The new Bachmann SDJR 7F (2017)

[mikesndbs]

Hi

 

I ordered one of the new 7Fs having been very pleased they made them again.

Got mine from Rails.

 

The first one arrived and while it looked lovely it had an annoying tick while running, would lock up when crawling and the crossheads would disengage from the slide bars while in use.

As its not a cheap loco I sent it back to Rails who arranged a new one to come out.

 

At the same time I read online that many others were having the same issues.

 

Rails said they had run my new one for a while on their rolling road and it was all ok.

 

While it is better it is not OK

 

It still ticks, and it part locks up crawling backwards.

 

 

So again I started looking for tight spots on the complex valve gear and I have come up with a question for you.

Check out this close up:

 

To me the angle of point one looks all wrong given that this is supposed to pump in and out, it would surely not be right on the real thing would it?

 

Point two, moves back and forth as the loco goes along, is that right? because if you set the loop of point two towards the cylinders the angle of point one is much better and the loco does not tick.

 

So I wonder what you all think about this?

 

The loop of point two appears to be unfixed and does slide back and forth.

 

Hope someone can help as I love this engine but it appears Bachmann have something very wrong

 

 

 

 

[Stevelewis]

I cannot  really  answer  your  query,  but   would  comment  that  I  had  locos  from  the  initial  release some  years  ago  now  which  all functioned  superbly,   so  obviously  something  may  be  different now?

 

I wonder  if  it  would  be  possible  to  compare  and  'early' production  loco  next  to  the  'latest' production?

[31A]

On a real engine, the rod at point two (radius rod) does move backwards and forwards as the engine moves.  I haven't got this model, but on some of the other Bachmann locos I have this part does indeed move - K3s I think, for example.  Most RTR models have this rod fixed, presumably for ease of manufacturing, so on at least some of their steam locos Bachmann have modelled the valve gear more realistically than is usually done!

[mikesndbs]

On a real engine, the rod at point two (radius rod) does move backwards and forwards as the engine moves.  I haven't got this model, but on some of the other Bachmann locos I have this part does indeed move - K3s I think, for example.  Most RTR models have this rod fixed, presumably for ease of manufacturing, so on at least some of their steam locos Bachmann have modelled the valve gear more realistically than is usually done!

 

Hi, while I like that it does seem this causes odd angles, or is it that something else is pulling it out of alignment maybe?

[mikesndbs]

I cannot  really  answer  your  query,  but   would  comment  that  I  had  locos  from  the  initial  release some  years  ago  now  which  all functioned  superbly,   so  obviously  something  may  be  different now?

 

I wonder  if  it  would  be  possible  to  compare  and  'early' production  loco  next  to  the  'latest' production?

 

It would be very good to compare I agree

[LMS2968]

The valve spindle (One) should be parallel with the centre line of the cylinder. This is often not achieved in models. The movement in and out of the valve chest would be small, being driven only, in this case, by the combination lever from the crosshead. The relative lengths each side of the combination lever's pin joints reduce the movement compared with the crosshead itself.

 

The expansion link (Two) rocks back and forth driven by the return crank on the driving wheel. Since the gear is represented as in mid-gear, no movement is transferred to the radius rod, so alterations here will have no effect on the angle of the valve spindle.

[31A]

On one of the K3s I've got, the valve spindle (the part at your Point 1) moves up and down as well as horizontally in and out of the valve - obviously, as you say, in reality it shouldn't do this!  On my other K3s the valve gear performs correctly and I haven't really investigated why this one is different, but I suspect one or more of the joints in that area such as at the end of the radius rod or either end of the combination lever (more or less vertical rod between the crosshead and the valve spindle) are too tight.  The K3 in question isn't one I regularly use, it's 'salted away' for a potential future project, but although it looks odd I don't recall it affecting the running of the loco.

 

Apart from potential tight joints in the valve gear, it might be worth checking the driving wheel electrical pick ups to make sure they're all running correctly on the back of the tyres and not getting jammed in the spokes instead?  That might account for why it ticks in one direction and locks up in the other?

[mikesndbs]

The valve spindle (One) should be parallel with the centre line of the cylinder. This is often not achieved in models. The movement in and out of the valve chest would be small, being driven only, in this case, by the combination lever from the crosshead. The relative lengths each side of the combination lever's pin joints reduce the movement compared with the crosshead itself.

 

The expansion link (Two) rocks back and forth driven by the return crank on the driving wheel. Since the gear is represented as in mid-gear, no movement is transferred to the radius rod, so alterations here will have no effect on the angle of the valve spindle.

 

Hi, when I slide 'two' forward it does change the angle and position of 'one' ??

[31A]

Hi Mike, I think maybe your "2" is the radius rod (which would affect the valve spindle) and LMS2968's "2" is the expansion link (which shouldn't)?

 

Have a look here for the names of the rods etc. - the diagram looks like a BR Standard loco, but the main parts are the same:

 

http://msts.steam4me.net/tutorials/anim_walsch.html

[mikesndbs]

Hi Mike, I think maybe your "2" is the radius rod (which would affect the valve spindle) and LMS2968's "2" is the expansion link (which shouldn't)?

