1976 350 Road

[Duccout]

Hi George,

Lacey Ducati sells the aluminium base gaskets in various thicknesses, including a 1.5mm, so it would be easy to lower the compression and as long as you are not bothered about performance, it would be easy to take it down pretty low. More learned people than me can advise what you would need to go to 7:1 or 8:1.

Interestingly, my brother-in-law recently did this to his Triumph 750 because he could no longer kick it over, but he swapped to low compression pistons.

Cheers,

Colin

[George]

Thanks for that Colin. I am thinking of fitting 1.5mm plus one gasket either side of alli compression plate increasing barrel height by 2mm. Not sure what difference it will make to compression has anyone tried this. Worth a try. Not sure if Nigel's fit Mototrans, I have sent him and email to confirm. Unless you could confirm they fit,

[Jordan]

Data from instruction manual for 1968 350SCR.

Swept volume 340.2cc
Compression ratio 10:1
Bore 76mm
----------------------------------

It can be worked out that the combustion chamber volume is 37.8cc

A 2mm added spacer will increase the chamber volume by 9.073cc
Adding that to the standard volume makes it then 46.873cc

That results in the new compression ratio 8.25:1

[Eldert]

Hi George

did you try a 450 kickstart lever ? they are a little longer .

by adding spacers under the barrel you have to much squish and therfore no swirl to help with burning the mixture .

i the roof of the piston is thick enough i would mill the piston a little lower .

Eldert

[Duccout]

Hi Eldert,

Will milling the piston affect the engine balance in a bad way?


Cheers,

Colin

[blethermaskite]

Could you not just put a 350 sebring piston in it ????? I think it was around 8.5 to 1.
Cheers,
(other) George

[George]

Thanks for all the replies. Sorry for the delay answering I have just got home from Stafford bike show.
I am going to fit the 2mm spacer under barrel and see if I can kickstart. If yes I will ride it for a while to let it settle down after engine rebuild and then see where I go from there.
At show I tried for a straight swop with a green frame 750 SS but for some reason owner was not interested.

[LaceyDucati]

Hi George,

Eldert's advice is correct, running a large squish is not ideal and machining the piston crown would be better. You should also consider that raising the cylinder disengages the bevel coupling, potentially leading to less driving surface and increased wear. The weight difference in machining the crown is unlikely to make a significant difference to the balance and anyway many original cranks are miles out anyway. A Sebring piston may work, but the deck height and squish angle are different, would need some checking/adapting. The Longer kickstart that Eldert mentions is also found on the 350 Condors.

Maybe a 2mm base shim may be worth trying just to prove a point. I'm sure it will be possible to effect a solution, maybe give me a call if you need some suggestions/help.

Regards Nigel

[George]

Thanks for the advice Nigel. I will order spacer and give that a try first. A cheap way to prove a point. Of course the fault is with the owner not the bike. As mentioned before my younger fitter friend has no trouble starting it.

[Jordan]

Is an electric starter worth considering?