piston preferences

Garry157 · Jan 29, 2016

hello all, I am at the final stage of gathering the last bits to reassemble my 72 750 combat engine, just wondering if installing the light weight pistons and rods is over kill for a street bike. I have done all the upgrades I deemed necessary from gear box to low end and camshaft, also had the head serviced by CNW.....so almost there. While all apart I am leaning towards going with the light weight setup and total seal rings....opinions pro and con welcomed....oh and wondering about a reputable painter I am in SW Va Thanks

pete.v · Jan 29, 2016

I think the JS stuff is good for any and all Commandos if you can afford it. Add the radius cam with lifter kit in conjuction with the Beehive spring kit and all will be awesome.

Fast Eddie · Jan 30, 2016

Garry157 said:
hello all, I am at the final stage of gathering the last bits to reassemble my 72 750 combat engine, just wondering if installing the light weight pistons and rods is over kill for a street bike. I have done all the upgrades I deemed necessary from gear box to low end and camshaft, also had the head serviced by CNW.....so almost there. While all apart I am leaning towards going with the light weight setup and total seal rings....opinions pro and con welcomed....oh and wondering about a reputable painter I am in SW Va Thanks

Garry, yes it is!

The engine will feel crisper and sharper. This is of course mainly due to the lighter pistons, but I believe the longer rods also assist in making the engine feel 'more revvy'.

Although it is claimed not to be strictly necessary, it is highly advantageous IMHO to have the crank assembly properly dynamically balanced at the same time.

Some argue that the lightweight pistons are not ideal for ultra high mileage use. I cannot comment on that, but in a street 'hot rod' they are perfect!

Please read my 'engine build prep' thread if you wish to see how I nailed my 850 engine together with JS internals.

B+Bogus · Jan 30, 2016

+1 on the JS pistons/Carillo rods setup.
Check your CR against the JS specs for a milled head though, as the pistons are high comp and may need some work to get things just right.

Note that the lifters are designed to work with the matching cam, so not sure if they're a benefit on their own.

Fast Eddie · Jan 30, 2016

B+Bogus said:
+1 on the JS pistons/Carillo rods setup.
Check your CR against the JS specs for a milled head though, as the pistons are high comp and may need some work to get things just right.

Note that the lifters are designed to work with the matching cam, so not sure if they're a benefit on their own.

JS 'medium compression' 750 pistons are stock height, so will have the same CR as stock.

B+Bogus · Jan 30, 2016

Fast Eddie said:
JS 'medium compression' 750 pistons are stock height, so will have the same CR as stock.

Job done

jseng1 · Feb 1, 2016

pete.v said:
I think the JS stuff is good for any and all Commandos if you can afford it. Add the radius cam with lifter kit in conjuction with the Beehive spring kit and all will be awesome.

There are hundreds of Commandos on the street now with the JSM lightweight pistons - mostly for street riding customers looking for less vibration/stress and more reliability. The 1st test bike has 25,000 miles on them now and they show less than 1% leakdown with the gapless rings. Many race bikes use them as well to avoid crank and case breakage. Below is a photo of Vics 920cc from down under (after 2 years of racing on alky and Castrol R40).

Garry157 · Feb 3, 2016

Thanks for the feedback , I have been on the fence (driving my wife crazy! she just wants it done!) so in for a penny as the saying goes...once I start the build I'm sure to have more questions , thanks again Gary

gortnipper · Feb 3, 2016

Garry157 said:
oh and wondering about a reputable painter I am in SW Va Thanks

Brent @ vintage-vendor - just a small commute up the road for shipping.

quality-motorcycle-painting-reasonable-prices-t4085.html

jbbudgor · Feb 3, 2016

I would be happy to talk with you about painting your bike. I have many folks here on Access Norton, including Jerry Doe himself that I have done paint work for and these testimonials below will attest.
Thanks,
Brent
www.vintage-vendor.com

quality-motorcycle-painting-reasonable-prices-t4085.html

Jerry Doe · Feb 3, 2016

Brent just painted my 750 tank and side panels. It looks great. I am going to do a write up about it later when i finish the bike. Highly reccomend. Thanks again Brent.

piston preferences

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