BIG valve gaps!


13 replies to this topic
  • dazzabb

Posted January 18, 2008 - 12:12 AM

#1

Guy's,

I posted here recently about checking the valve clearance, but I chickened out and got a very competent friend who works for Honda to do it while I "supervised".

Bad news, 3 valves were WELL out of spec between 0.1 - 0.2mm over standard. I know this is a massive amount over spec and I am now worried to even the start the engine. I'm afraid that if I start the engine with this much extra shim depth I might have valves belting the piston.

What can make a gap that large appear so suddenly when 1,000km ago NO adjustment was needed?

He suggested that running too rich could lead to carbon accumulation that can prevent the valves from fully seating and make it appear like the valves are in need of bigger shims.

But about 1,500km ago I put on a GYTR pipe, so that should in theory have made it leaner than before?

Anybody got any other ideas?

Thanks
Daz

  • graazzy

Posted January 18, 2008 - 12:26 AM

#2

which 3 valves ?

  • Rick1141

Posted January 18, 2008 - 04:45 AM

#3

dazzabb
Which side were the valve clearance out of standard? Usually the tight side bring trouble but the lose side bring good result.

It is the seory for the 4stroke racing motor to set valve clearance wider.:cool:

  • dazzabb

Posted January 18, 2008 - 05:03 AM

#4

Left Exhaust 0.1mm out of spec

Right and Centre Inlet both 0.25mm out of spec

Other two valves were in spec.

  • bg10459

Posted January 18, 2008 - 08:00 AM

#5

Left Exhaust 0.1mm out of spec

Right and Centre Inlet both 0.25mm out of spec

Other two valves were in spec.

Exhaust spec is .225 mm and intake is .125 mm. You've got one exhaust at .325mm? and two intakes at .375 mm?:cool:
Typically, valve clearances tighten with time, so those measurements don't sound right. I'd double check them, make sure you're using metric feelers and of the correct size. Make sure you're at TDC, cam chain and cam caps are tight. How does the cam look. Is there any sign of excessive wear on the lobes that are way out of tolerance?
Maybe do a solvent check on the valves to see if they're sealing properly.
IDK, something isn't right.

  • Alternative

Posted January 18, 2008 - 04:01 PM

#6

dazzabb
Which side were the valve clearance out of standard? Usually the tight side bring trouble but the lose side bring good result.

It is the seory for the 4stroke racing motor to set valve clearance wider.:applause:


This is a common misconception with Yamahas. If you set the clearances too loose you can get excessive wear on the lobes, causing them to get looser. Just set them to what Yamaha says and be done :cool:.

  • dazzabb

Posted January 18, 2008 - 11:06 PM

#7

Exhaust spec is .225 mm and intake is .125 mm. You've got one exhaust at .325mm? and two intakes at .375 mm?:cool:
Typically, valve clearances tighten with time, so those measurements don't sound right. I'd double check them, make sure you're using metric feelers and of the correct size. Make sure you're at TDC, cam chain and cam caps are tight. How does the cam look. Is there any sign of excessive wear on the lobes that are way out of tolerance?
Maybe do a solvent check on the valves to see if they're sealing properly.
IDK, something isn't right.


Thanks for your advice.

Today I got my mechanic to double check (he wassn't amused by that) as you suggested and the clearances ARE as I stated previously.

Feelers guage is a quality item in metric.
100% sure at TDC, cam chain tight and all bolts torqued as per manual.
No blueing or signs of wear on any of the cam lobes.

While valve tightening is the norm it is not un-common to have to larger gaps was his reply to my question.

So with that it mind I fired her up, started first time and ran significantly quieter than before.

Should I still be concerned and if so what should be my next course of action?

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  • bg10459

Posted January 19, 2008 - 07:30 AM

#8

At a minimum, I would re-shim, but those measurements are so way off that I would want to see what's wrong. Solvent check the valves to see if they leak. If so, maybe pop the top of the valve with a plastic hammer to see if they'll seat better. If all looks good, just re-shim.
You do have a mechanic, though, and he should be more qualified than me.

  • dazzabb

Posted February 03, 2008 - 03:03 AM

#9

At a minimum, I would re-shim, but those measurements are so way off that I would want to see what's wrong. Solvent check the valves to see if they leak. If so, maybe pop the top of the valve with a plastic hammer to see if they'll seat better. If all looks good, just re-shim.
You do have a mechanic, though, and he should be more qualified than me.


BG,

Again thanks for your advice.
An update.

Took the head off and the valves appear to be perfectly seated with no evidence of any carbon build up that could possibly have enlarged the gaps.
Gave the valve a wee tap as you suggested but nothing seemed to change.

Rebuilt and clearances were as stated before.

Started her up and ran a few miles and all seems OK, still a lot quieter than before and no nasty noises.

I think I've just gonna run her as normal and see what happens.
Not much else I can do really. But Like you, those numbers do worry me.

  • Frostbite

Posted February 03, 2008 - 05:49 AM

#10

When was the last time you had the valves adjusted (actually swapped shims) ?

