Valve Clearance Engine Tuning

I recently had a valve check done and they were all set virtually dead center specification. This made me wonder how playing with the clearances would affect the feel of the motor. I understand that there are a LOT more variables overall that would change the feel of the bike. Assuming the bike is completely stock and only able to adjust the clearances, how does changing the valve clearance affect the motor and power delivery? A few examples

1) all valves as tight as possible in spec?
2) Loose as possible?
3) Intake valves tight as possible, exhaust loose as possible?
4) intake loose, exhaust tight?

I'm not trying to gain HP, I'm just trying to better understand the flow in this aspect of tuning.

Thanks.

[image: View Post]daisy, on Jun 5 2009, 06:49 AM, said:

I recently had a valve check done and they were all set virtually dead center specification. This made me wonder how playing with the clearances would affect the feel of the motor. I understand that there are a LOT more variables overall that would change the feel of the bike. Assuming the bike is completely stock and only able to adjust the clearances, how does changing the valve clearance affect the motor and power delivery? A few examples

1) all valves as tight as possible in spec?
2) Loose as possible?
3) Intake valves tight as possible, exhaust loose as possible?
4) intake loose, exhaust tight?

I'm not trying to gain HP, I'm just trying to better understand the flow in this aspect of tuning.

Thanks.


Valve clearance changes within spec have a negligible effect on performance.  Theoretically tighter valves stay open longer so the engine would breath better.  Also as the valves get too tight they fail to close and cause damage as the valves over heat.

Valves tend to tighten over time as the valve seat wears away.  Valve checks are insurance against engine failure due to over tight valve clearance.  The odds of this happening are very minute within the life of the engine.  Given the excessively high cost and time consuming complexity of the VTEC valve check some feel the cost out weigh the risk.

Basically the more valve lift, the more power in general, also the more balanced each cylinder is to each other the better and smoother power will be produced.
So if you actually set all your valves at the tightest end of the clearence vs all at the loosest end, the engine will make more power.
This is one possible reason your enigine might feel like it's running better with more miles on it, because on most engines like ours, the valves get tighter (read more lift) as they wear.
Another thing here though is that the valve seats tend to be hammered further into the head over time and is actually the reason for the valve clearence to get smaller(the more the seat moves into the head, the closer the valve is to the cam lobe).
I think one reason most (non-vtec) vfr valves rarely need adjustment is because cam lobe & buckets wear (increase gap) at about the same rate as valves drop into seats(decrease gap) and as long as there wear at about the same rate, you'll never need adjustment! :biggrin:

There are many other factors that effect engine power and smoothness besides lift, there's duration and valve overlap for two biggies. :cool:
Just a few ramdom thoughts for ya!

I have to disagree about the statement above about valve clearance getting tighter with wear.  Wear all depends on the engine and the material used in the construction of the valve being used.  Most valves increase lash from wear, although there are a few that tighten up though such as the CRF450's.  Every engine I've worked on that needed adjustment required the valve clearance to be tightened up.

[image: View Post]Bad Boy, on Jun 5 2009, 11:13 AM, said:

Valve clearance changes within spec have a negligible effect on performance.  Theoretically tighter valves stay open longer so the engine would breath better.  Also as the valves get too tight they fail to close and cause damage as the valves over heat.

Valves tend to tighten over time as the valve seat wears away.  Valve checks are insurance against engine failure due to over tight valve clearance.  The odds of this happening are very minute within the life of the engine.  Given the excessively high cost and time consuming complexity of the VTEC valve check some feel the cost out weigh the risk.

Yes, i understand that valves move over time and for street riding it makes little difference. But would that little difference be noticeable by a track rider? Would that be something a chief tech for [insert your favorite professional rider here] do to adjust the compliance of the bike if all all the other variables are considered a constant.

