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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old November 7th, 2018, 09:08   #1
trevorbrady
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Default head gasket thickness

I have an AFN with a blown head gasket. I pressure tested the system and I have coolant weeping out of the head gasket just below the injectors. The coolant bottle was getting pressurised by compression gases but there's no oil in the coolant or coolant in the oil.

I also have a donor AFN engine with a good head. So I'm going to buy a new head gasket, new bolts and use the donor head.

My question relates to head gasket thickness. I understand the thicker ones are to compensate for material removed from the head during skimming/decking. If I am to use a good original cylinder head I presume I'm supposed to use the thinnest gasket?

Now, while I'm replacing all this stuff, is there any advantage to using a thicker gasket than normal? It will lower compression ratio but I'm using a bigger turbo/injectors/pump head already so is there any performance benefit to using a thicker gasket, lowering the compression ratio to maybe allow more boost?

I'm competent enough to do the work myself but the theory behind the performance aspect is an area I'm just learning about. Any advice appreciated.
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Old November 7th, 2018, 09:37   #2
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Thickness is chosen by the measurement of the protrusion of the pistons.

About performance, check this:

http://forums.tdiclub.com/showthread.php?t=13714
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Old November 7th, 2018, 11:22   #3
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Ditto, gasket thickness is chosen based on piston protrusion at the block by using a lift gauge.

If you're going to the effort of taking the cylinder head off the other engine you really ought to have it serviced at the machine shop. Rule of thumb is to have the head checked and leveled every time it's removed from a block since the act of torquing the head properly can warp it slightly. Also, depending on miles on the replacement head you might want to have a valve job or at least to valve stem seals and maybe even some exhaust valve guides too.

If your not decking the block then gasket thickness should remain the same but it's always good to check piston protrusion anyway.

The link that k_pt provided is a good discussion about what happens to performance when you alter gasket thickness.

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Old November 7th, 2018, 12:20   #4
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thanks for the input guys. I've read through that thread linked and I've decided use the standard thickness head gasket but to remove the tips from the glow plugs or remove them altogether and fit blanking plugs. They're currently fitted but the whole glow plug loom has been removed so they're not doing anything anyway. That will lower CR a little bit without altering the volume of the squish area.

Steve, good point about freshening up the donor head before fitting. I'll look into it.
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Old November 7th, 2018, 16:56   #5
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There is a tab on the head gasket right next to the IP. It will have an oval hole and possibly 3 other holes. Count the holes and buy the same sized gasket that was put in.
The thickness has nothing to do with the head, and everything to do with the deck height of the block.
Unless you deck the block, keep the gasket the same hole (1, 2, 3, or 4)

When you get your head (I suggest you keep yours and have it worked) you need to make sure its FLAT. It’s fairly easy to check with a true strait edge and a set of feeler gauges. (Pro tip) get a straight edge metal ruler, and put some 200 grit sand paper up against a mirror or window and sand it flat to grantee your strait edge is true, now feel around on the head and make sure it is.
You can send your head to franko6 if you want to know it’s done right.
If you keep your head and have it machined, you need to make sure that the valves have no play in them or within tolerance. Do not swap lifters around or the cam, cam and lifters stay as a pair.
Turbo engines rarely have an oil to water cross contamination on a head gasket failure, it’s usually due to boost levels and the compression gasses making it past the gasket and lifting the head. It’s a typical issue with AHU and ALH TDI's
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Old November 7th, 2018, 16:58   #6
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Quote:
Originally Posted by trevorbrady View Post
thanks for the input guys. I've read through that thread linked and I've decided use the standard thickness head gasket but to remove the tips from the glow plugs or remove them altogether and fit blanking plugs. They're currently fitted but the whole glow plug loom has been removed so they're not doing anything anyway. That will lower CR a little bit without altering the volume of the squish area.
Steve, good point about freshening up the donor head before fitting. I'll look into it.
there is no standard size, count the holes on the tab.
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Old November 7th, 2018, 17:28   #7
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Thanks mongler.

Since I'm here asking questions and you guys are being so helpful...

I have 0.280 nozzles, 12mm pump head, GT1749vb turbo. So far just on the factory map. Once i have the head gasket issue solved I'll be getting it dyno'd and remapped to get the best out of the parts.

What's a good max boost to go for? I'd like this car to be reliable and fun to drive. It's a 1983 mk1 Jetta so a relatively light car.
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Old November 7th, 2018, 17:50   #8
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well, maybe someone can chime in here, i have get to get my hands into an AFN, but i assume there virtually the same as the AHU. they look the same! So i would have someone confirm the headgasket hole sizing for the AFN.
Im assuming you did this as a swap!, thats fun. pictures would be nice.
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Old November 8th, 2018, 00:18   #9
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Yeah all my work. I'll post pics later.

AFN is almost identical to AHU. 110bhp vs 90bhp from the factory though.
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Old November 8th, 2018, 04:55   #10
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The problem in lowering compression ratio by using a thicker headgasket is getting air pockets outside the piston bowl, that do get the injector spray.

The way to go is work on the piston bowls.
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Old November 8th, 2018, 05:52   #11
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You need to count the holes. Always put in a gasket with the same number of holes. Gaskets are the same for 1Z/ AFN/..
Good example here:
http://rosten-performance.com/produc...n-1-2-3-notch/
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Old November 8th, 2018, 06:05   #12
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Quote:
Originally Posted by lisab4 View Post
You need to count the holes. Always put in a gasket with the same number of holes. Gaskets are the same for 1Z/ AFN/..
Good example here:
http://rosten-performance.com/produc...n-1-2-3-notch/
thats what i thought. i didnt know what differences are on the AFN vs AHU, my hunch is that its a 10mm IP vs the 9 the AHU has.
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Old November 8th, 2018, 11:20   #13
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yah, the AFN has a 10mm pump head to start with. I have a 12mm head fitted now. Pics soon...
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Old November 8th, 2018, 14:19   #14
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in no particular order...
ebay GT1749VB turbo core


Gibonta 0.280 nozzles


ebay 12mm pump head


PD130 inlet manifold. The EGR body is still there as it gives me somewhere to fit the MAP sensor but it's been totally gutted and machined smooth inside and out.

ebay intercooler & pipe kit



G60 flywheel
VR6 clutch
02A CTN (mk3 Golf TDI) gearbox
02J shift tower
9N Polo shifter
custom (DIY) engine & gearbox mounts
T4 Eurovan clutch master cylinder
mk4 Golf FBW acc pedal
mk4 Golf TDI engine bay loom and ECU
custom (DIY) 2.5" exhaust from turbo to tailpipe
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Last edited by trevorbrady; November 8th, 2018 at 14:24.
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Old November 8th, 2018, 14:21   #15
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I drag raced it for a while but really, FWD is a handicap and I never saved up the money to invest in a LSD for the 02A so I've given up on racing and it's going back on the road.


still on the stock mk4 ALH map from the mk4 ECU I used so it needs to be dyno'd and mapped properly but it pulls strong in all gears.


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Last edited by trevorbrady; November 8th, 2018 at 14:26.
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