Surface Marks?
Burning Brakes
Joined: Feb 2013
Posts: 776
Likes: 59
I am in the middle of my intermix repair and while checking my cylinder bores I see these marks. They seem to be non-structural and looks almost like simple blemishes on the casting. In doing some research I have seen hints of it in other pics but no real discussion on what they are. Can anybody help? These marks are on the four cylinders I have checked so far, I am sure they are on all 6.
Thanks
2000 C2 Cab with 176K miles.
Thanks
2000 C2 Cab with 176K miles.
Thread Starter
Advanced
Joined: Nov 2012
Posts: 76
Likes: 1
From: Arizona
I sent Hartech an eMail about these marks and here is their response. I post it here so that others can benefit from the explanation.
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"These marks can be puzzling and we have never been able to absolutely determine what they are or the cause.
The manufacturing process is for a liner to be constructed from a composite mixture of a resin and silicon particles forming a rough shaped porous tube.
These are then located inside a metal casting mould and the molten aluminium is forced in under high pressure that permeates the liner filling up some of the gaps between the particles while burning off some of the resin leaving a porous silicon rich surface with an outer aluminium casing.
Our tests show that the resulting Lokasil part (the bore par which is roughly half the thickness of the visible liner area) is more porous but also stiffer (more brittle and less flexible) than the aluminium.
The wall thickness of the cylinder composite tube combined with the open deck design allows the cylinder to flex under the load of the piston thrust face (that eventually can make the cylinder distort oval enough as a result of “creep” to remain oval by up to 0.25mm after which it usually cracks or “D” chunks).
The cylinder head gasket has circular cut out sections on the top and bottom layer of the triple steel gasket to allow the plastic sealing coating to remain in contact with the cylinder head while this flexing is taking place.
Putting all these facts together - we think these marks are probably minute surface cracks with no measurable depth in the make up of the Lokasil. They are effectively just surface marks that seem to have no mechanical or operational consequences.
There is a variation in the distribution of the aluminium and the amount of silicon and the proportion of resin and the penetration of the aluminium during casting that can very rarely result in some areas actually washing away the surface by up to a half a milimetre – so there is clearly a possibility that these marks are just where a trace of different bonding occurred such that as the cylinder expands and contracts during warming up and cooling and also distorts under load – one specific area is slightly less strong than others and the silicon particles just there – while perfectly well bonded to the substrate internally – never the less at the surface release their bonding strength to the circumferentially adjacent particles.
In any case we have never experienced them becoming a problem and so I think you should ignore it."
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__________________________
"These marks can be puzzling and we have never been able to absolutely determine what they are or the cause.
The manufacturing process is for a liner to be constructed from a composite mixture of a resin and silicon particles forming a rough shaped porous tube.
These are then located inside a metal casting mould and the molten aluminium is forced in under high pressure that permeates the liner filling up some of the gaps between the particles while burning off some of the resin leaving a porous silicon rich surface with an outer aluminium casing.
Our tests show that the resulting Lokasil part (the bore par which is roughly half the thickness of the visible liner area) is more porous but also stiffer (more brittle and less flexible) than the aluminium.
The wall thickness of the cylinder composite tube combined with the open deck design allows the cylinder to flex under the load of the piston thrust face (that eventually can make the cylinder distort oval enough as a result of “creep” to remain oval by up to 0.25mm after which it usually cracks or “D” chunks).
The cylinder head gasket has circular cut out sections on the top and bottom layer of the triple steel gasket to allow the plastic sealing coating to remain in contact with the cylinder head while this flexing is taking place.
Putting all these facts together - we think these marks are probably minute surface cracks with no measurable depth in the make up of the Lokasil. They are effectively just surface marks that seem to have no mechanical or operational consequences.
There is a variation in the distribution of the aluminium and the amount of silicon and the proportion of resin and the penetration of the aluminium during casting that can very rarely result in some areas actually washing away the surface by up to a half a milimetre – so there is clearly a possibility that these marks are just where a trace of different bonding occurred such that as the cylinder expands and contracts during warming up and cooling and also distorts under load – one specific area is slightly less strong than others and the silicon particles just there – while perfectly well bonded to the substrate internally – never the less at the surface release their bonding strength to the circumferentially adjacent particles.
In any case we have never experienced them becoming a problem and so I think you should ignore it."
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