ok to check valve clearance with cam lobes up instead of TDC?

[Bob K.]

I tried using T1 and T2, but could not get a feeler gage under the lobes.

Isn't it just as good to point the lobe straight up so there is no pressure on the valve train and then slip the feeler gage under there?

 

I got readings similar to Droneh8tr, except mine are a tad tighter, therefore my numbers look believable.

 

Was my measurement method acceptable?

 

Thanks, Kenny

(For archive's sake). Yes, I believe it is. Yamaha already has us measuring at different points on the base radius of the cam lobes depending on the cylinder when describing the official way to check clearance, so I see no reason why measuring anywhere on the base radius--including straight up--wouldn't give the same results.

 

Here are some pictures for contemplation: https://www.venturerider.org/forum/showthread.php?33290-Proper-way-to-measure-valve-clearances&p=1046013#post1046013

Edited March 31, 2020 by Bob K.

[Patch]

I thought I'd stay out of this and usually do so, and but; maybe this may help the understanding of and from a different point of view.

 

Yes I agree that you should and can measure from the bottom of the lobe but; I can also say that it can also provide a problem in doing so,,, if after you check the gap you don't recheck via the book procedures, you are overlooking the limit potentials.

 

Then why is that a potential problem can be missed one way and not the other?

Because cam wear should not be found at the bottom of the lobe but it is not impossible for it to happen. Such distortions on a bike with with high mileage, been neglected or, that has overheated is not far fetched!

 

It is the stems that stretch over time, the firsts few miles its stem and seats.

 

If your stretch has become no longer a matter of just shims, then you need to measure the lobes well for tolerances. How do you know you are at the limits? By properly checking the gaps at the scheduled points. Eventually the stems will narrow too much and need valve replacing along with guides and seats!

Will it matter to you, that is up to the individual.

 

That's my experience for what its worth

[Bob K.]

I thought I'd stay out of this and usually do so, and but; maybe this may help the understanding of and from a different point of view.

 

Yes I agree that you should and can measure from the bottom of the lobe but; I can also say that it can also provide a problem in doing so,,, if after you check the gap you don't recheck via the book procedures, you are overlooking the limit potentials.

 

Then why is that a potential problem can be missed one way and not the other?

Because cam wear should not be found at the bottom of the lobe but it is not impossible for it to happen. Such distortions on a bike with with high mileage, been neglected or, that has overheated is not far fetched!

 

It is the stems that stretch over time, the firsts few miles its stem and seats.

 

If your stretch has become no longer a matter of just shims, then you need to measure the lobes well for tolerances. How do you know you are at the limits? By properly checking the gaps at the scheduled points. Eventually the stems will narrow too much and need valve replacing along with guides and seats!

Will it matter to you, that is up to the individual.

 

That's my experience for what its worth

If "stretch" is a concern, why would Yamaha have us measure at a place on the lobes for Cyl 1 and 3 that is different from the place on the lobes for Cyl 2 and 4? It seems to me that if "stretch" were a concern, we'd measure from the same place on all lobes...the location most likely to "stretch". Plus, I'm unaware of any measurements for "lobe stretch" in the service manual.

[sldunker]

Yamaha would like us to adjust the valves when the piston is at top dead center(tdc). As long as the cams are timed correctly, Yamaha doesn't care where the position of the camshaft is. The lobes might be straight up or they may be off center a few degrees at tdc. Most cams are ground accordingly allowing for this.

I have always followed Yamaha's instruction for this and have checked them after adjustment with the lobes straight up. If I had feeler gauges that would go to .0001 increments there may be a difference but maybe not.

Yamaha also allows us a little slack when it comes to adjusting the valves. If they wanted it to be precise they could of said 'when piston is at tdc the clearance of the intake valve should be exactly .004 not a range of .004 -.006.

Anyway this is my take on valve adjustment. I could be completely wrong.

[Patch]

Morning Bob, first I recognize your confidence, and I certainly see how you reasoned thru the problem:thumbsup2:

 

I'm going to skip past mass, heat, and expatiation's tho they are definite considerations when developing required lash.

 

The "stretch" in in the valve stem length! The stem is always under shear load hot or cold. When the power is on the constant slamming of the valve at high temperature causes the stem to elongate, this also causes the stem diameter to reduce, and as a result the guides diameter also falls out of spec!

 

The longer this above mention remains out of spec the more wear to the lobe in unexpected places!

