Piston Protrusions

[wilharper2000]

Hi guys

Just rebuilding my 1.6td properly and have measured the piston protrusions, which are as follows:
Cyl. 1 - 0.98mm
Cyl. 2 - 1.02mm
Cyl. 3 - 0.98mm
Cyl. 4 - 0.98mm

This is right on the limit of a 3 notch gasket, i think due to the fact the block has been faced and new small end bushings have been fitted. I have removed and checked Cyl.2 assembly and reinstalled and got the same measurement.

I carried out a good analysis of my measuring equipment and I think I can be confident to 0.02mm, therefore my Cyl.2 may be slightly over.

What im trying to work out is if this may cause an issue with valve piston contact. Initially I was going to have the conrod reworked but then I remembered there is actually quite a lot of tolerance in the cylinder head, specifically valve recess depth (0.5mm - 1.50mm) for this engine. Mine are all 0.95mm

Can anyone tell me if i'm right to think that this allowance gives me a bit of room on piston protrusion? I've attached a little drawing to primarily help me understand this but it might help explain what im getting at. Ignore the cam position! Thanks, Will

 

[csstevej]

I’d give Franko6 a shout and see what he says.......

 

[Franko6]

Yeah, I'm an encyclopedia for obsolete European IDI engines..

 

[Prairieview]

If you had a short height among the other three, I would say to swap the two "opposing" (height-wise) pistons/holes and see if that corrects/lessens the "problem."

Is there any hint that one or more of the rods has been swapped? Are the pistons brand new from the same manufacturer and bought in a set? You fail to leave out pertinent details.

I have very successfully rebuilt a bunch of the 1.6 12mm engines in the last 15 years. One particular engine was torn-down (from previous owner's too-tight cam belt mistake with subsequent front int. med. shaft bearing hogged). The pieces of the bearing material stuck the oil pressure relief valve and popped the oil filter (common mistake over the years). So, I elected to totally disassemble and launder the entire engine block.

Upon reassembly (with the very recent high-end piston installation (Nurals)) of the engine (all new bearings and rings), I also had one piston which stood high-enough to warrant a 3-notch gasket. The other two were within 2-notch status. I wanted to stay 2-notch.

After much consideration, I elected to lay the block on it's side (for dust control) and carefully used a small precision-ground block and sand paper to "shave" the top of the offending piston. It did not require much and I knew the Nurals had very strong piston-pin to crown strength.

I also theorized that any removal of the top was not going to disrupt the dual-swirl indents. And, I was right. That engine continues to be one of the rockin-est 1.6's I ever put together.

In your case, I don't think you have to do anything. You are "within" spec. End of story. I don't even think you are going to have additional white-smoke on cold start-up either.

I sincerely hope you replaced the lower-end bearings and int. med. shaft bearings as well.....and checked the oil pump shaft bushings for play in the block. Don't run the cam belt too tightly.

Additionally, you really should have paid to have the conn. rods checked and re-conditioned. If this was not done.......not good.

You know, I have YET to ever have any of these blocks cut down. What I do, is to take the time to hand-sand the block deck with precision-ground block and sandpaper. I end up with a glass-smooth surface and never have head gasket problems. I also hand sand the head faces. I also do the same with the newer ALH engines. I just don't have any problems....period.

 

[Vince Waldon]

I sincerely hope you replaced the lower-end bearings and int. med. shaft bearings as well....

Or at least inspected 'em... so much easier to R&R while the engine is in the stand.

 

[wilharper2000]

Thanks for the replies, to answer some questions.

OS 0.5mm Kolbenschmidt Pistons (reused from last build but good condition)
New KS Piston Rings (gapped to new bores)
Spare 80hp SB Indirect Injection block, acid stripped and bored
Conrod small end bushes replaced and checked
New IM bearings
New KS Main and Rod Bearings
Crank checked and polished
New Genuine VW 36mm oil pump
New Genuine VW turbo diesel cylinder head (from VW Classic Parts)

Quite a lot of work gone into this build so I don't want to take the chance of something messing it all up!

I have rechecked my protrusions and I seem to be able to repeat 1.02mm on the Cyl.2 piston, so i'm pretty sure its around that height. I'd rather keep it at this than start taking it all apart.

The only time i've had unwanted valve piston contact on these engines is when a cylinder head I had had a very small valve recession (0.2mm).

The spec is 0.5mm to 1.5mm for valve recession on this engine and I believe this should give me some allowance if I am say 0.02mm over maximum piston protrusion if my valve recessions are about 0.95mm.

Someone please correct me if im wrong though!
Just to say I had also messaged Franko6 as suggested and he's been very helpful, so thanks!

