How many times can you shim the valves?

Joined
Jul 7, 2007
Messages
79
Likes
0
#1
How many times can you shim the valves before you need to get new valves? My friend is a mechanic but mostly car stuff. He claims you can only shim them once then you can do it again but you are going to have the vavles break. I guess I am really nervous about my bike having valve problems at some point and I dont want to let the bike motor just grenade on me and then I have to pick out shapnel out of the case. I am going to check clearances here soon just wondered what I have to do if i need to shim again.
 
Last edited:
Joined
Jul 7, 2007
Messages
79
Likes
0
#3
so if my clearances are off then I will need to buy new valves? or what am I supposed to do?
 
Joined
Oct 19, 2006
Messages
8,130
Likes
2
Location
Merrillville,Indiana
#4
You need to have a competent shop rework your head,I recommend calling Eric Gorr. This is also a good time to replace the top end and check the rod. If I had the money,I would go ahead and replace the crank also! How many hours do you have?
 
Joined
Jan 27, 2000
Messages
6,959
Likes
42
#7
Pele.

Your valves can be reshimmed multiple times. A lot depends on how you ride the bike. If you are a 'A' or Pro rider and run the bike against the rev limiter, then you will have to replace your valves often. You can replace them with the Kibblewhite stainless valve kit and they will last for a very long time.

If you are a trail rider or play racer (pro practice rider) and don't push the bike as hard as a serious racer would, you can get by with checking and adjusting your valves and keeping a hour meter on your bike to register the time on the engine. Do a leakdown test on your engine and it will tell you the condition of the valves and rings. How long you will be able to go on your engine parts is up to you and how you ride. Only you can determine that.

The main thing is to check your valve clearance often and make any necessary adjustments before the valve and seat become damaged. Tight valves will burn the valve and seat and then you will need head work. Keep in mind that letting the valves go for too long can result in losing the head of your valve and that can cause some serious damage to your engine.

As foxforks pointed out, there are several things in your engine that need regular replacement. But the intervals at which these parts are replaced will have to be determined by you and how you ride the bike. If you are fully sponsored or independently wealthy then, just go by the manual and replace everything at the required intervals. But if you are a working stiff like most of us, you will have to figure out your own maintainance/replacement schedule. You do this by tearing down the engine at regular intervals and inspecting and measuring the wear on the critical parts. Soon you will see a pattern of how often certain parts will have to be replaced. That is very important because these new engines have a way of taking themselves apart if you don't do it in time.
 
Joined
Jul 7, 2007
Messages
79
Likes
0
#8
Im the latter, a working individual, and I do not race. I hill climb, small jumps, and trail ride with this bike. I'm not an overly agressive rider and nor do I redline the bike much even when climbing hills. I'm a pretty conservative rider but I have put on countless hours of riding since I have bought this bike. I would say that I am in the 150 hour range. But like I said non of this even comes close to race-like condition.
 

Rich Rohrich

Moderator / BioHazard
Joined
Jul 27, 1999
Messages
22,724
Likes
529
Location
Chicago
#9
At a minimum you have to change the cam chain EVERY SEASON on a YZF250. The valves and springs will give you warning about when they are wearing out. If you drop 5% off the initial valve clearance your valves are likely worn out, if the clearance changes more than 10% (usually about .15mm) the valves are in danger of breaking the heads off from wear and need to be replaced ASAP.

If you are really at the 150 hour mark changing the piston, rings, valve springs and cam chain is a wise move. The Yamaha YZF is hands down the most reliable four-stroke on the market. The problem is, because they tend to be very reliable people confuse this with them not needing ANY maintenance. YZ250Fs tend to be really vindictive if you ignore service intervals for too long.
 
Joined
Jul 7, 2007
Messages
79
Likes
0
#10
I say I am at the 150 mark because I am on 60 days of leave so I have been out on the bike for 2 hours a day (actual riding) since I bought it about 3 months ago. I only have until the end of the month and then I go back on duty in Washington DC area. :( sadly