 

When the required shim schedule becomes no longer adequate it is time to open and replace or regrind.

A machinist will for example first check the stem specs before he/she chooses to lap and grind the length of the valves. Why is because he knows that if the stem is to narrow the lash will not hold spec! At which point the best fix is to replace the valves.

 

And of course there's more work to do once there but hopefully this brings a broader perspective to the reasons.

 

Just a reminder: the manuals only lists specs, required minimums and maximums, tools and procedures for trained mechanics, it in no ways teaches us theory or the specifics as to why or the consequences of....

[cowpuc]

Almost all OHC scoots I have worked on are not roller/ball bearing on the cams. They are line bored aluminum journals carrying the cam shaft which tend to be more susceptable to going high side on tolerances in the cam saddles over time,, especially on high mileage/poorly maintained engines (change your oil when the oil gets dark whether running full synthetic or dino,, unit motors running wet clutches that deposit clutch fibers into oil especially need clean oil). IMHO, making sure the cam lobe positioning for checking lash requires that the non testing lobes be putting pressure on valves to mitigate tolerance wear in the cam journals so that is added into the lash measurement.. If OEM spec on valve maintenance does not promote this (sometimes in dealing with scoots with valve overlap ground into cam grind, valve/cam pressure on non testing lobes is not spec), I like to set lash to spec in manual and then recheck with pressure on in different cam position.

IMHO, valve to valve seat wear is most common loss of lash tolerance causing valves to go tight.. This can be from either valve face wear or seat wear or both.. Modern valve/seat composition has greatly reduced a lot of issues causing tolerance loss and now adays, IMHO, the most common cause of failure/need for maintenance is abuse from not being ridden and corrotion taking place from lack of use.

Side note,, about the new Venture and valve maintenance.. I was recently chatting with a friend who spins wrenches at the local Yam shop.. He commented that he had a new one in that he adjusted the valves in and was not able to get it to quiet down and was thinking another cam/lifter replacement under warranty.. Chatting with him, something dawned on me,,, I asked him if he checked both valves being operated by the hydraulic uni cam being used in the new one.. He said he had checked the valve under the adjustment screw as that was the only valve adjustment there was.. I told him that I would actually also check the mating valve as face/seat loss on the valve under the adjustment screw could actually increase lash on mating valve as the adjustment valve lifted up the rocker.. Scratched his head, he nodded and said I will let you know - sounds possible..

[jfman]

I had one intake valve on my bike where this phenomenon happened:

 

The clearance as per the book with the lobe on the side was "adequate". right at .10

 

After replacing shims all over the bike, I rechecked the clearance for all 16 valves.

 

The same valve now with the lobe straight up had…. drumroll……. no clearance at all or not enough to fit my smallest shim on my set.

 

When you arent on the lobe of the cam, I dont care which section of the cam you are on, no clearance is bad because it means that soon the valve wont shut properly.

 

I was worried the vlave was toast so I squeezed some fuel in the actual port with a syringe to check if the valve held the fuel. Luckyly it did.

 

In the end I did not want the bike to run at no clearance so I called the Yamaha dealer and ordered another thinner shim for this one valve.

 

This was the most worn our valve on my bike btw.(running the thinnest shim)

[Bob K.]

Morning Bob, first I recognize your confidence, and I certainly see how you reasoned thru the problem:thumbsup2:

 

I'm going to skip past mass, heat, and expatiation's tho they are definite considerations when developing required lash.

 

The "stretch" in in the valve stem length! The stem is always under shear load hot or cold. When the power is on the constant slamming of the valve at high temperature causes the stem to elongate, this also causes the stem diameter to reduce, and as a result the guides diameter also falls out of spec!

 

The longer this above mention remains out of spec the more wear to the lobe in unexpected places!

 

When the required shim schedule becomes no longer adequate it is time to open and replace or regrind.

A machinist will for example first check the stem specs before he/she chooses to lap and grind the length of the valves. Why is because he knows that if the stem is to narrow the lash will not hold spec! At which point the best fix is to replace the valves.

 

And of course there's more work to do once there but hopefully this brings a broader perspective to the reasons.

 

Just a reminder: the manuals only lists specs, required minimums and maximums, tools and procedures for trained mechanics, it in no ways teaches us theory or the specifics as to why or the consequences of....

Ah, got it. You were talking about the valve stem not the cam lobe.

