JP 3 Change Over Valves

[steve.sharratt]

I am running a JP3 in my narrowboat and was recently pushing against a strong flow coming up the Thames. As I was working the engine I used the low compression option for the first time.  After the initial experience of the hissing and barking while going from high to low, I found that the engine ran very cleanly (after the engine was at running temp) in low.  I am now on a canal which doesn’t require the effort so have been leaving them set to high comp.  My problem is that I now have a slight leak in number two (although its seems to have had no effect on the performance).  It seems to be hissing through the nut holding the wheel in place.  I assume there is a bit of carbon build up - does anyone have a clever trick for getting a better seal?  

Note: I stopped reading the manual for removal when it was suggesting that I hammer chunks of wood into the block!

Cheers

Edited May 28, 2023 by steve.sharratt

[tommylad]

Sounds likely that it's carbon build up. They do need screwing in quite tightly even when clean & oiled (both hands). You could try oiling the threads and giving them some 'exercise' which should sort it I'd expect. If it comes to it, removing them just needs a big adjustable in my experience

[frangar]

As others have said try tightening/loosening a few times. There is also a spring washer around the thread on the valve which does become tired and causes the valve wheel to turn and leak. 
 

I usually start mine on high and run on low on canals as well as rivers. Keeps the valves clear and I’m my mind it’s less stress on the crank although probably not in reality. 

[steve.sharratt]

5 hours ago, tommylad said:

Sounds likely that it's carbon build up. They do need screwing in quite tightly even when clean & oiled (both hands). You could try oiling the threads and giving them some 'exercise' which should sort it I'd expect. If it comes to it, removing them just needs a big adjustable in my experience

I will try that.  Do the threads come out just by undoing the centre nut?  My read of the manual made it look a lot more complex.

2 hours ago, frangar said:

As others have said try tightening/loosening a few times. There is also a spring washer around the thread on the valve which does become tired and causes the valve wheel to turn and leak. 
 

I usually start mine on high and run on low on canals as well as rivers. Keeps the valves clear and I’m my mind it’s less stress on the crank although probably not in reality. 

I have considered running on low on the canal but when on the river, if I was in a lock for a while, it seemed to slowly get smokier which would clear again once I increased the revs.  On the canal, my cruising revs are lower although I am deep and heavy so even at slower revs I can be putting a load on the engine.

 

 

[tommylad]

I'd try and avoid any disassembly to start with, just oil the threads which are exposed when they're screwed out. If they're coked up it might be an idea to wire brush them before oiling. 

Mine is smokier on low compression when on light load too.