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Valve adjustment clearance issue


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#1 Rhino73z

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Posted 04 February 2009 - 01:09 PM

Hi Guys, looking for some advice on a valve clearance issue I have with my L28 engine (F54 block with a P90 head).  While checking the valve clearances, number 6 cylinder exhaust valve was very tight and I only just get clearance with the adjuster screwed down as tight as it will go.  Now my concern is, why is it just this valve when all the others have plenty of adjustment left?
I did the following checks;

  • Removed the rocker and checked for any visible problems.  No dramatic wear issues and valve collets looks to be seated correctly.
  • Measured valve spring between valve spring seat and valve washer at bottom.  6th cylinder exhaust measured 44.48mm and 3rd cylinder exhaust measured 43.50mm as a comparison, so valve on 6th cylinder certainly is higher therefore why my adjuster is screwed right down.
  • Measured the compression ratio, 155psi average across cylinders. So I’m not down on compression on the 6th cylinder.

All I can think of now is:
  • Valve seat is receding or was cut deeper (but I don’t seem to have a compression issue to indicate the valve seat is worn.
  • Valve stem has stretch.

Has anyone got any other thoughts what the issue could be and if I’m running any serious risk running the motor in this condition?

Thanks for your help in advance.  :-\


#2 Lurch ™

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Posted 04 February 2009 - 01:31 PM

P90 valves are SHORTER than the other heads, due to the P90 having deeper chambers.
Are you sure you don't have N42 etc exhaust valves in there?

My other suggestion is that maybe the valve seat on No.6 Ex is 'pocketed' more than the others.
And perhaps check your lash pad height.

#3 Rhino73z

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Posted 04 February 2009 - 05:47 PM

Not sure what valves are in there, came as purchased and I haven't had the head off to check...not yet anyway.  I'm more concerned that the valve may have stretched or something similar and I could have a serious problem on my hand!!

Is this at all likely?  ???



#4 chris240

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Posted 04 February 2009 - 05:50 PM

the value ??? LOL

#5 Rhino73z

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Posted 04 February 2009 - 06:04 PM

Thanks Chris for picking up the typo...got a better answer?  ;)

#6 Lurch ™

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Posted 04 February 2009 - 07:14 PM

Valve 'stretch' is very uncommon on Nissan engines - least I've never heard of it happening.
You could also check the height of the retainers & make some someone hasn't swapped an odd height one in.

#7 Rhino73z

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Posted 06 February 2009 - 07:43 AM

Thanks for the advice. I'll have to pull the head off to see what the issue really is but I'm confident it should be fine for the Thredbo trip.  Then the hard work can really begin!




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