"Andy Dingley" wrote in message news: snipped-for-privacy@4ax.com... | On Thu, 30 Jun 2005 08:14:44 +0000 (UTC), " Kenny" | wrote: | | >Worth bearing in mind that pistons are not round, but slightly oval, and you | >would need to consider this when attempting to make any sort of repair | >(which is not likely to succeed long term). | | These are cast pistons, and we don't know what they're for. But it's | quite possibly fairly low-stressed (if they're cast), in which case a | neat weld and hand-filing will reliably repair a burnt hole from a stuck | ring. For detonation I'm not so sure - has it lost a small length of | land, or the whole land in a ring ? You need to retain the original | land dimensions to guide the ring - filing a short length back to size | is one thing, starting from scratch quite another.
Trying to balance the risk vs the cost... I see the risk factor as all the hassle I have to go through if it fails, and a block wiped out, too, not just the immediately obvious stuff. The two ring lands between the compression and oil rings are broken out, for about an inch or two on the skirt side of the piston, not the pin sides. The upper ring land is good, so the issue for me is how the pressures will treat a softer aluminum repair vs a harder surrounding area. It might push the lands over, instead of breaking them off, making a wipe out even worse. The problem surfaced while I was investigating a low compression in that cylinder, so I think if it did break some time sooner, it wasn't enough to be an issue, but I had the head off because I bounced the intake valves off the pistons when a timing chain component let loose. The bore still looks great. I can see it, but I can't feel it at all, so the engine is still good. I had to cut the bores to match the pistons, so you can see how replacing the pistons will also be a bore job and a size up as well. It already has two sleeves, and that block is getting expensive! Maybe I should just quit while I'm ahead and rest easier knowing for sure I did it right. Sigh....
| | I once took an engine apart to find a _wooden_ piston in it, with a | piece of aluminium sheet screwed to the crown. Petrol engine of about | 6:1 compression and a not uncommon repair in post-war England. I had a | set of new pistons turned up for it (yes, on an oval piston lathe) at | _great_ expense, then found a Dutch guy with a warehouse full of WW2 | surplus and brand new ones!
That's a new one, but I can see completely why it was done. I suspect the mechanic who did it might have been a lot smarter than you initially gave him credit for, considering his circumstances.