[image: View Post]slowf2337, on Jun 5 2009, 10:26 AM, said:

I have to disagree about the statement above about valve clearance getting tighter with wear. Wear all depends on the engine and the material used in the construction of the valve being used. Most valves increase lash from wear, although there are a few that tighten up though such as the CRF450's. Every engine I've worked on that needed adjustment required the valve clearance to be tightened up.

I think that you would find that 90% on VFR valve adjustments are because the gap is too small, not too large and as were mostly talking about VFR's here it should be a safe statement. http://www.vfrdiscus...tyle_emoticons/default/tongue.gif

[image: View Post]daisy, on Jun 5 2009, 10:27 AM, said:

Yes, i understand that valves move over time and for street riding it makes little difference. But would that little difference be noticeable by a track rider? Would that be something a chief tech for [insert your favorite professional rider here] do to adjust the compliance of the bike if all all the other variables are considered a constant.
Fore sure, especially in Spec Racing series!  That is what they call blueprinting an engine!

[image: View Post]Baileyrock, on Jun 5 2009, 11:24 AM, said:

Basically the more valve lift, the more power in general, also the more balanced each cylinder is to each other the better and smoother power will be produced.
So if you actually set all your valves at the tightest end of the clearence vs all at the loosest end, the engine will make more power.
This is one possible reason your enigine might feel like it's running better with more miles on it, because on most engines like ours, the valves get tighter (read more lift) as they wear.
Another thing here though is that the valve seats tend to be hammered further into the head over time and is actually the reason for the valve clearence to get smaller(the more the seat moves into the head, the closer the valve is to the cam lobe).
I think one reason most (non-vtec) vfr valves rarely need adjustment is because cam lobe & buckets wear (increase gap) at about the same rate as valves drop into seats(decrease gap) and as long as there wear at about the same rate, you'll never need adjustment! :biggrin:

There are many other factors that effect engine power and smoothness besides lift, there's duration and valve overlap for two biggies. :cool:
Just a few ramdom thoughts for ya!
So easy answer, the tighter the clearances on all valves, the greater the lift which in turn gives more air and potentially more power. I'm guessing duration would be how long the valves remain open (changed by cam shaft lobe shape?)  and valve overlap would be where both intake and exhaust valves are open at the same time. These sound like they are bringing in other variables into the tuning process. Duration seems fairly straight forward, the longer the valves are open the more air can come through. In layman's speak, how does overlap improve or hamper the motor? Is overlap adjusted by the clearances or by some other means.

I never realized how much one can do with just the valves to change the feel of a motor until today.

I have to agree with BR on this one, it has always been my experience that valves tighten up as an engine wears.  I use to get a chuckle when I had my bike shop and people would come in for valve adjustments complaining that their valves were loose.

To elaborate on BR's comments on spec racing.  Most of the really fast guys (read full or semi-factory support) are getting new/fresh top ends after practically every race.  They have the $$$$ so all they have to worry about is the motor making it through that weekend.  Set it up as precise/loose as necessary and not worry about getting 100k miles out of it.

"Identical" things aren't always "indentical".  I know in certain automotive racing series, you are limited to a certain size carburetor (measured in cfm).  The really serious racers will go to the carb supplier and test all of their stock of "identical" carbs to see which one truly flows the most.

[image: View Post]Pete McCrary, on Jun 5 2009, 03:07 PM, said:

"Identical" things aren't always "indentical". I know in certain automotive racing series, you are limited to a certain size carburetor (measured in cfm). The really serious racers will go to the carb supplier and test all of their stock of "identical" carbs to see which one truly flows the most.
Exactly right, spec engine builders will go through a 100 stock intake manifolds to find the ones that flow best, these are kept for their National Championship contending customers or themselves, the other crap go on regular customers engines. Pretty much done with almost all stock components, some just flow/work better than others. Saturn actually made "special" stock castings heads for their factory SCCA teams that no regular race customer ever saw. :biggrin:
In spec racing every 1/10th hp makes a big difference! :rolleyes:
I remember when I was road racing Mazda wankels, one year only stock intake manifold made over 10hp more than any other year intake on a 12a, Hot commodity right there.

