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Old 21-11-05, 08:33 PM   #1
BillyC
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Default A question of valve clearance...

Okay, nothing outragiously technical, but something for those of some experience please:

When checking the valve clearances, you must rotate the engine crank, so that each piston is in a TDC position when taking the measurement.

You have to rotate the crank in the correct direction when doing this... my rather sheepish question is - what is the correct direction?

When looking at the crankcase on the left of the bike, do I go clockwise, or anti-clockwise?

TIA.
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Old 21-11-05, 08:40 PM   #2
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Anti-Clockwise.
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Old 21-11-05, 08:51 PM   #3
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Quote:
Originally Posted by Flamin_Squirrel
Anti-Clockwise.
Ta muchly!
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Old 22-11-05, 01:36 PM   #4
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Right... covers off, engine cranked to put the cams in the right positions, and the feeler gauge felt its way around. So, again, some queries for the more experienced among us:

My inlet clearances appear to be nicely within tollerance. The 0.10mm gauge slips in with a hint of tightness, getting tighter on the way to 0.20mm.

The exhaust outlet is a bit different. These were tight. I'd say that the front and rear were about 0.18mm, below the 0.20-0.30mm range. This strikes me as rather odd.... that an engine with over 20,000 miles on it should be this tight. Perhaps it's something that will wear with more time and miles?

The engine certainly was cold, and has been started only once in the past 3 months, last week. I'm guessing that my measurements indicate a machine that's still relatively un-worn, and that with time the exhaust clearance will increase.

No, really I'm just looking for reasons *not* to adjust this

Comments please, TIA.
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Old 22-11-05, 03:30 PM   #5
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Maybe it,s time to adjust the exhaust valves
after 20000 miles!!
Your exhaust valve clearence will not increase,it
will decrease as the valves"hammer"their way into
the cylinder head

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Old 22-11-05, 04:11 PM   #6
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The valve clearance check is scheduled every 15,000 miles, so at 20,000 miles it's slightly overdue, yes it is entirely normal to find some clearances out of tolerance - that why it's a scheduled check. That said the SV is known for not needing a lot of adjustment, that doesn't mean it's never needed though.

Generally speaking exhausts close up and inlets open a bit, so your finding the exhausts a little tight is not something that can be ignored. As you're going to be removing the cams I'd reset everything to as near the middle of the allowable range as is possible, that way it's odds on the longest period until it needs doing again.

Every time the inlet valve opens it receives a nice cooling rush of incoming gas, and when it's closed it dissapates heat through the valve seat, even though that's a small area for conducting away heat - every little helps - in short the valve itself has an easy life, and thus wear in the opening mechanism commonly outweighs the wear to the valve - thus the clearance often opens up a bit. Exhaust valves however don't have such an easy time, they get and stay very very hot, their primary way to dissapate heat is the thin ring of the valve seat, and a little up the stem, everytime the long suffering exhaust valve opens it gets fried with gas at/near combustion temperature - typically 300-700C - thus in the case of the exhaust, the valve tends to wear more than the opening mechanism, hence the clearance reducing.

Also we have a nasty Catch 22 - if the clearance becomes significantly reduced, (or worse still if there's no clearance and the valve never fully closes), the valve spends less of the already small amount of time that it should do closed, thus it never disspates the heat it should do and can literally melt, this is called burning a valve, no surprise there, and you really don't want to get into that.

A round of applause for your exhaust valves please - the hardest working bit of your bike, full stop.
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Old 22-11-05, 05:15 PM   #7
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****!

You mean I've got to take more or it apart? I'm in no hurry to do that! I mean, that's a whole different section in the workshop manual.

I think this could be a miniature project!
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Old 22-11-05, 07:16 PM   #8
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Quote:
Originally Posted by BillyC
@rse!

You mean I've got to take more of it apart?
Yes.
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Old 22-11-05, 07:29 PM   #9
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So that's why you're the evil Doctor Squid!
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Old 22-11-05, 10:19 PM   #10
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Northwind's Guide to Valve Clearances

1) Check the clearances
2) They're in tolerance
3) Thank ****, I can leave them alone
4) have a beer
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