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What is the best way to repair top of cylinder corrosion on 928.
Alright, as the thread states I need to repair some corrosion on the top of the alusil cylinder in my 5.0 block.
I have been looking at options and some that stood out are JB Weld, aluminum brazing ( hts2000 ), and of course TIG welding.
In the picture below the corrosion is on a part of the cylinder that will not interfere with the fire ring and at most will see 18 PSI from the coolant.
I want to avoid machining the block as much as possible as I really do not want to split the case for such a small repair.
Alright, as the thread states I need to repair some corrosion on the top of the alusil cylinder in my 5.0 block.
I have been looking at options and some that stood out are JB Weld, aluminum brazing ( hts2000 ), and of course TIG welding.
In the picture below the corrosion is on a part of the cylinder that will not interfere with the fire ring and at most will see 18 PSI from the coolant.
I want to avoid machining the block as much as possible as I really do not want to split the case for such a small repair.
I see this problem way more than I like....and I have not found a simple solution.
Welding on this Alusil material is, at best, very difficult. The silicon component makes the welding puddle very "dirty" and making any aluminum rod "stick" to this liquid mess requires heating, grinding away of the "dirt", and then more heating and welding.
Obviously, this would not be suitable for the area you need to repair.
Looking closely at your picture, makes me think that although the corrosion damage may not be all the way through the fire ring area, part of the damage protrudes under a percentage of the fire ring.
I do not believe any sort of an "epoxy" repair would be a "long term" solution....more of a "used car lot get it sold" approach.
From your picture, I can not tell how much parent material is eroded from the side of the cylinder, but if the damage is limited only to the top of the cylinder (very rare), it might be possible to "deck" the block until the pit disapoears. Of course, this would also require machining of the pistons to keep them below the new deck height and then rebalancing.
Sadly, a replacement block might be the most practical long term solution.
Sadly it seems as though you are caught between a rock and a hard place with this one. Either you replace the block or you have to implement a bandaid type of solution in the hope that it works.
Given the cylinder head seal was holding previously, the fire ring is still [mostly] intact and thus has a finite life left in it, if you can arrest the further growth of the pitting corrosion by sealing the pit from the coolant with the likes of high temperature silicon RTV [or some other high temp non hardening compound] it may well be that the joint still has plenty of life in it. If such approach works all well and good, if it fails you are down a head gasket and a pile of your time- thus it boils down to how you value your time and only you can determine that part of the value proposition.
From your picture, I can not tell how much parent material is eroded from the side of the cylinder, but if the damage is limited only to the top of the cylinder (very rare), it might be possible to "deck" the block until the pit disapoears. Of course, this would also require machining of the pistons to keep them below the new deck height and then rebalancing.
Sadly, a replacement block might be the most practical long term solution.
There is no corrosion on the side of the block, just this odd soft spot of corroded metal on top the the cylinder.
Sadly this is the replacement block -_-
Since it doesn't go into the combustion chamber I'm going to try aluminum brazing to fill the gaps with metal. As I don't want to have to have another set of pistons machined to match another block.
Worst case scenario I would bore the block to 104mm and machine the block down 2mm to match the deck height of 944 S2 pistons. But the $$$ involved to do this is a bit hard to swallow for a 21 year old pastry cook.
Update: the soft spot was a filler of some sort. I could easily scrape it away with my finger nail and removed it with a felt tip on a dremel. It turned to liquid from the friction on low speed, not very Alusil like.
I don't think the car this engine came from had ever had the engine removed or head gaskets done judging from the amount of oil and dirt caked onto it when I got it from 928 int.
The head gaskets went on this engine because the PO drove it with low coolant and they blew out as I was told.
Any welding or brazing solution needs to bring the temp there up close to melting, maybe in the case of brazing with a low-melt alloy it won't be serious. Danger is that the heating will warp the top of the hole.
Greg shard a few years ago the saga of going through used engines, on the hunt for a usable block core that wasn't cancer-stricken. This was for a clean rebuild, nothing like a striker or other performance project.
Any welding or brazing solution needs to bring the temp there up close to melting, maybe in the case of brazing with a low-melt alloy it won't be serious. Danger is that the heating will warp the top of the hole.
Greg shard a few years ago the saga of going through used engines, on the hunt for a usable block core that wasn't cancer-stricken. This was for a clean rebuild, nothing like a striker or other performance project.
Good luck with your search!
The alloy I'm using melts ~780F which is well below aluminum's melting temp. I'm still going to heat up the entire cylinder to 300F minimum to mitigate the risk of warping the cylinder then hit it locally with a butane torch.
This alloy is also good for work with magnesium alloys as well so I'm going to use it to smooth out an S4 intake I have as an experiment and then paint it to see how well it smooths everything out and adheres to the base metal.
Should be interesting to see the results. Maybe If I have luck with it others might try it as well as blocks get scarcer and until the proper cylinder replacement mentioned in other threads becomes more cost effective/necessary.
Just try some test pieces on the same material, try to find some similar surface degradation and use the smallest rod size they have just to get the "feel" for what you are trying to do. Also practice getting the surface flush once more- that is probably easier said than done. It would be most interesting to see how you get on with this- the demo video makes it look so easy to work with.
Worst case scenario I would bore the block to 104mm and machine the block down 2mm to match the deck height of 944 S2 pistons. But the $$$ involved to do this is a bit hard to swallow for a 21 year old pastry cook.
can't use 944S2 pistons without a stroker crank.
the 944S2 piston pin is moved up 4.55 mm relative to a 2.5 944/non-GTS 928, to compensate for the 9mm longer stroke of the 944S2 and use the same length rod.
03-26-2018, 01:56 AM
What is the best way to repair top of cylinder corrosion on 928.
