Piston Protrusion

[dh13]

Okay small question here. So I finally got to the stage where I needed to measure for piston protrusion. I measured all 4 cylinders and retrieved the same results. Even after 2 or 3 times, my measurements remained the same.

On all 4 cylinders I measured a 0.023" protrusion.

My measurements seem on the low size, considering the information in the Bentley.



Piston Height                       Head Gasket Thickness

.0260-.0339"                       1 (1.4mm thick)
(.66-.86mm)                       

.0343-.0665"                       2  (1.5mm thick)
(.87-.90mm)                   

.0358-.0402"                       3 (1.6mm thick)   


Is there anything wrong with having low values?

This is a fully machined and rebuilt motor. The only things reused were the rods, crank, block, and head. Everything else is new.

So I would assume running a 1 notch head gasket would be totally fine. Correct? Also would stepping up to a 2 or 3 notch be better for increased boost and fuel? Although I plan on running stock (ish) boost pressures, but who knows I might want to get crazy so..

[Vincent Waldon]

Thicker headgaskets when you're using more boost is more commonly a gasser trick to help control detonation...not really an issue with a diesel.

[dh13]

Did you have the deck shaved?  If not, then I would and then fit the appropriately sized head gasket.  Using a larger than necessary gasket is a bad way to lower compression if you want to. 

No the block was not shaved. That was the only thing that was not done. The surface checked out so we chose not to do it. I was planning on running the right sized headgasket, I just asked because I have seen some people doing the next step up to lower compression for more boost. I do understand that It will reduce compression by quite a bit and is not benifical.

So if we forget about stepping up to a 2 or 3 notch will a 0.023" piston protrusion be fine with the thinest headgasket? Or do I have to tear it down and have the block shaved?

Thanks

[dh13]

It will run fine.

Alright. I asked my friend at work and I he pretty much said the same thing. It's only 0.003" under the specs for a 1 notch so its not all that bad.

[Turbinepowered]

I just asked because I have seen some people doing the next step up to lower compression for more boost.

Not much of any difference, actually.

Difference between the gaskets, uncompressed, is only .1mm. That's .01cm.

3.14 x (7.65/2)^2 x .01 = volume of the additional space.

That evaluates out to a mere .46cc.

23:1 compression...

3.14 x (7.65/2)^2 * 8.64 + X = 23X

X ≈ 18.04

X + .46 / X = percentage of original ≈ 1.0255


That's less than 3% increase in chamber volume. It won't significantly impact compression at all.

[edit] 22.5:1 static compression.

[dh13]

Not much of any difference, actually.

Difference between the gaskets, uncompressed, is only .1mm. That's .01cm.

3.14 x (7.65/2)^2 x .01 = volume of the additional space.

That evaluates out to a mere .46cc.

23:1 compression...

3.14 x (7.65/2)^2 * 8.64 + X = 23X

X ≈ 18.04

X + .46 / X = percentage of original ≈ 1.0255


That's less than 3% increase in chamber volume. It won't significantly impact compression at all.

[edit] 22.5:1 static compression.

Thanks. I was more concerned with the fact that my piston protrusion was not within the range for the thinest head gasket available. I didn't know if I was screwed something major, or it was not a problem due to the fact that it is only a matter of 0.003".

Thanks for the greatr information.

[dh13]

You are close enough...

That said, having a greater than spec space between piston and head is more of an issue with "Squish and Quench" than it is with compression and thus the reason I never condone using a greater than spec head gasket.  My understanding is that "Squish" is a major factor in creating the proper turbulence in the combustion chamber and "Quench" is a major contributor to transferring heat from the piston crown to the cylinder head cooling system and so cooling the crown.  Lower compression, IMO, is a lesser issue.

I just feel stupid for not having the block shaved. Would it be worth the time and hassle to tear it down for a difference of 0.003"?

The engine had a 2 notch on it as I was tearing it down. I did not have any history on the engine and knew nothing about it. I guess I assumed that with new pistons the piston protrusion would remain the same, but then again this is my first build ever.

What would you do if this happened to you? ( it probably wouldn't because I'm a noob and have no idea what I'm doing so)

[Mark(The Miser)UK]

You are close enough...

That said, having a greater than spec space between piston and head is more of an issue with "Squish and Quench" than it is with compression and thus the reason I never condone using a greater than spec head gasket.  My understanding is that "Squish" is a major factor in creating the proper turbulence in the combustion chamber and "Quench" is a major contributor to transferring heat from the piston crown to the cylinder head cooling system and so cooling the crown.  Lower compression, IMO, is a lesser issue.

I just feel stupid for not having the block shaved. Would it be worth the time and hassle to tear it down for a difference of 0.003"?

The engine had a 2 notch on it as I was tearing it down. I did not have any history on the engine and knew nothing about it. I guess I assumed that with new pistons the piston protrusion would remain the same, but then again this is my first build ever.

What would you do if this happened to you? ( it probably wouldn't because I'm a noob and have no idea what I'm doing so)

Forget throwing money away on skimming the block, as pointed out, 3 thou is minimal. As for squish in an IDI diesel, where are the references to this research Its a DI issue AFAIK

[dh13]

You are close enough...

