which VW IDI pistons?

[TurboJ]

I wonder if someone will be able to solve a mystery:

I came across a set of pistons that were fitted onto a VW 1.6 TD SB block.
They are definetely diesel pistons, and they are .05 mm oversize, making the bore 77 mm.
They look exactly like normal 1.6 pistons, and have the same style crown, and they also weigh about the same as normal 1.6 pistons. Thing is, with a 1.6 crank and rods, these pistons do not protrude above the block at all - they come about 5.5 mm short.

What pistons could these be?  They seem to be in a very good condition so I'm wondering if they could be used on a 1.6 block with some other rods. Wrist pins are just like 1.6 pistons ( 24 mm ) and there's also the familiar clearance for oil squirters.

Is there a full list of VW diesel pistons with measurements somewhere?

[Rabbit TD]

I see you are in Finland, what do you mean by an SB block.  If the bore is right  and the crown to center of wristpin heigth is the same, wristpin dia. the same and they have the squirter notches I don't see what else could be wrong by using them.  I just got a set here in the US and the crown to wristpin heigth was .005 shorter than stock but then I realized they did this to allow you to have the block decked .005 to straighten it up which I did when I had it bored.  They are an off-brand aftermarket piston called {KING} but they work fine so far after  5,500 mi.

[Zulfiqar]

5.5mm short of TDC - thats a big gap

I think they maybe the daihatsu 1.0 litre std size diesel pistons

[Rabbit TD]

5.5mm short of TDC - thats a big gap

I think they maybe the daihatsu 1.0 litre std size diesel pistons

  No it's just 5 thousandths that I was refering to, 5.5 m/m damn that sure would make them short wouldn't it

[myke_w]

how bout some pics?

[TurboJ]

I can't post pictures at this point, my home computer is broken... 

But this is very interesting.
It was a fully functioning SB engine  ( SB being one of the VW 1.6 TD engines, the ones with intercooling and 80 hp )

And the pistons indeed look exactly like other VW IDI pistons, but they come 5.5 mm lower than the deck level at TDC. Yes, 5.5 mm lower, that's like 1/5 of an inch.

Now, the pistons are currently fitted onto the block, and I'm just wondering since I didn't yet measure the compression height of these pistons, that maybe it isn't the pistons after all??

Is there a VW rod that has 24 mm upper and 56.1 mm lower hole, that is shorter than the 136 mm 1.6 D one?
Or perhaps a crank shaft with shorter stroke, but still fits 56.1 mm rod bearings?

Thing is, I can't get to this particular engine for a while, to inspect it more closely.

Can someone help me solve what parts these are?

[myke_w]

it sounds like you're in the right track with the short rod or crank stroke idea.

I have no idea how it even ran with 5mm of head space.

All the similar gas rods have way smaller small ends.

I suppose a 1.8 16v crank "might" be close because they have a short stroke, but I have NO idea how big the big ends are.

Just a guess

[MJF]

1,6 gasser have 80mm stroke and same journals than diesels. Btw the big end is 50,6mm. 1,8 gassers have same dimensions as 1,6 diesel.

[TurboJ]

I don't have access right now  

...besides this topic heas already proven VERY useful - I am now closer to the solution, even without the block in my hands and without any pictures.

Now, after some more research:

The pistons are VERY likely to be VW 1.6 IDI  0.5 mm oversize pistons.
Correct bore, correct wrist pin, correct shape even down to those little cuts for the oil squirters.
(there just aren't any other pistons that fit the bill)

Rods must be 1.6 IDI - they have 24 mm small end, they have 50.6 big end , so they must be 136 mm long, 1.6 IDI rods right??  There aren't any other VAG rods that have that combination of end sizes, are there?

So, this dilemma now boils down to what type the crankshaft is.
It must fit 50.6 mm big ends, but is also causes the pistons to sit 5.5 below deck at TDC.
1.6 or 1.8 gasser crank?  Which one would fit this situation?
I see from a listing that most VAG 1.6 engines have 77.4 mm stroke. How would this compare?

1,6 gasser have 80mm stroke and same journals than diesels. Btw the big end is 50,6mm. 1,8 gassers have same dimensions as 1,6 diesel.

You mean crankshaft dimensions? The rods at least have smaller small ends.
 

[kd4yor]

Any updates?

[Zulfiqar]

While building a Mazda PN I got some oversize pistons that were sitting 0.5mm below the block top surface at TDC - they were made in taiwan somewhere but VERY VERY good quality - the kit also included a shifted woodruff key for the cam sprocket

comes out that they are made for the machinist to true the block surface and the PN having a woodruff key cam pulley the timing would be dead on again..

because you have Oversize pistons and Im thinking they are not KS - this is the same idea behind it..

[TurboJ]

Any updates?

Well, I just stripped a spare engine yesterday and I'm going to weigh the crankshaft to see if the weight tells me the story. Currently I strongly suspect that the crankshaft muct have been wrong type, possibly a 1.6 gasser one. I'll post more info when I have it...

[TurboJ]

Yep, it was a gasser crankshaft that caused the strange compression.
Really surprising that the engine ran just fine, no problem at all.
Luckily I now have a correct crankshaft courtesy of my spare engine. I just hope it's straight...


EDIT:

After studying some old German data tables, I noticed that this crank has to be either from a rarer 85-hp version of the 1.6 gasser engine or a 1.5 diesel engine.
Those seem to be the only two 4-cylinder VAG engines that have 80.00 mm stroke.

Now a couple of questions:

1. Does the 1.5 D crankshaft have the fully counter-weighed crankshaft the same style as the 1.6 and    1.9 IDIs?

2. Does the 1.5 D have the 50.6 mm big ends?

3. What are the rod dimensions of a 1.5 D engine?

4. Could someone please post up a picture of a 1.5 D crankshaft!

I just want to know what I just found in there 

[TurboJ]

OK, things just got even more confusing.

Would any of you ever believe the following?

-The engine started the first time, every time without a single cough
-It pulled very well, and had decent torque from low down too
-It topped 100 mph with a stock turbo


....and the engine was a 1.6 TD, with a 1.5 gasser crankshaft.

The pistons were brand new, fitted by a well known engine shop. But somehow they threw in a 1.5 gas crankshaft!
The pistons were 5.5 mm below the deck level at TDC when they should have been 1.0 mm above.
That's 6.5 mm less protrusion than specified ( that's more than 1/4 inch )
The pistons and rods were correct after all, so that requires a crankshaft with 13.1 mm shorter stroke.
(6.55 cm each way) -> and it just so happens, that a 1.5 gasser crankshaft has 73.4 mm stroke.
As this is the only possible crankshaft that could cause the odd phenomenon, and still fit the TD rods, it's the only possibility.

Now, anyone care guess what the compression ratio was?
The combustion chamber in this case was 19,5 cc's more than the stock 12.794 cc. That means a total of 32,2 cc volume.  Compression ratio around 13:1 , right?

I would never have believed it if someone told me an IDI diesel engine would run with 13 comp. ratio.
But this one did, and without any problem! It even gave very, very good mpg. Mind you, the glow plugs were brand new Bosch.

Now what can we learn from this? A monster turbo IDI would not need a 17:1 compression ratio to detonate properly....!  

[Zulfiqar]

I cannot cannot believe that a diesel engine would run at 13:1 compression.

BUT

I have seen a VW diesel 1.6 NA vanagon with 190 psi compression start and run for years as a delivery van - pretty much same territory