Cylinder rust again

[jamespetts]

When I last ran my engine, I noticed that a large amount of steam leaked from the exhaust even when the engine was not turning. I thought that this was wrong, and so spoke to a few people in my local model engineering club, who agreed that it was wrong.

I had noticed that the port faces on the cylinder had become rough and blackened, and they suggested that I file them down with some wet and dry on a flat surface (such as glass - I used an old mirror in the end) in a figure of eight motion.

I have done this, and it seems to have worked: the port faces are now flat. However, to do this, I had to take the cylinders completely apart. When I did that, I noticed that the insides of the cylinders were rough and blackened, too. Looking closely, the problem appeared to be rust: the substance seems to have a rusty colour. When I clean them with tissue paper, a quantity of black dirt comes off, but much of the stuff is hard.

I now have two problems: firstly, how to get the stuff off so that the cylinders are smooth again, and secondly, how to stop it from happening again.

I thought that one solution might be to take both cylinder castings to the club and use a reamer to ream the cylinder bores clean of the rust, and then fit some sort of piston ring. I had considered cast iron piston rings, but then realised that, if they were to rust again, cast iron piston rings would cause the whole thing to seize. I recall also reading threads on here recommending Teflon piston rings. The pistons presently have three very fine oil grooves. Would the best thing to do simply be to put a ring of Teflon in there?

As to the second problem, I took people's advice here of back-filling the cylinders with oil after every run, but that seems to have done no good, and had the additional benefit of making an oily mess on the next run. I have some "preserving fluid" from Stuart - would that help, or would the steam drive that away? The rust seems to affect the port faces, which might have been the cause of the leaking steam in the first place.

[jasonb]

Are you using some form of lubricator whils running the engine? and what oil while running and at the end of the run?

Reaming the cylinder may take off more material than is required, you could possibly get away with honing the bore which will only take off 1 or 2 thou. If you do ream it then you will need an expanding reamer which will take less off than going to the next size up from the bore.

"O" rings are another option for piston rings but you need to size the grove & cyl bore to suit the ring.

Jason

[jamespetts]

Thank you for your reply :-)

I am indeed using a displacement lubricator, using steam oil, which is the same oil that I try to suck back into the cylinders at the end of the run.

What sort of O-rings would you suggest?

[jasonb]

Silicon Rings which you can get from Blackgates or Bruce Eng(Pollymodels).

I have an "O" ring on my minnie TE piston but Graphite Yarn packing on my Stuart Beam.

Jason

[jamespetts]

Ahh, thank you :-) I shall have to try that. How do I fit them? Any tips on stopping my cylinders from rusting in the first place?

[baggo]

Hi James,

I would forget O rings for use in cast iron cylinders. I think it's generally accepted that they have a very short life in a cast iron bore due to the great difficulty (impossibility?) of getting a fine enough finish on the bore. They are fine for gunmetal cylinders which can be lapped and polished to an almost mirror finish.

You could try gently cleaning up the cylinder bores with some very fine carborundum paper. This should remove the rust without removing any significant amount of metal. Hopefully the rust will have not formed pits in the bores and will just be on the surface.

I presume at the moment the pistons have no packing at all, just the oil grooves? The easiest option would be to machine a groove in each piston and just use graphite packing. Fitting rings is another option but more fiddly.

Not sure why you are having so much trouble with rust, especially if you are putting oil into the cylinders after each run. Have you stripped the engine before? Just wondering if the rust damage was caused before the engine came into your possession.

John

[jasonb]

Interesting what you say about CI & O rings John, once the current traction engine is finished I plan to make a Hoglet IC engine that has CI cylinders and uses O rings, have also read of several hit & miss engines that run with them although I used CI rings on my H&M. Will just have to get a good finish on the bores

Re fitting O rings, both Blackgates & Reeves give the sizes of groove required in their catalogues.

Jason

[baggo]

Hi Jason,

It just seems to be the general opinion on O rings and cast iron for steam use. I must admit that O rings do seem to used in hydraulic cylinders etc which are often cast iron. Perhaps it depends on the piston speed, temperature etc. ? The compression of the ring may have a lot to do with it. Many people tend to make the O rings far too tight a fit leading to rapid wear and short life, especially if the surface finish is poor.

