Restoration of BringaTrailer 240z - HLS30-35883

[inline6]

22 hours ago, Racer X said:

Are you also eyebrow notching the cylinder block deck to unshroud the valves?

Hmmmmmm.  I chose not to do that for this engine.  Prompted by your question, I did some researching of eyebrow notching the L24.  I found that some people's L24's had valve to block contact.  I became a bit concerned that I missed a required modification to keep the larger exhaust valve (or the intake) from hitting.  I found a couple of relevant threads:

 

It looks like I should have checked mine out specifically for clearance issues.  The head has been bolted and torqued with a new Nissan gasket at this point.  I don't know if it can come back apart without replacing the gasket.  Kind of a pain...  So, my block is bored .030" over which is more than the .5mm Carl mentions.  From a valve clearance standpoint, I am probably ok.  That said (and I will attempt to verify as best I can without removing the head), is it highly beneficial to do?  

Edited March 20, 2021 by inline6

[inline6]

Well, thanks @Racer X for getting me to look at this closer.  I continued looking at pics and reading through some old posts and I see a problem that I did not before.  Coolant holes in the gasket are not to my liking.  My head gasket:

My block and head:

    

 

A Nissan Comp MLS gasket:

 

So, at this point, I don't feel good at all about the gasket I used.  I should have checked the coolant holes.  It seems best to pull my cyl. head off at this point.  I still have the issue of pistons above the deck by .025" and all the thoughts shared earlier in that regard.  So, will have to see about how best to proceed.  First step is to take the head off.

[Racer X]

8 minutes ago, inline6 said:

Well, thanks @Racer X for getting me to look at this closer.  I continued looking at pics and reading through some old posts and I see a problem that I did not before.  Coolant holes in the gasket are not to my liking.  My head gasket:

My block and head:

    

 

A Nissan Comp MLS gasket:

 

So, at this point, I don't feel good at all about the gasket I used.  I should have checked the coolant holes.  It seems best to pull my cyl. head off at this point.  I still have the issue of pistons above the deck by .025" and all the thoughts shared earlier in that regard.  So, will have to see about how best to proceed.  First step is to take the head off.

When I build a bottom end for the E31 head I use on my race car I eyebrow the cylinders for valve clearance and to unshroud the valves at maximum lift. I do it before any bore honing or boring, so I can see how far down the bore the upper limits of the piston ring travel is ( you don’t want to go that far down).

After I cut and polish the eyebrow, I assemble the crank, a piston, the head with cam and valves for that cylinder with clay on the piston top, to check my work. I don’t recall the measurements, but it is clear that with larger valves this work is required to prevent valve to cylinder contact and unshroud the valves adjacent to the cylinder walls. It also gives me an idea how close the valves come to the tops of the pistons.

 

[siteunseen]

I put a N47 head on my 2.4 block. Chucked up the valves and spun scratches in the smaller bore block. Notched them then used clothes line wooden pins to hold the larger valves in place on the N47. Put it back on then unclipped the pins letting the valves drop without any contact. Worked good and gave me some quality drinking time in the coldest of winter. Provided but not required. Like I need an excuse to drink!

[inline6]

Alright then.  I took the head off today.  The head gasket didn't stick to the block or the head, so I think it is reusable.  After I got the head off, I went to work on modifying the gasket.  

  

 

I used a washer with a 1/4" hole to guide the drill bit.

  

 

With the gasket modified, I turned my efforts on eye-browing the block.  Hopefully, I have not royally screwed up here.  I removed the timing chain, rotated the crank to get the pistons below deck, and then covered the block with a plastic bag, and cut out the top of it so I could access the tops of the bores.

