Exhaust Valve clearance

Sbinf74

Sbinf74

Developer
Developer
Hi, looking at the valves of my motorbike I noticed that the exhaust stem, where the tappet works, has a convex surface facing upwards. I wonder how it is possible to adjust the valve clearance since we would be working on the edge with the feeler gauge.

I only have this photo but the problem is visible.
Has anyone who is more experienced ever noticed this?
1.jpg
2.jpg
3.jpg
 
since we would be working on the edge with the feeler gauge.
Click to expand...

I do not understand what the problem seems to be. The feeler gauge is inserted between the valve and the "hammer". that determines the clearance. it matters not IMO if the surface is convex or flat.
 
I have noticed that inserting the feeler seems to be "easier" if coming in from the convex sides. Just a field observation. Particularly when working on the intake.
 
It looks like your exhaust stem top is concave? It has a hollow in the centre? If that is what you are asking about then a feeler gauge can't work. You can use a different device which will measure the gap from ontop of the rocker, a dial gauge with a little leg which is held in place and measures small movements accurately.
Alternatively for a coarse setting you can turn the rocker adjuster down till it just touches the valve stem top then turn the adjuster 1/4 turn back. The thread pitch is 1mm so 1/4 turn will give 0.25mm, it's crude but can work in the short term.
 
Ottimo, hai capito il problema. la cosa strana è che alcune valvole nascono così, non è un problema di usura. E' decisamente di bassa qualità
 
It has not happened on my own bike but have seen a few comments from owners that have the same issue. Every dished valve stem I have seen on Himi's has been the exhaust valve. Don't think it is a real big problem, a dial gauge can set the clearance nicely if you can get one to fit in the space above the rocker covers.
You could always cut the tip of the correct feeler gauge down to a narrow finger and put a curve in it so it follows the dished shape and can set the gap? Might be worth a try.
 
I have seen this on OEM and other Valves, mostly the Exhaust.
Perhaps it is quality related and as the Exhaust of course gets much hotter it fails quicker.
Easy solution is as suggested, to make the adjustments by the number of turns back from tight.
Loose Tappets exacerbate the problem of course so tight is better.
 
Dool said:
I have seen this on OEM and other Valves, mostly the Exhaust.
Perhaps it is quality related and as the Exhaust of course gets much hotter it fails quicker.
Easy solution is as suggested, to make the adjustments by the number of turns back from tight.
Loose Tappets exacerbate the problem of course so tight is better.
Click to expand...
I'm starting to think that the recommended clearance for the ex valve is way too much and causes this premature wear.

probably a more reasonable value would be like 0,18-0,20max, more in line with other bikes...

I think 0,23-0,25 is too much, specially if they make a mistake in the factory during first assembly...
 
Smart people use Dial Gauges,
DAMHIK :cool:

@Sasa may contribute shortly
:ROFLMAO::ROFLMAO:
 
Well it turns out that if the tip of your valve is worn things could get out of control quickly!

I positioned the tip of the dial gauge on the squared tip of the tappet register and here are the results:

WhatsApp Image 2024-03-03 at 09.40.15_501eb075.jpg
WhatsApp Image 2024-03-03 at 09.40.16_c8e9afbf.jpg


The clearance was adjusted to 0,23mm.

The depression in tip of the stem adds up almost 0,19mm by itself!!!

To add insult to injury a bigger than needed clearance exacerbates the issue, creating a vicious cycle.

I dialed back the value, using the dial gauge this time, and now the bike is super quiet!

Long story short: check yours with this method!!!
 
Sasa said:
Well it turns out that if the tip of your valve is worn things could get out of control quickly!

I positioned the tip of the dial gauge on the squared tip of the tappet register and here are the results:

View attachment 1638View attachment 1639

The clearance was adjusted to 0,23mm.

The depression in tip of the stem adds up almost 0,19mm by itself!!!

To add insult to injury a bigger than needed clearance exacerbates the issue, creating a vicious cycle.

I dialed back the value, using the dial gauge this time, and now the bike is super quiet!

Long story short: check yours with this method!!!
Click to expand...
@Sasa you mean you pressed the stem tip down against this part?
1709567553414.png
 
Sasa said:
I'm starting to think that the recommended clearance for the ex valve is way too much and causes this premature wear.

probably a more reasonable value would be like 0,18-0,20max, more in line with other bikes...

I think 0,23-0,25 is too much, specially if they make a mistake in the factory during first assembly...
Click to expand...
The upper range always makes my bike very weird. No sharp throttle response and very loud noise. Always used a feeler gauge at a tight 0.08.-0.23, that is feeler slinding with certain resistance and not smoothly.

Willing to try the dial.
 
@Sasa : I have no clue how to use this instrument and gauging by the fact that our workshop does not even use a torque wrench it is save to say my mechanic does not either. So first thing: how to obtain a dial gauge from Amazon? They offer a range from 2500 to 15,000 INR - will the cheap one do? what are the differences. please have a look here and suggest a model (cheaper = better for me):

 
Here in India it may actually be cheaper to replace the valves - a pair is under 1000 INR and the work is about the same. At what KM approx. does this deformation occur to a degree where it leads to measurable differences in clearance? I have a 500cc Hima with over 50.000 km and the tappet noise is still in the "acceptable" range (with HT-b cam so a bit louder anyway).
 
sam2019 said:
@Sasa : I have no clue how to use this instrument and gauging by the fact that our workshop does not even use a torque wrench it is save to say my mechanic does not either. So first thing: how to obtain a dial gauge from Amazon? They offer a range from 2500 to 15,000 INR - will the cheap one do? what are the differences. please have a look here and suggest a model (cheaper = better for me):

Click to expand...
you don't require the precision to be exactly 0,01, so i guess one of the cheap one would give you a good estimation.

It goes without saying that the more expensive the more precise.

Those are all knock-off of a real mitutoyo, the real ones are 100$+, but they work reasonably well...
 
well, lets not go into politics here - discuss trump and this other idiot in section 42
 
Thread pitch is the easy answer I believe ;)
From closed to the correct clearance is a number of turns and that is the Magic of math or something 😎.
 
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