350 lightweight piston

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350 lightweight piston

Postby Marty » Fri Mar 27, 2015 9:12 am

Hello All
Would anyone have a piston for a 350 lightweight easily accessible ? I don't have one but am looking at the feasibility of fitting one to my longstroke G3LC. I need to know the distance from the top of the gudgeon hole to the top of the piston (without the crown height).
I want to find a piston of non longstroke dimensions as a sleeve was fitted to the barrel (spectacularly unsuccessfully) and it was counterbored to stop it moving (again, failed). The counterbore is 10 thou under a G5 +20 bore size. There is still a lot of meat on the original cast in bore. If the gudgeon height is the same as the longstroke I will bore the barrel and make a 3/4" small end bush.
Has anyone done this ? I know the factory made 410's out of the l/s 350's. They used the piston from the s/stroke scrambler engine (same height as the l/stroke), but that has a bit more squeeze than I am looking for.
Thanks
Marty

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Re: 350 lightweight piston

Postby Ozmadman » Fri Mar 27, 2015 11:47 am

Hi Marty
Here is a picture of a +040" piston, I measured from the top of the gudgeon pin hole (not from the slight taper you will notice in the picture but exactly from where the pin goes through) it measures 1 and 5/16" or 33.5mm. The lightweight piston has a flat crown
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Paul
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1974 Yamaha RD250B US Model 6 speed

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Re: 350 lightweight piston

Postby Rangy65 » Fri Mar 27, 2015 2:55 pm

Hi Marty, just for you to compare- I have an original piston which does not have a taper as per Paul's photo and measured 34.19mm.
G5 piston.jpg



Hope this helps

Cheers
Steve
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Re: 350 lightweight piston

Postby Marty » Fri Mar 27, 2015 4:44 pm

Thank you both for your info. I will get back to you when I compare dimensions

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Re: 350 lightweight piston

Postby Marty » Sat Mar 28, 2015 11:22 pm

Well, gudgeon heights are near enough to identical, so now the search starts for a +20 G5/Model 8 piston.
Thanks again for your help
Marty

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Re: 350 lightweight piston

Postby Ozmadman » Sat Mar 28, 2015 11:41 pm

Marty wrote:Well, gudgeon heights are near enough to identical, so now the search starts for a +20 G5/Model 8 piston.
Thanks again for your help
Marty

Try here

http://www.jp.com.au/MCA.html
Paul
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Re: 350 lightweight piston

Postby Marty » Sun Mar 29, 2015 5:06 am

Thanks Paul. I have used JP in the past when I am unable to source BHB or hepolite. For the amount of use I am going to give it, a good used piston would be fine. Would anybody in the group have one in their shed ? I will put a Wanted in the potty
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Re: 350 lightweight piston

Postby 39speedtwin » Sun Mar 29, 2015 9:01 am

Why not try John Harding 01989 750731

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Re: 350 lightweight piston

Postby Rangy65 » Sun Mar 29, 2015 5:19 pm

Hi Marty this is an extract from the technical section on this web site and may help you widen your search for a suitable piston

''Most wearing engine parts are readily available from either the Club Spares Scheme or the London shops. However, do not expect them to be cheaper than other new parts. The 25Occ piston had either a circular or steeply ramped crown while the 35Occ one was fiat. Over-weight pistons should be avoided since the loads on the crankpin are increased, giving a short crankpin life, and vibration will be worse. On the 350cc engine, an AMC 600cc piston can be used. This will give a higher compression ratio''

I am sure someone will know what year and model 600 is best for piston donation.

Good luck with your project

Steve

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Re: 350 lightweight piston

Postby ajscomboman » Sun Mar 29, 2015 5:37 pm

Rangy65 wrote:Hi Marty this is an extract from the technical section on this web site and may help you widen your search for a suitable piston

'' On the 350cc engine, an AMC 600cc piston can be used. This will give a higher compression ratio''

I am sure someone will know what year and model 600 is best for piston donation.

Good luck with your project

Steve


The info given above relates to the use of a Twin piston in a Lightweight 350 and is incorrect. It is actually a 1959 only 650 Twin piston that fits into the Lightweight 350. If you fit a 600 piston the compression is very low due to the gudgeon pin being nearer the crown.

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