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Valve clearances.

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Nobby the Bastard
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PostPosted: 10:50 - 13 Oct 2018    Post subject: Reply with quote

Fizzer Thou wrote:
Nobby the Bastard wrote:
Really. The head typically expands more than the valves (different metals) and so the clearances open up as the head warms up.
Yes, it will be a bastard to start, but as fuel burns it warms up and will suddenly start and then work fine until it gets a chance to cool down.

WHAT!!!!!

All metals expand as they heat up.If there is little or no valve clearance as the engine gets hotter the valves will be held open.

You really do need to read what you have posted.It does not follow at all Shocked Rolling Eyes Thumbs Down


Different metals expand at different rates. Look up bimetal strips.
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Nobby the Bastard
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PostPosted: 11:04 - 13 Oct 2018    Post subject: Reply with quote

I know that's what happens because it happened on my fz. Went through the ignition and the carbs trying to fix the fault with no success.

A mechanic friend suggested that I have the clearances checked as they tend to close up rather than open up. Got a bike shop to check them. They described them as murder tight and the problem went away.

Until about a year later. Then it recurred.

This time I found out how to do it myself (5 vqlve heads are a bit of a tough one to do valve shims for your first attempt ) and found that the bastard bike shop had only done the exhaust valves.

Once the inlets were done the problem went away again and didn't recur at any point until the bike got stolen.

So I do know what I'm talking about.

Would you like me to find the thread on the fz forum that I made at the time?
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Hong Kong Phooey
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PostPosted: 16:22 - 14 Oct 2018    Post subject: Reply with quote

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.
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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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PostPosted: 16:47 - 14 Oct 2018    Post subject: Reply with quote

So, what happens when clearances are marginal because they've not been reset and the engine does 160 miles in a hit?

When the engine cools the head contracts slightly more than the valves, resulting in the clearance going negative (the valves being fractionally open).

A little heat and the head expands fractionally more than the valves, meaning that they shut.
And
Why do you think that the clearance quoted in the first place?it assumes that the head will expand more to take up the clearence.
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Fizzer Thou
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PostPosted: 12:16 - 15 Oct 2018    Post subject: Reply with quote

Nobby the Bastard wrote:
The best indicator of clearences getting too tight is the bike not starting until it's warmed up but then runs fine.


Nobby the Bastard wrote:
Really. The head typically expands more than the valves (different metals) and so the clearances open up as the head warms up.
Yes, it will be a bastard to start, but as fuel burns it warms up and will suddenly start and then work fine until it gets a chance to cool down.

When the engine cools the head contracts slightly more than the valves, resulting in the clearance going negative (the valves being fractionally open).
A little heat and the head expands fractionally more than the valves, meaning that they shut.

And why do you think that the clearance quoted in the first place?it assumes that the head will expand more to take up the clearence.


Oh dear.....
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Fizzer Thou
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PostPosted: 12:25 - 15 Oct 2018    Post subject: Reply with quote

Nobby the Bastard wrote:
So, what happens when clearances are marginal because they've not been reset and the engine does 160 miles in a hit?

When the engine cools the head contracts slightly more than the valves, resulting in the clearance going negative (the valves being fractionally open).

A little heat and the head expands fractionally more than the valves, meaning that they shut.
And
Why do you think that the clearance quoted in the first place?it assumes that the head will expand more to take up the clearence.


When the engine is up to normal running temperature then clearances are reduced.That is what engines do.They are engineered into the design.There is no in between when the engine is slightly warm and slightly cooled.If the valve clearances are within service limits then the engine will run correctly.If they are too tight then problems occur.

I fully understand about the FZ.My FZR-R is exactly the same.As is my YZF-R1.

Reshimming after lapping in all twenty valves is a lot easier when the engine is on the bench Wink

http://i1073.photobucket.com/albums/w384/Rhencullen5/R1%20Engine%20Rebuild/Picture086.jpg~original
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Nobby the Bastard
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PostPosted: 15:48 - 15 Oct 2018    Post subject: Reply with quote

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?

I have done and know what the symptoms are as a result.
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Nobby the Bastard
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PostPosted: 16:08 - 15 Oct 2018    Post subject: Reply with quote

https://uk.answers.yahoo.com/question/index?qid=20101210020921AAJUrl4
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Riejufixing
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PostPosted: 16:23 - 15 Oct 2018    Post subject: Reply with quote

Nobby the Bastard wrote:
The best indicator of clearences getting too tight is the bike not starting until it's warmed up but then runs fine.


Doesn't that depend on the configuration of the engine? For an engine with the cam bearing "directly" on the valve tips, yes. For all others?
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Nobby the Bastard
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PostPosted: 16:46 - 15 Oct 2018    Post subject: Reply with quote

It will depend on the engine. High revving shim and bucket tend to close up. On engines that tend to open, they just get a bit tappy.
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Islander
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PostPosted: 20:29 - 15 Oct 2018    Post subject: Reply with quote

@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. Thumbs Up
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Ste
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PostPosted: 20:57 - 15 Oct 2018    Post subject: Reply with quote

Different metals, or any other solid for that, expand at different rates when heated.

This is basic GCSE science, c'mon people. Laughing
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stinkwheel
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PostPosted: 21:33 - 15 Oct 2018    Post subject: Re: Valve clearances. Reply with quote

ThatDippyTwat wrote:


If you're running a gear driven VFR - fair enough. Otherwise, I'd have a check at prudent intervals. Not necessarily specified mileages, but sensible ones.


I checked the clearances on my last 750 at 45k miles. To my certain knowledge this was the first time they had ever been checked. They were all within tolerance.

On my current one, I took the cams out of the current Japanese home market engine at 16k miles. I replaced them with a set of cams from a pair of scrap heads of unknown mileage from a European model made 3 years later... I had to buy two shims and even those weren't strictly necessary.
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Fizzer Thou
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PostPosted: 13:17 - 03 Nov 2018    Post subject: Reply with quote

Islander wrote:


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.
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Fizzer Thou
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PostPosted: 13:26 - 03 Nov 2018    Post subject: Reply with quote

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.
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Islander
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PostPosted: 17:29 - 03 Nov 2018    Post subject: Reply with quote

Fizzer Thou wrote:

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.


Standard flasher relays use a bimetallic strip - which is why they're load dependent. Thumbs Up
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ThatDippyTwat
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PostPosted: 18:17 - 03 Nov 2018    Post subject: Re: Valve clearances. Reply with quote

stinkwheel wrote:
ThatDippyTwat wrote:


If you're running a gear driven VFR - fair enough. Otherwise, I'd have a check at prudent intervals. Not necessarily specified mileages, but sensible ones.


I checked the clearances on my last 750 at 45k miles. To my certain knowledge this was the first time they had ever been checked. They were all within tolerance.



113K - Not been checked since 45K (I know the PO). Nothing makes me think they need checking.
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