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Author Topic: NF Compression test figures.  (Read 38 times)

Il Feronne

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NF Compression test figures.
« on: August 29, 2022, 06:13:19 pm »
Hi All.
Sorry for the length of posting but as a newbie I'm as ignorant as can be.
My newly acquired NF has developed a noise that at first I thought it was noisy tappet(s), but now suspect the "clacking" is lower down in the cylinder.
New to this wonderful old Militare and having only covered approx 250 miles since collecting the beast, today I decided to perform a compression test to try and diagnose whether it's piston ring(s) or valve guide(s) may be the culprit.
I understand that no engine likes to sit not run for long periods and these engines can be heavy on exhaust valve seat and guide
The compression test results were:
Warm=60/65psi. For all three tests.
Warm with a shot of oil in the barrel=105/110psi for all three.
Seems a little extreme to me and on my other engines would suggest a broken or stuck ring, or very worn bore. But with less than 8K kms what would you far more experienced folk day?
It doesn't use oil that I can determine, but I haven't put enough miles on it as yet to know for sure. It does have smoke from the exhaust whilst idling and reving, but probably more black than blue! It does run rich. Better now the needle is on 2nd notch, but Spark plug very black.
So before I strip top end or do more damage riding it whilst weather lasts, I'm seeking advice.
I'm not looking to up the rather Conservative horse power, or make it something it wasn't designed to be. Making the head ready for E10 fuel wouldn't be a bad thing though. I'm using Valve master plus at the moment. Hope that hasn't been a reason for the smoke and noise????
Any help and comments most appreciated.

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NF Compression test figures.
« Reply #1 on: September 17, 2022, 07:17:13 pm »
Hi Il Ferrone, and sorry for the delay in replying.
Unfortunately, most people have deserted the forum in favour of Facebook, so there are not many people to answer you.
I have no idea what the compression figures should be, but your numbers do seem very low, and the increase with oil does suggest an issue with rings or bore, as I think you are suggesting. However, I don't see that being related to noise.
Excessive noise is most likely valve gear: mine was a worn inlet rocker, almost inevitable if you don't have the extra oiling modification.
I'd suggest you start by lifting the rocker box, and checking the condition of the rocker face.
See my post on that for details.
Black smoke? Check the face on the enrichener plunger. If perished, it will allow excess fuel, especially at low rpm.
« Last Edit: November 06, 2022, 11:35:06 am by banquo »

Rob vW

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Re: NF Compression test figures.
« Reply #2 on: September 21, 2022, 09:59:17 pm »
Have a look & see if the cylinder head is leaking. The bike will run, but you will get a distinctive clack at the point of leakage.

Nip up the 4 big bolts to 32nm. Ride the bike. Simples!

You might want to check the valve clearances while you are at it.