Author Topic: valve adjustment  (Read 1155 times)

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  • Grease Monkey
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Reply #30 on: March 22, 2020, 12:56:14 pm
The confusion is that the maintenance manual seemingly contradicts itself and contradicts common practice.

Yes the cam need not be exactly TDC as the cam has a certain duration of valves closed...but good practice to always adjust at TDC for consistency.

RE650 is about as easy and straight forward as they get.

  We adjust valves, mostly (especially exhaust valve) for heat the valves don't burn.  You are really not going to get much, if any "performance" change by using non-standard valve clearances.

Valves have to be really out of spec to notice performance degradation.  Guys claim "performance improvement" after simple valve adjustment.....placebo...

Not all 4 stroke engines are adjusted the same way.  While the general principle is the same, there are subtle and not-so-subtle differences in the methods:

I have bikes with shim and bucket  (these have a tolerance range) and math required to set. And special tool to hold valve open during change of shim

My suzuki has one cam position to adjust three of the 4 valves...and a second cam position to adjust the last exhaust valve.

Bikes like the RE have simple lock nut and slot adjusters

My Yamaha needs a special tool to move the adjusters. (and tiny hole to work through)

My Honda had eccentric adjusters...different method altogether.

4 stroke engines with pushrods are slightly  different than overhead cams (slop in the valve train) sometimes pushrod length can be wrong.

some 4 stroke engines have hydraulic lifters  (usually no adjustment needed unless out of major spec)

Probably more I don't know of.

Just sayin.....

RE uses the most simple adjustment method... anybody with a RE should learn to do their own valve adjust....with even the tiniest mechanical skill, one wrench and one screwdriver.....and a bit of patience, you can save yourself a couple hundred $$$, do them on your time schedule, not trip to the dealer, no leave your bike overnight,  and you also know they are done correctly!  My2c



   It's a four stroke engine, they all get adjusted the same way .... what's the confusion?    Piston at the top of it's travel and both valves closed ... ON the compression stroke .   You can do it even if there were no reverence marks, by looking at the piston position and were the rockers are on the cams.    The rockers will be on the base circle of the cam lobes , when there is NO lift or push on the valve stems.   You CAN rotate the engine in either direction .. BUT...  you want to rotate it in it's normal direction, so as not to potentially damage an anti- rotational  mechanism on the starter.. like a sprag gear.    The normal direction that an engine rotates is clockwise when your on the RIGHT side of the motor.   Your turning the motor counter clockwise , because you are on the LEFT side of the motor adjusting the valves.      The base circle ... or bottom round part of that Egg shaped cam lobe ...  is perfectly  ROUND all the way around it.   So as long as you are on the ROUND part of the Cam with the piston at the top of it's travel, and valve closed,  you can set your valve lash.  It will make no difference in  cam duration  at the stock valve clearance.   IF valve lash  is wider or tighter then the stock lash,  It WILL effect  cam  duration.     If... it is loose,  your valve timing will be shortened  or less duration that the valve is opened.  If it is tight , the longer your valve will stay open.  More bottom end power on a loose setting, more top end power with with a tight setting.   But in either case, they should not be too loose or too tight .  ;D


  • Grand Gearhead
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Reply #31 on: March 22, 2020, 05:20:59 pm
    Agreed... absolutely different method's  to adjust valves on different four strokes , to do the exact same thing.   Clearance between the rocker and valve tip, ALWAYS  when the piston is at or near TOP DEAD CENTER  of the compression stroke.   It could be a one piston engine your dealing with  or a multiple piston engine.   To simplify things , especially if there is confusion in the book.... one should be able to look  at an engine and identify  top dead center of the compression stroke , and all mystery's about it are gone.  You have simple marks on that motor , and from what I have sen in the book , you can't go wrong.  But , for piece of mind and if one wants to understand what they are doing better .  And not wonder afterwords and to keep it simple.   