There's not much room to stuff feeler gauges in under the lobes and it's easy to get a false reading. I bought a new set of feeler gauges a few months ago and checked my clearances and a few seemed super tight, which was odd since it was all of a sudden. I checked with my old feeler gauges and the clearances were correct. The new feeler strips were straight and stiff, and didn't easily follow the curve of the cam. I prebent the new feeler strips and they slipped in easily and gave the correct readings.

Since the valve springs are very light on the WR's and the space is tight, it's sometimes tricky to get a good feel.

It is possible that the last time you had them checked, they may have felt tight due to straight feeler strips or inexperienced mechanic, and looser shims installed which would provide the correct "feel" on the gauge. It could easily happen, almost did it myself.

  • dazzabb

Posted February 03, 2008 - 06:57 AM

#11

When was the last time you had the valves adjusted (actually swapped shims) ?

Since the valve springs are very light on the WR's and the space is tight, it's sometimes tricky to get a good feel.

It is possible that the last time you had them checked, they may have felt tight due to straight feeler strips or inexperienced mechanic, and looser shims installed which would provide the correct "feel" on the gauge. It could easily happen, almost did it myself.



Good point you made Frostbite, that had never crossed my mind at all.

I have recently changed mechanic the old guy was U/S (not easy to find a solid mechanic in Thailand) and now I have a ex-Honda Japan, Japanese dude who takes great pride in his work.

The old fella used to tell me the valve clearances were OK, but you now have me wondering if he actually checked them at all.

Time I learnt to check and adjust myself, problem with that is I wouldn't trust the above clearances and would have assumed I had messed up, so then i would be back to the mechanic.......

  • Frostbite

Posted February 03, 2008 - 10:45 AM

#12

Good point you made Frostbite, that had never crossed my mind at all.

I have recently changed mechanic the old guy was U/S (not easy to find a solid mechanic in Thailand) and now I have a ex-Honda Japan, Japanese dude who takes great pride in his work.

The old fella used to tell me the valve clearances were OK, but you now have me wondering if he actually checked them at all.

Time I learnt to check and adjust myself, problem with that is I wouldn't trust the above clearances and would have assumed I had messed up, so then i would be back to the mechanic.......


In your case, the mechanic may have been slipping in the proper clearance feeler strip which could feel good even if the clearance was larger, and assuming it was OK. If my clearance feels good, I always slip in the next thinner and thicker gauges to make sure they feel looser and tighter. If the next thickest feels the same then you're feeling the drag from the stiff straight feeler gauge and not the actual clearance.

Loose valves won't cause a meeting of the piston, but tight valves may. Also, incorrect cam timimg will arrange a meeting like this one last summer - now I use a degree wheel to install my cams.

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  • tarmac_terrorist

Posted February 03, 2008 - 10:55 AM

#13

In your case, the mechanic may have been slipping in the proper clearance feeler strip which could feel good even if the clearance was larger, and assuming it was OK. If my clearance feels good, I always slip in the next thinner and thicker gauges to make sure they feel looser and tighter. If the next thickest feels the same then you're feeling the drag from the stiff straight feeler gauge and not the actual clearance.

Loose valves won't cause a meeting of the piston, but tight valves may. Also, incorrect cam timimg will arrange a meeting like this one last summer - now I use a degree wheel to install my cams.

Posted Image

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Whats the name of the TDC guage. Is it a TDC finder / guage? I was going to use one on a pinto rebuild. Its a very accurate way to find true tdc. Maybe using a tdc finder might help eliminate that line of enquiry.

  • Frostbite

Posted February 03, 2008 - 11:16 AM

#14

Whats the name of the TDC guage. Is it a TDC finder / guage? I was going to use one on a pinto rebuild. Its a very accurate way to find true tdc. Maybe using a tdc finder might help eliminate that line of enquiry.


I bought the degree wheel kit from HotCams, since I have adjustable/degreeable cams.

The kit comes with the metal degree wheel, dial indicator with adjustable magnetic base, and 3 positive TDC stops, for 3 different size sparkplug holes.

Posted Image

The positive stops are the key to finding true TDC. Sticking a screwdriver in the sparkplug hole and watching it reach the highest point can be off by 20 or 30 degrees, because the piston actually stops moving as the connecting rod changes from going up to down.

You install the degreewheel on the crank, set up a pointer, and then thread in the positive stop. Then you turn the engine over slowly until you feel resistance - the piston touching the positive stop. You place a mark on the degree wheel where the pointer is indicating. Then you rotate the engine slowly in the opposite direction until the piston touches the positive stop and mark the degree wheel at that spot. Halfway bewteen those 2 marks you made is Exactly TDC.

When I was setting up my cams I found that even if the valve clearance was a bit off it would change the cam timing 5 to 10 degrees. My new cams were 20 degrees off of what the specs called for. A lot of factors affect the cam timing like the valve clearance and the amount of wear in your cam chain. I was nervous at high RPM after I snapped a valve, but now that I know the timing is bang on, I rev it mercilessly.




 
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