Your thoughts on valve clearances

[Mr Fro]

I've just found my valve clearances are almost all too tight so I'm going to have to buy a party pack of shims to sort them out.

The question is: whereabouts in the range do you aim for when you do yours?

Say for example the tolerance is 0.18 to 0.25mm - would you go for 0.18, midway at 0.21/0.22 or 0.25?

[Tango]

I aim for midway.....coz you never know which way they're gonna go once they're set.....

[mattycoops43]

I aim for midway.....coz you never know which way they're gonna go once they're set.....

 

Well..... they are going to close up as they wear. I never worry about ones that are a bit near the upper end of the scale.

[megawatt]

If they closed up before, they will close up again. Go for maximum clearance, ie thinnest shims.

[runningman]

Heard it said that a noisy tappet is a happy tappet. Therfore, upper end of the range.

[Fozzie]

If it tightens once, it will again so go for the opposite end of the spectrum and buy yourself more time

If it loosens, chances are it will again but I'm always dubious as I've heard one bike loosened off a bit over 2 checks, then remained the same, then tightened. Think the wear on the valve accelerated past that of the shim bucket/cam lobe.

But it sounds consistent, so put the thinner shim in

[Mr Fro]

Interesting opinions - cheers chaps!

Normally I'd go mid way but seeing as it's a track toy I was thinking that tighter clearances would equal higher valve lift... I've only done the old fashioned screw and nut jobs before and never changed shims so I'm going to make a note of what went where when I change them out, just to be on the safe side!

I'm curious as to why they were mostly too tight in the first place - could be someone had done some fiddling in the past but I think it's unlikely seeing as the engine seemed standard when I got it. The joy of previous owners!

[Stu]

Track bike?

For power tight side but not too tight

For longevity loose side

If you go tight you get more valve open space more air and fuel but you have to check them twice as often

[mattycoops43]

They are mostly too tight because as the valves wear the clearances drop. perfectly normal.

[Mr Fro]

They are mostly too tight because as the valves wear the clearances drop. perfectly normal.

But then the lobes and rockers will also wear!

Mid way it is then, especially seeing as it spends quite a lot of it's life at or just beyond the redline.

[Stu]

Its the valve seats that wear you don't get a lot if any wear on the cams unless you run without oil

The buckets can wear as can the shims

You are supposed to measure the shims to check the size and not go by the stamped size

[Tango]

I'm sure someone on here had an Excel spreadsheet with a macro that you could put your target clearance, measured clearance and the shim sizes you already have fitted and it would juggle them and then give you a list of the shims you needed......can't remember who it was now.....

Yeah...the shims and buckets can wear....which will open the clearances.....so they don't always close....

Your clearances could have been set on the tight side by the previous owner .....

[Mr Fro]

I'm going to measure the current ones as I'm aware that they can lose a bit height.

I've made a little excel sheet already which I can post up if I can figure out how to do it and if anyone's interested.

[Stu]

All Haynes manuals have a chart in them

[Mr Fro]

All Haynes manuals have a chart in them

Yeah, I have a Haynes but I'm a sad git and had a few spare mins at work earlier.