Just whipped the top end off. Head perfect. No traces of detonation at all.
Nice colour. Top of piston the same. Quick tap on piston top with hammer
block of wood and it freed off easily. Off with the barrel and the only
damage is where a piece of broken ring has picked up on a port. Gudgeon pin
came out easily and small end bearing is perfect. The real shocker is the
piston. The rear half of the skirt is in large pieces, a good 25mm of piston
ring land is missing, and there are 2 _old_ cracks in the piston from skirt
to crown. The edges of the pieces of the skirt show that where they cracked
off the piston were preexisting cracks. Not clean metal.
So broken ring and mechanical fatigue would be my diagnosis. Certainly not
mixture or lubrication thank God. Pity the barrel plating above the port
copped it. Otherwise it would have been in with a new piston and off again.
Must look at the spare barrel this wekend.
Not a bad result for a 20+ yr old stroker trail bike which sees a regular
3000+miles offroad per year.
JB

On Tue, 10 Aug 2010 13:52:49 +0100, "JB" <(E-Mail Removed)> wrote:

>Just whipped the top end off. Head perfect. No traces of detonation at all.
>Nice colour. Top of piston the same. Quick tap on piston top with hammer
>block of wood and it freed off easily. Off with the barrel and the only
>damage is where a piece of broken ring has picked up on a port. Gudgeon pin
>came out easily and small end bearing is perfect. The real shocker is the
>piston. The rear half of the skirt is in large pieces, a good 25mm of piston
>ring land is missing, and there are 2 _old_ cracks in the piston from skirt
>to crown. The edges of the pieces of the skirt show that where they cracked
>off the piston were preexisting cracks. Not clean metal.
>So broken ring and mechanical fatigue would be my diagnosis. Certainly not
>mixture or lubrication thank God. Pity the barrel plating above the port
>copped it.

Can it be replated?

Otherwise, not as bad result.

--
-Pip

"Pip Luscher" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Tue, 10 Aug 2010 13:52:49 +0100, "JB" <(E-Mail Removed)> wrote:
>
>>Just whipped the top end off. Head perfect. No traces of detonation at
>>all.
>>Nice colour. Top of piston the same. Quick tap on piston top with hammer
>>block of wood and it freed off easily. Off with the barrel and the only
>>damage is where a piece of broken ring has picked up on a port. Gudgeon
>>pin
>>came out easily and small end bearing is perfect. The real shocker is the
>>piston. The rear half of the skirt is in large pieces, a good 25mm of
>>piston
>>ring land is missing, and there are 2 _old_ cracks in the piston from
>>skirt
>>to crown. The edges of the pieces of the skirt show that where they
>>cracked
>>off the piston were preexisting cracks. Not clean metal.
>>So broken ring and mechanical fatigue would be my diagnosis. Certainly not
>>mixture or lubrication thank God. Pity the barrel plating above the port
>>copped it.
>
> Can it be replated?
Could be but the groove/gouge is ~1.5mm deep and it would end up too large
for available O/S pistons. However there is a loca firm which can do steel
linners all ported etc for ~£115.
I picked up my spare engine from the barn tonight so we'll see what that can
offer a donor spares tomorrow.

> Otherwise, not as bad result.
Too right! Bit cheaper than your Guzzi though. That sort of unexpected
outlay _always_ hurts.

cheers,
JB

> -Pip

JB wrote:

> > Can it be replated?

> Could be but the groove/gouge is ~1.5mm deep and it would end up too
> large for available O/S pistons. However there is a loca firm which can
> do steel linners all ported etc for ~#115.

That sounds pretty reasonable to me.


> > Otherwise, not as bad result.
> Too right! Bit cheaper than your Guzzi though. That sort of unexpected
> outlay always hurts.

The Jag is not going to be cheap - I may have found an ex-Mk2 3.8 to act
as a temporary engine and am looking at ?2.5K - ?3.5K for a rebuild of
the original.

Fortunately a rebuilt engine from a 'known' builder tends to increase the
value by a similar amount.

I suppose it could be seen as the equivalent of three years depreciation
on a similar value Mondeo/Astra.

Still a pain in the arse expenditure.

--
Simon