Jump to content
Sign in to follow this  

Partial valve replacement - looking for guidance

Recommended Posts

I have an '08 head with an unknown number of hours on it.  The valve train was all OEM Honda.  I shimmed all the valves and put it on one of my bikes 7 hours ago with a stock '08 cam.  I checked the clearances after the head had been on the bike for 3 hours and they were all where I set them.  I ran the bike pretty hard on a MX track between hour mark 3 and 4.6.  There was no indication that anything was wrong.  A week later in 40 degree weather I could not kick start the bike but was able to bump start it.  Once it was warm, it started normally.  I put ~2 hours on the bike that day.  

 

After cleaning the bike I took a look at the valve clearances.  The intakes had no clearance at all while the exhaust valves were still at .011".  I took the head off and reassembled the cam on my bench to measure again. There really was not clearance.  In fact, the cam was dragging the intake lifters even at full closed.

 

I know the valves move quickly at the end of their life.  If this means anything to anyone, here is a profile of one of the intake valves:

 

08%20Valve_zpsmftpqexl.jpg

 

Here is the "looking for guidance" part.  I'd really like to put in Kibblewhite SS intake valves and leave the stock exhaust valves in the head.  I have a full set of Kibblewhite '08 intake and exhaust valves but no springs or other components.  Is replacing only the intake valves a bad idea?  I ask because the Kibblewhite springs are expensive.  It looks like Kibblewhite does not recommend a partial replacement unless it is a low-time head.  I just don't have any way of knowing the total hours on this head or the valves.

 

If I were reading this I would probably respond with something like this: "if you are trying to build a reliable head then, just do it right.  Send the head off, get the valve seats cut and replace all the valves, springs and seals and be done with it for a while."

 

Thanks for the long read. Didn't intend for this to be so long.

 

Henryrifle

Share this post


Link to post
Share on other sites

You can put in the new valves and it will likely start and run fine for a time. I have heard of of this and the bikes run for quite a few hours. I know someone with a rental fleet and he's done it with those bikes.

If it was one of my bikes (or sons) I would have the seats cut & new valves & springs. At the very least have the intake seats ground, put in the new intakes, and replace ALL the springs. The only thing you'd be leaving is the exhaust valves and seats.

Now you have 3 options to choose from. I believe you'll do the right thing.

Share this post


Link to post
Share on other sites

Exhausts sound fine, so you could leave them alone, but I would install new OEM springs and valve seals while the head is apart, keeping valves in same side of head.

You absolutely have to install stiffer intake springs to work with the heavier stainless intake valves or they will float and hit your piston, and you should have the intake seats touched up and the lap the new intake valves in.

Edited by Eddie8v

Share this post


Link to post
Share on other sites

I usually do my exhaust valves every other time that I do my intake valves for my '06. I've never had any problems doing this and my exhaust valves hold up just fine.

I usually change my intakes about every 40 hours which is about all the life I get out them.

And for reference I run all OEM.

Hope that helps.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...