Piston Uneven In Bore

[aspekt9]

I just put together my motor and it seems that on the some of the pistons one side sits slightly higher than the other side. Is this a problem? I did have the deck resurfaced so maybe it's from that? Will this cause any issues?

 

[BogusSVO]

did you rock the pistons in the bore? should have a very slight amount of movement

measure the block, from the head gasket surface to the oil pan rail

I hope rhe machine shop did not have your block tilted when surfaced.

 

[wranglerunner22]

did you rock the pistons in the bore? should have a very slight amount of movement

measure the block, from the head gasket surface to the oil pan rail

I hope rhe machine shop did not have your block tilted when surfaced.

x2 .....

 

[aspekt9]

did you rock the pistons in the bore? should have a very slight amount of movement

measure the block, from the head gasket surface to the oil pan rail

I hope rhe machine shop did not have your block tilted when surfaced.

I did rock the pistons in the bore, they do have very slight amount of movement. I know the mains were honed, not sure if this would affect or not. I'm pretty sure it's only one piston that I'm having issues with, I need to check again when I get home. I have a 3 hole bridge and two dial indicators, so I'm going to get accurate numbers.

As far as I know left to right height is perfect, it's front to back that the intake side of the piston is a tad higher. They're a very reputable machine shop so I would think not.

So the piston should sit flush? Would you suggest I don't run it how it is?

Also, is there an allowed variance between front and back piston height? Would I average front and back for each piston to for each cylinder and then compare variance?

Lastly, what exactly is piston rock and how doe sit affect the height of the front and back of the piston? I can push the piston down on the side that's up and level it out, I'm not sure what that means though?


UPDATE:

So I measured everything out with a bridge stand and dial indicator. I placed the dial indicator on the block and zeroed it out each time then moved it over the piston and rotated the crank to find the highest point and recorded it for each piston for the Front and Rear and also for the Firewall and Radiator sides. Here's the results attached.

Now I'm thinking I know why #2 is off. This was a piston that fell out of the block when I had it upside down and it put two little tiny dents on the piston where the top meets the side. I brought it down to a machine shop and had them look at it and the guy said just to file them down and it'll be fine. Is it possible thats why my measurements are off?

I can also push the high side of the #2 piston down in the bore and get 0.05 out of the bore and 0.01 in the bore on the opposite side.

So what do you guys think? Do I need to look into getting a new piston?

 

[aspekt9]

Are the other measurements within reason?

 

[mjag60edsm]

If the unit of measurement in your table is inches, piston #2 has a definite problem. You state that the #2 piston has almost an 1/8" slope?? If the unit of measurements are in millimeters then the slope is only approximately four thousandths of an inch and that is well within the normal range. I also may humbly take issue with how you are measuring. Try and re-do the dimensional information with the following idea in mind:

First of all you have to establish a "plane" of reference that is stable. For this task I would make the assumption that if the machine shop surfaced your block then this is the plane that you would assume to be your reference (whether or not the shop had your block tilted when they surfaced it or not doesn't matter at this point). I would make sure your indicator post is stable (doesn't move as you slide the base along the surface of the block) and zero the indicator to the top of the block only once. Since pistons are relatively free to rock inside their respective bores with only one degree of freedom (axially on the center-line of the wrist pin) then you really should make your measurement from the top surface of the block (reference plane) to the top of the piston perpendicular and coincidentally to the axis of the wrist pin). Slide the indicator base to each piston bore and take the four measurements as indicated ensuring that each piston is TDC before recording the measurement. If I was doing this I would position my indicator on top of each piston with the piston slightly below TDC, rotate the crank until the indicator rises and then falls and measure the smallest indicator reading (distance from reference plane - block surface). If the delta from each of those four measurements differ greatly then you have issues, either the block was not surfaced parallel with the crankshaft center-line, your rods' center-lines are off, etc. If all four measurements are within reason to each other then your block was surfaced parallel to your crank, which states the reference plane is good in one direction.

Have you checked your cylinder bore to piston clearance? In my opinion you cannot measure piston edge to block surface with any accuracy without jumping through some hoops. Just think what the delta measurement from side to side of piston would be if your bore was say .0015" over and the piston was free to rock, depending on the preload of rings, etc.

Let us know after you take the new measurements and we will keep digging into your problem for you.

GOOD LUCK!!

 

[aspekt9]

If the unit of measurement in your table is inches, piston #2 has a definite problem. You state that the #2 piston has almost an 1/8" slope?? If the unit of measurements are in millimeters then the slope is only approximately four thousandths of an inch and that is well within the normal range. I also may humbly take issue with how you are measuring. Try and re-do the dimensional information with the following idea in mind:

First of all you have to establish a "plane" of reference that is stable. For this task I would make the assumption that if the machine shop surfaced your block then this is the plane that you would assume to be your reference (whether or not the shop had your block tilted when they surfaced it or not doesn't matter at this point). I would make sure your indicator post is stable (doesn't move as you slide the base along the surface of the block) and zero the indicator to the top of the block only once. Since pistons are relatively free to rock inside their respective bores with only one degree of freedom (axially on the center-line of the wrist pin) then you really should make your measurement from the top surface of the block (reference plane) to the top of the piston perpendicular and coincidentally to the axis of the wrist pin). Slide the indicator base to each piston bore and take the four measurements as indicated ensuring that each piston is TDC before recording the measurement. If I was doing this I would position my indicator on top of each piston with the piston slightly below TDC, rotate the crank until the indicator rises and then falls and measure the smallest indicator reading (distance from reference plane - block surface). If the delta from each of those four measurements differ greatly then you have issues, either the block was not surfaced parallel with the crankshaft center-line, your rods' center-lines are off, etc. If all four measurements are within reason to each other then your block was surfaced parallel to your crank, which states the reference plane is good in one direction.

