Author Topic: crack head, now what? (Read 8033 times)

EcoMod · « **on:** November 21, 2008, 08:49:17 am »

Well, I pulled my lil 1.6td head last night, in the dark.

I found cracks in the center of each combustion chamber between the valves.
This tends to quite common, so I hear?

My question is: Is this an automatic head replacement? I do not like welding on cylinder heads, especially diesels.

the good news is that the only bad this found on the block so far is a little rust at the top of the cylinder wall(from sitting)

:roll:

VW_Commuter · « **Reply #1 on:** November 21, 2008, 11:09:11 am »

My understanding from everyone on the boards, reading on the internet, and my Bentley manual is that cracks up to 1mm are acceptable, but 2mm is too much. Others might have actual experience running heads with cracks larger than 2mm. My head has cracks between the valves but they are <1mm so I'm using the head again.

zukgod1 · « **Reply #2 on:** November 21, 2008, 11:25:35 am »

The cracks between as mentioned are fine if 1mm or under.

I've seen like maybe 3 heads that were not cracked..

EcoMod · « **Reply #3 on:** November 22, 2008, 09:20:08 am »

Thanks for the info. I have yet to get a manual for the mk2's. I will need one before I start putting this thing back together.

I guess my plan of attack will be to take this head to the machine shop and get it checked for cracks and distortion. If it is not bad, I will get it ever so slightly resurfaced, reseat the valves and put in some new lifters. slap it back on with new valve seals, ARP headstuds and headgasket.

Just going to have to weigh the outcome of cheap vs. my usual tuner methods, which turn out to be non wife friendly. :wink:

I have seen stock, high mileage jetta diesels going for over 2,000usd.... is this pretty common? If I have 2k into this car after a partial rebuild and cosmetics I shouldn't too upside down on it.

jtanguay · « **Reply #4 on:** November 22, 2008, 03:50:13 pm »

doesn't matter how big the cracks are, if they leak they leak.. if they dont leak, then you're fine. getting it pressure tested isn't too much coin if you want some peace of mind.

would suck if you bought a new head and your head was fine. but if you have the money for it, it's not a bad thing. only if you buy an inferior product.

Smokey Eddy · « **Reply #5 on:** November 22, 2008, 10:49:49 pm »

I had to buy a new head because my cracks grew too large and my coolant became pressurized.

Jet A · « **Reply #6 on:** November 24, 2008, 05:59:08 pm »

Quote from: "Smokey Eddy"

I had to buy a new head because my cracks grew too large and my coolant became pressurized.

Just run it with the radiator cap off!!!

Just kidding^^^^

The mechanic that did my head, peened the cracks slightly to prevent them from closing. Later found out that it was a prothe head, and the valve guide holes were all outa wack.

What was the problem before you pulled the head? were u suspecting a damaged head?

fatmobile · « **Reply #7 on:** November 25, 2008, 03:39:53 am »

Many times a large crack doesn't just mean a large crack,... leaking or not.
It sometimes means the head was overheated and is probably warped.

Rabbit TD · « **Reply #8 on:** January 15, 2009, 01:06:51 am »

Quote from: "jtanguay"

doesn't matter how big the cracks are, if they leak they leak.. if they dont leak, then you're fine. getting it pressure tested isn't too much coin if you want some peace of mind.

would suck if you bought a new head and your head was fine. but if you have the money for it, it's not a bad thing. only if you buy an inferior product.

Talking about these cracks btween the valves I think I've had 7 different heads over the years and they were all good and all had cracks between every valve. I just got a new Top-Line head for this engine which isn't in the car yet and I'm wondering what actualy causes the cracks in the first place and how long it will take to get cracks in this new one, evidently they appear no matter what you do, any thoughts :?:

Smokey Eddy · « **Reply #9 on:** January 15, 2009, 04:39:07 am »

Quote from: "Jet A"

Quote from: "Smokey Eddy"
I had to buy a new head because my cracks grew too large and my coolant became pressurized.

Just run it with the radiator cap off!!!

Just kidding^^^^

The mechanic that did my head, peened the cracks slightly to prevent them from closing. Later found out that it was a prothe head, and the valve guide holes were all outa wack.

What was the problem before you pulled the head? were u suspecting a damaged head?