 

[Franko6]

The KS pistons are good stuff. Since you told me Will, that they are coated, I would not touch them. The difference is a grand total of .002", which in the scheme of things is really closer than VW is normally going on that engine. Swapping rods will not do a thing. Piston to piston, KS pistons are 'peas in a pod'.

Don't get me wrong, Prairieview, on Nurals and KS for the ALH engine, we have a very simple method that works just fine. If you check, the outside edge of the Nurals, in particular, have a tall perimeter and shrink slightly to the middle We have reduced the overall height of a piston .002" without removing the engraving on top of the piston. Weight-wise, it is insignificant.

Go with the tallest piston height to determine the correct gasket thickness.

I'm inclined to go with the minimum spec for valve recession, but milling off a brand new head is NOT what I'd do. The pre-chamber cups are properly done and it's brand new. Don't mess with it! As I said and you mirrored, the cups are protruding slightly, which is exactly correct. You won't get anyone to improve on what's been done.

LEAVE IT ALONE!

Footnote: Decking a block with a piece of sandpaper has to be a time-consuming and arduous affair. But you can't really say you aren't decking the block. That is exactly what you are doing. The head bolts aligned the way they are, have a very high tendency to pull the sides of the block up. This is exacerbated with later engines and the higher torque load bolts. So, albeit, it's a lesser issue with the 1.6's, it's still there.

The second issue is actually, there is a correct roughness average that is supposed to be on the head and block surface. I believe it's RA 125, but the reason it should NOT be 'glass smooth', or RA 3-4 is because the MLS head gasket is supposed to basically 'adhere' independently to the head and the block, with the center gasket being the sandwich either side slides on. The reason is the different expansion ratios between the cast iron block and the aluminum head tend to break the seal, if there isn't a great bonding between the gasket and opposing engine surfaces.

An 800rpm head with a single point PCD cutter, moving across the head in 40 seconds is
just about perfect RA for this and later cylinder heads with the MLS head gaskets. CBN is what we use on the block and the same speed. The block is less critical, as the grain in the cast grips by and of itself.

The older engines, regardless of any of my attempts, have a bad habit of 'micro-fractures' and very minor head gasket leaks. Historically, I have found no matter what you do, the head gaskets on the 1.6's tend to last about 150,000 miles. But talk about an easy engine to work on...CopperCoat seems to help. And that, my friends, is very 'old school'.

 

[Dh4276]

The KS pistons are good stuff. Since you told me Will, that they are coated, I would not touch them. The difference is a grand total of .002", which in the scheme of things is really closer than VW is normally going on that engine. Swapping rods will not do a thing. Piston to piston, KS pistons are 'peas in a pod'.

Don't get me wrong, Prairieview, on Nurals and KS for the ALH engine, we have a very simple method that works just fine. If you check, the outside edge of the Nurals, in particular, have a tall perimeter and shrink slightly to the middle We have reduced the overall height of a piston .002" without removing the engraving on top of the piston. Weight-wise, it is insignificant.

Go with the tallest piston height to determine the correct gasket thickness.

I'm inclined to go with the minimum spec for valve recession, but milling off a brand new head is NOT what I'd do. The pre-chamber cups are properly done and it's brand new. Don't mess with it! As I said and you mirrored, the cups are protruding slightly, which is exactly correct. You won't get anyone to improve on what's been done.

LEAVE IT ALONE!

Footnote: Decking a block with a piece of sandpaper has to be a time-consuming and arduous affair. But you can't really say you aren't decking the block. That is exactly what you are doing. The head bolts aligned the way they are, have a very high tendency to pull the sides of the block up. This is exacerbated with later engines and the higher torque load bolts. So, albeit, it's a lesser issue with the 1.6's, it's still there.

The second issue is actually, there is a correct roughness average that is supposed to be on the head and block surface. I believe it's RA 125, but the reason it should NOT be 'glass smooth', or RA 3-4 is because the MLS head gasket is supposed to basically 'adhere' independently to the head and the block, with the center gasket being the sandwich either side slides on. The reason is the different expansion ratios between the cast iron block and the aluminum head tend to break the seal, if there isn't a great bonding between the gasket and opposing engine surfaces.

An 800rpm head with a single point PCD cutter, moving across the head in 40 seconds is
just about perfect RA for this and later cylinder heads with the MLS head gaskets. CBN is what we use on the block and the same speed. The block is less critical, as the grain in the cast grips by and of itself.

The older engines, regardless of any of my attempts, have a bad habit of 'micro-fractures' and very minor head gasket leaks. Historically, I have found no matter what you do, the head gaskets on the 1.6's tend to last about 150,000 miles. But talk about an easy engine to work on...CopperCoat seems to help. And that, my friends, is very 'old school'.

Great explanation and info!


Sent from my iPhone using Tapatalk