Rebuild alh and question about deck flatness

[lyricbaritone]

I have finally gotten around to my rebuild and everything was going fine as I nervously tiptoed my way around assembling the short block. The shop that did the work is in the bumper to bumper family down in Illinois. Great communication during the whole process. So I get to checking the deck fatness and I'm concerned. Checked using a digital depth mic sitting an a 123 block. Checked the left and right side of the pistons for protrusion. Mind you these are brand new pistons that I had shipped to the machine shop to verify size and appropriately hone the cylinders. And they also milled the block. From left to right when looking at the block from the front where the oil stick is. .029 and .024 .032 and .026 .034 and .024 .032 and .025. The 3rd poston shows a .010 difference. So any advice on if this head should be refilled or am I checking it wrong?

20250608_183335.jpg

drive.google.com

 

[csstevej]

I suspect that rod #3 is a bit too long.
Are they new too?
They are supposed to be a matched length and balanced with the pistons.
I would pull that rod and one of the others and do a measurement……

 

[turbocharged798]

You want to take your measurements closest to the wrist pin centerline as possible as the piston will rock in the bore and give you inaccurate results.

What did they set your piston bore clearance at? Should be 0.002" MAX.

Its also possible that the machine shop fixtured the block on the oil pan surface instead of the main journals which will results in a crooked deck. I had a machine shop do this. I don't think this is your situation fortunately.

 

[lyricbaritone]

I suspect that rod #3 is a bit too long.
Are they new too?
They are supposed to be a matched length and balanced with the pistons.
I would pull that rod and one of the others and do a measurement……

Rods are original. When I initially pulled the engine apart I was not aware of the matching of the piston rod to the end cap for connecting to crank shaft. Im not sure if the machine shop numbered them or if they come numbered. Not sure if it matters. The pistons are new along with all the bearings. Pistons came with all the rings too. How do I measure the matched length. My understanding is the two outer pistons are 1 and 2. The inner two pistons are three and four. Not sure if that has any connection to the numbering on the rods.

 

[lyricbaritone]

You want to take your measurements closest to the wrist pin centerline as possible as the piston will rock in the bore and give you inaccurate results.

What did they set your piston bore clearance at? Should be 0.002" MAX.

Its also possible that the machine shop fixtured the block on the oil pan surface instead of the main journals which will results in a crooked deck. I had a machine shop do this. I don't think this is your situation fortunately.

All the cylinders are within a .001 to .0015 window. There was no mention of any issue with the piston diameter. I saw that in a video and the guy used a caliper as a demonstration and got close as well to what he got checking on the centerline. I'll try using my wide base depth mic. The mic i used was spring loaded like an indicator making it ease to find the high point of the piston.

 

[lyricbaritone]

You want to take your measurements closest to the wrist pin centerline as possible as the piston will rock in the bore and give you inaccurate results.

What did they set your piston bore clearance at? Should be 0.002" MAX.

Its also possible that the machine shop fixtured the block on the oil pan surface instead of the main journals which will results in a crooked deck. I had a machine shop do this. I don't think this is your situation fortunately.

All the cylinders are within a .001 to .0015 window. There was no mention of any issue with the piston diameter. I saw that in a video and the guy used a caliper as a demonstration and got close as well to what he got checking on the centerline. I'll try using my wide base depth mic. The mic i used was spring loaded like an indicator making it ease to find the high point of the piston.

I have finally gotten around to my rebuild and everything was going fine as I nervously tiptoed my way around assembling the short block. The shop that did the work is in the bumper to bumper family down in Illinois. Great communication during the whole process. So I get to checking the deck fatness and I'm concerned. Checked using a digital depth mic sitting an a 123 block. Checked the left and right side of the pistons for protrusion. Mind you these are brand new pistons that I had shipped to the machine shop to verify size and appropriately hone the cylinders. And they also milled the block. From left to right when looking at the block from the front where the oil stick is. .029 and .024 .032 and .026 .034 and .024 .032 and .025. The 3rd poston shows a .010 difference. So any advice on if this head should be refilled or am I checking it wrong?

20250608_183335.jpg

drive.google.com

UPDATE: I checked in center line and I think I'm good but what I am seeing is that cylinders 1 and 2 have movement on high point with every turn. It's not consistent and so inwonder if it's normal. As a machinist, i think I'm ok. Though the world of combustion engines is new still to me as this is my first rebuild. The fluctuation is within .002 on 1 and 2. 3 and 4 checked nearly the same. I have torque all the bolts thus far as you know torque spec + 90 deg. That seems to stabilize the readings on the protrusion of the pistons.

20250609_045841.jpg

drive.google.com

20250609_045809.jpg

drive.google.com

 

[Prairieview]

This is horrible! According to your photos, you have two of the pistons in the WRONG hole. The #2 piston needs to be in the #4 hole and vice-versa.

And, you are saying you did not keep the connecting rod caps MATED with the corresponding rod?????????
Wow....I just pulled all of my hair out.