The new head i got is a prothe head. I hope it works better than how you said

I spent a lot of money on it. (well relatively cheap in the realm of engines but expensive to my small wallet)

I had already had that head off and on about three times because i kept nievely trying to fix bad starting.
The compression was terrible due to toast rings and the cracks between the valves went into the coolant.
Also, now that i've had it off and looked at it, all the prechambers are cracked.
I hopefully fixed this problem... all the parts i bought were extremely cheap except for the HG and ARP's. Time can only tell.

MY thoughts on the crackin is perhaps it's just from temperature changes?
Anyone know about these cracks on heads apart from VW?

jtanguay · « **Reply #10 on:** January 16, 2009, 08:05:12 pm »

Quote from: "Rabbit TD"

Quote from: "jtanguay"
doesn't matter how big the cracks are, if they leak they leak.. if they dont leak, then you're fine. getting it pressure tested isn't too much coin if you want some peace of mind.

would suck if you bought a new head and your head was fine. but if you have the money for it, it's not a bad thing. only if you buy an inferior product.

Talking about these cracks btween the valves I think I've had 7 different heads over the years and they were all good and all had cracks between every valve. I just got a new Top-Line head for this engine which isn't in the car yet and I'm wondering what actualy causes the cracks in the first place and how long it will take to get cracks in this new one, evidently they appear no matter what you do, any thoughts :?:

i think it has to do with the fact that the swirl chamber takes up a lot of room, and leaves little meat between the valves. plus the fact that they are dissimilar metals (different expansion rates-aluminum vs inconel). thats why the TDI's don't have these cracks between the valves.

i wouldn't be too concerned with the prothe head. i would highly recommend going with the 1.9 MLS gasket & arp head studs (which you have). if you plan on turning up the fuel and running the motor really hard, it might not last though...

Rabbit TD · « **Reply #11 on:** January 18, 2009, 12:01:16 am »

Quote from: "jtanguay"

Quote from: "Rabbit TD"
Quote from: "jtanguay"
doesn't matter how big the cracks are, if they leak they leak.. if they dont leak, then you're fine. getting it pressure tested isn't too much coin if you want some peace of mind.

would suck if you bought a new head and your head was fine. but if you have the money for it, it's not a bad thing. only if you buy an inferior product.

Talking about these cracks btween the valves I think I've had 7 different heads over the years and they were all good and all had cracks between every valve. I just got a new Top-Line head for this engine which isn't in the car yet and I'm wondering what actualy causes the cracks in the first place and how long it will take to get cracks in this new one, evidently they appear no matter what you do, any thoughts :?:

i think it has to do with the fact that the swirl chamber takes up a lot of room, and leaves little meat between the valves. plus the fact that they are dissimilar metals (different expansion rates-aluminum vs inconel). thats why the TDI's don't have these cracks between the valves.

i wouldn't be too concerned with the prothe head. i would highly recommend going with the 1.9 MLS gasket & arp head studs (which you have). if you plan on turning up the fuel and running the motor really hard, it might not last though...

That makes pretty good sense about different metals, I never heard it mentioned before. I guess they do have to be made out of some pretty good stuff and as tight as they fit expansion rates could probably cause it.

rallydiesel · « **Reply #12 on:** January 19, 2009, 04:01:28 pm »

Rehab. Someone had to say it. :roll:

smutts · « **Reply #13 on:** January 19, 2009, 04:49:34 pm »

When you have a cold engine, be gentle with the gas pedal. More fuel, more heat. Cold metal with a thin layer of very hot metal will prevent that hot metal expanding fully, hot metal yields as hot metal is more plastic than cold metal. When everything cools down, tha yielded metal now has a tensile prestress, cracks. Repeat a few hundred times, wonder why there is a bloody great crack in it. The following gives a idea to the principles, but me being a Civils Bod, it might be on too big a scale.

http://www.fhwa.dot.gov/BRIDGE/steel/01.cfm

When that engine is nice and hot, THEN give it some welly! :twisted:

1.6Lmarine · « **Reply #14 on:** January 25, 2009, 08:56:05 am »

Took my head into machinist Friday.

There's a hairline crack between valves on cyl #3. Will be pressure tested this coming week. Don't know how far up the felts this crack runs, but he'll look at. He said that there is likely nothing wrong with it - lots of meat between crack and water jacket? Said he'd raither not try to fix it with a drill and spot weld...may create a problem where there is none.

He's done good work for me in the past.

Does this check out with your experience? Seems to me that it does...

... minus 45 windchill here now - gotta go plow - dreaming of summer!