1.6D head cracks/piston questions

[dbird]

Hello all,

I have been working on my 81 Rabbit 1.6 non-TD for a while now after it wouldn't start because what seemed like a bad head gasket. I am pretty amateur as a mechanic, so bear with me as I am not too well-versed in the mechanical jargon.

I guess I'll start from the beginning. I could not get my Rabbit to start up, it turns over without any results. I did my troubleshooting, no air in the lines or injectors, fuel injector is drawing fuel. I figured I was getting bad compression. I noticed bubbling where the block meets the head. I figured the head gasket was bad and started the process.

So, I am now at the point where I have the head out, inspecting everything. For starters, the head gasket looked original, it is a relatively low-mileage engine at around 130-140,000. The head gasket was warped and bent pretty bad. I looked at the engine block, and it looks like there are no cracks, but a few things did catch my eye when it came to the pistons and the cylinder walls.

Piston 1 has an imprint of an intake valve that I can physically feel. I was wondering if this is significantly bad and if I should replace the piston head.


It looks like the walls for cylinder 2 have some crap on them, but I will clean it all and lubricate it.



It looks like piston 3 might have a very tiny crack around the 10:00 of the image.


I took the cylinder head to the machine shop today and one of the guys pointed out little cracks between the valves. They pretty much told me that I needed a new aluminum head, then when I came home, I did some research. Apparently, even on the diesels, little cracks no wider than a dime will have any effect on the engine or compression and most if not all 1.6 heads have that issue. That had me relieved, but won't the cracks just get worse over time until they actually do matter? I did not find any cracks on the pre-combustion chambers, or anywhere else besides in-between the valves.







Finally, another thing I noticed was that two of the valves on cylinder 2 and 3, which I believe are both exhaust valves, are slightly sticking out. I found that odd, since the piston with the imprint of the valves is piston 1. The camshaft is at TDC with the cam lock tool in. It looks like the cam shims/lifter things are fine. They look straight and consistent.


I am posting to this forum because it has proved very helpful to me while working on my Volkswagen. You guys know what you are talking about, and I would like your opinions before I make the decision to spend the money to get the head cleaned/resurfaced or buy a new head. Please please please yell at me if you see something I am doing wrong! This is only the second time I've ever taken the head off of an engine and it's my first diesel. I also was wondering about machine shops using a 'conventional lathe' that will tear the head apart? I read about it on vwvortex I believe.

Oh, and before you guys tell me, yes, I am chasing the threads with brake & part cleaner with a tap. I also have the ARP studs.

Thank you guys so much for the help in the past as well as now!

[ORCoaster]

First of all, dbird, thanks for signing up with us!  Yes, we get a ton of spammers, but I'd love to see a real person signing up now and then.

So let me say this second to calm your fears.  That head looks great, small cracks and all.  Don't sweat it, you can fix the problems. You already have the clamping ARP studs that are a godsend for this diesel engine.  I won't bore you with all the times I have pulled the head off of mine.  But I will say that having those studs makes it a whole lot easier and I know I won't have to keep checking the torque to yield studs all the time.

Let's start with the idea that you do have low compression; bubbling at the gasket may have been caused by diesel getting down there.  IT happens at times, especially when you have leaky nuts and seals on the IP.  But let's just say it was doing that because the gasket was toast.  The stated condition of the gasket was that it was bad and probably original.  With the miles you have on it, I wouldn't doubt it.

You took it to the machine shop, and they told you wrong about those cracks.  So I wouldn't trust them to do any work on that head.  It only needs to be cleaned off well with a Scotch-Brite pad and some carb cleaner. 

Maybe a bit of scraping with a stiff plastic blade, as aluminum is soft, and you might cut into it with a regular putty knife. 

The imprint on the piston is a non-issue except for the clearance that is not there due to the wrong spacer puck under the cam/ on top of the followers.  You are going to want to get the right MM size under there to make more of a gap between the cam and that cap.  Too close and it shoves the valve down too far and BAM, into the piston.  Yours is just enough to allow the valve to touch the piston, but then it gets tight against the cam.  It may be that the valve stem is now swollen and therefore weak and might be an issue in the near or far future.  Pull it all the way out and look for it to be fat in one section or maybe even bent.  Buy a new one if it is. 

