B6T Running Lean?

[sketchman]

Compression is 90, 90, 110, 120. 1-4.

FSM says high of 156 and low of 109, so they're all low, and some are lower than acceptable.

Plan is to rebuild the spare and swap it out. Verner, WV seems to be where Mazdas come to die unfortunately.

[sketchman]

A friend brought up an interesting argument. If #2 is dead @ 90psi, why isn't #1?

I pulled the plug in #1 and it is black but was still firing when pulled. Is it possible that #1 has ring issues and #2 has valve issues causing the difference?

Would that cause it, or is he right and I'll have more problems than I know right now when I go to put the "new" engine in? When I was cranking the engine to test compression I did smell gas through all the plug holes, so it is getting spark and fuel to all cylinders. Compression seems the last piece of the puzzle, yes?

Hopefully it'll just be a rebuild and go. I'm thinking I'll hook up the rail and injectors and make sure they are all clean and opening enough before I throw it all back in.

Thoughts?

[sketchman]

Hehe. Now what would have caused this?

Hmm. I believe I see a crack.....


Whaaaaaa???:eeeeeek:


Sneaky little combustion gases done sneaked through my piston. Also welded some aluminum spray onto the little end of the rod while it was at it.:nono:

If you're wondering, this is the original engine, not the one in the car right now. On a positive note, the bottom end (minus the piston) is factory original and in great shape.

[Advancedynamix]

You should perform a leakdown test, but chances are your going to have to pull this thing apart anyway. Head gasket could be blown between 1 and 2, that would cause the low comp and no fire on #2 but fire on #1.

[Rocketman]

Somebody done melted that good. Too much boost, not enough fuel

[sketchman]

You should perform a leakdown test, but chances are your going to have to pull this thing apart anyway. Head gasket could be blown between 1 and 2, that would cause the low comp and no fire on #2 but fire on #1.

At this point I'm going to rebuild the spare for it anyway, so I don't know if I'll do much more with the other engine till I pull it for the swap. Before the rebuild goes in I'll check the fuel system to death and make sure it's all good before I run it. Then I may open the bad one and see what happened.

Too much boost, not enough fuel

My thoughts exactly. This time around it'll have adjustable fuel pressure and 30s.:twisted:

[sketchman]

OK, need some help guys. I'm not a huge fan of the stock B6T piston crown design. Read: I hate them with a passion. I'm OCD like that. Can't stand the thoughts of them.

Anyway, I have some pistons with only one valve relief (that I will smooth out as much as possible to avoid sharp edges as well as other things I'll do to them) so I want to use them if I can. Thing is they have no provision for the spring clip to hold the pins in.

What would you do if you had no way to get a machine shop to cut those grooves in to retain the free floating pin design with the new pistons?

[sketchman]

Current state of one piston vs stock finish. I may find the enthusiasm to grab some 2000 grit paper and take it to total mirror, but this is pretty close. Closer than it looks in the pic. 180 dry, 400 wet, 1000 wet, and finished with Turtle Wax brand heavy duty rubbing compound. My CCs in the head will get similar treatment, when the flash flood watch is over, again.


Think I may know what I'm doing for wrist pin "captivation". We'll see. Still want ideas if anyone has them.

[sketchman]

Interesting little tidbit I learned today claying the CCs with both shallow dish 1 relief pistons and stock deep dish 4 relief.

You can use the shallow dish ones and keep the same C/R as stock. I will admit the test I did is not the most accurate in the world. For instance I came up with 7.3:1 instead of the mazda spec'ed 7.9:1, so take it all with a grain of salt. BUT I repeated that measurement twice in a row. Things making it technically "inaccurate" were a used HG not torqued down to spec, and using the spark plug hole to vent the extra clay. So I had to pinch off a bit to simulate the spark plug tip being in there and taking up room. But again, I repeated it twice within 0.005%.

Why do I want to do this? I get a piston with only 1 valve relief(a feature I hate in a piston, so the fewer the better IMO). The resulting setup will also be a full floating pin because the original app was with an interference fit in the rod instead of using retainers at the pin ends. When I removed the stock pins I saw scuffing in the bores, so I like the idea of full floaters.

A pic for ya. Pistons are from a 1.5 GLC from 83-85.

[sketchman]

Something else. You also get thicker 2nd rings (2mm vs 1.5) with the GLC pistons, and the top ring is closer to the top of the piston. Both things I want in the design.