Piston Rings and Blowby

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gamh44
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Re: Piston Rings and Blowby

Post by gamh44 »

Julian

Thanks for your feedback here. The video was taken earlier, before the blowby issue arose. This is indeed how the engine has run for 60 odd years. On its last run though, it had much less of a defined beat and was exhausting some excess steam. I didn't video it unfortunately.

The lubricator is a twin cylinder mechanical pump which has two delivery tubes. One of these splits for the outside cylinders. I understand that there would ideally be a pump for each cylinder but as it has run for sooooo long in this configuration with no problem, I can't see a reason to change it. While I believe the current issue to be related to a short period of a lack of lubrication, I am confident it is to do with blockages rather than a design flaw.

I would be interested in what the Black Book suggests. I am guessing these are not readily available for purchase though?! Can anyone who has one summarise the procedure.

Regards


Geof
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Bill Shields
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Re: Piston Rings and Blowby

Post by Bill Shields »

Geof:

in reality = 'lack of lubrication' with our steamers is rarely an instant problem....even if run for a lengthy period (as in all day...?)

I have often found that the lack of lubrication ends up causing not 'wear' but rings that end up stuck to the pistons and / or bull rings, and as a result don't seal properly around their intended contact with the cylinders the next time they are run.

I have always made a point to unscrew something (depends a lot on the design) and douse the cylinder innerds / piston / rings with steam oil at the end of the day's running.

years ago I found that one of the lubricators on my Hudson had stopped working but I didn't notice it because the tanks were inter-connected with a 'balance line' for the oil. For all I know, I may have run the loco all year that way (here was a time when I was young and crazier).

It really didn't seem to matter since at the end of every day of runing, out came the plugs, in went a good squirt of oil (or 6)...

Then there is the Raritan...look in the design for a lubricator....tain't there....
Too many things going on to bother listing them.
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gamh44
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Re: Piston Rings and Blowby

Post by gamh44 »

Bill Shields wrote: in reality = 'lack of lubrication' with our steamers is rarely an instant problem....even if run for a lengthy period (as in all day...?)
Bill

Interesting ... you are quite right. I could well be focusing on the lack of lubrication as a cause when it could be something altogether different. Which could mean the solution is also completely different. Had that happen too many times to count! This is indeed one of the reasons I have been cautious with making changes or repairs too quickly.

Thinking back to the run where I noticed the blowby, it was quite a distinct time. I had been hauling passengers for around 2 hours and was about to pack up. On the second to last circuit, I felt that there was a heap of excess steam coming from the exhaust and somewhat of a lack of power. I initially though that the superheater element may have a crack but did a (basic) hydraulic pressure test with the regulator open and no leaks. That was when I turned my attention to the lubricator and found that there was some *muck* in the pickup which appeared to be causing a blockage. By the time I realised what I was doing, I had cleaned it out so couldn't actually test if it was actually stopping the flow of oil.

The lubricator on this loco has a manual operation that is religiously used after every run, dispensing copious amounts of steam oil into the cylinders for storage. This is particularly important for this loco as the cylinders are steel (yes, ... steel!).

I think the next activity will be to mic up the bore of the cylinder that I have apart and see what the numbers say.

Regards


Geof
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Bill Shields
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Re: Piston Rings and Blowby

Post by Bill Shields »

sometimes something in the valve gear will slip and you will put steam right from the boiler out the stack....
Too many things going on to bother listing them.
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gamh44
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Re: Piston Rings and Blowby

Post by gamh44 »

Thanks again for all the replies. Progress to date is as follows.

The piston (just one at this stage) has been removed and a micrometer run over the piston and into the cylinder. Results were the piston has a diameter of 1.074" and was quite round (well within 0.001") and the cylinder has inside diameter of between 1.075" and 1.076". I would think these are reasonable results. It should be said that only the front of the cylinder was measured as getting the inside micrometer to the rear will be difficult without removing the rear cover (maybe later).

Next was to try the light behind the ring trick (thanks Bill). After removing the front ring, it was slipped onto a mock up piston to hold it in place and to block most of the light. The diameter was just slightly less than the inside of the cylinder.

Image

A lamp with a grain of wheat globe was knocked off form the HO gauge set up and set up to illuminate through the piston rod gland. It wasn't overly bright but did the job. A torch globe was attempted but was just too large in the 1.075" cylinder.

Image

The result was good. There was no light outside the ring unless the setup was twisted out of square. This was tried in a number of places and the ring rotated as well, just to be sure. Still all good.

Next up was the ring gap. Squared up in the cylinder, it measured around 0.022", which appears to be quite large by all accounts. With a diagonal cut, it was a little difficult to measure so with the set up used above - outside the cylinder - the ring was compressed to 1.075" and the gap was around 0.020" so around the same ball park. Either way, quite large. Fred suggests 0.003" above, Martin Evans says practically closed and IC engines around 0.003" per 1" of bore. 0.020" is BIG.

