Low Compression

[cudabob496]

lean on one side of engine due to intake manifold leak?

[cwestra]

Well at least you have found the problem , too lean , probably , excessive heat one the exhaust valves , weird on the exhaust manifold though , most dual plane intakes feed both center ports from the same side of the carb , what intake are you using ?

Stock aluminum 6 barrel.

[72cudamaan]

That valve isn't burnt. Looks like aluminum deposit between valve and seat. Guess you'll find out when the valve
gets pulled. The light tan condition is quite common with today's fuel and the additives in it. Though it does appear
that you were running a bit lean.

[cwestra]

That valve isn't burnt. Looks like aluminum deposit between valve and seat. Guess you'll find out when the valve
gets pulled. The light tan condition is quite common with today's fuel and the additives in it. Though it does appear
that you were running a bit lean.

You are correct.  It was not burned.  No signs of debris holding it open, though, but the valve was fairly loose in the guide.  The machine shop believes that the worn guide may have caused mis-alignment with the seat resulting in the leak.  They are going to install a new bronze guide and see if they can clean up the valve and hardened seat to get it to seal.  Should be an easy fix.

[72cudamaan]

    Good to hear. I assume they are going through the whole head(s)? I've seen one bad guide before, but it is rare.
I wonder if that deposit in the exhaust port might have been created by the constant rush of burnt gasses running through it.
As opposed to only when they were supposed to?

[Strawdawg]

    Good to hear. I assume they are going through the whole head(s)? I've seen one bad guide before, but it is rare.
I wonder if that deposit in the exhaust port might have been created by the constant rush of burnt gasses running through it.
As opposed to only when they were supposed to?

Would seem reasonable as it would be burning on the way thru rather than retained longer in the cylinder for a more complete burn and a leaner exhaust stream......



Most definitely want to go thru all the valves...I would say both sides to avoid another problem a few thousand down the road

[Chryco Psycho]

I agree , heat of the exhaust especially if it is on the lean side , hard seats should prevent the valve welding to the seat as it cool when it closes but cheap seats or valve could be welding themselves , so erosion of the valves could be causing the gap

[jimynick]

If my feeble mind is reading those A/F charts right, that thing is way too lean. In days of old the magic # was 14.2:1 for  a stoichiometric ratio and now they talk 14.7 at cruise. However, the generally accepted best ratio for power making is in the mid to low 12's and your #'s show you nearing 16! Look closely at the pistons, because they're the only source of aluminum that close to the valve and it's possible the engine may have detonated while lean and knocked some off one. There's no reason you couldn't touch up that valve once the guide works been done and the shop will check it for concentricity when they grind it. Good luck! 

[cudabob496]

If my feeble mind is reading those A/F charts right, that thing is way too lean. In days of old the magic # was 14.2:1 for  a stoichiometric ratio and now they talk 14.7 at cruise. However, the generally accepted best ratio for power making is in the mid to low 12's and your #'s show you nearing 16! Look closely at the pistons, because they're the only source of aluminum that close to the valve and it's possible the engine may have detonated while lean and knocked some off one. There's no reason you couldn't touch up that valve once the guide works been done and the shop will check it for concentricity when they grind it. Good luck! 

I'm running about 13 to 13.5 when cruising, and around 12.5 when full throttle.

[cwestra]

Engine back together.  All other valves on that head were fine.  May have been an overlooked guide during rebuild 5 years ago.  Anyway, compression back up to 140 psi on #8 with 91% efficiency in leak test.  Glad to have it back on the road.  Thanks for all the assistance from you guys.

[Strawdawg]

Glad it turned out so well!

Steve

[Chryco Psycho]

 

[cwestra]

If my feeble mind is reading those A/F charts right, that thing is way too lean. In days of old the magic # was 14.2:1 for  a stoichiometric ratio and now they talk 14.7 at cruise. However, the generally accepted best ratio for power making is in the mid to low 12's and your #'s show you nearing 16! Look closely at the pistons, because they're the only source of aluminum that close to the valve and it's possible the engine may have detonated while lean and knocked some off one. There's no reason you couldn't touch up that valve once the guide works been done and the shop will check it for concentricity when they grind it. Good luck! 

Yes, at a cruise it seems lean but wasn't sure if that was normal or not.  I did notice when I pulled the intake manifold that it seemed a bit oily in areas where I expected it to be dry, indicating that I may have had a leak.  I've included a picture to show it.  That would tend to create a leaner condition, I believe.  I do plan on hooking up the AFR meter again this year and I'll see if I get similar readings with the new gaskets in place.  I also may try bumping the jets up a bit if I am still running lean.