KB 107 piston valve reliefs : Are they symmetrical?

[Kern Dog]

I asked this in my build thread but didn’t get a response. I figured I’d ask out in the open.
Looking at this piston, can you tell which valve relief is bigger than the other ?

At first glance, you’d think the notch on the right is bigger, right?
Look again…

You move the piston around and now they look the same to me. Many pistons with valve reliefs seem to have a clear difference in size. These are so close, it leads me to think that they are symmetrical and can go in any cylinder. I couldn’t find anything stating that online. A call to Summit Racing and the man found a tech bulletin that stated that both were .28” deep and the same width but he would not come right out and say that they are symmetrical.
Google searches don’t help since I’ve read both a YES and a NO.

 

[abdywgn]

first picture looks like the right side is larger, second ?. must be the light. set an intake valve in both reliefs and see if there is a difference in side-to-side space.

 

[413]

Put something round in each relief as a gauge and see how they look. Compare each side. Do the pistons have numbers on top or inside? All 8 part numbers the same or 4 and 4?

 

[crackedback]

Call uem and look up the instructions/specs on their site.

I wouldn't trust a summit rep on that question.

IIRC, older versions were left right.

 

[toolmanmike]

I asked this in my build thread but didn’t get a response. I figured I’d ask out in the open.
Looking at this piston, can you tell which valve relief is bigger than the other ?

View attachment 1716390299

At first glance, you’d think the notch on the right is bigger, right?
Look again…

View attachment 1716390300

You move the piston around and now they look the same to me. Many pistons with valve reliefs seem to have a clear difference in size. These are so close, it leads me to think that they are symmetrical and can go in any cylinder. I couldn’t find anything stating that online. A call to Summit Racing and the man found a tech bulletin that stated that both were .28” deep and the same width but he would not come right out and say that they are symmetrical.
Google searches don’t help since I’ve read both a YES and a NO.

The intake is usually bigger. Get out your calipers.

 

[Kern Dog]

I have measured but maybe I am doing it wrong. I don't see much difference.
I really thought that this would have been a slam dunk question and answer since so many members mention these pistons in their engine builds.

 

[RustyRatRod]

Call Marco at United Engine.

 

[Kern Dog]

I was wiped out yesterday afternoon so I refrained from responding with my usual sarcasm.
I’m well rested now.
Measuring a rounded shape against another rounded shape might be within the skill set of some people but not me. I’d measure and get inconsistent numbers. On visual, the pocket on the right would look bigger on some but then measure slightly smaller.

Put something round in each relief as a gauge and see how they look.

THIS was an excellent idea.
The pistons all have the same numbers and markings on them so…

Take a guess as to which side looks larger than the other….
Here is a 2.19 valve from a big block Edelbrock head.

I see almost no gap around the valve. Now on the right side….

The SAME. There is no difference.
Mystery solved.
The pictures may give you the impression that the left pocket shows a bigger gap. That is just an illusion. With the valve moved UP a fraction, it meets the piston edge the same as it does on the right. If there is a difference, it is so slight, I can’t see it.
My heads have the standard 1.88” intake valves so yeah…I don’t think I’ll encounter any issues here.

 

[Robbie2734]

I used them in my 360 build, I had 5 right and 3 left from the seller. I ordered one from KB for the drivers side and it came with 4 valve reliefs. Same weight so no problem. I wasn't sure if there was a offset so I have the unused one on the shelf. KB felt it was better to use the replacement and they were talking about using the 4 relief and making them universal.

 

[Bobzilla]

The currently produced KB107 pistons only have two valve reliefs. They also have symmetrical valve notches; no left and right specific locations.

The instructions that come with KB107 are universal and tell you which engines have left and right pistons. None of listed engines are Mopars. All of the engines listed are actually using different part numbers, not KB107.

 

[mopowers]

Based on the photos, it's too close to matter. Run 'em either way.

If they were directional, you'd want to double check that the rods are installed in the correct orientation (if the rods have one beveled side to clear a bearing journal fillet). Damn these details.

 

[Kern Dog]

The rod bearings are offset in the rod journals from what I see here. I remember that the rods with the bearing shells that are flush to the edges of the journal are meant to face the other rod on the crank-pin. The side of the rod journal where the bearing is recessed in....that faces the counterweight.