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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
Joined: 16 Aug 2013 Karma :
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Posted: 10:50 - 13 Oct 2018 Post subject: |
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Different metals expand at different rates. Look up bimetal strips. ____________________ trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050 |
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Hong Kong Phooey |
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Hong Kong Phooey World Chat Champion
Joined: 30 Apr 2016 Karma :
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Posted: 16:22 - 14 Oct 2018 Post subject: |
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There's predominately two types of wear with valves, valve to head interface and cam to bucket wear.
If the cam profile is worn then clearances get larger.
If the valve seats are gone then clearances get tighter as the valve can ride higher in the seat and push more on the bucket.
Shims don't wear under normal circumstances.
Manufacturers calculate the differential expansion rates at the design stage, and If within the normal operating temperature range of the engine, plus some in built tolerance, it should not be an issue.
Edit, just had me tea.
Above was under 'normal' circumstances.
Obviously the measurements are quoted stone cold, and give a range of tolerance.
If you are too tight, then as the engine heats up the clearances get tighter. That's not differential though, it's natural expansion of the valve, mainly in the length. This pushes more on the bucket, too much and it won't close properly. This means compression leakage and harder to restart when hot.
Too slack, and the tappety sounds gets better as it warms up as there's less room to move around in. ____________________
'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8
Last edited by Hong Kong Phooey on 17:04 - 14 Oct 2018; edited 3 times in total |
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Fizzer Thou |
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Fizzer Thou World Chat Champion
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Fizzer Thou |
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Fizzer Thou World Chat Champion
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Riejufixing |
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Riejufixing World Chat Champion
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Islander |
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Islander World Chat Champion
Joined: 05 Aug 2012 Karma :
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Posted: 20:29 - 15 Oct 2018 Post subject: |
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@Fizzer Thou have a read of this:
https://en.wikipedia.org/wiki/Thermal_expansion
If you can't be arsed, then just scroll down to the bottom of the article to the table of materials and compare the different metals. |
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Ste |
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Ste Not Work Safe
Joined: 01 Sep 2002 Karma :
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Posted: 20:57 - 15 Oct 2018 Post subject: |
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Different metals, or any other solid for that, expand at different rates when heated.
This is basic GCSE science, c'mon people. |
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Fizzer Thou |
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Fizzer Thou World Chat Champion
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Posted: 13:17 - 03 Nov 2018 Post subject: |
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An interesting article and several points are worthy of note :-
Quote One:One of the reasons for the poor performance of cold car engines is that parts have inefficiently large spacings until the normal operating temperature is achieved.
There is no in between when the engine is slightly warm or slightly cooled.An engine will only work efficiently when at its proper operating temperature.
Quote Two: Induction shrink fitting is a common industrial method to pre-heat metal components between 150 °C and 300 °C thereby causing them to expand and allow for the insertion or removal of another component.
When I have installed new valve guides there was a definite difference between inserting new cast iron and new aluminium /bronze guides.The reamer that had to be used to give that final clearance with the stem of the valve is more critical with one than the other.
As for a bi-metallic setup,the only place that I can think of where this is used is in a thermostat.When the coolant gets to the required temperature,the valve opens and lets coolant pass into the heat exchanger.From what I understand,engines work best at 65-70 degrees centigrade. ____________________ Just talk bikes.What else is there?
Always have a 'Plan B' |
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Fizzer Thou |
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Fizzer Thou World Chat Champion
Joined: 06 Aug 2011 Karma :
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Posted: 13:26 - 03 Nov 2018 Post subject: |
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Nobby the Bastard wrote: | So, have you left the shims until there was no cleqrence or even negative clearance? If not what makes you so sure that you are right? |
Not personally,but several friends have had this problem.
When one friends R1 5PW just would not restart when out on a hot days ride,we got the bike back to my workshop and found that all cylinders had zero clearances measured when cold.This made things difficult to determine what size shim to fit until we had removed the cams,measured the fitted shim,then guessed at the correct size to fit.This took several attempts to get right and having a large selection of shims of all sizes did help.
When another friends FZR1000Ru had problems starting even from cold,the majority of the shims needed to be changed for thinner ones.The same procedure was needed as for the R1 5PW.
In both cases,the shims had never been checked at the relevant service intervals,even though the bike shop had been paid to check the clearances.The R1 5PW was at 26,000 miles and the FZR-Ru was at 32,000 miles when both bikes finally stopped working. ____________________ Just talk bikes.What else is there?
Always have a 'Plan B' |
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Islander |
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Islander World Chat Champion
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ThatDippyTwat |
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ThatDippyTwat World Chat Champion
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Old Thread Alert!
The last post was made 5 years, 192 days ago. Instead of replying here, would creating a new thread be more useful? |
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