 

[lyricbaritone]

You miss understand me i have 1 and 2 pistons in the first and fourth holes. I did keep the caps....I just didn't know that they were matched. The machine shop figured all that out for me after I sent the block in. So ignoring your hyperbolic statement....let me understand then that the 3/4 labeled pistons are for cylinders 3 and 4? I was understanding that it was in reference to firing order.

 

[JETaah]

Yikes.
The pistons fire in 1,3,4,2 order starting from the pulley side of the engine.

Take a look at how the valve pockets on the piston tops should match the valve positions on the head.
Yes, piston 1 and 2 are oriented alike and pistons 3 and 4 are oriented alike.
The piston in #4 position has no markings on it and by the looks of the protrusion numbers looks like it is mismatched to the others.

If your piston do not actually protrude anymore than what you show then the shop did not remove enough material of the block deck.
Or it is very close. It is hard to tell.
The minimum the pistons should protrude above the deck is .033". and that is with using the thinnest head gasket choice.

What brand of pistons did you get?

And if one piston protrusion is actually .010" shorter than the others then you have a bent connecting rod.
Or it is due to a mismatched piston.

All these dimensions are highly critical for a diesel engine.

The correct way to measure piston protrusion is with a dial indicator along the wrist pin line.
Your method may work OK.

What kind of piston to cylinder wall clearance do you have? Yours looks huge but it could be deceiving.
Should be a maximum of .002" on the skirt.



If you want help with all this contact @Franko6 .
Perhaps he will stroll by.
I would stop at this point until you get real help or you will be wasting materials.

 

[lyricbaritone]

Yikes.
The pistons fire in 1,3,4,2 order starting from the pulley side of the engine.

Take a look at how the valve pockets on the piston tops should match the valve positions on the head.
Yes, piston 1 and 2 are oriented alike and pistons 3 and 4 are oriented alike.
The piston in #4 position has no markings on it and by the looks of the protrusion numbers looks like it is mismatched to the others.

If your piston do not actually protrude anymore than what you show then the shop did not remove enough material of the block deck.
Or it is very close. It is hard to tell.
The minimum the pistons should protrude above the deck is .033". and that is with using the thinnest head gasket choice.

What brand of pistons did you get?

And if one piston protrusion is actually .010" shorter than the others then you have a bent connecting rod.

All these dimensions are highly critical for a diesel engine.

The correct way to measure piston protrusion is with a dial indicator along the wrist pin line.

What kind of piston to cylinder wall clearance do you have? Yours looks huge but it could be deceiving.
Should be a maximum of .002" on the skirt.

If you want help with all this contact @Franko6 .
Perhaps he will stroll by.
I would stop at this point until you get real help or you will be wasting materials.

I checked on center the best I could and if you look at the pictures. The pistons are protruding about 23 to 25 thousandth. I sent the Rods with the block and crank to the shop and they didn't say anything about a bent rod. And the numbers I'm getting with the pistons on center say there are no bent rods. Im gonna pull the pistons and check the rings. I'll update when I have another question or issue.

 

[JETaah]

The time that I’ve bought replacement pistons, usually oversized by .020” in diameter(Nural brand) they were.010” shorter than the originals.
The thinking here is that if you have to correct the blocks surface for whatver reason it gives you .010” to do so and retain the original protrusion .
Most engines from VW had pistons that protruded right about .040” above the deck.
The fine tuning is done we with a choice of three different thicknesses of head gasket.

 

[JETaah]

.023-.025” is not enough protrusion.
.033-.035” is barely enough.

 

[Prairieview]

Quite frankly, I think there are very few machine shop employees out there that remotely understand these engines or care to attempt to understand squat. I have 5 machine shops here and I avoid all buy one of them like the plague. The only one I work with took me 15 years to convince them of the importance on the tight clearances in VW diesel cylinder bores.

The young guys that come out of trade schools tend to only work on a 350 Chevy......ONCE. They have no clue. They wear their ball caps sideways on their heads and never get off their cell phones.

I still think his protrusion irregularities could be due to mis-matched or mis-oriented conn rod caps. I bet his holes have been cut to 350 Chevy specs. 250,000 miles of chips on the floor.

 

[turbocharged798]

That's why I mentioned that. I had one shop cut the bores at 4 thou and that engine always piston slapped and burned oil.

Nural oversize pistons are known to have a short crown and will result in lower than factory protrusion if the deck isn't cut sufficiently. I am not really a fan of those pistons for that reason. I prefer KS or Mahle pistons.

 

[AndyBees]

Where's the popcorn?

 

[favid6]

Looks like you’re measuring carefully, which is great. A 0.010 difference across the deck might be borderline but usually still acceptable if within the manufacturer’s specs. If you’re unsure, getting the head resurfaced could be a safe bet to ensure a perfect seal. Would love to hear what others think on this !

Tutuapp​

 

[Yaro]

Great to hear the rebuild’s coming together! Those protrusion numbers look a bit uneven, especially the .010 difference on #3. Ideally, they should be within a few thou of each other for proper gasket sealing and longevity. Might be worth double-checking your measurement method, but if it holds, I’d definitely talk to the machine shop before sealing it up.