piston 1 - pic taken from passenger side - front of piston is toward the top of the pic:

piston 2 - pic taken from passenger side - front of piston is toward the top of the pic::

piston 3 - pic taken from passenger side - front of piston is toward the top of the pic:

piston 4 - pic taken from passenger side - front of piston is toward the top of the pic:

piston 5 - pic taken from passenger side - front of piston is toward the top of the pic:

piston 6 - pic taken from passenger side - front of piston is toward the top of the pic:

piston 1 - pic taken from driver side - back of piston is toward the top of the pic:

piston 2 - pic taken from driver side - back of piston is toward the top of the pic:

piston 3 - pic taken from driver side - back of piston is toward the top of the pic:

piston 4 - pic taken from driver side - back of piston is toward the top of the pic:

piston 5 - pic taken from driver side - back of piston is toward the top of the pic:

piston 6 - pic taken from driver side - back of piston is toward the top of the pic:

A few more pics:

    

  

 

I did this with a die grinder and oval cutter.  Tape and bag is still in place.  I think I will switch over to a tapered roll and try to look for inconsistencies to address... as well as smooth the eye brows to final finish.  I am well above the top ring land currently, and inside the fire ring on the head gasket as well.  I was being cautious (I hope!).  I will check clearances and continue - before I bolt the head on.

[grannyknot]

Looks like it was done on a milling machine! 👍  As long as the head gasket didn't go through a heat cycle by starting the engine you should be fine to re-use the HG.

[inline6]

On 3/22/2021 at 6:20 AM, grannyknot said:

Looks like it was done on a milling machine! 👍  As long as the head gasket didn't go through a heat cycle by starting the engine you should be fine to re-use the HG.

Thanks. I appreciate the positive reinforcement!  I have been studying it and the cylinder head for a few minutes each of the past couple of days.  I want my next steps to be right ones.  

Checking the gasket against work that has been done so far on the head (valves are marked with cylinder number):

    

    

The work already done to open up the breathing on the exhaust for #1 and intake for #2 puts the edge of the combustion chamber at the gasket edge, but only for these two edges: 

  

It seems desirable to do further work on the other sides of each of these chambers to align the chamber edge to the fire ring also... and to do the same for the areas where the chamber wall is close to the valve heads in the other chambers as well.  That said, the tops of the bores are not as wide as the chambers in the matching areas, even after eye-browing.  So, the question is should I open them outwards to match?  And, should this be done for both the intake and exhaust valve sides of the cylinders (safely above the number 1 piston rings of course)? 

 

Edited March 25, 2021 by inline6

[Captain Obvious]

1 hour ago, inline6 said:

It seems desirable to do further work on the other sides of each of these chambers to align the chamber edge to the fire ring also... and to do the same for the areas where the chamber wall is close to the valve heads in the other chambers as well.  That said, the tops of the bores are not as wide as the chambers in the matching areas, even after eye-browing.  So, the question is should I open them outwards to match?  And, should this be done for both the intake and exhaust valve sides of the cylinders (safely above the number 1 piston rings of course)? 

I'm sorry, but you completely lost me with your description stuff above, but I will throw out some general notes that may be applicable.

First, any material you remove from the chamber area in the head will reduce your compression ratio. You could gain that back in other ways, but not sure you were planning to do any of that. If you like the compression numbers where they are, you might not want to remove any more material than you really need to.

Second, Not sure it matters, but I've measured a couple head gaskets, and I've found that the hole in the gasket is not round. Not sure it was an anomaly (or just a 280 thing), but they were oval-ish. Have you checked yours to see if it's oval or round?

Third, when you're removing material from the head to bring the edge out to the fire ring, keep in mind that the metal band portion of the gasket will squeeze out into the chamber area a little as the gasket is compressed. If it were me, I would want the entire fire ring area to be supported on both sides by engine metal. In other words, I wouldn't want to ever have any portion of the fire ring hanging out unsupported (on either side) into the chamber area, and because of the extrusion that occurs on compression of the gasket,  I would probably leave a small amount of extra material there to be sure that would not happen. I believe the gasket you have there is the one that was already compressed once? That may minimize that effect?

I'm no engine builder expert, but those are my thoughts. Hopefully someone who actually knows what they're talking about comes in and provides better guidance.    

[inline6]

Thanks for your comments!

8 minutes ago, Captain Obvious said:

I'm sorry, but you completely lost me with your description stuff above...

