Issues with Foden motion gear

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Issues with Foden motion gear

Post  TheFodenBrothers on Wed 18 Apr 2018, 10:59 am

Hi all!

Hoping to get some advice from fellow builders. We have recently completed a 4.5" STW foden and have had a fire in it around 6/8 times now but we are having issues with the motion gear locking up.

Story so far - We built the engine and had it running on air lovely! finally got round to lighting it and we had a few issues getting the timing perfect, we now believe that we have the timing spot on and it ticks over beautifully. We do however still have a serious issue with being under powered and the motion gear locking,

What happens is you will be steaming along - not at any great speed (infact very poor performance) and then its starts to slow, the engine gets slower and slower till you hear the motion gear groan a bit and stop. at this point the motion gear AND reverser lever are almost locked solid!! Trying to turn the engine over by hand feels like steam has entered both sides of the piston and locked it.

With this information we decided to strip down the slide valves and inspect them for wear marks - sure enough the wear was uneven and they had quite bad 'high spots'. So out came the engineers flat and both valves were polished with very fine paper to an almost mirror like finish. Reassembled and the improvement was massive!

Now comes the odd bit, on wet boggy grass with low tyre pressures and 4 adults on the foden it will still happily chug around the garden, put it into second or third however and the performance is appalling (wont really move off in 3rd) and eventually locks all the motion gear again.

So my questions are:
- Has anyone experienced this before?
- Do you think its the valves still not sealing well?
- Can we flat the cylinder block in some way?
- Could it just need bedding in for them to seal properly?
- Could running the engine with the unflat valves cause the block to wear unevenly (bearing in mind the small number of steams)
- Could this be piston rings not sealing or bore issues? (oilers are working very well)

Sorry for the essay! but always think its good to have the complete picture!

TheFodenBrothers

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Re: Issues with Foden motion gear

Post  LiveSteam on Wed 18 Apr 2018, 6:58 pm

Just a thought, but is it anything to do with the boiler "growing" as it all heats up and putting everything out ? although the Foden's boiler isnt as long as a Agri.

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Re: Issues with Foden motion gear

Post  TheFodenBrothers on Wed 18 Apr 2018, 7:20 pm

Hi Live Steam,

We have set the timing with the boiler hot and at full pressure, so not that Sad

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Re: Issues with Foden motion gear

Post  atomenter on Wed 18 Apr 2018, 7:58 pm

Hi Guys
Have you tried it with the back end jacked up and in all the gears to see if anything is binding? Try running it like this on air for a start.
I have never managed to set my valve timing with any great pressure in the boiler due to the regulator passing but I have never experienced the problem that you are having (not sure about pulling away in top with 4 adults on it mind!!)
Regards
Tom
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Re: Issues with Foden motion gear

Post  TheFodenBrothers on Wed 18 Apr 2018, 8:08 pm

Hi Tom,

We are very lucky that our regulator seals very well so were able to time it hot. We have checked and nothing is binding that we can see.

Sorry I should have clarified, it won't pull in second or third with just one person and on solid ground.


Last edited by TheFodenBrothers on Thu 19 Apr 2018, 8:25 am; edited 1 time in total

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Re: Issues with Foden motion gear

Post  mikero on Wed 18 Apr 2018, 8:35 pm

It will take a while for the engine and especially the gears to wear in, they may work fine on air but when everything gets hot they seem to tighten. I shimmed the crank shaft bearings up a bit and they now all work fine. The selecter slides need to be grease often as they tend to dry out. Another factor is boiler pressure, my engine only pulls well at over 100 psi, inject some water which you need to do often and the performance drops of rapidly. I managed to get up the playpen at Dorset with three adults and four children but the safeties were blowing when I started and half a pump on.
.
I am looking at ways of improving the breathing of the engine such as the grate and fitting an exhaust ejector, all of whch will increase coal consumption, but I have a 10' trailer with a 65lt tank under it so that will not be such a problem.

Mike
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Re: Issues with Foden motion gear

Post  TheFodenBrothers on Thu 19 Apr 2018, 8:29 am

Hi Mikero,

Thanks for the replies, thats good news, I do wonder if it just needs a bit longer to all bed in and settle. We have our steam test this Sunday (22nd April) in Tewksbury, so hopefully if it passes we can get a lot more use out of it and help it all settle.

Anyone on here attending the same steam test (MSTVS) and/or Castle Combe steam rally this year?

Cheers

TheFodenBrothers

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