[image: View Post]slowf2337, on Jun 5 2009, 09:26 AM, said:

I have to disagree about the statement above about valve clearance getting tighter with wear. Wear all depends on the engine and the material used in the construction of the valve being used. Most valves increase lash from wear, although there are a few that tighten up though such as the CRF450's. Every engine I've worked on that needed adjustment required the valve clearance to be tightened up.
Shim under bucket design virtually never widens the gap , unless you get cam journal wear or something

Other designs I agree

CRF450.  

At first I thought you said CB450.  Gawd I hated those bikes.  Torsion bar valve springs.  What was Sochiro thinking when they designed that engine.

[image: View Post]daisy, on Jun 5 2009, 12:19 PM, said:

[image: View Post]Baileyrock, on Jun 5 2009, 11:24 AM, said:

Basically the more valve lift, the more power in general, also the more balanced each cylinder is to each other the better and smoother power will be produced.
So if you actually set all your valves at the tightest end of the clearence vs all at the loosest end, the engine will make more power.
This is one possible reason your enigine might feel like it's running better with more miles on it, because on most engines like ours, the valves get tighter (read more lift) as they wear.
Another thing here though is that the valve seats tend to be hammered further into the head over time and is actually the reason for the valve clearence to get smaller(the more the seat moves into the head, the closer the valve is to the cam lobe).
I think one reason most (non-vtec) vfr valves rarely need adjustment is because cam lobe & buckets wear (increase gap) at about the same rate as valves drop into seats(decrease gap) and as long as there wear at about the same rate, you'll never need adjustment! :rolleyes:

There are many other factors that effect engine power and smoothness besides lift, there's duration and valve overlap for two biggies. :biggrin:
Just a few ramdom thoughts for ya!
So easy answer, the tighter the clearances on all valves, the greater the lift which in turn gives more air and potentially more power. I'm guessing duration would be how long the valves remain open (changed by cam shaft lobe shape?)  and valve overlap would be where both intake and exhaust valves are open at the same time. These sound like they are bringing in other variables into the tuning process. Duration seems fairly straight forward, the longer the valves are open the more air can come through. In layman's speak, how does overlap improve or hamper the motor? Is overlap adjusted by the clearances or by some other means.

I never realized how much one can do with just the valves to change the feel of a motor until today.

Over lap can be "adjusted" by indexing the cam shafts - in other words, you make the position of the cam sprocket on the camshaft adjustable.  Adjustable camshaft sprockets are easily available for the SV650 Suzuki among other.

You have to really be looking for every ounce of power to go to that extreme.  Indexing cams is not for the weekend warrior either - it needs to be done by an experienced wrench.  Unless you're a serious racer, it ain't worth the time and money.  And if you were a serious racer, I doubt you would be racing a VFR.

[image: View Post]Pete McCrary, on Jun 5 2009, 11:30 PM, said:

Over lap can be "adjusted" by indexing the cam shafts - in other words, you make the position of the cam sprocket on the camshaft adjustable.  Adjustable camshaft sprockets are easily available for the SV650 Suzuki among other.

You have to really be looking for every ounce of power to go to that extreme.  Indexing cams is not for the weekend warrior either - it needs to be done by an experienced wrench.  Unless you're a serious racer, it ain't worth the time and money.  And if you were a serious racer, I doubt you would be racing a VFR.
Ah D,
Something else i forgot to ramble off when i was talking to you about the "variables" in tuning.  
A big plus 1 to that being a PITA.  And we just indexed them on a Single Cylinder and one twin at school.  It is also interesting to see that the TDC mark on the flywheel isn't necessarily where TTDC is.  Find one to do the other.  Lovely amount of time spent just loosening up the cam shafts from the sprocket, spin, tighten down...to still be off!  There is so much that can be changed in just the top end of a motor to make power.  

But, like i said, you would definitely get some answers on here!  Continue on...