critter

iTrader: (9)

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.

64post

iTrader: (5)

If the piston is allowed to rock in the bore you will get a lot of errant readings.

critter

iTrader: (9)

They are a tight fit. I can't measure more than 0.001". And in any case, errant readings should be consistent.

Exidous

iTrader: (11)

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?

critter

iTrader: (9)

No. Not rock. Those measurements are without rock.
I don't know what the piston clearance is. I would have to take the short block back apart to measure. But the issue is not different size pistons, it is that the piston top is not perpendicular to the centerline of the bore.
Proved? What do you mean? I measured first with a depth mike and then, not believing what I saw, repeated with a dial indicator.

Exidous

iTrader: (11)

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.

KCS

iTrader: (20)

This.

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.

critter

iTrader: (9)

Didn't change the numbers.

Exidous

iTrader: (11)

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.

RockinWs6

Before you do ANYTHING more, pull the pistons, measure the bores and measure the pistons to see where you are at. How can you assemble a engine with out checking the piston and bore sizes?

critter

iTrader: (9)

You find it hard to believe? You think I don't? That was the point of this post, to see if it was normal. Back in the day, this never would have happened.

I have been doing this for 50 years. My measurements are accurate.

Exidous

iTrader: (11)

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.

critter

iTrader: (9)

Yeah, the short block is coming apart again.

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.

critter

iTrader: (9)

Yeah, the short block is coming apart and I think I will start from scratch. Go 60 over, square the block, etc.
That isn't an option. It is a long story, but with divorce, remarriage, cam sensor going bad, other stupid gremlins, too much time has passed.

Exidous

iTrader: (11)

That's a pretty crazy short story! Get the dial bore out and mic the pistons. At least that way you can see how bad(or maybe no so bad) things are.

machinistone

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.

critter

iTrader: (9)

I don't have a bore gauge or big mic anymore but I checked with a feeler gauge. A 0.002" one one piston and 0.010" on another. I also stuck #3 back in without rings so it was easier to rock, and those crazy number are good. The pistons were custom made - Diamond does not stock 40 over - and it look like they did not do a good job. Obviously the machine shop did not do a good job either.

So, new pistons and back to a different machine shop.