   That is .... look into the spark plug hole , is the piston all the way UP ?   You can use a flash light,  or a wooden dowel on top of the piston and watch it rise to it peak height.    Now , go look at your valve springs , rockers and Cam.... both intake and exhaust.     Are the rocker arms on the ROUND part of the Cam lobe ?   Does the rocker arms feel slightly loose when you grab it and shake it ?  Are the valve springs ALL the way UP , and not compressed ?    Yeah ?    Then your at or near TDC of the compression stroke.  Go a head and check and adjust your valve clearance.  It's as simple as that, don't over think it.

  Cookie... it's just a fact that valve lash plays a role in valve timing.   It's not a placebo effect.    If lash is loose , the time the valve is open is shorter.  If lash is tight, the longer a valve is open.     When lash is adjusted at the SAME air gap on the base circle of the cam ... and as long as one is on the base circle of the cam , as the cam rotates and the rocker, or follower, or lifter  hits that flank of the cam.... all things are consistent.
An thaibhsí atá rattling ag an doras agus tá sé an diabhal sa chathaoir.


  • Grease Monkey
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Reply #32 on: March 22, 2020, 05:54:40 pm
Well yes, but....

with a simple engine such as the don't want to try to change valve timing by changing valve clearances....yes if you change the clearance (off of spec.) you will change the timing (off of spec.) ...(very slightly)  but why?  And you jeopardize other parameters which are far more important.

From the manual:

"Do not adjust tappets with less or no clearance as it will result in poor compression, valve burn out, and wear-out of the tapped adjuster foot.

Do not adjust tappet with high clearance as it will result in noise and insufficient opening of the valves."

If you want to change valve timing, you design and install a new cam with the desired profile.  Same for duration, overlap,  and "lift".

So to reiterate, the reason we adjust the tappets to spec in not to "change" valve timing.  It is to get the correct valve opening.  (and to make sure the exhaust valves seat and transfer heat away from them). If we get the clearances to spec the "timing" will take care of itself

Just watched a video on an engine with pneumatic actuators for opening valves..  Completely controlled by the computer.  It controls when the valve opens, the duration, when it far it opens.  It can even open only one exhaust valve at at time if needed! (to run only one of the two turbos)  So instead of "one size fits all conditions"  cam shape  This engine can give whatever you need at any particular instance, be it economy, power, emissions etc.

But then have to buy the $1,000,000 car to get this precision!


GHG said:
  Cookie... it's just a fact that valve lash plays a role in valve timing. 
« Last Edit: March 22, 2020, 05:57:38 pm by twocoolgliders »


  • Scooter
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Reply #33 on: March 22, 2020, 08:42:48 pm
I did the valve clearance check and adjustment at 300 miles, all the valve clearances were tight. I noticed no change in performance other than possibly a slightly noisier top end.


  • Grease Monkey
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Reply #34 on: March 22, 2020, 09:22:58 pm
Right.....if the valves are "out" by just a bit....the bike will still run just fine.  You want to keep the valves in spec for other reasons.  A bike that runs just fine, is not going to "run better than fine" with just a small adjustment needed.

If the valves are so far out, as to make the bike run poorly, then yes, adjusting the valves will make it run "better".

Some of mine were tight while others loose....but none more than one feeler size (or 1/1000 of an inch)...didn't make a bit of difference in how the bike runs.

The big worry with valves (and I know this from my VW days) is "burning" the exhaust valves.


I did the valve clearance check and adjustment at 300 miles, all the valve clearances were tight. I noticed no change in performance other than possibly a slightly noisier top end.


  • Grand Gearhead
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Reply #35 on: March 25, 2020, 10:06:33 pm
One of my mates likes to say "slappy valves are happy valves". Within reason, of course but you get the idea.
simon from south Australia
Continental GT


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Reply #36 on: March 26, 2020, 02:56:55 am
Just turn the back wheel in gear and look at the crank turning bolt on the left hand side.....
It’s turns anti clockwise.

This is what I was thinking.
2010 Classic 500 - 40,000km and keeps thumping
2013 Harley XL1200C