 

Have a look here for the names of the rods etc. - the diagram looks like a BR Standard loco, but the main parts are the same:

 

http://msts.steam4me.net/tutorials/anim_walsch.html

 

Yes, the loop is connected to the radius rod which moves the spindle back and forth, it appears to have no actual setting and can be moved about easily.

 

I am sure this is causing issues with the crossheads, making them in one case lift up at the end of the slide!!

[mikesndbs]

Just by way of explanation, here is a photo with the radius rod moved towards the cylinders.

As can be seen the angle is much better.

At this point the loco also moves smoothly but soon goes back.

 

[34theletterbetweenB&D]

Looking at the photos, while the valve spindle is clearly entering the valve chest at a mechanically impossible angle, it also looks to me that the piston rod isn't running on the cylinder axis either, though not as badly 'off' as the valve spindle. Why is it all wonky like this?

 

Mention of the crosshead coming out of the slide bars on your first example leads me to suspect that the motion bracket moulding that supports both the expansion link and the slide bar ends is slightly out of position. If it can be raised a tad, that will probably correct the visual appearance and may well fix the running problems.

[mikesndbs]

Just uploading a video of the motion. Oddly it shows that the spindle ets itself in that odd angle and does not move much.

I used low feedback control which smoothes out the lumps, normally I am DC only

Should be online in next ten mins.

I'll sadly have to head off to work so advanced thanks for any replies but I won't be able to respond until later.

[mikesndbs]

[New Haven Neil]

I have often found sand pipes the reason for the described locking and clicking, they get into the wheel spokes.  The valve gear does look wonky though!

[No Decorum]

Interesting. Your video seems to show the left-hand valve gear operating as it should but the right-hand not. I have two of these on order but they haven’t arrived yet. However, I have just returned a Stanier Mogul. The left-hand valve gear worked beautifully but the right-hand flails about. I think it’s a different problem from yours in that it’s the expansion link is the cause. It should be attached to something but I’ll let Bachmann sort it out.

 

The underlying cause is the same, I think: delicate valve gear. As 31A points out, on this model the valve gear isn’t in neutral as it so often is and, I think, looks the better for it. Well done, Bachmann (nearly)!

[mikesndbs]

 

2.5 sec in you see the crosshead lift, this happens a lot more when going a bit faster! 

[31A]

Not sure how relevant this is to Mike's problem, but he has prompted me to seek a cure for my K3 with dancing valve gear, which turned out to be quite simple.

 

I took the cylinder block moulding off, and found some brass tube that was a sliding fit on the valve spindles.  Not sure what dimension the tube actually is, but it was a tight push fit in a 1.5mm hole so I drilled out the valve spindle holes in the rear of the cylinder block to that size, and pushed in bushes made from short lengths of said tube.

 

First picture shows one of the bushes slid onto a valve spindle:

 

 

And the second one shows one of the bushes partially pushed into the cylinder block; I later pushed it all the way in:

 

 

As No Decorum says, the 7F's left hand valve gear looks fine but on the right hand side the valve spindle is at an impossible angle; bushing the valve spindles as I have done would certainly cure that, if you feel like doing it.  That should in turn lift the combination lever, radius rod etc. into the right place, and possibly prevent a conflict between them and the crosshead?

 

However looking at the video at 2.5 seconds, as you say, the crosshead lifts and it may be that the crankpin on the leading driving wheel is hitting it from behind?  In which case it might be worth looking to see whether the slide bars on that side have been bent inwards, such that the crosshead and leading crankpin can come into contact?

 

As you might have guessed I suppose I'm the sort of person who tries to sort these things out (and my K3 was a second hand purchase years ago anyway), but if you don't feel up to 'having a go' you might be better off returning this one to Rails as well as it can be disheartening having to fiddle around trying to rectify a new model with no guarantee of success at the end of it, it's not as though these things are cheap, after all!

 

 

 

[SDJR7F88]

I've had the same trouble as Mike with this one. First one locked up completely on corners with a loud bang when something was snagging. Got a 4MT with the same issue.

However, I've just picked up a replacement '89' which runs a dream. Just like my 53810 and 53808. Very happy 

[mikesndbs]

I've had the same trouble as Mike with this one. First one locked up completely on corners with a loud bang when something was snagging. Got a 4MT with the same issue.

However, I've just picked up a replacement '89' which runs a dream. Just like my 53810 and 53808. Very happy 

Hi Callum

 

Could you put up a video of both sides of your 89 similar to mine so we can compare?

[mikesndbs]

I found another issue! looks like the crank is bent and the arm that goes to the valve gear is hitting the pin on the rod as shown in this.

 

Should I try and ease it away a bit?

 

 

Feeling fed up

[31A]

So is it the crank pin, or rather the pin in the knuckle joint, on the second driving wheel which is hitting the inside of the connecting rod and causing the crosshead to lift?

[Elvinley]

Send it back til you get a good one

[mikesndbs]

Hi guys.

 

I tested the loco on my railway today and confirm that it runs around corners without locking up.

I also eased that bar away from the crank pin last night and that has helped.

Something still locks the loco up but I just can't find what.

 

Maybe something in the gears????

 

Anyway, I love it so I am going to stick with it.

 

What I need now are other ideas to get that spindle to stay at a better angle, unless the brass pipe is the only way?

[31A]

Good luck; it's certainly a fine looking machine!