Have you checked your cylinder bore to piston clearance? In my opinion you cannot measure piston edge to block surface with any accuracy without jumping through some hoops. Just think what the delta measurement from side to side of piston would be if your bore was say .0015" over and the piston was free to rock, depending on the preload of rings, etc.

Let us know after you take the new measurements and we will keep digging into your problem for you.

GOOD LUCK!!

Thanks for the correct information on measuring. I went back and remeasured everything. My piston to wall clearance is .002. Here's a photo attached of the excel sheet with the new
measurements.

Why would the two middle pistons rock higher on one side? Is that normal? Also an issue to keep in mind is that these are 2g pistons and the top-sides of the piston are not perfectly flat, so their surface plays a part in actual measurement. Is the Front-to-Rear play on the 2nd one (0.05) too much? What kinds of "allowable" readings am I looking for when looking at the variance?

 

[mjag60edsm]

could you please answer what the unit of measure is in your spreadsheet? inches or millimeters?

 

[romeen]

aspekt9, just curious if that is just some lint or something and not a crack right above where the wrist pin goes in this pic:

Picasa Web Albums - aspekt9

I guess it's fine since the machine shop checked it out?

 

[aspekt9]

could you please answer what the unit of measure is in your spreadsheet? inches or millimeters?

Unit of measure is inches.

And above the wrist pin is a scratch.

I think I'm going to swap out that #2 piston because the front to rear clearance compared to the other 3 is way off. I think it was from when it was dropped. After that, I don't really see there being an issue, my head gasket is 0.057" thick so piston to valve clearance should be fine. Using the highest recorded measurement of 0.11" gives me 0.046" of quench but I wont know exactly until I measure. I mean how much difference can 0.01"-0.02" make? Most of it probably comes from the inconsistent surface of the 2g piston. What do you guys think? It probably also doesn't help my dial indicators only measure with accuracy to 0.01".

 

[mjag60edsm]

According to your chart and based on the fact that you said your unit of measure is inches I think you have an issue that needs resolving before you go further. Pistons DO NOT rock in cylinder walls this much. Based on your .002" stated piston to cylinder measurement you are on the high side of the limit but should be okay. Did you measure your ring gaps? I would definitely do that next. If I am understanding correctly you are saying that piston #2 (and piston #3 is almost as close) is out of parallel with the block surface by almost an eight of an inch across the piston??? NO WAY can this be right. I think that most of your problem might be on how you are measuring... using a dial indicator that only indicates hundredths is like measuring ring gaps with a yard stick. Machining specs on engines are measured in thousandths and ten thousandths. Hundredths don't give you enough resolution to determine much. I suggest borrowing a precision indicator or take the assembly to the shop and have someone re-do the measurements. Your math is wrong on the .057,.11,.046 argument you make in your last post... you have a decimal issue. Anyway, my opinion is you need another pair of eyes looking at this with you to help determine what is going on. I would not assemble further without resolving this because I see a big issue. Hope this helps and sorry for your problems.

Piston Clearance
N/T .008 - .0016
Turbo .0012 - .0020

Ring Gap
#1 .0098 - .0177
#2 .0138 - .0197
Oil .0079 - .0276

 

[aspekt9]

According to your chart and based on the fact that you said your unit of measure is inches I think you have an issue that needs resolving before you go further. Pistons DO NOT rock in cylinder walls this much. Based on your .002" stated piston to cylinder measurement you are on the high side of the limit but should be okay. Did you measure your ring gaps? I would definitely do that next. If I am understanding correctly you are saying that piston #2 (and piston #3 is almost as close) is out of parallel with the block surface by almost an eight of an inch across the piston??? NO WAY can this be right. I think that most of your problem might be on how you are measuring... using a dial indicator that only indicates hundredths is like measuring ring gaps with a yard stick. Machining specs on engines are measured in thousandths and ten thousandths. Hundredths don't give you enough resolution to determine much. I suggest borrowing a precision indicator or take the assembly to the shop and have someone re-do the measurements. Your math is wrong on the .057,.11,.046 argument you make in your last post... you have a decimal issue. Anyway, my opinion is you need another pair of eyes looking at this with you to help determine what is going on. I would not assemble further without resolving this because I see a big issue. Hope this helps and sorry for your problems.

Piston Clearance
N/T .008 - .0016
Turbo .0012 - .0020

Ring Gap
#1 .0098 - .0177
#2 .0138 - .0197
Oil .0079 - .0276

UPDATE:

I'm an idiot. My dial indicator measures to .001"... Add an extra 0 after that decimal to my measurements. So does that put me in the safe zone now?

 

[mjag60edsm]

I am feeling a WHOLE LOT better about this now. There is a big difference between .11 and .011. Based on the way you are measuring it is probably ok.