Weird diamond pistons
Weird diamond pistons I measured deck clearance so I could order head gaskets and got a big shock. None of the pistons are square with the bore. The best is only 0.002" difference intake side to exhaust side and the worst is 0.032". Some are higher on the intake side; some on the exhaust side. The range is from 0.005" below deck to 0.027" above. Is this normal for Diamond pistons? I don't know what to do at this point. The pistons were purchased by the shop that assembled the engine but only have a few miles on them because the idiot left something in the pan that plugged the oil pickup and took out the front two rods and the journal. I decided to assemble it myself this time but am now stuck.
Are you saying you have one piston with a total of .002" rock and another with .032" ? The low point on exh or intake should be the same unless the piston has an offset pin. Just as the high points should be the same. The avg between the two (int/exh) is how much you are above or below the deck.
All 8 of the pistons should be the same size. I'm inclined to think your bores are not the same. .002" rock is way too tight for a forged piston.
Based on your drawing, could you proved the min/max on each side of the piston?
All 8 of the pistons should be the same size. I'm inclined to think your bores are not the same. .002" rock is way too tight for a forged piston.
Based on your drawing, could you proved the min/max on each side of the piston?
Are you saying you have one piston with a total of .002" rock and another with .032" ? The low point on exh or intake should be the same unless the piston has an offset pin. Just as the high points should be the same. The avg between the two (int/exh) is how much you are above or below the deck.
All 8 of the pistons should be the same size. I'm inclined to think your bores are not the same. .002" rock is way too tight for a forged piston.
Based on your drawing, could you proved the min/max on each side of the piston?
With a dial indicator, measure min and max on int and exh sides. just rotating the engine around till TDC will give you VERY wild results. You must measure min and max on both sides and create an average. Piston rock can also give you an idea of piston to wall(PtW) clearance.
Make sure to use a dial indicator to find TDC for the piston.
With the dial indicator and bridge, on the exhaust side measure min and max(measure about .5" from edge). Using the deck at a zero ref. As an example, you get -.005 min and .013" max on the exh side. This averages to .004" out of the hole. Do the same for the intake side. You should get the same numbers if the piston pin is not offset. If the numbers are different take an average again. Say int is .006" out. You'd avg overall at .005" above deck.
Now the rock of -.005" to .013" is where you get an idea of PtW clearance. The piston manufacturer should have an idea of what rock the piston will give you for a given PtW clearance.
Make sure to use a dial indicator to find TDC for the piston.
With the dial indicator and bridge, on the exhaust side measure min and max(measure about .5" from edge). Using the deck at a zero ref. As an example, you get -.005 min and .013" max on the exh side. This averages to .004" out of the hole. Do the same for the intake side. You should get the same numbers if the piston pin is not offset. If the numbers are different take an average again. Say int is .006" out. You'd avg overall at .005" above deck.
Now the rock of -.005" to .013" is where you get an idea of PtW clearance. The piston manufacturer should have an idea of what rock the piston will give you for a given PtW clearance.
With a dial indicator, measure min and max on int and exh sides. just rotating the engine around till TDC will give you VERY wild results. You must measure min and max on both sides and create an average. Piston rock can also give you an idea of piston to wall(PtW) clearance.
I tried to google the correct way to measure this to get some illustrations and there is a lot of bad info on the subject. No wonder it's done incorrectly so often.
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With a dial indicator, measure min and max on int and exh sides. just rotating the engine around till TDC will give you VERY wild results. You must measure min and max on both sides and create an average. Piston rock can also give you an idea of piston to wall(PtW) clearance.
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Verdad Gallardo So you're saying on piston 3 exh side you got an average of -.005" and int side .027"? I find that extremely hard to believe.
Could you make another drawing before any averaging? Each side of every piston should have two numbers, a min and max.
Could you make another drawing before any averaging? Each side of every piston should have two numbers, a min and max.
I have been doing this for 50 years. My measurements are accurate.
It's very odd that the int and ext are so different. They should be darn near the same. If you are certain of the measurements it's time to pull the pistons and rods and measure the bores.
I'd take it back to the builder if that's an option.
I'd take it back to the builder if that's an option.
Why didn't I measure everything? Because the engine was professionally assembled. However, they left something in the pan that plugged the pickup, as I said in my first post. Should be a no brainer - get the $2500 crank fixed, buy two new rods and bearings, button it up. I will grant that the fact that I had to take it apart in the first place should have been a clue. I guess I have too much faith in humanity.
I'd take it back to the builder if that's an option.
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Joined: Aug 2006
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From: North Bay, CA
Did you measure the piston skirts when they were out after the first blow up to make sure they were not collapsed?
It's very likely that your original issue has done more damage than just the two rods vs. this being an issue with Diamond.
It's very likely that your original issue has done more damage than just the two rods vs. this being an issue with Diamond.
So, new pistons and back to a different machine shop.