Hi guys , when I started my MC28 in the Spring it spewed raw fuel/oil from the right side expansion chamber - yes you guessed it , carb float valve stuck.
Cleaned out carbs and reset the float height but I was seeing a light "white" haze from the right side chamber so became concerned and decided to do a "health check"
I just performed my 1st "leak down" test ( many thanks for all the threads ) and I am a little confused with the results :
when pressurizing the upper cylinder to 7psi , it held the full 7psi for 5 mins with 0 loss and 0 psi on the other cylinder
when pressurizing the lower cylinder , it also held the full 7 psi for 5 mins with 0 loss but there was 4.25psi in the other cylinder ??
Not sure if I have a problem or not with the centre crank seal ( or something else )
the bike starts with only a couple of kicks and runs OK
Any help will be appreciated
Piet Oosterwyk

It's not uncommon to see pressure bleed one way and not the other, because of the nature of the labyrinth seal. In an ideal world it should hold full pressure both ways though.

White smoke from the RHS cylinder (I say cylinder, as on some models/systems the exhaust pipes can cross over) if often a failing RHS crank seal, and is drawing in a little transmission oil into the crankcase.

Unfortunately the centre seal is the biggest weakness of the later NSRs, and to make matters worse, seems to be affected even quicker than ever these days by modern fuels. It's probably OK for now, but expect to replace it in the not too distant future. But please keep us updated, as I'm only speaking from personal experience.
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Andy.
NSR-WORLD.COM

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many thanks Andy for your quick reply - I continued checking the pressure drop on both both cylinders and these are the results : - Both cylinders held pressure for a considerable amount of time but the 4.5 P.S.I on the lower cylinder never changed even after 24 hours.The motor is really "tight" - at what point in time does it become necessary to change out the crank ??

AFTER 5 MINUTES AFTER 8 HOURS AFTER 12 HOURS AFTER 16 HOURS AFTER 24 HOURS

PRESSURIZING THE LOWER CYLINDER INTAKE 7 P.S.I 5.25 P.S.I 3.5 P.S.I

EXHAUST 7 P.S.I 5.25 P.S.I NO RESULTS NO RESULTS 3.5 P.S.I

UPPER CYLINDER 4.25 P.S.I 4.25 P.S.I 4.25 P.S.I


PRESSURIZING THE UPPER CYLINDER INTAKE 7 P.S.I 5.25 P.S.I 4.75 P.S.I

EXHAUST 7 P.S.I NO RESULTS 5.25 P.S.I 4.75 P.S.I

LOWER CYLINDER 0 P.S.I 0 P.S.I 0 P.S.I

Sorry Andy - my table of results didn't send as it was typed but basically the upper cylinder continued to show 4.25 PSI in it while pressurizing the Lower cylinder - even after 24 hours and a drop from 7 PSI to 3.5 PSI
The upper cylinder showed 0 PSI in the lower cylinder over a 16 hour period and a drop to 4.75 PSI from the original 7 PSI

Andy wrote:
...expect to replace it in the not too distant future.

On reflection, this is probably a little pessimistic, but bear in mind that during my time with Performance Engineering alone, I saw a large number of dead cranks! Although I can say, without fear of contradiction, that every crank we had in to rebuild, that had often been claimed to have come out of a running bike, had had a wrecked centre seal!

In my experience, you will generally know when it's on the way out. The bike usually gets harder to start, and idle often becomes a little erratic, and will either "hunt", or the revs will hang until you load the motor a little. As the seal gets worse the bottom-end will deteriorate somewhat, but at higher RPM will quite often run well. It's something you'll just have to develop a feel for really, but seeing as you have the kit, it wouldn't hurt to do a leak-down test every 6 months or so.
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Andy.
NSR-WORLD.COM

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