GregBBRD

Please do not misunderstand what I'm saying, here.

Certainly, the prefered method of repair is to replace one of these 928 engine blocks. when there is any crack involved.

Any welding and subsequent repair on one of these engines involves risk. The silicon in the aluminum makes these engine blocks very brittle and very prone to cracks and crack migration. The person welding must be very familiar with the material and the processes required to do this kind of repair.

Taking the idea of sleeves in these blocks one step further, some high performance 928 engine builders completely remove all traces of the original sleeves and bore the remaining area to accept larger bore sleeves, which greatly reduces the strength of the "webs" in these blocks and virtually guarantees cracks in this area. This did not work in the 944 GTR engine program....with thicker webs. It's almost stupid to expect this to work in the thinner webbed 928 engine!

Used 4.5 liter, 4.7 liter, and 5.0 liter engine blocks are so common that there would need to be an extreme reason to attempt this kind of repair (like the client insists the original serial numbered block be retained and understands the risk.) As far as the repair you are referencing is concerned, that repair should have come with a letter explaining the risk, which the original client should have signed off on....anything else would have been foolish.

There's an unwritten rule in the automotive repair industry that everyone in this business needs to know and think about...daily.

"Never turn a client's problem into your own problem, by attempting anything but the absolute proper repair."

All this being said, 5.4 liter GTS blocks are so difficult to find (because of thrust bearing failures in the automatic versions were/continue to be so common) that these blocks are essentially non existant. ( I recently found a block for a client that looked for a suitable "donor" for three years!)

In short, I wouldn't even suggest this repair as being an option, if this wasn't a GTS block. And if the client did not care if an original 5.4 engine block be used (not interested in resale value), I would certainly use a 5.0 engine block, instead.

And the client needs to be aware of all the risks!

Jerry Feather

If there were such an animal I wonder why this kind of crack could not be welded up with an alusil welding rod and then refinished to stock.

jcorenman

Alusil is not an alloy, it is an aluminum alloy mixed with silicon (i.e. powdered sand). So the best you could do would be a rod of the base alloy, grind out the crack (from the inside of the bore would be the only access), weld it up without the silicon, pray it doesn't crack on cooling, then bore and hone. Which would leave a stripe of plain aluminum (non-sil Alusil), which cannot be a good thing.

A better option would be to weld, pray, bore, and then fit a thin Alusil sleeve as Åke described. But that is neither simple nor cheap, and for anything other than a numbers-matching GTS it is hard to image that being worthwhile.

Jerry Feather

I understand that, Jim and Sue, and that is why I started my post with the phrase about if there were such an animal. Then it strikes me that if a thin wall sleeve can be made out of aluminum with sand in it why can't some welding rod be made out of aluminum with sand in it? And if such an aluminum rod could be made, since the 928 block was molten aluminum with sand in it when it was made, why can't a weld be made with an aluminum rod with sand in it.

Speedtoys

...because welding is not casting?

Strosek Ultra

Years ago I bought a S4-engine with thrust bearing failure. It turned out to be a factory exchange engine. When I took the engine apart I noticed it had alusil sleeves installed in all eight cylinders.
The outside diameter of the sleeves can be measured to 104mm. With the stock bore the sleeve wall thickness is 2mm or .0787".
Åke

Jerry Feather

Maybe its two different words to describe essentially the same thing--that is, putting a molten metal in a particular place and allowing it to cool to achieve a particular purpose, and in this case the same purpose.

In fact, I think it is a common practice in the casting industry for the caster to repair minor defects in their castings with welding.

In this same train of thought I am now wondering, in regard to Jim and Sue's concerns and the actual welding process, if in fact welding Alusil with straight aluminum rod might still result in an Alusil weld. Since the parent metal is heated to molten and then aluminum rod added, isn't the result still Alusil? That is, aluminum with sand in it although perhaps at a different percentage of mixture. Some experimenting and microscopic evaluation might tell if there is enough silicon in the resulting weld to meet the need in the cylinder wall.

Still, I think a simple mold can be made to pour some molten 928 block Alusil into to make some suitable welding rod. I'll make the mold and if someone will send me a chunk of Alusil I'll mold some Alusil welding rod for someone to try the weld in someone's cylinder--perhaps the OP's?

Imo000

Call your local welding shops and ask if this will work.

Jerry Feather

Greg B. says that they "repair the crack" which presumably restores the strength to the cylinder, and then install his custom iron sleeve which provides a suitable running surface for his custom pistons. Ake S. presumably also would repair the crack to restore the strength before boring to install a very thin (2mm) Alusil sleeve to restore the surface.

My point is simply that if the crack can be repaired by welding to restore the strength, and even then less strength since some of the cylinder is then bored away, why can't we repair the crack in the same manner (welding) with something that does not require being bored away, except to conform to the original surface, and which itself provides a suitable surface?

This is thinking outside the box because there is no such animal as Alusil welding rod. My welding shop says they do not know of any such rod, but if I can provide it bring it and the block down and they will weld it for me. They also suggest stop-drilling the crack and grooving the crack for maximum penetration of the weld. It will be up to me of course to get the cylinder bored.

Imo000

Are yo are suggesting to weld the crack and then try to get the bore to the same size as before?

GregBBRD

This is the process that I was familiar with (new actually seen one, but had heard about) and figured that this was going to be the sleeves that KS offered.

Looking at the OD and ID of the sleeves you originally posted about, those sleeves appear to be entire cylinders.

Are you aware of where the thin sleeves can be obtained?

Speedtoys

For common castings yes.


This is not, and I would guess nobody accepts a casting for an engine block, and they just throw it back in the bucket at near 0 cost, and with an absolute 0 risk to future problems.

And casting and not welding are not the same thing, unless wood glue and tree rings are also the same thing.

Wisconsin Joe

It could be done, but doing it and making it work properly would be...

Challenging.

Keep in mind that molten alusil is a mixture, not a solution. The silicon is just floating around in the aluminum.

Keeping the mix even during the casting process is the key to a good cast.

Making a welding rod would be similar to casting the block. Not easy, but doable.

Trying to keep the mixture even and correct while welding with it (and on it) would be somewhere between extremely difficult and impossible.

Jerry Feather

Contrary to what you, Joe, and Jim & Sue have to say about it, everything I can find on the internet says that Alusil is an alloy. There is no suggestion that it is only a mixture, solution or otherwise. There also is no information anywhere that I know that suggests that the silicon is "floating." I also suggest that there is absolutely no particular procedure in the casting process to keep the silicon from either settling or floating during the process, and certainly no particular handling of the casting between the time it is poured and it sets. Where did you come up with all of that?

There is already welding rod available with silicon in it, but not as much as the 928 block. The Block has 30 percent silicon, and 4047 welding rod has only 12 or 13 percent silicon. There is no suggestion anywhere that it is hard to make. Perhaps even welding with 4047 might provide enough silicon in the weld to provide a suitable cylinder finish.

Jerry Feather

Jeff, I stopped drinking and posting a long time ago, mainly so that I would not end up posting something like this.

Your analogy is way off. Wood glue is more like brazing or soldering where the parent metal is simply heated enough for the brazing or soldering medium to stick to it, but not enough to melt as in welding where the parent metal is actually melted and mixed with the molten welding rod. A better analogy would be the grafting of part of one tree onto another where they actually grow together, as with tree rings.