Lister startomatic - decompression control ?

[veggie]

Did the early Lister startomatics provide any automated decompression when the gen head acted as a starter motor?
Just wondering if the starter had to overpower the compression stroke.


veggie

[Bottleveg]

The change over valve is left screwed out on the 5/1 and 6/1 SOM's.
I guess the idea is that the alternator has the power to start the engine on low compression and then the engine will be running at above prescribed medium load to drive the alternator.

[AdeV]

Did the early Lister startomatics provide any automated decompression when the gen head acted as a starter motor?
Just wondering if the starter had to overpower the compression stroke.

Yep - there's a solenoid attached to the engine near the exhaust valve lifter; this is connected via a bar to a rack closer. When the starter begins to spin the engine, the solenoid is in (inactive), the exhaust valve held open & the rack held shut. After a pre-determined time spinning up, the solenoid operates allowing the exhaust valve to close & simultaneously opening the rack.

You can see it here on my dismantled engine:



The exhaust valve holder resembles a  Yale door lock, so the cam is able to push the valve past the lifter, but it won't drop back down past it.

Aha, here's a slightly better picture (unfortunately, you still can't really see the shape of the exhaust valve holder-opener):



Click either picture to see it full-size BTW.

[veggie]

AdeV

Thanks very much for the explanation and pictures. Makes it all clear.
Although it breaks my heart to see Lister's in pieces. 

cheers,
veggie

[oiler]

This might be of some help. Look closely at the fuel pump.

http://www.youtube.com/watch?v=sbXUkHRRfP0

[AdeV]

Thanks very much for the explanation and pictures. Makes it all clear.
Although it breaks my heart to see Lister's in pieces. 

No problem - although if you watch the video that oiler has linked to, you'll see that the decomp solenoid operates as soon as the plant starts motoring (as Lister put it), so the starter does pull the engine over compression. From reading the manual, I thought there was a delay, but obviously not.

Don't worry about my 2nd engine being in bits.... it's scheduled to be restored "at some point in the future" & returned to working order. I have to get the cylinder jacket welded first, it has a huge piece blown out of it (frost damage), but is otherwise largely complete. I also have a base for it, I just need a S-o-M alternator; but they sell for mad money on eBay, even if untested. My alternator has a badly bent shaft & a blown starter winding, and is currently in bits. I need to find someone who can re-wind it for £not-too-much...

[Derb]

Hi Boss. My SR2 has a 24 volt actuator on the decompressor which reverts to decompressed mode with power off. Upon start up it doesnt release until engine is spinning over quite fast and then there is a cloud of smoke and she's away up to 1500 rpm.

[contaucreek]

Great picture AdeV. I was in need of that as I am going to look at an engine next week that may be missing this control gear and I need to know what I was looking for in case it was there on a shelf, thanks.

[listeroil]

On the cs engined Start-O-Matics there are two types of decompression system. 

The single cylinder types use a 24 volt DC  solenoid and it is operated as soon as the engine starts spinning there is no delay apart from the fact that the solenoid has not got enough power to operate until the engine turns over and the exhaust valve lifts. There is no electrical delay. When the engine is up to speed the microswitch on the engine stops the starter motor and inserts a resistance in the wiring to the solenoid to reduce the power to the solenoid to stop it burning out.

On the twin cylinder cs engines (and SRs )the solenoid is AC operated (230 volts 50 hz or 110 volts 60 hz ) and is connected to the alternator AC output. When the engine is being spun over the alternator eventually produces enough AC voltage to energize the solenoid to put then engine onto compression. Thus giving the engine a good time to get up to speed before compression and then start.

One other point is the decompressor solenoid unit also operates the fuel on and off as well.

Mick