 

I'm trying to follow your explanation. Your claim, if I understand it correctly, is that the only way we can determine valve stem stretch correctly is if we take the measurement from where Yamaha tells us to take the measurement on the lobe...which is in a different place for Cyl 1 & 3 than it is for 2 & 4. Does that mean that Yamaha thinks the valve stem stretch would be different between the front and rear cylinders and that's why Yamaha is having us measure in different places on the lobes?

[Bob K.]

I had one intake valve on my bike where this phenomenon happened:

 

The clearance as per the book with the lobe on the side was "adequate". right at .10

 

After replacing shims all over the bike, I rechecked the clearance for all 16 valves.

 

The same valve now with the lobe straight up had…. drumroll……. no clearance at all or not enough to fit my smallest shim on my set.

 

When you arent on the lobe of the cam, I dont care which section of the cam you are on, no clearance is bad because it means that soon the valve wont shut properly.

 

I was worried the vlave was toast so I squeezed some fuel in the actual port with a syringe to check if the valve held the fuel. Luckyly it did.

 

In the end I did not want the bike to run at no clearance so I called the Yamaha dealer and ordered another thinner shim for this one valve.

 

This was the most worn our valve on my bike btw.(running the thinnest shim)

 

Interesting. In your case, measuring at the spot on the lobes where Yamaha directs us to measure resulted in an incorrect valve lash for that particular valve. Were there any indications that that lobe was worn oddly or machined incorrectly?

[jfman]

Interesting. In your case, measuring at the spot on the lobes where Yamaha directs us to measure resulted in an incorrect valve lash for that particular valve. Were there any indications that that lobe was worn oddly or machined incorrectly?

 

Yes but I only observed this for one valve. I checked others and did not have that issue.

 

BTW: nothing "looked" worn out by eye but this bike does have a lot of miles and poor oïl change practices according to sludge build up that I could notice Inside the motor. Impossible to know mileage of the engine because it's a 1300cc motor that was swapped in a 1985 for this bike.

 

The bike does start and run just fine even prior to me adjusting valves.

[Patch]

Ah, got it. You were talking about the valve stem not the cam lobe.

 

I'm trying to follow your explanation. Your claim, if I understand it correctly, is that the only way we can determine valve stem stretch correctly is if we take the measurement from where Yamaha tells us to take the measurement on the lobe...which is in a different place for Cyl 1 & 3 than it is for 2 & 4. Does that mean that Yamaha thinks the valve stem stretch would be different between the front and rear cylinders and that's why Yamaha is having us measure in different places on the lobes?

 

 

There's a lot to this so let be mention some reminders: everything about or that bolts to the heads begin around air induction, this leads the way to estimated ratios, percentage of fills and efficiencies. If we get that right and we maintain it thru service then we can maintain power bands, after all these are performance machines.

The valve seating is the dummy end of the combination of measurements all the way up to atmosphere beyond the air box induction.

The valve seating should be a given but it must be confirmed and way to often it is simply ignored as an essential step.

Can you lock compression?

What is the cause of compression readings?

Then the lash what role is it playing if any in the compression readings?

 

What temp is the engine when checking lash?

When the engine is at operating temp the measurements are not what they are when you are checking lash!

So lash has to be a compensating number. It should not be more or less it should be as true as it can be. The distance and duration is effected by cam design it is also true that lash can alter it. Too tight and loss of heat, initial vacuum, backfire, exhaust issues, and of course compression losses.

 

The mileage and overall condition should guide your initial approach to the maintenance you are scheduling.

In the case of cam and your question the intent is to have it sing in harmony and so it is wise to measure in more locations then lit it time to restore, reason the why's and make the best choices you can given budget and plans.

 

A quick comment on COWPUC's comment: " They are line bored aluminum journals carrying the cam shaft which tend to be more susceptable to going high side on tolerances in the cam saddles over time,, especially on high mileage/poorly maintained engines (change your oil when the oil gets dark whether running full synthetic or dino,,"

 

Yes and certainly a drawback: But in theory it shouldn't yet as you say we know it is a consequence of lobe pressures and rotation. The journals should not be able to cause such wear. And yes I agree with your reasoning as to why and also how to reduce the friction effects... for what its worth;)

Again how would we know or how can we check this type of wear issue? The same way we would at the crank, by performing another step, measure oil pressure!

 

I'd like to also say that Jfman (Jeff man?) solution suggests that at some point that head had a sicking bucket, so I think because it was one valve his decision makes sense! But if it were more than the one, no its teardown time;)