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Hi Guys;

What seemed like a relatively simple base gasket change has revealed that the cylinder bores look corroded/worn.

I measured the bore diameter with a vernier, and they are 61.96mm - 61.98mm, close enough to the original 62 mm bore as stated in the specs of the bluebook. I assume that the pistons are therefore standard/originals and its never been rebored.

The bluebook states that the cylinder should be rebored with a slight taper - and gives the details, also stating that the pistons are available in +0.2, 0.4 and 0.6mm oversizes.

Q. Where would I get these oversized pistons and what Company could perform the rebore? I contacted Mdina Italia - but still waiting for a response.

I've never gone through the process of reboring a cylinder before so your advice in this matter would be greatly appreciated.

- D

1978 Moto Morini 350 Sport
(London area)

Hi Guys,

I got a response from Mdina - which has answered my questions. I've posted it here in case anyone else has similar questions:

Maybe the other option would be to get them honed and and go with a set of oversize rings first which would save you some cash.

https://www.mdinaitalia.co.uk/piston-ri ... e-350.html

The 64mm Pistons are the only oversize piston I have in stock and the taper you refer to is on the external face of the liner the idea being that if the fire ring on the liner failed the liner itself will not slide down into the crank.

The 64mm piston can be fitted to the existing liner but once this is done a new liner would be needed thereafter.

Other sources of 350 pistons exist, notably King of Pistons in Italy.
I have ordered pistons from them, its not a cheap option but for some models like pre Lambertini singles and modular 125 and 250 the only option.
They are or at least for me easy to deal with. Note you will need to add UK import VAT to the prices quoted on their website, which you will pay to the carrier. Be aware that Ferragosto 15th August is nearly upon us its and many factories and suppliers will be closed for summer holidays soon.

We recently went down the route of oversize rings suitably gapped in rusty and pitted bore rather like yours honed and it was not succesful, after 1500 kms i decide to rebore and fit new pistons.

Good luck
Mark