Do you have a Bentley manual for this engine?  HIGHLY recommended!  But we can provide specs if you need them for the Intake and Exhaust clearances.  Looking at the side of the head will keep you straight on the Exhaust or intake valve you are looking at.  Exhaust on the outside to start, then intake twice, then exhaust, I think.  Double-check my pea brain before trying to change anything.

It is best to do a compression check before dismantling if you think you have a gasket problem.  Future work or work for others tip.  You could have noticed air building up in the cooling reservoir after about 15 seconds of startup, if it was running.  I would have done a compression test if in your place.  But then I have a gauge for a diesel for that exact purpose.  Auto parts stores may not have a diesel gauge, but they would have a regular gas engine one.  But you are looking at 480 psi on a good cylinder, and that is outside the range of a gas compression gauge. 

In my 15 or so years of fiddling with that 1.6 engine I have come to the conclusion that it is great until the head gets too hot.  The measurement for being out of tolerance on the head is very, very small.  .004  or 4  thousands.  Like paper thin, maybe thinner.  The only thing the machine shop could have done to help you would have been to take one of their finest metal straight edges and laid it along the block in several places and tried to slide a feeler gauge under the straight edge.  Putting a light behind it works too. 

Now I have had success smoothing out a head using oil, very fine wet sand, sand paper, and a glass plate.  You tape the sandpaper to the glass and oil it some and slide the block in circles around on it, moving it left or right as you go.  Then bring it back the other direction and make a measurement.  Sometimes marking the low spots with a Sharpie has helped me know I am getting the high points down when the lines disappear.  Following me on this one? 

So now that the pistons are able to rise up out of the top of the head, you should measure how far they do that.  This will be your guide when buying a new gasket.  Hopefully, you have not already done that.  Or you can take it back if it isn't the right one.  The number of notches on the tab of the gasket tells you how thick it is.  3 notches is what most throw in, but doing that might sacrifice compression.  And you need compression to fire off that diesel, so measure that rise, buy the thickness of gasket for that range, and you will not have to be pulling on that cold start cable very often in the cold mornings.  Trust me on this. 


Your pistons are fine; in fact, the lack of any carbon ridge on the top of those tells me this engine was doing very well the way it was set up.  It is clean in many of the areas where others are not.  Pre-cups good, how about GPs,  all clean and heating red hot when you short them over the top of the battery?  Hold with a pair of pliers or lose your fingers doing it bare-handed.  How often do you touch the glowing stove top?  The GPs are just like that element on an electric stove.  Glows red for a reason, not to touch it. 

Rebuilding is not difficult; timing might be.  Do you have the proper tools for that?  The Bentley is your guide to doing a timing adjustment. 

Oh, those two valves stick out when at TDC, they have to, as they are ready to let air in or out at that point.  No problem there. 

Keep us up to date on this.  We are here to help, not hound.  At least some of us are.  Good to have you aboard.

[fatmobile]

 I concur.
 Those cracks aren't bad at all.
 The valve mark on the piston looks old.
 Might have been from an old incident.

[dbird]

Thanks for the replies!

To start off, I indeed own a Bentley manual for this car, and it is very helpful. I was lucky enough to find one a while back for only $60, which is still crazy, but I know they are usually $100+. I replaced the glow plugs recently, and I tested all of them when the car didn't start. I have all of the tools for timing, including the ones that some might find unnecessary, like the IP pulley lock pin. Timing isn't too hard, the worst part for me personally is getting the lower timing cover off, since my Rabbit has an A/C compressor. I will include that I did have some trouble getting that crankcase inspection port loosened. Mine was pretty much welded into the threads.

As far as the head, I have plenty of those Scotch-Brite pads and should be able to clean it off. I'm not sure if I would be comfortable doing that method to get it level. I did run a straight edge across it at several points, and it seemed fairly flat and straight all around. I haven't had a chance to work on it recently, but I will definitely check those valve stems.

The head gasket that I pulled off of mine had two notches. If more notches mean thicker, I assume that I should get one with three notches? I'll be honest, I didn't really understand what you meant, ORCoaster, about measuring how far the pistons the pistons rise above the top of the head. I know that they rise a little bit over the top of the block when at TDC or 180 degrees. In that case, my measurement of how much higher the piston rises above the block should tell me how thick the head gasket should be (with a little clearance so the pistons don't touch the valves)? I just figure the gaskets with three notches instead of two because it would be the next thickest gasket so the issues with the piston slapping the valves doesn't happen again. Please correct me if I am completely wrong. 



