U67 head dimples

[HRH]

This may be a dumb question, but I only just noticed it now. On the U67 head I have, there is a circular depression directly below the spark plug tip on cylinders 1 and 4 only. 2 and 3 do not have that depression cast in. I check my U60 head (race motor head, copy of U67) and it has the same thing.

 

Anyone know what those are there for?

 

 

[datzenmike]

Seen them before and have no idea.

 

Some intakes have grooves in the intake runners too.

 

 

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[HRH]

Seems like that would have an effect on compression, I wonder if it's to relieve heat at a certain spot to reduce detonation or something? Has to be a reason for it. I'm tempted to fill them in, but it sure seems like they were cast with a purpose.

[ggzilla]

The grooves in the runner are mentioned in Datsun Service Bulletin. But not really explained.

[Zeusimo]

My Truck Has Grooves Alone The Bottom Of The Intake Too

But Only Goes On Cyl 1 And 4

[HRH]

Zeusimo, if you ever come to Canby, please bring your keyboard. I have a .45 cent solution for that shift key. :)

[Zeusimo]

I Haven't Been On My Computer For A While...

Been Using My iPhone Ever Since I Got It

Decided To Keep Annoying Everyone :D

[DAT510]

Lol I Got Used To It.

[ggzilla]

Found it. The grooves are to help with cold starting.

 

 

This is from the Datsun 1981 Service Bulletin (New Models) under A-series engine

== Intake Manifold ==

The intake manifold has been re-designed to match the cross-sectional contour of the oblong intake port. In addition, the riser has been installed in a slightly higher position and a groove has been added to the intake ports for easier starting when the engine is cold. The manifold gasket has also been modified.

 

Groove at bottom of runners

* Datsun 210: #1 and #2 branches

* Datsun 310: All branches

The Datsun 310 being FWD, the engine sits at a different slant, which may be why the runner differs from the Datsun 210.

[datzenmike]

Maybe to catch raw fuel?

[HRH]

Cool! That explains one mystery. Still wondering about the dimples though. They would be on the top of the cylinder head with the head installed of course. I forgot to ask some of the Datsun old timers at Jaremko about it. I'll try and remember to do that today.

[DRIVEN]

Those Bosch platinums are probably a bigger negative effect than the dimples.

[ggzilla]

I seem to recall dimples like that on other brands of engines too. It must be either a casting artifact or an actual design feature.

[HRH]

Those Bosch platinums are probably a bigger negative effect than the dimples.

 

Haha, true that! This was one of the motors I got with the two 510s I picked up. If it was mine it would have NGK. ;)

 

I'm pretty sure the dimples are by design. Here's a thought I had. What about a difference in the two strokes to keep a little dissimilarity between the vibrations of the motor? Slightly less compression so the harmonic vibration wasn't EXACTLY the same between 2/3 and 1/4. Thus the motor would stay together better? Just a thought.

[datzenmike]

Head dimples. Just like dash light dimmer switches for gauges you can't read at night even when turned up full. WinTF Nissan engineers? You fuckin' with our heads for???

[HRH]

I like the harmonic vibration theory. If all cylinders and explosions are the same, the vibrations are detrimental to the engine. I could be off-base though, I just listened to The Wall in it's entirety. Wrapping up with Stairway to Heaven while contemplating the Datsun Gods' desire for the motor for my 510. Something representative, yet different....

[paradoxx]

I have a theory, what if the dimples gives the explosion a certain shape, something like to reach the cyl entirely?

[EricJB]

My guess is if they had a purpose, they would have put them on all cylinders. Maybe they are a witness mark to check for casting shift.

[HRH]

I talked to Datsun gurus and cylinder head guys and full on engine shops today. No one knows over here. I think you might be right Eric, they may just be something internal to check for something. The amount of compression change from them is very very little. Possibly a leftover from the injection mold or something when they cast the heads.

[DAT510]

My 210 head on my L16 has those too

[DAT510]

1

4

[LenRobertson]

It would be interesting to show the dimples to a pattern maker or foundryman. It might be very obvious to them what the dimples are for or caused by. I've read enough about foundry work to understand the way it works and quite a few of the terms - drag, cope, sprue, runner, core, shrink rule, all those exotic sounding words. But these dimples, assuming they are somehow related to the casting process, are possibly a very specialized detail.

 

If anyone is curious about metal casting, search YouTube for "mrpete222", then search his channel for Foundry or Casting. He does rather simple pattern making and casting for model engines, but shows how the processes are done.

 

Len