Building a 31/2" Gauge Locomotive Engine

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NickG:
Stew,

I meant on the drawings for mabel it calls for a valve 15/16" long, and the distance between the extreme of each inlet port is 3/4".

I've just stripped the cover plate off and my valves are exactly 15/16" long as per the drawing. Valve travel is almost blob on 1/2".

With the reverser set fully forward and the right hand piston at TDC (fully forward) the front inlet port is just starting to crack. By the time the crank gets to about 45 degrees after TDC the port is fully open and it stays like that until the crank is at 90 degrees after TDC. At this point it starts to shut, and by about 45 degrees before BDC the front inlet port is shut. Once at BDC the rear inlet port is starting to crack to push the piston back the other way.

I've taken some photographs, will upload them now but I don't think they will have come out too well due to the light conditions.

I realised looking at mine that when I set the timing many moons ago, I didn't have the instructions from model engineer and was chasing myself around in circles too. I managed to get it to run well forwards, but looking at the way I have the eccentrics set, there's no bloomin' wonder I couldn't get it to go in reverse! It also reminded me of those pathetic little grub screws that 'lock' them onto the shaft. How that was ever meant to work I don't know, will need to do something about it for sure, but I forgot how thin the eccentrics were.

Hope this is of some use. Don't skim those valves yet!

TDC

TDC again

45 deg after TDC

90- deg after TDC

45 deg before BDC

BDC

Nick

sbwhart:
Nick

Thanks for all the trouble you've taken, thats certainly helped me, it would appear that my engine hasn't get enough valve travel, I won't touch the slide valves but check the linkage out again to see why I'm not getting 1/2" of travel.

Also noticed you're engine has oil feed holes on the rockers, drawing didn't call for them so I left them out, but I'll now add them.

Thanks again

Stew

NickG:
Stew,

No problem. I'm going to start stripping the engine down now to clean and paint since my son keeps going on about it. I've promised it will be ready for Christmas - maybe a bold claim! When the bits are easier to get at I will take any other pictures / measurements you might need.

if you're getting 7/16" travel I don't understand why your ports don't open fully. Mine probably open around 1/32" past fully open so yours should I think.

I think something is still a miss with the timing some how, puzzling! :scratch:

Do you have any ideas on what to do with the eccentrics?

Nick

sbwhart:
Hi Nick

Just completly stripped the linkage down and inspected it for signs of fouling and measured it all up:- found that I was a bit short with the slot in the sliding link and the little sliding block was slightly over size so I've corrected this and whilst I was at it for good measure I extended some of the slots so that nothing would stick.

I'll put it all back together tomorrow and see how it goes

Thanks for your help

Stew

NickG:
It's handy this because you've seen the thing from scratch and I've got the complete thing so we can help each other out!

That is the only thing I could think that would give you more valve throw as well.

There are only 3 things. The offset on the eccentrics, the length of the slot and sliding block in expansion link as you said, and the length of the bottom lever on rocking arms.

I think that should do the trick, it'll be a matter of timing now. Fingers crossed. :smart: :thumbup:

With regards to putting the oil holes in rocker arms, I presume you can get under the boiler with the oil can, in which case it be a good idea I guess. Will check if you like.

I was looking at the lubricator, I found an old file the other day with some scribbled notes. I don't think it gave enough throw on the lubricator. There isn't much soace for the arm to move on it, from one extreme to the other it only gives 1 click on the ratchet on mine, so maybe it needs a ratchet wheel with more teeth if I can't get it to throw enough. The problem will be if you get too much throw it will foul the frames etc, but not enough will not be enough to turn the wheel!

does your axle pump have a by pass valve anywhere in the plumbing? Mine doesn't but the bore seems tiny so maybe it's assumed it just needs to pump all the time? Seems strange not being able to adjust it though.

Good luck.

Nick

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