Yeah, is hard to explain.  Basically, if you look at each of the pics of chambers 1 through 6, and look at the 3 o'clock and 9 o'clock positions specifically for each, only chambers 1 and 2 have edges that match up with the fire rings... and further, for the #1 chamber, it is only the exhaust valve side that matches up (3 o'clock position in the pic), and for the #2 chamber, only the intake valve side matches up (also the 3 o'clock position in the pic).  All of the other combustion chamber edges (at 9 o'clock for all chambers, and at 3 o'clock for chambers 3 through 6) are not yet cut as far as the edge of the fire ring.

So, I am saying it seems like I need to open the chambers at those positions for each chamber so that they all align with the edge of the fire rings in the gasket.  

8 minutes ago, Captain Obvious said:

Any material you remove from the chamber area in the head will reduce your compression ratio. 

Understood.  I have to provide clearance for the valves, so trying to do that, and I am assuming that breathing benefits that come from what I have outlined will be worth more than compression lost from the mods.  I have no idea though - so if there is an expert who chimes in, that will be great!

8 minutes ago, Captain Obvious said:

Have you checked yours to see if it's oval or round?

Yep, it is oval.  It is wider at 3 and 9.  And I'm not touching anything at 6 and 12... or 5 and 11, or 7 and 1 for that matter.  I probably went a bit far north and south with the eye brows I already cut in the block at the 3 and 9 positions.  The rest of my mods to the block will be more central to the 3 and 9 positions, generally.

8 minutes ago, Captain Obvious said:

Third, when you're removing material from the head to bring the edge out to the fire ring, keep in mind that the metal band portion of the gasket will squeeze out into the chamber area a little as the gasket is compressed. If it were me, I would want the entire fire ring area to be supported on both sides by engine metal. In other words, I wouldn't want to ever have any portion of the fire ring hanging out unsupported (on either side) into the chamber area, and because of the extrusion that occurs on compression of the gasket,  I would probably leave a small amount of extra material there to be sure that would not happen. I believe the gasket you have there is the one that was already compressed once? That may minimize that effect?

Agreed.  And yes, the gasket has been compressed once.  But I will leave a small amount of material there so I am not precisely at the fire ring with the edges of the chamber.  The two edges mentioned above that are already matching up are REALLY close.

[grannyknot]

CO covered it,  the gains in flow to result in more HP are so small as to be unnoticeable, what you are talking about is the sort tweaking that is done a race engine to squeeze the last bit of potential out of it and you would only benefit from those possible gains at WOT and how much time do you really spend up there?  If I were you I would reassemble with some molding clay or a bit of Plasticine at the 3 and 9 position, just tighten the head bolts down a little snug and cycle the engine by hand a few times to see if you have covered your clearances. If at anytime while rotating the engine by hand you feel the engine stop or resist, back it off and remove the head to figure out where the interference is coming from. The thickness of Plasticine at the bottom of the valve dent will give you a good idea of how close you are.

I understand perfectly the desire to make the engine as perfect as possible while you are in there, it's fun just be aware of the law of diminishing returns.

[Captain Obvious]

Agreed. I guess now that you have moved the chamber edge back on E1 and I2, if I were you, I would do something similar to the rest of the valves, but making sure I didn't push it to the hairy edge and left a little material to guarantee that the head gasket ring didn't squeeze out past the material.

Other than that, the only other thing I would do is make sure I broke the sharp edge where the new head planing surface meets the chamber. And I wouldn't even use power tools... Some fineish (400?) grit sandpaper ought to knock down any burrs and put a small radius on that edge.

In other words... When they plane the head, they usually use a large cutter spinning in one direction. Because of that, it usually results in a burr (most prevalent on the downstream side of the cut). I would take some fine grit paper and work it around the chamber something like this to knock off any smeared burrs and/or make sure there aren't any sharp edges:

[inline6]

Chambers 1 to 6 in order from left to right after very little ground away, only nearest the valve and to the fire ring:

    

    

I put the entire head inside a plastic bag and taped off everything so I didn't get any grinding dust anywhere in the head or valves, etc.  

I will check valve to block clearances next.  Before the head goes back on for good, I will address any sharp edges that remain.

Edited March 28, 2021 by inline6