Going nuts - Piston height - deck

[Bryan]

22 minutes ago, Loren said:

0.002?

 

I hope I didn’t spoil your day.

Look again..most of what I stated was .02 difference in compression heights for pistons.  2.00 vs 1.980 for rebuilder pistons.   At least you didn't end your post with "Just sayin".  

[FarmerJon]

Any whichaway $95 for a set of 6 pistons inst bad at all. Please post what you find when you weigh them, and a picture of their underside

[Bryan]

39 minutes ago, FarmerJon said:

Any whichaway $95 for a set of 6 pistons inst bad at all. Please post what you find when you weigh them, and a picture of their underside

Arbitrary numbering 1-6:   1. 475.9 grams   2. 475.8 g    3. 480.0 g    4. 477.7 g   5. 476.9 g   6. 481.0 g   I haven't cleaned them yet, but no heavy deposits.  The ring lands are tight, unlike my used pistons.   Pictures of 2 pistons' undersides. Most the same.

[Sniper]

I will be curious to read your research into the best way to clean them.  Chemical cleaning might etch the ring lands.  Abrasive cleaning might do worse.   

[Bryan]

1 hour ago, Sniper said:

I will be curious to read your research into the best way to clean them.  Chemical cleaning might etch the ring lands.  Abrasive cleaning might do worse.   

The sides though discolored are very smooth to the touch.  I'll leave the ring lands alone, they're shiny & clean. Going to try baking soda and lemon juice mixture. Also read that Cream of Tartar can clean aluminum, and coffee cups. If the spots don't come out, I'll leave it.  Only the tops are rough with deposits, probably corroded aluminum.  Always have my glass plate and 2000 grit sandpaper to smooth the tops.  As long as I don't take off more than a 1/2 hair width. ? Looks like someone has already been using fiber pad on the sides.

[Bryan]

More pics. I'll clean a little tomorrow.   Spots are smooth.

[Sniper]

You know I vaguely recall that Chrysler plated pistons with something (tin?) to help with the break in procedure.  I wonder if that is what is coming off?

[Bryan]

9 minutes ago, Sniper said:

You know I vaguely recall that Chrysler plated pistons with something (tin?) to help with the break in procedure.  I wonder if that is what is coming off?

Don't know. On the skirts I won't scrub too much. Don't want to remove too much material.  It's smooth to the touch. Let the cylinders do all the work. I'll try it tomorrow.

[Bryan]

Cleaned one up with a damp paper towel and brasso.  About 3 times.  Looks like VPW polished them a little before sending off but no scratches you can feel.   Forgot I have to go off and cut grass today. I think they will clean up well. Heck, only the tops are visible.  On the top "spiel" means play. .06?  Sounds a lot.

[Bryan]

On one piston except for the top, think that's about as clean as it will get. Still measures the same on skirt as others.  Not perfect but will work.

[Bryan]

On 5/18/2022 at 6:39 AM, Bryan said:

 I think they will clean up well. Heck, only the tops are visible.  On the top "spiel" means play. .06?  Sounds a lot.

Sometimes got to get the brain to working.  .06 mm is .0024" duh.  Other number 83.26 mm is 3.28".   Namely .030 over.

[Bryan]

On 5/17/2022 at 9:29 PM, Bryan said:

 Only the tops are rough with deposits, probably corroded aluminum.  Always have my glass plate and 2000 grit sandpaper to smooth the tops.  

Cleaned 2 piston tops up. Not feeling well today.  Maybe got too hot yesterday.   Was using the glass plate/sandpaper method but on one piston the top is slightly dished (one on the right). Not trying to make them flat. Went to use 0000 steel wool but got to generating metal fibers, even using it wet. Too much for me inside. Might go to Scotchbrite pads..

[FarmerJon]

Somewhere there is a chart/list of abrasive blasting media vs what it removes. There are several that should work iirc. 

I know that piston coating companies blast the areas to be coated. 

