OK here's what the instructions say





That second picture is what threw me off. So I have a D16Y8 which is standard bore 75.0 mm or 2.952". I purchased the 75.5 mm pistons which are 0.020 over or 2.972". So does that second pic mean every 0.001" over standard bore or over the 75.5?

Based on the first pic of bore x 0.0055 I have
2.972" x 0.0055" = 0.016" for the first ring.
It says the second ring needs to be 0.004 ~ 0.008 larger so I will go with 0.006 which is right in the middle. So second ring will be
0.016" + 0.006 = 0.022"

So my initial calculations bring me to
1st ring = 0.016"
2nd ring = 0.022"

But what about that statement in the second pic? Is it meaning that I went with a 0.0035 piston to wall clearance so I'm 0.0035 over intended bore size?
Humm so 0.016 + (0.00314 * 3.5) = 0.027 for first ring
2nd ring = 0.033.

That's a big difference from my initial calculations. Am I doing that right?

OR

When they say intended bore size are they referring to the factory spec of 75.00 mm or 2.972". I'm thinking not because when you calculate an additional .00314 for every .0001 over that out ring gap gets huge.

OR

Am I safely able to ignore that statement in the 2nd pic?

Thanks for any pointers or directions.

 

...and what pistons/rings did these instructions come with?

 

Sorry CP 2618 alloy part # SC7051. They are 75.5 mm or 0.020" over standard bore. 9.0:1 CR if that matters.

 

What did others who used CP pistons do?

 

I interpret the second pic to say that the rings are manufactured for proper gap on stock size bore, when increasing the bore the gap gets larger due to a bigger hole (obviously). I don't believe you should change the calculation. Just bore x .0055 /end

 

I'm starting to think the same thing as you. I had already opened up the first set of rings beyond stock x .0055 so I'll have to repurchase one set of rings if that's the case. I just stopped and will wait till I can get a hold of CP and get a definite answer.

 

The calculation stays the same regardless of bore. You use ONLY the bore and piston to wall clearance isn't factored. Piston to wall is based on piston size and bore size, while ring gap is STRICTLY bore size. I only asked the piston manufacture as some of us that have been doing this long enough don't go by their recommendations.

Are you measing out to your stock bore? NO, OBVIOUSLY YOU ARE 0.020" OVER!!! So use BORE X 0.0055" to get proper ring gaps just as suggested and add or multiply by whatever number for the second ring. To get your proper bore size you MUST measure the bore. A 0.020" over piston isn't actually exactly that, ESPECIALLY aftermarket pistons clearanced for correct P2W.

The little quip at the bottom is clearly for estimation on how wide the gaps will be depending on bore size. Either way, you should always measure and file as needed regardless of their calculations.

 

If your uncertain and not comfortable doing the gap yourself (wasn't mentioned) might want to have a machine shop do it for you.

Just a thought

 

Thank you for the clarification.

I'm perfectly fine doing the gap. Have done it before, I was just confused by that statement in the second pic that started making me think there was some additional consideration I needed to take with these rings.

 

I took the block to the machine shop and had them measure the bores for me while I waited and each cylinder was exactly 2.972" which is dead on the CP ring spec.

I then called CP and verified all I need to do is bore x 0.0055".

Since the first cylinder I gaped at .0019 & .0025 and the other three .0016 & .0022 I ordered a replacement set of rings for the first cylinder and will redo it to match. I wasn't sure if one cylinder been gaped so slightly different would matter but rather safe than sorry.