Decompression valve / leaver

[Karrier]

Hi

I am posting this for someone else who isn't online.

He was having trouble with a sticking leaver so he took it apart and cleaned it up, he decoked as best he  could but now it's all back together it's smoking, not a lot but enough to warrant sorting out.

I personally know nothing about this my experiance is with BMC and Perkins. 

I had a look when it was apart and wondered if the valve seat needs to be ground in like a valve / cylinder head. 

Is it just a basic valve? This interests me as I want to learn about these engines, I used to service single  cylinder hand cranked listers that we used for mobile traffic lights back in the 80s but they had nothing on these lovely engines.

Any help would be great,  I've added some pics of the offending part and the engine and it's zerial plate too. 

[MoominPapa]

That not a decompressor. The engine is a Lister FR2 and it does have a decompressor, it's the small lever on the end of the rocker cover.

The assembly you've highlighted is a compressor change-over valve, used to change the compression ration for starting, By "smoking" do you mean that smoke is emerging from the valve, or that the engine's exhaust is smoky? I'm guessing the later. The FR was the last Lister engine to have compression change-over valves and the design used is notorious for leakage problems.The only way to cure then is to remove all the sealing parts of the valve (which needs special pullers) and clean them and grind the valve seats. Even having done that, the cure may be temporary.

My FR2 has the valves welded up in high-compression mode, which has given no problems with the engine and a complete absence of leaks.

 

Cheers,

 

MP.

 

[RLWP]

It is slightly worse than a basic valve, it's a double sided valve with a seat on both sides. There's also two valve seats in the stationary bits

We have a puller and a selection of used parts for the FR

Richard

[Nightwatch]

Two potential solutions for your friend there. Great innit?

[RLWP]

Oh, and for completeness, the decompressor is a lever on the front of the valve chest, the alloy bit on top of the engine

Richard

[Karrier]

16 hours ago, MoominPapa said:

That not a decompressor. The engine is a Lister FR2 and it does have a decompressor, it's the small lever on the end of the rocker cover.

The assembly you've highlighted is a compressor change-over valve, used to change the compression ration for starting, By "smoking" do you mean that smoke is emerging from the valve, or that the engine's exhaust is smoky? I'm guessing the later. The FR was the last Lister engine to have compression change-over valves and the design used is notorious for leakage problems.The only way to cure then is to remove all the sealing parts of the valve (which needs special pullers) and clean them and grind the valve seats. Even having done that, the cure may be temporary.

My FR2 has the valves welded up in high-compression mode, which has given no problems with the engine and a complete absence of leaks.

 

Cheers,

 

MP.

 

Hi, ah right thank you for explaining,  when I had a look after he had put it back together and he started the engine, the smoke started to show coming from exactly there, not the exhaust but what looked like the left side of the mounting / leaver, I said I thought it might need grinding the valve seat but didn't realize there were two.

So it needs to be removed and ground in on both valve seats which may fix it?

 

Thanks for all the other replies, these engines are so different to what I know, why do they need this to start, I did think it was very slow to start up compared to my bmc 2.52 but this is the first narrow boat engine I have looked at, all others have been in  cabin cruisers. 

Edited April 13, 2018 by Karrier

[MoominPapa]

7 hours ago, Karrier said:

 

Thanks for all the other replies, these engines are so different to what I know, why do they need this to start, I did think it was very slow to start up compared to my bmc 2.52 but this is the first narrow boat engine I have looked at, all others have been in  cabin cruisers. 

These engine don't have glow plugs and are designed to hand start-able. In fact they're designed to be usable without an electrical system at all.  The Compression change-over valves increase the compression ratio so that the air in the cylinder gets hotter to make it easier to start, and then allow the engine to be run at a lower compression ratio which is easier on the mechanicals. All Lister diesel engines up to this point have the system. (The classic single cylinder Lister is called the CS, which stands for "cold start" and refers to this.) In the engines earlier than the FR the valve is operated with a hand wheel and screw thread, which allows plenty of force to seat the valve. The FR was a new design with easier-to-use levers, and the force holding the valve closed comes from springs - and is often not enough. Designs after the FR did away with the valves - probably because improvements in bearings and metallurgy allowed higher compression ratio in running state.

[RLWP]

We have manuals for the FR