the new cylinder. I was pretty peeved that I did it. But that was the only thing that I screwed up so I guess it could have been worse. Bike runs great, although I have noticed a bit more vibration on the 351. Not bad but slightly more than the 250.
#12
03-23-2010 | 11:39 AM
Senior Member
Joined: Oct 2006
Posts: 3,106
From: Misawa Japan
1st Gear Member
Isn't the head on the 250 the same basic head as the 300? I noticed when pulling the 250 top end off that the valve reliefs in the 250's piston went down past the crown. This seems indicative of a valve design and spread that was designed for a bigger bore. The KLX 300 piston that's going in now obviously has the reliefs located in what I'd classify as a more normal location on the piston top. I'm no authority on this whatsoever, but it makes me think the cylinder head was designed for the 300 to begin with and just accomodated the 250 later. On the other hand, it looks like the 250 has been around for some time if the 1993 designation on the back of one of my factory manuals is any indication. I've hardly seen every piston in every motorcycle, but the somewhat extreme valve relief location on the 250 seems different to me. Most of my 4-stroke motorcycle engine dealings have been with various XR's, Z1's, and such, so we're not talking high tech, cutting edge.
#13
03-23-2010 | 04:02 PM
Senior Member
1st Gear Member
Joined: Oct 2009
Posts: 262
From: Sonoran Desert, Arizona
Yes sir; same head/chamber design on both models with exception of KCAS valve on the 250s head. The two bikes share many of the same parts in the top and bottom-end. The original off road model (KLX250R) had a different cylinder and the case opening was smaller. When the 300R was introduced in 97 the bore and outer diameter of the jug was increased along with a bigger opening in the case for the larger diameter cylinder skirt.
Ron
#14
03-24-2010 | 12:37 AM
Senior Member
Joined: Oct 2006
Posts: 3,106
From: Misawa Japan
1st Gear Member
Yes, and interestingly enough, the 96/97 KLX250R uses the same size of exhaust valve and same PN as the 300R (alt PN for 12005-0031 which is 12005-1192). Looks like Kawi just used some of the same tooling for the 300R head, since they didn't need KCAS for the off-road only model. Typically thrifty move by the green machine.
Last edited by tremor38; 03-24-2010 at 12:50 AM.
Thread
Thread Starter
Forum
Replies
Last Post
jhoffy22
KLX 250S
2
06-18-2011 12:17 AM