Another problem is that even silicon O rings are operating towards their maximum temperature limit in steam cylinders with high superheat. They do go soft and gooey (been there!) A better alternative would be the Kalrez rings but they are not easy to get hold of and very expensive!

Mind you, having fitted PTFE rings to Helen with success, I don't think I shall be using any other sort from now on!

John

[jamespetts]

The pistons do indeed have three very small oil grooves each: no packing of any sort. Would PTFE piston rings work well in cast iron? Where might I find carborundum paper?

[baggo]

HI James,

I believe people do use PTFE rings in cast iron cylinders, I don't see any reason why they will not be ok.

You can use the ordinary Wet and Dry paper (often silicon Carbide) for cleaning up the bores. Have a nip down to your local Halfords store- they sell grades down to 1500 grit and also packs of mixed grades. 1200 or 1500 grade should do the job. LBSC used to suggest final polishing of cylinder bores by wrapping a strip of fine emery paper around a suitable wooden dowel held in the lathe chuck whilst holding the cylinder in the hand (bit like lapping with a metal lap)

John

[jamespetts]

John,

thank you very much for your reply :-) I am putting it back together at present without having addressed the cylinder issue, but I plan on fitting piston rings at some point in the future, and will use fine grade wet and dry to clean the cylinder bores at that time. Thank you very much for your help.

[GWRdriver]

James,
You may indeed have some rust, however you should be aware that when the "old hands" took the covers off their engines for a look-see what they expected to find was a dead black, rather matte oxide finish on all the surfaces exposed to steam. This finish was a combination of carbon, iron, oil resdue, and oxides built up over time and was their indicator that the cylinders and valves were properly lubricated and cared for. It sounds to me, if whatever actual defects there are are minor, that what you see is this baked oxide finish and if so you are actually better off leaving as much of that as you are able.

[jamespetts]

Harry,

thank you for the interesting reply. In some places, the stuff appears to be black, in others, it appears to be rust coloured. It has made the insides of the cylinders rough - is this a problem? Thank you again for replying :-)

[GWRdriver]

James,
I really can't know or tell from this distance. I do think that reaming or skim boring or something akin to that is a bit too much cure, at least at this point. If I found myself in this situation the first thing I would try is running a 3-stone brake cylinder hone through the bores for a while, until differences in the cylinder wall finish began to appear. The hone would begin to polish the good areas while the damaged surfaces or pitting would remain colored. The brake cylinder hone does need to be used carefully, keep it moving and keep the stone pivots within the bore length, to avoid bell-mouthing the bore ends.

[spurley]

Hi James

I think Harry has the right idea and if you don't have one this might interest you (and others?):

cgi.ebay.co.uk/Horizon-H330-Brake-Four-In-One-Hone-Kit_W0QQitemZ160266330657QQcmdZViewItem?hash=item160266330657&_trkparms=72%3A12|39%3A1|66%3A2|65%3A12|240%3A1318&_trksid=p3286.c0.m14

No connection but looks a useful kit at a reasonable price.

Cheers

Brian

[Deleted]

Forgive me if I sound old fashioned, but I was taught that a bit of pitting in bores was a good thing, as the condition encouraged the retention of oil. If I remember corectly, there were people offering chrome plating of worn bores and selling the fact that 'microscopic indentations' as a result of the plating would improve lubrication. What am I saying? T'would appear that you shouldn't worry too much......
JB

[jamespetts]

Thank you everyone for all your help. Should I worry that, after I stripped it all down, cleaned all the oil off, and put it back together again, it squeaks when turned over by hand, the squeak coming from one of the cylinders? Is the black stuff on the port faces something to be worried about? I stripped the engine in order to remove the detritus from the port faces in order to enable the slide valves to seat properly.

[Tel]

Of course, the ancients (including yours truly) believed in adding some graphite to the lube oil for a reasonable running in period. This produces a nice, rust resisting glaze on the surfaces of the innards.

[GWRdriver]

James,
I can't really say anything more without being able to see the cylinders first hand.

[jamespetts]

Thank you both for your replies! Here are some pictures of the cylinder, piston and other innards to get an idea of what things look like in there. Any feedback on that would be much appreciated.







Cylinder interior






Port faces, before cleaning








Piston




Port face, after cleaning