Mk1 Diesel Head question

**sparkie** · 31-08-2008, 08:18 AM

Hi I have had a good look at the threads her on Mk1 diesel heads, but no-one seems to have discussed this. I have recently got a secondhand head through ebay on the condition (at my mechanic's suggestion) that it passes a head density test. My mechanic told me that if an alloy head has been over-heated the main problem is that the heat changes the density of the alloy and this stuffs the head up for skimming and re-using. He says that the test is easily done using a tool which has a ball-bearing in a calibrated tube, the ball runs down the tube, bounces off the allow head and the distance it bounces back shows the density of the alloy.

Anyone heard of this? All the posts here talk of is warped or cracked heads, no mention of density.

While I am on a roll, if I have an unknown head, what head gasket do I get as there seem to be a few thicknesses. Do I still get a replacement for the one on the engine now even though the head is different?

Thanks

**Russ59** · 31-08-2008, 08:57 AM

Hi, I haven't seen or heard of this technique until I just did a quick Google search. It would appear from what I could find that it is a test for the overall fatigue of the alloy in the head. I am guessing that the ball bearing being solid, and when bounced back and forth of the metal, will be able to confirm if there are any hard / soft spots which have been subjected to excessive heat and thus made the alloy unstable. I'm not sure exactly which result is better (harder or softer alloy) but I would think that the higher the ball bearing bounces it must mean that the alloy at that point is harder and vice versa. From memory I think alloy goes harder after being heated and then cooled, so as a guess it would be best if it tested consistently softer overall ?? (someone please correct me if I'm wrong) and I am then guessing that if you needed to have the head surface machined slightly and the alloy was fatigued (ie hard in some areas and soft in others) then it would probably warp ?? The thickness of the head gaskets will probably depend on how much machining has to be done to the head ? Just used google and a bit of my logic (god help you !!

) but it sounds fair enough to me !!

**Transporter** · 31-08-2008, 04:04 PM

Originally Posted by sparkie

Hi I have had a good look at the threads her on Mk1 diesel heads, but no-one seems to have discussed this. I have recently got a secondhand head through ebay on the condition (at my mechanic's suggestion) that it passes a head density test. My mechanic told me that if an alloy head has been over-heated the main problem is that the heat changes the density of the alloy and this stuffs the head up for skimming and re-using. He says that the test is easily done using a tool which has a ball-bearing in a calibrated tube, the ball runs down the tube, bounces off the allow head and the distance it bounces back shows the density of the alloy.

Anyone heard of this? All the posts here talk of is warped or cracked heads, no mention of density.

While I am on a roll, if I have an unknown head, what head gasket do I get as there seem to be a few thicknesses. Do I still get a replacement for the one on the engine now even though the head is different?

Thanks

Just make sure the head was not welded up.
Aluminium cylinder heads cannot be welded, since Aluminium alloy changes structure when heated above some 260 deg. Celsius or more. If the engine overheated and head was removed it could be distorted (warped) and if heated up during straightening in the repair shop AL alloy metal will change structure (will get softer and cannot be brought back to it’s original hardness).
There are some simple methods how to test the hardness of the cyl. heads.
You can compare the brand new head or good known head against your old one.
Here is how it could be done:
Put the glass tube about 15mm in diameter and about 100mm long on the surface(mating surface to engine block) of the known good cylinder head, drop the steel ball inside it thru open end and mark how high does it bounce inside the glass tube with permanent marker.
Do the same on the surface of your old cylinder head and if the ball bounces much less than on the good cyl. The head is probably softer and you can’t tighten the cyl. head bolts reliably to proper tension. The bolts will lose tension over the time, because of the softer cylinder head.

Cheers,
MM

**gldgti** · 31-08-2008, 08:22 PM

the vw heads are generally pretty good as far as warpage goes - since they are tall and have large webbings, they are very stiff. the most important thing to check is cracks between the valve seats and that the head has not been skimmed previously.

the diesel head does not have combustion chambers in the casting itself (it has inconel inserts), the base is flat. skimming the base of the head is a bigger job than it sounds since the valve seats need to be reground and the inconel insert would also need to be machined (its tough).

several books state that the heads "cannot be machined" and this is true to an extent (some have succeeded).

your ebay head might be fine. another option is www.dieselvw.com - you can purchase brand new head castings on this site. there is not a 1.5 specific head, however there is availalbe the 1.6n/a head, which is a direct swap.

the heads are cheap and not german, however they do work fine (dads got one on his 1.5 and its now got ~100,000 km on it)

i cannot say the same for some of the other parts from that webiste, but the injector tips, injectors and castings are fine, cheap and good value.

good luck

**Peter Jones** · 31-08-2008, 08:29 PM

Originally Posted by MRL T5

Just make sure the head was not welded up.
Aluminium cylinder heads cannot be welded, since Aluminium alloy changes structure when heated above some 260 deg.

Don't know where you heard this, 100's of aluminium heads get welded every day.

Pete

**sparkie** · 08-09-2008, 06:26 PM

Have had the ebay head tested for density and cracks and it has passed (it's not actually a VW head it's an aftermarket one I forget the manufacturer now and it is still at the engine grinder's place. All they did was to clean it and replace 2 studs and charge me $150. Still it gets the Mk 1 back on the road cheaply so who am I to complain.

**gldgti** · 10-09-2008, 11:40 AM

Originally Posted by sparkie

Have had the ebay head tested for density and cracks and it has passed (it's not actually a VW head it's an aftermarket one I forget the manufacturer now and it is still at the engine grinder's place. All they did was to clean it and replace 2 studs and charge me $150. Still it gets the Mk 1 back on the road cheaply so who am I to complain.

well done

**gtimk5** · 10-09-2008, 02:18 PM

You must measure the piston projection out of the block on TDC on a couple of cylinders to ascertain which head gasket is required. There are 5 different thickness gaskets to get the compression correct.
i keep most of them here if you can measure. Alternatively, how many notches were cut into the orginal one where the gasket hangs out the front of the engine block?
Andrew