Light pitting. Weird surface wear on domes.

[twisterad3]

I have an ADA head that was torqued to spec (slightly beyond). I have a new JM735 that's in the process of being broken in, and after my first tank of 91 w/32:1 gas, I realized that my compression was low (150) so I ordered a new o-rings and reinstalled the head. I did notice a very small amount of pitting on one of the domes. I know pitting is usually debris in the cylinders, but there is 0 pitting on the piston, and no scuffs on the cylinders. Any thoughts?
-62t bottom end (Raider)
-61x 735 (ported)
-ADA Head with 35cc domes.
-Carbs at default settings (per recommendation)
-No more than 3/4 throttle pulled for the first tank (second tank is filled, but not ran)

 

[keith t]

Those domes run O rings not gaskets !!!!!!

 

[twisterad3]

Yes. I meant ordered new orings. Good catch.

 

[twisterad3]

did the compression go up after you put new o rings? those pix show nothing/ no pitting. are the dings sharp or just tiny dents like sand would make? was the head new and only used on this new motor or was it used before on something else? could the dings have already been there from before and you didn't notice them?

@TheBuzzard- The compression did go up to where it's suppose to be after the new o rings. I suppose they could be tiny dents like sand would make. Here's a better photo, not in a thumb nail.
The head was new and installed from the moment this motor ran.
The dings in the head were defiantly not there prior to install, or the weird wear marks on the mating surface of the domes.

 

[37]

What pipe do you have? What ignition are you running? Has your stator plate been advanced at all from stock? What is your compression now that you've sorted out your o-ring issue? Can you post a photo of the tops of your pistons?

My initial thought is detonation from too much timing, too low of octane, running too lean or a combination of these. 91 really needs 37cc domes, not 35, and that's assuming good 91 that's known to be fresh. If you're on 35cc domes with 91, porting, advanced ignition or an MSD Enhancer, and a Factory B pipe then you're almost guaranteed to be detonating.

If you had sand in your cylinders you'd see scratches, scuffs and pitting on both the domes and tops of the pistons. And, you'd really have to have screwed something up to get sand in there.

 

[Proformance1]

Call JM, hes your key to tuning that in properly.

 

[DAG]

From the pic that looks like fretting to me. If the o-ring was not holding the dome off the cylinder all the way the surfaces were slightly rubbing each other. Nothing to be worried about especially if you said you replaced the orings and compression came back up.

 

[twisterad3]

What pipe do you have? What ignition are you running? Has your stator plate been advanced at all from stock? What is your compression now that you've sorted out your o-ring issue? Can you post a photo of the tops of your pistons?

My initial thought is detonation from too much timing, too low of octane, running too lean or a combination of these. 91 really needs 37cc domes, not 35, and that's assuming good 91 that's known to be fresh. If you're on 35cc domes with 91, porting, advanced ignition or an MSD Enhancer, and a Factory B pipe then you're almost guaranteed to be detonating.

If you had sand in your cylinders you'd see scratches, scuffs and pitting on both the domes and tops of the pistons. And, you'd really have to have screwed something up to get sand in there.

I have a b pipe. Although the carbon chamber is poorly made and found an exhaust leak.
The timing is in stock position and I have OEM electronics.
The compression is now up to 185 per cylinder with the o rings sorted out.
It is in the rear cylinder, so running too lean may be the issue.
I was using fresh 91 with 32:1 Yamalube. Gas was from 76 station.
There is carbon build up on top of the pistons in the rear, but I don't have a photo of the pistons. :-/
I will probably mix in a few gallons of 100 octane going forward.

 

[TheBuzzard]

I've seen a few domes with this exact pitting but I haven't been able to come up with an exact cause. I didn't think it was sand, I was just using sand dents to describe the ding type, sharp or rounded. since the motor is brand new, no bearing cage particles or any other debris could be going thru it, i'm betting its detonation. a local shop kept blowing up a brand new rebuilt 701 superjet and come to find out , the new ADA head squish was way too tight and that was the reason.

 

[37]

@TheBuzzard - My mistake, I didn't see the sand description in your post. I thought it was something twisterad3 had said.

@twisterad3 - It's most likely detonation. I'm sure many will disagree but 35cc domes are too small for 91 octane regardless of what ADA claims on their site. Others have burnt down pistons with 35cc domes and a similar setup and you're thankfully on the bleeding edge rather than over it. There are far more factors that play into octane than just cranking compression. You can either go to 37cc domes and most likely eliminate the problem or mix in a gallon of 100LL to get you up in the 92.5~93 octane range.

We also don't know your exact squish. If your cylinder has been decked at all or your domes weren't made correctly, you could be tighter than ideal. 91 probably needs to be in the 0.050~0.055" range for safety. You can get by with less but I'm not sure what squish angle ADA uses.

Being lean or loading the engine hard could also explain why the rear cylinder detonated and the front hasn't yet.

32:1 on your oil mix is perfect. Keep it there. Just be sure to adjust your jetting accordingly as this will run your fuel leaner than suggested jetting for 50:1. Jetting is a baseline, not an absolute, and should always be fine tuned.

Last, be sure you're running at least #8 plugs and not #7. You might be able to move down to BR9ES and solve a lot of this.