So essentially, my main question is, if the head is flat and straight, according to a straightedge and my sight, should I be able to put the head back on once I clean it up and get the right gasket? I already cleaned up the block surface pretty well.

Thanks again! Like my account says, I am a newbie, so I really appreciate your guys' experienced help.

[ORCoaster]

Well that all sounds about right.  But if you had a 2 notch gasket I would lean towards getting another of that thickness.  You are correct that at TDC you would measure what they call protrusion of the piston over the top of the block and use that measurement to buy the right thickness of a gasket.  I think I said head and that is not correct.

Normally you don't need to add any to get the pistons to clear.  The gaskets are meant for a range of height of protrusion.  So a 2 notch gasket might still be able to give you some clearance.

I too had to muscle that transmission port with about everything I had around here when I first went to time it.  It is just a bugger to get anything lined up on it right and the hex is so big I don't remember what I even used to get it to budge loose.  Been too many years now since I had to do that. 

It very well might be that the gasket just gave up the ghost on you due to age and the head is still just fine.  Most people have an over-heating engine and run it that way for a while and that does in the head.  It sounds to me that you did not have that problem.  It just quit firing, trying to save itself from ruining the head. 

Go at it.  would really like to know that a simple gasket replacement is all it takes to get this one back on the road. 

[fatmobile]

 That valve print in the piston probably isn't because the piston was hitting the valve while driving.
 Probably a one-time incident, maybe right after the previous timing belt change.
Maybe they forgot to torque the cam sprocket bolt.
 Maybe slipped during idle or low RPMs
 It doesn't look fresh.
 It only effected one cylinder, barely on one valve and some on the other.
 I have broken a timing belt when going 55mph.
 The valve impressions were much deeper and it effected more than on cylinder.

[dbird]

Just an update, pretty much waiting for gaskets and the thread chaser as well as some new belts as of now. I wanted to show you guys what the head gasket looked like on top of the block. I just put it back on there the best I could, but you can see the head gasket is warped and looks pretty bad on cylinder 4. I'm assuming that's what the issue was as to why it wasn't starting. The gasket didn't seal around the cylinder well enough to provide enough compression. Let me know what you guys think, if that would stop the engine from running.

Also, I was looking for any tips on lubricating the engine before I start it up? I was just thinking of spraying some Aerokroil in the cylinder walls so it isn't completely dry on first startup. I'm not sure where the oil pump is or how to prime it, but I heard that works too.

[fatmobile]

That 4th one is messed up.
Haven't seen that before.

[ORCoaster]

Me neither. I think I have seen a good share of gaskets in the past, but never one that looked like that.  I believe you have found the problem. 

Oh, the oil pump you asked about.  I see that your engine has the newer/better vacuum pump on it that provides the necessary vacuum to the brake booster.  You take that off, and you will see a shaft in there; it pokes up into the vac pump.

That shaft drives the oil pump.  You get that to spin with a drill somehow, and the oil will be pumped around the engine.  Now, please don't ask me what to use to do that because I have never needed to do that.  But that is what needs to be done to circulate the oil on a diesel VW engine.  I will leave that up to you to solve.  Something that can go in a drill that has a slot that fits over the flat end of the shaft.  Think about that.

[VWSmokr]

Manual pre-assembly lubing is good. After final assembly, but before you snug down the cam/valve cover, you can remove the 12V+ lead from the fuel cut-off solenoid & give the engine a few revolutions on the starter to pressurize oil flow all around. Stopping, you can lift the cam/valve cover to check that the cam & followers are definitely getting lubed. (anal, I know, but reassurance is a good thing at this stage of the project!)

Best of success!
J.R.

[ORCoaster]

I wasn't thinking he was tearing it down more than the head.  But even then, he could put a bit of oil in each cylinder and turn it over with the head off.  By hand or with the starter.  That would at least get the rings wet and prevent scoring.  I have never pulled a head off any engine that has been sitting long-term and not running. 

In fact, I have pulled a head off one I just shut down from a drive, and it was still hot when I took it off.  Yes, getting those exhaust nuts off went easily that way.