Piston protrusion How to figure out what HG thickness to run?

[Dozerboy]

I don't want to just run Cs without checking.

I understand the concept of finding protrusion and needing to check valve recession. I don't know the correct way to take the mesurments. I have a dial indicator with a mag base.

My heads are at the shop getting checked and decked. I'm not sure how much they will have to take off yet.

I have a stock cam. Do I need to take lift into account?



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[PureHybrid]

The correct way to measure is with a "sled gauge" or liner height tool. You can get away with a straight edge across the piston and feeler gauges, but it's not as easy / quick. I had a chart saved that showed what gasket to run with a certain amount of protrusion, but I can't find it. Stock cam I wouldn't worry about lift unless the heads are skimmed and valves aren't recessed too.

 

[techperry]

Grade the gasket on the truck gm measured it so you dont have to. The gasket have holes in a certain position to tell the grade.

 

[TheBac]

Post a pic of the gasket you removed. That'll tell what grade it is.



Henry posted the specs years ago. The pics dont show any more, though.

https://www.duramaxdiesels.com/forum/showthread.php?t=6148

 

[KyleC4]

You can use a dial indicator setup like you have just fine. Just zero out the dial indicator to block deck surface. Then place the pointer over the piston top at piston pin centerline and rotate engine over through tdc.

.0088-.0108in protrusion is Grade A
.0108-.0128in is grade B
.0128-.0148in is grade C

Is the machine shop measuring for warpage across surfaces first or are they just going to mill the head a little anyway ?

 

[Fingers]

I place a vice parallel or other flat piece across the bore and set my dial indicator to zero on top of the piece. Run the piston up and it will push the piece up and indicate on the dial.

I also rock the piston and take the highest value for my protrusion.

 

[Dozerboy]

I'm probably beating a dead horse and should just do Cs, but there is only 1 cylinder that pushing me close to Cs. Over the pin I'm 0.011 on the left and 0.012 on the right. Factory I had B left and C right. The problem is #5 wasn't playing nice and sometimes would mesurment 0.0135.

I checked the rock out on the top and bottom had a max of 0.020 on the left and 0.23 on the right with #5 being 0.021.

Valve recession was 0.024 intake and 0.035 exhaust. Except on #5 which had 2 of 4 valves lower at a 0.023 and a 0.032.

I should probably this as a sign I need Cs. Maybe I should just put some clay in there and check.

I got fuel and air for 700hp max and might get twins before building the engine. Probably wouldn't be pushing it with twins since I'm already playing with fire.

Thoughts?

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[Chevy1925]

What did you use to measure? How clean of carbon were the pistons?

Your talking about so small between the C and B, I wouldn’t worry. I would say run a D on both sides for that power if the D was .002 thicker than a C but they are .010 thicker. Don’t do that lol.

Run a C on both sides and run the power you want. Considering you had no piston to head/valve contact before, it won’t change now. Your also not turning a ton of rpm or running forge pistons.

 

[Dozerboy]

What did you use to measure? How clean of carbon were the pistons?

Your talking about so small between the C and B, I wouldn’t worry. I would say run a D on both sides for that power if the D was .002 thicker than a C but they are .010 thicker. Don’t do that lol.

Run a C on both sides and run the power you want. Considering you had no piston to head/valve contact before, it won’t change now. Your also not turning a ton of rpm or running forge pistons.

Thanks James

Dial indicator. Not very well they where just like you can see in the pics. I didn’t even think about that until doing 5# since it was giving me hell and reading 0.017 on one side. Of course it was on the second to last one, so I only cleaned up the last 2. They where the worse ones though.

I'm sure most know this, but clean (sand) up the deck of the block before aswell. I checked the left side after just scrapping it good with a razer and was coming up with 0.012-0.013. After sanding it was 0.011.

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