That said, having a greater than spec space between piston and head is more of an issue with "Squish and Quench" than it is with compression and thus the reason I never condone using a greater than spec head gasket.  My understanding is that "Squish" is a major factor in creating the proper turbulence in the combustion chamber and "Quench" is a major contributor to transferring heat from the piston crown to the cylinder head cooling system and so cooling the crown.  Lower compression, IMO, is a lesser issue.

I just feel stupid for not having the block shaved. Would it be worth the time and hassle to tear it down for a difference of 0.003"?

The engine had a 2 notch on it as I was tearing it down. I did not have any history on the engine and knew nothing about it. I guess I assumed that with new pistons the piston protrusion would remain the same, but then again this is my first build ever.

What would you do if this happened to you? ( it probably wouldn't because I'm a noob and have no idea what I'm doing so)

Forget throwing money away on skimming the block, as pointed out, 3 thou is minimal. As for squish in an IDI diesel, where are the references to this research Its a DI issue AFAIK

Alright that is what I needed to hear.

[dh13]

I just feel stupid for not having the block shaved. Would it be worth the time and hassle to tear it down for a difference of 0.003"?

The engine had a 2 notch on it as I was tearing it down. I did not have any history on the engine and knew nothing about it. I guess I assumed that with new pistons the piston protrusion would remain the same, but then again this is my first build ever.

I've found that the protrusion is typically less with new oversize pistons.  I believe that they move the wristpin bore in order to allow for the deck being shaved.  It's a tough call for me to know how to proceed with that on builds.  You definitely want to avoid the unlikely and very difficult situation of too much protrusion for a 3 notch gasket.  On one of the last builds I did, the deck checked out just fine, but now is weeping at the front of the block where the high pressure oil channel is.  On the next one I build, I have been planning on having it planed for sure even if the deck is fine (I'm also planning on using hylomar).  So the process then would be having it bored, installing pistons and rods on the crank, measuring the piston protrusion and then removing the pistons/rods/crank and having the deck planed.  I think that's pretty much where you're at, although you might have done the TTY spec on rod bolts (I was just planning on doing the initial torque).  At the same time, I think you're engine will run just fine.  It's a fairly minimal difference from spec.

Yes, that was my initial thought. I did not want to have too much for a 3 notch gasket, and then be screwed. You are right about installing the entire rotating assemb. and measuring the protrusion and than tearing it down to machine it. I actually have ARP rod bolts but I don't think I will be tearing it down. Unless someone tells me its not going to run..

[Powered by Spearco]

Sorry for asking this question in this thread, but it is still relivent.
I'm building an engine that has been fully machined which inclueds, boared, honed, line honed and decked.
The machinist said he decked the block .003" and the rods .003". He said that the protrusion would be the same as before.
Well, I assembled the rotating assembly to ckeck the protrusion and it measured out less that before.
Here is the before measurments-

#1= .60mm

#2= .57mm

#3= .57mm

#4= .60mm
So I used a 1notch gasket.
Now it measures out to,
#1= .35mm
#2= .40mm
#3= .43mm
Or did he destroy what I have  .
#4= .27mm
Thats way less than a 1notch gasket. Should I have the block decked more to be sure of correct squish and quench?

[Powered by Spearco]

Your kidding, right. Deck the block at an angle  .
Why would'nt you resize the rods to make the same protrusion, or take some off the top of the pistons.
I don't know that I'd want to off square the blocks deck just to match the protrusion.

I'm wanting to know, if the measurements I gave would cause any ill running conditions?

[Powered by Spearco]

I planned on having the tops and bottoms of the pistons coated anyway. The pistons are KS brand.

I'm not out for cutting you or anyone down on their ideas for this issue. Sorry for the remark  .

I'll see what he says on Monday.

[Mark(The Miser)UK]

I planned on having the tops and bottoms of the pistons coated anyway. The pistons are KS brand.

I'm not out for cutting you or anyone down on their ideas for this issue. Sorry for the remark  .

I'll see what he says on Monday.

What 's wrong with you guys over the pond? Clearly more pocket money  to burn, than the rest of the world
You are not the first to have a slight variation in piston height, and you have the good fortune to be be able to  use  any of the current 3 gasket thicknesses without fear of physical damage to your engine. These engines will run 'well' with compressions down to late 200's psi

 I'm still waiting for the 'Clever Trevors' on this forum to reference specific details linking squish-squash-quench, to INDIRECT injection DIESEL.
All I've seen is research on DI gassers with, argument that squash is naturally required in DI diesels for swirling, but this is achieved with chamber shape and groves in piston crowns.

The tangential entrance to the prechamber on our TD's, cannot avoid accelerating the compressed air into a vortex [apparently optimised by the late great Ricardo to achieve 10 x the rotational speed of the crank.]

Looking at that Quench stuff with my half brain, tells me that it would apply more where combustion takes place in a chamber built into piston.
Good luck with your decisions