When valve clearance cannot be arrived at with thinnest shim ....

[qcktvr]

Hi there,
I have worked around motors for many years and "stretchy valves" is a new one for me; maybe that was a joke?
Air cooled motors, when pushed for max power, will typically fail in the area of the exhaust valves, and yes, they could drop their head. BUT you said this is on an intake valve, where heat is not usually an issue, unless maybe if the valve is held open / no clearance.
If the head was off / on the bench then the valve could be removed and an amount ground from the end of the stem to get things back in spec;
Good luck

 

[Grimly]

Hi there,
I have worked around motors for many years and "stretchy valves" is a new one for me; maybe that was a joke?
Air cooled motors, when pushed for max power, will typically fail in the area of the exhaust valves, and yes, they could drop their head. BUT you said this is on an intake valve, where heat is not usually an issue, unless maybe if the valve is held open / no clearance.
If the head was off / on the bench then the valve could be removed and an amount ground from the end of the stem to get things back in spec;
Good luck

No joke. You've never heard of stretched valve stems?

 

[2BRacing]

......BUT you said this is on an intake valve, where heat is not usually an issue, ......

Don't know where you read that it was an intake valve? He clearly says in post # 7 that ..."mine is the exhaust on cyl 4."

 

[tkent02]

No joke. You've never heard of stretched valve stems?

I have always heard it as a joke, like "Get me 50' of water line" or "Go find some relative bearing grease"

The valve stems get longer because the valves recede into the head.

 

[1948man]

Don't know where you read that it was an intake valve? He clearly says in post # 7 that ..."mine is the exhaust on cyl 4."

Post 15, not the original poster. Shims range from 2.20 to 2.70?????

 

[qcktvr]

I'm getting old, but I am still learning as well as forgetting....
I gather "valve stretch" is a concern with old air cooled VWs, but I cannot believe that it an issue for our street driven GSs
Must have dreamt that it was an intake, but still would not want anyone to panic re their valve breaking after a rebuild and moving valves between heads, I believe that would be extremely unlikely.
I would expect Suzuki to give a dimension from the spring seat to the top of the valve stem as a reference for machine shops to adjust valve lengths after grinding valve seat and valve faces..
Thankfully no shims in my 1150, so I will go and install a new petcock and rethink a charging concern.
Then go for a ride...
Regards

 

[Fjbj40]

Valves will stretch. Especially the exhaust valve. Valve stretch is checked using a radius gauge between the stem and the valve face back. Or you use a vernier micrometer and measure the lower stem and compare to the upper stem, if it is narrower on the lower half then you have stretch.

This is a check that we do on aircraft engine valves.

Not sure if other engines have a similar check or if they just use height/length, either free or installed. Some stretch is acceptable.

A reduction in shim/valve clearance, depending on the tune of an engine, can be stretch or valve recession into the seat, or valve seat wear.

 

[qcktvr]

Good morning,
interesting re the radius gauge for the aero engines, I had heard of that, but would that not really be identifying distorted valve heads rather than what I would think of as actual "stretch"? The eventual failure mode likely being the valve head parting company with the stem, but also showing up as reducing valve clearances.
Have a good day

 

[rustybronco]

The valve stems get longer because the valves recede into the head.

Or the valve heads themselves tulip (dish out).

 

[Fjbj40]

Good morning,
interesting re the radius gauge for the aero engines, I had heard of that, but would that not really be identifying distorted valve heads rather than what I would think of as actual "stretch"? The eventual failure mode likely being the valve head parting company with the stem, but also showing up as reducing valve clearances.
Have a good day

The stretch usually takes place where the head meets the stem. As it stretches it gets narrower and the radius changes. Placing the radius gauge there during inspection will reveal the change in radius, therefore the valve gets rejected because of this.

Alot of the aircraft engines use hydraulic lifters, therefore the reduced valve clearances are not seen, they are automatically compensated for by the lifter. The hydraulic lifter has an allowable range during installation, and unless you remove the lifter, bleed it down, reinstall it and measure the "dry" lifter clearance you would not realize it is approaching the minimum allowable clearance. Which would occur if the valve is stretching, tuliping or the seat is receding.

Removal of the lifter may never occur during the life of the engine. Only if the engine does not perform as designed or there is rough operation may this inspection be carried out during trouble shooting.

I have never worked on a bike engine newer than my 83 1100.

Do new bikes have hydraulic lifters today?

 

[chuck hahn]

Some do and some dont.

 

[Guest]

When doing the head rebuilds, upon disassembly, pick a valve that is in the middle of the shim range. Measure fron the tip of the valve to tjhe bottom of the shim bore where the base sits. Write that number down. After you finish your work, tip the valves all to that dimension. You will find that most are back in the middle of the shim range,

 

[ukjules]

That is a good idea .. but can you explain for me where you are measuring :
(I can see that as long as you take a valve in the middle range as long as you measure at the same points it will be ok but
where are you measuring ?

"Measure from the tip of the valve" -
to tjhe
" bottom of the shim bore where the base sits"

the total / overall length is just fine ?
(I attach a picture so we are signing from the same hymnsheet)

 

[chuck hahn]

Total length...."L"

 

[Fjbj40]

When doing the head rebuilds, upon disassembly, pick a valve that is in the middle of the shim range. Measure fron the tip of the valve to tjhe bottom of the shim bore where the base sits. Write that number down. After you finish your work, tip the valves all to that dimension. You will find that most are back in the middle of the shim range,

What I am interpreting is, measure from the tip of the valve, installed, to the bottom of the shim bucket bore, for a valve which has the mid range shim installed prior to disassembly. Measure the overall length of that valve, then machine all valves to that length, as in dimension "L", as chuck said.

is this what you mean Jay?

 

[ukjules]

Understood and thanks.

 

[qcktvr]

Hi again,
After seats have been cleaned up and valve faces reground it is unlikely that you can just make all of the valves the same overall length, that is the problem that you are struggling with now.
I believe that they should be measured individually, in their specific position, and then ground to be the same as one that is in the mid range of shim thicknesses. You should measure from any common machined face on the head.
In an earlier post I said:
I would expect Suzuki to give a dimension from the spring seat to the top of the valve stem as a reference for machine shops to adjust valve lengths after grinding valve seat and valve faces..
That is what I was trying to say, and I think that is what the previous poster was also saying?
My apologies if I am wrong, again; at least this is not a panic job..
Regards to all

 

[Fjbj40]

Hi again,
After seats have been cleaned up and valve faces reground it is unlikely that you can just make all of the valves the same overall length, that is the problem that you are struggling with now.
I believe that they should be measured individually, in their specific position, and then ground to be the same as one that is in the mid range of shim thicknesses. You should measure from any common machined face on the head.
In an earlier post I said:
I would expect Suzuki to give a dimension from the spring seat to the top of the valve stem as a reference for machine shops to adjust valve lengths after grinding valve seat and valve faces..
That is what I was trying to say, and I think that is what the previous poster was also saying?
My apologies if I am wrong, again; at least this is not a panic job..
Regards to all

I agree. My post was my interpretation of what Big Jay posted.

After the seats are machined then valve height should be checked and valves machined to bring into mid shim range. However, if there was extreme stretch then the valve would need replacement because you would cut below the top of the keepers.

Hope Big Jay chimes in here.