Norton 961 Compression Test

TonyA · Dec 9, 2021

Hello , I thought I would test my compession again and I was surprised to find it so high. I was expecting 150-160 psi and I was wrong.

Left cylinder 176 psi

Right cylinder 180 psi

Current mileage

BritTwit · Dec 9, 2021

Holy cow, that's great!

BritTwit · Dec 9, 2021

Manual says 120-170 is standard.

TonyA · Dec 9, 2021

I can't even imagine how much blow by you would have at 120 psi , or a leaky valve ?

BritTwit · Dec 9, 2021

That motor seem pretty healthy.
Whatever you're doin', keep doin' it.

cliffa · Oct 3, 2022

Folks, what is the correct procedure to carry out a compression test on a 961 ?

Stu Bodycote · Oct 3, 2022

Hot engine, both spark plugs out, WOT and crank until the needle stops rising.

City Garage · Oct 3, 2022

And unplug the fuel pump if you are so inclined

City Garage · Oct 3, 2022

Leave spark plugs in the boots as well

cliffa · Oct 3, 2022

Thanks @Stu Bodycote & @City Garage I should have been more specific. I was wondering if I need to pull the fuel pump relay, but I hadn't thought of disconnecting the fuel pump.

City Garage · Oct 3, 2022

No, just unplug under the tank. It will keep you from getting an initial blast of air-fuel at 150psi ish or more coming out.

Also, you can do it cold( you will get lower numbers than warm), but the consistency is really what you are looking for. Cold tests happen all the time on no-start conditions.

Ideally, like Stu said, warm, WOT

cliffa · Oct 4, 2022

Carried out the test tonight straight after riding home from work ( yes I commute on mine).160 psi left & 155 right, so right in the middle of the spec.