Welding Tips and Tricks

Gentleman,

I present to you a fine example of German engineering that's made it's way to the good old US of A.






Pictured are two cracks in the cylinder head between the exhaust seat and the water drain back from the head to the block. One is complete, the other is just starting.

I suspect that there is one other that is cracked based on the condition of the exhaust valve and the sealing surface, but I won't know for sure until the seats are removed.

Removing the seats a fairly straightforward process. Basically, you heat it up with a DC TIG arc without filler, and when the metal contracts, the seat just pops out. All aluminum cylinder heads have some sort of hardened valve seat, with steel being the most common, although some alloys are used as well. Regardless, the process is the same.

I will post more pics as the repair progresses, and whether it will work or not is yet to be seen. It will definitely be a learning experience nonetheless!!

Stay tuned for my foray into head repair, and hopefully we all might learn something in the process!!!

Sam,

I regularly use the weld/shrink method to remove steel bearing races from aluminum hubs on both Meritor and Hendrickson axles. At that size, the don't "fall" out, but tap out quite easily.

Since your heads are already cracked, I'd pre-heat the whole works, so the sudden expansion of the steel seats does not "grow" the cracking.

After that, I'll be interested in your repairs.

Steve S

Sam,
I am interested as well. I have never welded on a cracks cylinder head or even repaired one. If you remember a while back someone posted a pic of that CAT head that the fire ring was damaged on. The company contacted me privately about handling the repair since we were not that far from one another but I turned it down and offered to consult only. I wonder how or if they repaired it.

Anyway, good luck and I look forward to the pics and story.
-Jonathan

From the impression/mark on the head it ooks like the fire-ring in the head gasket is a reasonable width. That should help to keep the repaired head working once it has been repaired and re-machined/planed. Most likely this BMW head is not a hardened alloy.

On engines where the fire ring is more narrow (sometimes only around 1 to 2mm) the material of the cylinder heads is often a hardenable alloy and needs to be >90 on the Brinell scale to stop the head gasket fire ring from deforming and 'sinking' into the head during service. Often this is in engines with wet loose liners where the head is used to stabilise/fixate the liners and the contact area is quite narrow so pressure at these points from the head torqued onto the block are higher.

These types are very hard to repair succesfully for longer duration as the welded area and HAZ gets annealed and end up too soft in these conditions and not many sites have the equipment to re-harden the material. Sometimes a thin copper shim in these cases can work when a softened head (can also be caused by overheating or simply age) has to be re-used at the cost of a small reduction in engine compression.

Bye, Arno.

Arno, good information. In this case it's a fully closed deck, which makes life a lot easier as you pointed out. We already discussed with the machinist how we thought it would turn out, and this is actually the second head for the same engine (out of a different car) that the head is cracked almost identically. So, if we can't fix this one, the other one will be sent out to the guy that normally repairs their heads. So, it will be a learning exercise, even if it doesn't have success!

I've changed a few but never tried to weld a cracked head. Looks like you've got a tough repair there. Good luck.
-Eldon

i'we used 4047 filler for all automotive cast alum parts. Just welded a tricky lotus omega cyl head.. it was pretty tricky job. One combustion chamber was cracked in 6 places, rest just in 4-2... pretty crack sensitive head. opended the cracks till there was no crack (check with crc red dye penetrant)

Ther preheat to ~180c, weld some, heat some, weld some, heat some, allthetime over 150c. after welding postheat to ~220c and kept it over that temp for some time, then wrapped it with insulation woll all-around. Worked out OK.

Showed up today and Brent, the owner of the shop had started that repair yesterday after I left for my other job. He apparently didn't have any luck with removing the seat as I saw he had to repair the port throat on the opposite side of the cracks. Additionally, he couldn't get down far enough into his crack to hit the bottom and will have to re-grind it out and start fresh after I leave again lol. He is a good welder, but sometimes his solutions aren't all that well thought out