More adventures with my 'Troublesome SL1K'

[Chris Cairns]

Spurned on by recent postings from fred I decided to do a bit more work on my 'Troublesome SL1K'.

You may recall I got this running again by replacing the faulty reverser/regulator with one from an SL3. Unfortunately in order to get another SL1K running to be sold on, I had to use the SL3 one to sort out that SL1K's one, which was recently seen running well in steam at the Dorset Show.

So I tried fitting an MSS replacement valve which I bought for my IPS Janet project, but this did not work very well - too much restriction caused in the steam path.



This is the replacement MSS valve on the left with one of the bodies from the faulty Mamod SL1Ks on the right. Note the chamfering of the steam holes on the Mamod one. I have just had a reply from Mamodevon (Alan of Dream Steam) saying that he has not come across this chamfering in 30 Mamod & MSSs he has serviced, but the one from my SL3 has this chamfering, and looking at my mint boxed SL1K it has it as well. So it must have been done by Mamod at some point but has not been carried on by MSS.

The advantage of using the MSS gaskets is that it makes removal of the cylinder assemblies easier without breaking the old paper gaskets that Mamod used. So looking at my chassis frames (which are actually MSS replacement ones), the MSS replacement valve & the MSS gaskets clearly showed that there are restrictions in the steam path due to the tolerances associated with producing these locos at an affordable price.

Reading the Mamod modification notes that were produced by the 16mm NGM, one of their recommendations is to open out the steam holes in the chassis frames (the inside 2 of the 4) to 1/8" or 3mm. So I did this. Then mounting the gasket on its own showed that the cut outs for these steam holes needed adjusting, and finally fitting this modified gasket to the cylinder back plate showed that the cut outs which line up with the rear steam holes on this plate also need adjusting.

So after all this work I fitted the repaired SL1K valve and I now have an SL1K which achieves derailing speeds backwards, but not so well forwards (this had those badly shaped cut outs in the valve that I tried to file out properly). Sadly due to not having a proper planning machine the rotating part of the valve is not sitting right (difficult to lap the surface exactly at 90 degrees to the pivot bolt fitting), and so still leaks a little steam.

So I’ll be putting a posting in the Wanted Forum to try and get 2 of these rotating valve parts, otherwise as they are not available as spare parts I'll need to buy the complete valve assembly and chamfer those steam holes.

Chris Cairns.

[SillyBilly]

I shall have to trry opening the frame steam ports on my friend's troubled loco, then apply some graphite grease between the frames, might pick up some lapping paste and do the valve at the same time, thanks for that Chris.

[ACLR]

I will be pulling my sl1k apart soon so will take a good look at the valve here also

[grumpfuttock]

Thanks for that information Chris, I have learnt something new today. The rotary valve on my 2 Mamods are the original Mamod SL1 type with the chanfered holes. I hadn't heard of drilling the frame holes larger, before today.
One thing I have noticed after buying a set of replacement upgraded cylinder units from PPS last year, is that the steam passage ways in the cylinder and backplate are smaller than those on the Mike Chaney cylinder units I have used for many years. I have been wondering if this would account for a significant decrease in power that I have experienced since fitting the PPS replacements to one of my loco's.

[Chris Cairns]

And some interesting information from you as well John.

I'm only used to Mamod/MSS cylinders so far, but I have a Mike Chaney upgraded SL1K which awaits its turn in the workshop, so I'll have a look at the cylinders on that one as well. But it could just be normal Mamod cylinders fitted with the Mike Chaney 'O' ring pistons and replacement rear cylinder end cap. I've got a set of these Mike Chaney ‘O’ ring pistons en-route from ebay shortly.