Z1OwnersClub GB

Morning all.
How much metal is it safe to remove from the tip of a new valve?
Dropped an exhaust valve and have had the seat re-cut to remove the scar but had to take quite a bit of metal off. Have replaced with a new set of valves but have no valve gap even with a 200 shim so was going to shorten the stem by 1mm to see if i can get the gap back.

0.3mm is the recomended max...

Ok! Going by the book you can take 0.3mm off the valve stem to gain some shim clearance back.
Taking more and you are risking the bucket riding on the collets and retainer and dropping the valve again and going by the book again you are now really in fitting a new seat territory.
Another common solution is to fit a bigger valve as this will sit on the wider portion of the seat and should get the clearance back ( ideally the whole head gets bigger valves )
However! it is possible to trim the collets and retainer by 1mm to allow further shortening of the stem.
I've done it plenty of times with no issues.

Thanks for the advice. Shaving the collets and retainer seems the most straightforward option then. I only suggested 1mm as I currently have no gap and it would hopefully bring a gap back. It may need less than that to get a gap. is there a way of measuring the valve height as it sits in the head to see if it's tenths of a mm or millimetres i'm looking for? Could i remove the buckets and put a straight edge over the four exhaust valve stems? That sounds like a three pairs of hands job but would a straight edge see the tops of the stems in situ does anyone know?

I have used some sub 2.0 ground shims i have as a guide to give you what you need to take off.simple maths if you know the shim thickness.

and that's what i love about this forum. So much experience of familiar problems = several different 'fixes'. If i got a shim ground to 1mm, would the cam lobe still have clearance?

ChrisB wrote:Thanks for the advice. Shaving the collets and retainer seems the most straightforward option then. I only suggested 1mm as I currently have no gap and it would hopefully bring a gap back. It may need less than that to get a gap. is there a way of measuring the valve height as it sits in the head to see if it's tenths of a mm or millimetres i'm looking for? Could i remove the buckets and put a straight edge over the four exhaust valve stems? That sounds like a three pairs of hands job but would a straight edge see the tops of the stems in situ does anyone know?

Should have asked first that this is for a shim over bucket Z900/Z1000/Z1100 isn't it ???
otherwise the following is of no use as this can't as easily be done with the shim under set up...

The minimum valve stem height is 37.2mm, Max is 38.2.
You want to be closer to the min figure.
Putting a straight edge across the adjacent stem tops won't be accurate enough,you need to take a direct measurement of the installed height.
With just the valve pushed firmly in its seat and all the springs and spring seat removed you measure down from the stem tip to the alloy of the head.
You can use a Vernier depth gauge but it is tricky because of the valve guide getting in the way and can give inconsistent results and it really needs the special go/no go depth tool to get the correct reading
Look towards the bottom on page 7 of my Z9 road racer project build (top of 2nd page in projects)to see pics of the tool i made and the trimmed retainers.
Once you have the stem height you will know how much needs taking off the stem, collets and retainer.

ChrisB wrote:and that's what i love about this forum. So much experience of familiar problems = several different 'fixes'. If i got a shim ground to 1mm, would the cam lobe still have clearance?

You cannot use a ground shim to fix the problem it will shatter or fail rapidly in use.
PAULJAC47 is only suggesting using a thinner ground shim to get a gap you can measure to determine how much stem to trim.
You need a thin shim of a known thickness to enable this to work.

Yes, i got that but thanks for the warning! Does this mean that even if i only need to shorten the stem by 0,3mm or less i'll also need to trim the collets and retainer? Are they all pretty flush then, i always assumed there would be some clearance and that the underside of the bucket only touches the valve stem.
Got to say, i've read your Z9 Roadracer post before and was super impressed with the skills and the end result. Absolutely brilliant and fascinating watching your bike take shape. Regarding the height measuring tools, how do you use them? How do you take a reading from the tool top to the stem, with a vernier? Thanks again for your patience with a keen but poorly equipped enthusiast!

ChrisB wrote:Yes, i got that but thanks for the warning! Does this mean that even if i only need to shorten the stem by 0,3mm or less i'll also need to trim the collets and retainer? Are they all pretty flush then, i always assumed there would be some clearance and that the underside of the bucket only touches the valve stem.

You have to have the stem slightly proud of the collets and retainer so that the bucket doesn't ride on them ( even though there is a raised portion on the underside of the bucket that sits on the stem) so it's best to at least skim the retainer and collets by the same additional amount you remove from the stem after the factory recommended 0.3mm just to keep at least the same clearance between parts.
What i do is take an old valve, set it in the lathe chuck with the collets and retainer fitted , skim the whole lot flush then take off what i need to match the amount off the stem..
I've done a few like yours with minus clearance and took up to 1mm off to get back to shims in the 280 range.
I already have a skimmed valve that I just match the collets and retainer to.
If you do it, don't just go the minimum to get some clearance as it may soon close up once the new valves have settled.
0.3mm may only put you with a 220 shim and you really need to be at 255/260 minimum to give reasonable future adjustment so you are probably looking at around 0.8mm.
The height tools (one is max height and the other is min height) are initially simple quick check go/no go tools that make it easy to see if any stems are close to the maximum installed height and may need trimming.
Once this is established i use the min height one and vernier to establish how much needs removing.

So just to keep you posted, three of my new exhaust valves gave a shim size of around 220-230 so i took 0,30mm off these to get them into the 250-260 range. The valve which had no clearance, i pushed in a piece of 0,35mm shim stock after removing the 200 shim i had in there. This allowed me to rotate the cam lobe away and measure a gap of 1.64mm. I then used your excellent advice zed1015, put an old valve in the lathe to hold the collets and retainer and springs tight and took around 0,80mm off the retainer and collets. Job done and five shims currently in the post to Jerry for swapping out. All clearances now between 245 and 270 so should be back in the bike next week.
Thanks again zed1015.