S1 Publishing(Oxford)©2007

World of motorcycleS
S1 Publishing(Oxford)© 1999-07
 Maintenance - Engines
Valves & Tappets
What should I look for in the rocker?:
1. The part where the cam runs over the rocker, if it grooved, then it will need replacing.
Note: I've never had that happen in any motor I have worked on or owned, but it's worth knowing.
2, The bush which holds the rocker in position, if there is any sign of wear, replace the cocker.
Note: I've never had that happen in any motor I have worked on or owned, but it's worth knowing.
No photo as yet


What is a collet?:
Collets come in pairs and the hold the valve springs compressed holding the spring plate over the spring and fixed to the valve stem with a small groove
No photo as yet

What should I look for in a valve spring?:
1. You'll need your manual and your vernier gauge. Check the length of the spring and make sure they are between the recommended lengths
No photo as yet

What should I look for in the valve stems?:
1. Check the top of the condition of the groove in the top of the stem, this is where the two Collets fit, if they are worn, then the valve stem should be replaced.
Note: I've never had that happen in any motor I have worked on or owned, but it's worth knowing.
No photo as yet
2 Check the valve stem for carbonizing, and clean it if necessary. I usually use a knife or screw driver to get the worst off, it's made od hardened steel and is not easily scratched, but take care where the valve meets the seat., that part wont be that carbonized, and if you scratch it, you'll have more re-grinding to do  

A clean valve stem

A carbonized valve stem
3 Check the valve stem for pitting, 
if you see black marks on the valve where it meets it's seat in the head, feel it with a fingernail, and if it catches or feels uneven, it will need re-grinding or replacing
see re-grinding
check the lowest part of the stem...
No photo as yet
4.  Check the valve stem for warping or bending by rolling it along a flat surface. a mirror or a plate of glass will do if you haven't got a piece of laser cut metal like I used here.
if the valve head wobbles as you roll it backwards and forwards, or the shaft rattles, then it is a sign or a bent valve. 
 Note: if this happens, both the valve and the valve guide will need replacing, and you'll need a good engineering place to get that sorted. 
 Sometimes it's better to replace the whole head with a second hand head (make sure you get the valves/cam & cam carriers etc. too if you do this)
You should also and check the rubber seeals at the head, where the valve comes through the valve guide, and indide the spring(s), if it is split or perished, it will need to be replaced.
No photo as yet

What do I look for in the Valve seat?:
Look for splitting and for carbonizing. 
 If pitted then it will need re-grinding, if carbonized, then clean.
 If the seat is too thin then replace the head.
Note: I've never had that happen in any motor I have worked on or owned, but it's worth knowing.

A good valve seat, shown just inside of the white circle, is essential, for compression.
Under Construction

This is just a general guide.
If you are about to do your own maintenance, using these pages, I take no responsibility if you get things wrong!
Modified for 2009
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