I wouldn't be afraid to use 400-600 grit sandpaper on the crown, on the glass. You aren't going to take .001 off with 400 grit without major effort. 

Usually when a shop bores a block, they hone it to match each piston. If your skirts 'shrink' by a tenth or two, there will be no consequence. Now, to be fair, usually the piston skirt isn't just a cylinder, but has some barrel shape to it, but again, with ultra fine abrasives and some care, you aren't likey to take enough off to matter.

 

[Bryan]

Seems like Scotchbrite is faster than 0000 steel wool. Made sure I rotated the piston so any scuff pattern on sides would be horizontal. Slow work.  Still not going to get all the spots on the sides out but you can't see them anyway.   Before starting I measured the distance from the top of the pin hole to the top of the piston (front and rear). To later see if I was changing the compression height as I cleaned the tops.  Checked 2 pistons a 2nd time after all measurements to see if I was consistent.  Yep, same.

 

#1 - 1.5730 front    1.5750 rear  Checked twice

#2 - 1.5715 front     1.5725 rear

#3 - 1.5700 front    1.5725 rear   Checked twice

#4 - 1.5735 front     1.5740 rear

#5- 1.5740 front       1.5745 rear

#6 - 1.5735 front     1.5745 rear

 

Example:  On #3 1.5700 + .42965 = 1.999" compression height

[Sniper]

Nice work

 

[Bryan]

On 3/24/2022 at 2:24 PM, James_Douglas said:

I have three blocks sitting in the corner and two in cars. ALL had different piston deck heights when I took them apart. Some as much as a 1/4 inch difference.

That made me check my block . Somewhere, you or someone else mentioned that there could be a difference in height from front to back.  Glad I did check.  I used one of the older 48 Dodge pistons with the rings off, and a # 1 rod.   It measured 1.5730" from top of pin hole to top of piston. Just like my VPW NOS pistons which were between 1.5700 & 1.5750.  Well, the D46 block top is straight (flat) as I knew, but lower at rear than at front. #1 piston - .012 clearance,  #3 piston - .009, # 5 piston - .003.  This was at the tightest spot, a model number embossed on piston top near middle. The pistons are slightly domed on a 1" circle in the middle. Even if I sanded the tops perfectly flat, still would have #1 piston - .016,  #3 piston - .013, # 5 piston - .006.  One funny thing is that the #5 piston seemed higher at the rear than 1 & 3.

[kencombs]

Could be the block tapered, top of block to main bearing bore difference, Or crank stroke not identical on all throws.  I'd bet the latter would be common on reground cranks from mass production shops from back in the day.

[Bryan]

13 minutes ago, kencombs said:

Could be the block tapered, top of block to main bearing bore difference, Or crank stroke not identical on all throws.  I'd bet the latter would be common on reground cranks from mass production shops from back in the day.

Probably the block top is tapered. It is progressive from front to back. What fooled me at first was the deck is perfectly flat.  Didn't think about it not being level.  I tired to keep things constant by using the same rod and piston.  Any guess at why the #5 is higher at the rear (with same rod & piston)?  Would suggest the #5 crank journal is not parallel to top.

[Bryan]

I'm going bonkers. Started checking the even pistons using the #2 rod.   First check on # 2, expecting .011-.010 since # 1 was .012".   Freaking piston is about .010 over the deck on # 2.   I'll check #4 and 6, to see if the piston gets higher towards the back (block lower) as 1 ,3 and 5 did.

 

Reckon I'll start comparing rod lengths, I'm using the same piston as I did with the previous check.

 

Bryan

[Bryan]

So, that doesn't make sense. After #2 was off, I used the bearing inserts from the first rod I used to check #s 1, 3 and 5, thinking maybe it was different.  Still did not help. 

#2 still .010 above deck at front (of piston), almost flush at rear.   #4 - flush at front and rear of piston,  # 6 flush at rear,  .006 above deck at front.

 

Anybody ran across this before?  

Edited July 1, 2022 by Bryan
clarified front/rear of piston