Piston - Cylinder Wear

[themoudie]

Thank you Nigel, I shall still have the conversation and see what transpires.

Bill

[frankfast]

Are the pistons interchangeable between NC and WC since bore and stroke are the same?

The edited question was a stupid one since you've already given me the answer at least four times. Excuse my ignorance.

[LaceyDucati]

Generally speaking yes with the exception of W/C pistons in 350 Sebrings. The reason being the short n/c rod means the w/c original pistons foul the crank wheels. Also the Sebring has a slightly different deck height and squish angle (40 degrees) due the the Sebrings 76mm head. All other 250/350's have 74mm heads with a 45 degree squish.

For your 350 SCR unless it's a Sebring specific piston they should all be interchangable. That said any 250/350 piston can be made to fit any 250/350 with a bit of fettling and acceptance of different C/R.

Regards Nigel

[frankfast]

HPIM1047.JPG

HPIM1046.JPG

Nigel - Thanks for the response. Not sure that you can get the attachments. The piston on the right is the one I installed years ago. Can you identify It? The only markings on it is the number 666147. As you can see it is a much higher compression than the one on the left which I believe to be the original. I have to take measurements of the bore so I can replace it with one that has a lower CR. My weak knees can't kick it over.The piston is almost new since I've only statred the bike a few times since it was installed. Thanks.

[LaceyDucati]

Hi Frank

That piston is a race piston and not really suitable for road use. It's an American made piston, probably either an Arias or JE. I would use a road piston with similar crown to the original, it will probably run better and save your knee! I can of course help with a piston, but you may wish to source one locally.

Regards Nigel

[Eldert]

Hi Frank

piston looks like JE to me . they put their job numbers in that place .

they did internal milling into the dome so shaving or milling some material from the top of the dome
is not a option .

Eldert

[frankfast]

Thanks Nigel and Eldert - I didn't consider milling the top of the crown because I'm looking for something with a much lower compression ratio. Many of the pistons I see are for the Mark 3 and are of a higher CR than the original piston shown above. I'm not even sure it is original for a WC Scrambler. Perhaps someone can confirm. - Frank

[frankfast]

Nigel - As a slightly cheaper option to purchasing a new piston and boring the existing liner, since the original piston is in decent shape (maybe with new rings), I wonder if replacing the liner and boring to accept the original piston would be as effective. How difficult is it to replace the liner? I've had experience heating aluminum and removing bearings and other steel bits but would the liner have to be pressed out and the new one pressed in? Shipping to New York would be another consideration, Do you have an approximate cost? - Thanks - Frank

[Duccout]

Hi Frank,

I'm not an expert, but I have replaced four of the cylinder liners in my time. I don't suppose that I did it the correct way, but it worked. I heated the barrel in the oven until water droplets sizzled, then placing the barrel over a partly opened Workmate, so that the barrel muff was supported, and with some sponge on the floor underneath to catch the liner as it fell, I tapped the liner out with a copper mallet and then a 1" aluminium drift. I then reheated the muff (wiped clean and re-lubricated) and using the Workmate in the same way, dropped the cold (kept in the freezer) liner in and tapped it home.

The hardest part is ensuring that the liner bolt cut-outs line up with the holes in the muff. I guess that to do it properly would require a press, but I don't have one. See what Nigel and Eldert say, but I wouldn't be frightened of doing it.

Colin

[frankfast]

Thanks Duccout. I would have done exactly as you have described. I also do not have access to a press. I now favor replacing the liner and boring it for my original piston. Seems like the cheaper way to go. Attachment is the piston that I removed.