Recently I had a detonation issue with a motor and broke two of the ring
lands, essentially scrapping a high compression piston set I special ordered
from the UK. With the exchange rate, replacing them will even be more
expensive, and the engine bores were cut to match the pistons, hence I'd
like to see how feasible it is to fill in the damaged areas and cut the ring
grooves again. The pistons are cast. Is this something most machine shops
that do aluminum head repair can do, or should I shop the welding and
machine work out to different places? Is heat treating going to be needed
after the welding?
I cannot help you with your piston but perhaps a knock sensing device could
prevent a similar situation in the future. Have a look at my website.
Got Knock? - see:
Viatrack Printed Circuit Designs (among other things)
Not being a motor head, but a fair fixit..would it be feasable to
simply widen the groove and stick in a second of ring? Perhaps an oil
"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you
for torturing the cat." Gunner
You have a few issues at hand,
If you change the weight of the rotating mass the engine will fail soon
as the bearings will cook and most likely a rod will blow out as you are
looking for a seizure. All the groves and compression surfaces of the rings
must be the same (leakdown test) question if the detonation was caused by
too high of compression and too low of an octane fuel (the most common cause
I see next to kids putting Nos on a motor and burning it up) Replace the
damaged piston too as if you put it under magnification or NDT it, I bet you
find hair line fractures. Assuming the bore was not harmed and a wet hone
will clean it up or you need to scrap the set and go up a .10th on the whole
Filling the ring gap is "asking for it" try contacting the manufacturer,
not the vendor, you will need to have the rings ground to fit the bore and
re-weigh the complete piston against a comparison slug from another cylinder
as even the smallest deviation will put your rotating assy. at risk. If this
is a high-dollar engine, a band-aid is not going to cause anything but
premature failure and most likely, worse than what you have to deal with
If you E-mail me directly I can prob. hook you up with better info as
this is sort of off-the-cuff but I do this on 5 second alcohol and nitro
engines so I know the value of a dollar and this is something you don't want
to screw up, especially with a conical piston.
let me know if I can help,
Fraser Competition Engines
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.
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!
| >Worth bearing in mind that pistons are not round, but slightly oval, and
| >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.