Restoration of BringaTrailer 240z - HLS30-35883

[Zed Head]

I see "taking things apart" but not the corrective actions to be applied.  Trying to help formulate a plan of action. 

Assessing the wipe pattern before going further will tell a lot.  Might be that many of the others are actually off the edge but just not too noisy yet.

[inline6]

As I mentioned yesterday, the problem appears to be only with the exhaust valves.  So, it is with interest that I made the following observation for valves 5 and 6 (with 1 to 12 being from the front of the engine to the back).  These rockers are both actuating exhaust valves and are "adjusted to correct valve lash".  Note the very different adjuster heights between the two:

 

Wild - right?  Well... have a look at this picture - the rocker on the left is the number 6 valve (exhaust) and the one on the right is the number 7 valve (intake):

 

So... what is going on with the rocker on the valve on the left?  Do you see how the tip of that rocker appears to be "floating"?  And compared to the intake valve on the right, the rocker tip on the left appears to be sitting quite a bit higher (above the retainer) actually:

 

Here is a picture showing the underside of the rocker - see the shiny part where the arm was contacting the retainer?

 

Summarizing what I have found tonight, each of the 6 exhaust valves are hitting the top edge of the Isky retainers.  When I was setting valve lash, I was setting it with the rocker arm sitting on the retainer instead of the lash pad.  The rocker was floating above the stock .118" thick lash pads on each exhaust valve.   During the total of about 1 to 2 minutes of engine operation at low revs, the cam was operating the exhaust valves, initially by rocker to retainer contact, but as the rotation continued, the rocker tip came into contact with the stock lash pad, and operated the valve.  

And note that the lash pads look very different.  The ears on the lash pad of the intake valve (right) are sitting quite a bit further outside the retainer.  I removed that rocker and took a measurement of the lash pad:

Each gradient is .025".  So the reading above is .177" and 7 tenths, or '.175'.  These are the lash pads that came with the cam when I ordered it. 

I am hoping to get lucky here.  My plan at this point is to put the .175 lash pads in each of the 6 exhaust valve locations and to modify the undersides of the rocker arms for clearance with the aftermarket Isky retainers.  I'll just have to see if between the two, the rocker arms actually sit lower at the tip than before.  If so, then I should be able to raise the height of the adjusters for these valves.  Fingers crossed.

Edited 20 hours ago by inline6

[Diseazd]

Isky performance springs have deep valve spring retainer pockets. If you use any lash pads less than about .140’s, they will hit the retainers. It looks like you have two different size lash pads. Lash pads should sit high like the .175’s you show. You shouldn’t have to modify anything if you use thicker lash pads. 

[inline6]

While talking with my engine builder last night, we discussed that he purposely sank the valves into the head to address problems with the combustion chamber's archaic design.  The location of the top of the exhaust valve stem is the issue I am dealing with.  If the .175" lash caps are too thick for me to use (I will put them in and check wipe patterns), then I will go with his suggestion to remove the valve spring retainers from the exhaust valves, and send them off to him to have the ridges on the tops of them  turned down to work with the thinner shims.   

Edited 6 hours ago by inline6

[Captain Obvious]

Well smoking gun at least. The combo of sinking the exhaust seats, the extra deep retainers, and longer than stock exhaust valve stems. A little disconcerting that the two adjacent exhaust valves are that different in adjustment. Makes me wonder how much variability there is between how deep he sank the seats.

I'm no engine expert, but I'm not totally comfortable with modifying the rockers. You would be removing material right at a stress point and introducing a stress riser right there. How much material do you think you'll have to carve out?

You could stuff some rope into the cylinders and swap out the retainers for something shorter, like stock. That would take care of it, and still not require pulling the head off. More work, but no stress risers that way.

Edited 7 hours ago by Captain Obvious

[Zed Head]

2 hours ago, inline6 said:

he purposely sank the valves into the head to address problems with the combustion chamber's archaic design. 

This is interesting.  How deep did he go?  This would also change chamber volume.

Considering the variation and the odd logic it might actually be worthwhile to remove the head and take a close look at what's been done.  Trying to grasp sinking the valve seats to deal with "archaic design".  Esthetics, function, machining problems?  Curious about what he was trying to fix.