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Discussion Starter #1
Ok. So, I’m in the midst of performing my 20k service. I’m trying to do my valves.

I took initial measurements, and then removed the rocker arms to measure the shims. Then, when I re-measured clearances after, they weren’t the same.

I find it exceedingly difficult to get the cam lobes in the right spot and both the Haynes manual and official shop manual are kind of vague as to the placement (having to move the rear wheel is to rotate the engine also makes it difficult). There’s also an extra little bump on the exhaust cam that isn’t mentioned anywhere and I’m not sure if I should measure before or after this touches the rocker.

Since this is a rocker arm setup with rollers, I’m essentially also measuring the free play of the rocker, as opposed to the direct distance between the cam and the valve like my other (much easier to maintain) bike.

Is the cam perfectly round outside the “lobe” part?

The official shop manual specifies to re-tighten the inner bolt first when replacing the rocker arm, the Haynes manual does not. It also specifies to tighten it to 10nm, however I don’t have a small torque wrench, only a large one. So, I’m tightening, but being careful to not over tighten. Could this account for some
of the discrepancy?

Has anyone else run into frustration with this? The discrepancy in the readings is anywhere from .01mm to .03mm
 

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Why is .01 to .03 a problem?
The specs for the R clearance range for example: Intake is 0.05 - 0.13 mm and for Exhaust 0.08 - 0.18 mm.
 

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Discussion Starter #3
Why is .01 to .03 a problem?
The specs for the R clearance range for example: Intake is 0.05 - 0.13 mm and for Exhaust 0.08 - 0.18 mm.
So is it normal for there to be a discrepancy? I'm just worried that I'm doing something wrong. If I get two measurements that are .03 off, that's more than a whole shim size of difference. So, if I measure an intake clearance .05 once, and .02 once, how am I to know how many shim sizes to go down?

And I know there's a tolerance for a reason, but I've also read in a lot of places that it's good to shoot for the middle of the range and round up if needed.
 

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So is it normal for there to be a discrepancy? I'm just worried that I'm doing something wrong. If I get two measurements that are .03 off, that's more than a whole shim size of difference. So, if I measure an intake clearance .05 once, and .02 once, how am I to know how many shim sizes to go down?

And I know there's a tolerance for a reason, but I've also read in a lot of places that it's good to shoot for the middle of the range and round up if needed.
It isn't normal for there to be a discrepancy but I think the clue is in the name "feeler gauges", it's not like using a micrometer when it's down to feel. When I did my clearances on the Daytona I think I rechecked mine three times and got slightly different readings on a couple of valves nearly every time, although I think that was partly the very tight access and having to make the correct size from 2 or 3 feeler gauges.
I'm not familiar with doing clearances on a Thruxton but the exact position of the cam shouldn't be important as long as the cam lobe is opposite where you are measuring (not to a degree or two), the base circle of the cam should be accurately ground.
It would definitely be easier and more accurate to turn the engine on the crank rather than using the rear wheel, not sure which cover you take off on the Thruxton?
Putting them back to middle tolerance is a good idea while you're in there anyway, there's no point leaving any that are just within tolerance because they might go out before the next check.
I know with bucket and shim adjustment, and presumably it's the same with the roller type, exhaust valve gaps normally close up and inlet valve gaps normally open up over time so bear that in mind if you're rounding them up or down around the middle tolerance.
 

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Discussion Starter #5
It would definitely be easier and more accurate to turn the engine on the crank rather than using the rear wheel, not sure which cover you take off on the
I just realized I didn't even specify my bike, haha. I'm on a 2017 T120. so, same valve procedure as the thruxton. As far as I can tell, there's no easily accessible way to turn the crank. My other bike has an easily accessible 19mm nut under the points cover that turns the engine with in neutral. I'd love something like that on the T120.

as far as where to shoot, I've seen a few different schools of thought. Aim for the middle, aim for the top on exhaust, bottom on intake. aim for the top when the bike is new, aim for the bottom when the bike is old. I'm going with as close to the middle for intake and exhaust.
 

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It's easy to get paranoid about this job. Forget the precise initial clearance, cam position and the torque wrench. Your measurement consistencies are within 'tolerance'.

Keep in mind also that when you first measure the clearance it has been well and truly hammered into final position. Once you replace a shim, and even more so if you use assembly lubricant, it will definitely not be bedded in. Ideally best not to re-measure, but as a 'stuff-up check' do a rough measure and if it's a bit tight leave it.

As for using the rear wheel, for mine this much better than taking covers off.

Cheers.
 

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Stepped feeler gauges (also known as go/no-go gauges). If you don’t have a set, get them.

Also, if you use the rear wheel to spin the engine, put the bike in the highest gear.
 

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Good job, pat yourself on the back. You just saved yourself a bunch of money and learned so things. That's a Win, Win.

I would recommend getting yourself a torque wrench that will be in the lighter torque areas for that job. Two things need to be consistent. The torque of the cams needs to be exactly the same to get accurate repeatable measures and the temperature should be as close to the same each time to get repeatable readings.

Safe riding.
 

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I just started my first valve check on my 2016 T120. Anyone else have a LOT of trouble getting the valve cover off? That was the most difficult valve cover removal ever. I've done all my previous bikes included inline fours and never had near as much trouble getting the valve cover off.
 

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I just started my first valve check on my 2016 T120. Anyone else have a LOT of trouble getting the valve cover off? That was the most difficult valve cover removal ever. I've done all my previous bikes included inline fours and never had near as much trouble getting the valve cover off.
Yes it's a pain. I've done my 2016 Thruxton R and I found that taping up the hose clip on the radiator filler cap hose stops it scratching the rocker cover. Remove as much clutter from the top frame tube as you can. You can't shortcut the process by thinking you can leave things in place like the immobilizer unit. It all has to come off. A bit of gentle force to move the radiator top hose is also required. You can just squeeze the cover through the gap by tilting it and pulling it towards you from the the rhs of the bike

On reassembly, I used a smear of "Welseal" on the rocker cover gasket to help it stay attached to the rocker cover when refitting.
 

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Discussion Starter #12
I just started my first valve check on my 2016 T120. Anyone else have a LOT of trouble getting the valve cover off? That was the most difficult valve cover removal ever. I've done all my previous bikes included inline fours and never had near as much trouble getting the valve cover off.
What part of it was difficult? There are definitely some clearance issues. I found holding the radiator hose completely out of the way with one hand allowed it to be removed easily with the other. That is, assuming you’ve already removed the immobilizer, ignition wires, etc from that area.
 
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