The question is whether this is by design or due to wear. There are what appear to be original machine markings on (around) the ring close to the gaps, but the rest of the marking is definitely longitudinal. The width of the ring (difference between ID and OD) is quite consistent, including where the machine marks appear to be. Only using a vernier but these are all between about 1.075 and 1.125mm so a difference of around 0.002". Doesn't sound like wear to me, but ...

So, unless there is something else that jumps out to me, I am thinking to just replace the rings and see what happens. Not a big job (at least not on the outside cylinders - not sure about the inside) and could only help. Either that or put this one back together and run it some more and do some further testing.

Any thoughts appreciated.

Regards


Geof
jma1009
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Re: Piston Rings and Blowby

Post by jma1009 »

hi Geof,

i am afraid it is far more likely to be a problem with the piston valves/liners.

your pistons look fine to me and well within acceptable tolerances.

cheers,
julian
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Re: Piston Rings and Blowby

Post by blff cty lcmtv wrks »

back in the early 80s, my mentor, the late rf wilson, suggested that we machine a one groove in the piston the width of the of both rings, install rings and stagger the gaps 180 degrees from each other and let it go. its worked for me, and btw, one big groove is easier for me to make than two little grooves. i don't have a problem with making one of thing, but, when it goes plural, it sometimes presents a problem.
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gamh44
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Re: Piston Rings and Blowby

Post by gamh44 »

Julian

Thanks. I'll have a go at pulling the valve on this cylinder shortly and see what we find.

I am a little concerned about the timing so my plan at this stage will be to make as many measurements as I can. If I then dismantle one component at a time, hopefully things will return close enough to be much the same. Hopefully a few thou either way will be forgivable!

I just wish I had more time to dedicate to this!!

Geof
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gamh44
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Re: Piston Rings and Blowby

Post by gamh44 »

All

Have managed to remove the valve from this cylinder (see below) and the results are that the front diameter of the bobbin valve is 0.565" and the bore is as close to this as I can measure. I reversed the valve to match the front of the bobbin and the front of the cylinder and it was indeed a very snug fit so no sign of wear there at all. The rearward section of the bobbin measured slightly smaller at 0.562" and the bore was again much the same - 0.561". I am guessing that the difference in front and rear must be a design feature as the piston and cylinders match particularly well.

So, it appears to be a case of back to the drawing board. Reassemble and give it a run to get some further information. I will definitely heed Fred's advice and give the lubricator a thorough clean and test beforehand to ensure that is not part of the problem.

Now, with this cylinder showing a complete lack of any wear, is there any reason to suspect either of the other two? I would think it would be a case of one in all in as far as wear goes, unless it is some sort of foreign object damage.

If it turns out not to be wear in the cylinders and not a lack of lubrication, what else might cause excess exhaust?

Image

Regards


Geof
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Fred_V
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Re: Piston Rings and Blowby

Post by Fred_V »

Geof, It looks to me like there are 2 rings at each end of that bobbin and that they are totally stuck in the groove.
Fred V
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Bill Shields
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Re: Piston Rings and Blowby

Post by Bill Shields »

i agree on that (stuck rings)...might just be a mirage however....
Too many things going on to bother listing them.
RET
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Re: Piston Rings and Blowby

Post by RET »

Hi,

If I remember correctly, it seems that the engine was running fine as you can hear in the video, then in a short period of time it started to perform poorly. So far, the things you are checking are not the kind of problems that usually appear overnight. What CAN fit the symptoms as Bill said earlier, is if the valve timing has slipped on one or more of the cylinders.

If it were me, I would put everything back together as close as possible to the way it was, then I would put 2 to 5 psi. air in the locomotive boiler and slowly rotate the wheels with the throttle open to see if a steady stream of air comes out the stack at any one position. I would do this first in mid-gear, then gradually work my way off center, first in forward, then in reverse and see what I got. Rolling the locomotive back and forth on a short piece of track would make this easy to do.

What would also help to narrow it down is if you can block off the valve chest (probably by disconnecting the valve linkage) on the two outside cylinders first, see what happens and then (depending on the results you get) one at a time add in the two outside cylinders. I think Bill is probably right and the valve timing has changed on one of the cylinders. From the video, the original valve timing sounds very good but something has changed and not gradually. Do several experiments and then see what the results are.

I've found that the "Scientific Method" can be a very powerful tool. Develop a hypothesis to explain the observed condition and then say to yourself "If this hypothesis is true, then so & so should also be true." Then go and see if it is! If it isn't, then come up with a new hypothesis that fits the facts.

Maybe this will help.

Richard Trounce.
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