Welcome to the club!
I can only attest to the engine I removed from my 1967 Sunbeam Funwagon,
which had those exact marks, holes, and piston ring bits in it. Upon
disassembly, I discovered that two out of four pistons had broken top rings,
and those broken pieces had enlarged parts of the ring groove to about 1/4
inch or so before escaping into the combustion chamber! I found my answer
when I looked at the underside of the pistons - every one had been bashed on
the wrist pin bosses with what looked to be an air hammer.
My guess - some hamfisted "mechanic" somewhere did a re-ring job, and didn't
bother to cut the ridge at the top of the cylinder - he just beat the
pistons past it. Thus, when the new rings were installed, there wasn't
enough clearance when the pistons reached the top of their stroke, and the
top rings broke.
I went for a total rebuild, but elected not to use that particular block
during my rebuild - I didn't want to take any chances on what OTHER work may
have been done by the same "mechanic"!! I only used the flywheel and the
front mounting plate from that engine - everything else came from other bits
and pieces scrounged up over the years.
Jon Arzt
Omaha, NE USA
----- Original Message -----
From: "Scott Donnelly" <oharajem@free.midcoast.com>
To: "Alpine list" <alpines@autox.team.net>
Sent: Monday, June 25, 2001 7:23 AM
Subject: expensive engine noises - update
> Engine tear down in search of expensive sounding noises...
>
> Removed the oil pan - no chunks or pieces found.
>
> Removed rocker assembly. Push rods, rocker arms, valve springs and
> lifters all look good.
>
> Removed head - dents in number 3 piston top. Closer examination revealed
> a small chunk out of the top edge of the piston missing. Disconnected
> connecting rod and pushed the piston up through the cylinder from below.
> The top ring was in pieces. The head has small dents from a piece to the
> broken ring floating around in the combustion chamber. There is a fine
> vertical scratch in the cylinder wall. No ring ridge at the top of
> bores.
>
> Removed remaining pistons. Two others had broken top rings. Connecting
> rod bearings look a little pitted and one had started to "smear". Crank
> shaft looks good and should just need a polishing.
>
> Any ideas on why the top piston rings would break? Improper winter
> lay-up? Age? Compression was good at 135-150#.
>
> So, since the engine is nearly all apart, it looks like a full rebuild
> is the way to go. Assuming the cylinder wall scratch can be honed out,
> do I replace just the damaged piston or all four? I'll replace the
> rings, bearings and seals well as have the head rebuilt. Should probably
> replace the clutch...
>
> Any other rebuild tips or advice?
>
> Scott Donnelly
> SV
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