P class problems?

[Isambard Smith]

Hello.  The other week I decided to , after putting it off for years, to get myself one of those lovely little se&cr p class tank engines from hattons. It arrived the next day, and out of the box it was very pretty but ran horribly, lurching all over the place,  so back it went . 

 

Hattons service was excellent as ever and they replaced it straight away with no issues. And the replacement is just as nice...and it runs a lot better...but its still not great.

 

Now every review I can find of these is glowing, so its odd to me that I've had a pair of duffers.  And hattons have already said I can swap it again...and i may yet, but I'm wondering if its an issue that is fixable, and fixing things is much more fun than returning things, so I'm here to see if anyone can suggest what the problem might be....

 

So the loco is on a small circuit, 12" radius. Running clockwise its runs perfectly no matter which way it faces.  No noise. No stalling, no stuttering, perfect performance at all speeds from glacial crawl to escape velocity.

 

Not so running anticlockwise. Again facing doesn't matter. The loco pauses slightly after each rotation of the wheels. At speed this makes it lurch around rather a  lot. At low speed it keeps stalling. There is sweetspot of sorts where it'll complete a circuit but any wagons its hauling will get left behind...

 

I thought at first maybe the pickups were losing contact, but this definitely isn't the case. When I got down to eye level with the rail what I saw was the the loco is picking up each wheel off the track in turn...even the sprung first axle! Doesnt seem to happen at all going clockwise...but anti clockwise its never got more than 5 wheels down at once and often only 4. 

 

Now as far as I can see the quartering is fine, the back to back spacing seems fine (tho i can't find my gauge or callipers to be certain) , the coupling rods aren't bent or twisted or anything like that. 

 

So I'm baffled. The bit that gets me is that direction matters but facing doesn't....

 

Has anyone encountered anything similar or have any suggestions?

 

Thanks!  

[D9020 Nimbus]

I'd have thought 12” radius was simply too small for any OO loco — even radius 1 is nearly 15”.

[Isambard Smith]

Lol, lot of short wheel base locos manage those curves with ease, all the Bachmann junior locos, Hornby terriers  even my old airfix 14xx and a couple of tender engines! The circuit is actually oval so its not all as tight as that...

Edited December 1, 2020 by Isambard Smith

[GreenGiraffe22]

I had issues with both my Ps, one got 'repaired' but still wasn't fantastic after and the other was replaced because it was irreparable, the replacement  is better but they're still both quite disappointing performance wise for modern spec RTR, I don't live with my layout anymore so most of my collection is living in boxes now aside from a few favourites I kept on the layout for when I visit it, I'm sure I'll have a look at them both again one day, they both had quite a bit of paint on the wheels I had to clean off.

[JSpencer]

12in radius is about what a Heljan Lyn (a OO-9) loco will just about cope with and the P is twice the size. You might be pulling the gear train to the limit causing it to bite the end of the worm or the worm biting flank of the gear.

 

I remember a customer when I worked in the Single box who kept bring back a new Hornby Jinty every week with a completely worn gear. After the 4th had suffered the same, my boss went round his house and found he had use flexible track to make tighter than radias 1 curves. The worm biting the sides of the gear instead of the middle causing very rapid wear.

Edited December 1, 2020 by JSpencer

[Isambard Smith]

Hmm?  but why would it only be sn issue anticlockwise ?  And as I say , I've run larger locos on this circuit with no trouble. 

 

 

Edit...just setting up a larger circuit for testing.

 

Edit 2; on a much larger oval, 20" radius,  its now stuttering both clockwise and anti clockwise, tho a little bit less running smoke box first.  

Edited December 1, 2020 by Isambard Smith

[JSpencer]

40 minutes ago, Isambard Smith said:

Hmm?  but why would it only be sn issue anticlockwise ?  And as I say , I've run larger locos on this circuit with no trouble. 

 

 

Edit...just setting up a larger circuit for testing.

 

Edit 2; on a much larger oval, 20" radius,  its now stuttering both clockwise and anti clockwise, tho a little bit less running smoke box first.  

 

On 20inch radias, should be fairly smooth. There are several possible reasons (pickups, worm not correctly seated, note quite quatered, hard grease on a gear......)

[Isambard Smith]

Pickups were the first thing I checked...when I googled p class problems it was the only that seemed to be commonish occurance , and they're fine on this one ,maintaining full contact at all times..

 

Thanks for the help guys!

[Isambard Smith]

Thought I'd better mention the outcome of the problems rather than leave the thread hanging with no conclusion...

 

The problematic "p" now runs perfectly!

 

I found my wheel back to back gauge and when I checked all the 3 axels were out of gauge by different amounts...one was too narrow,  two were too wide. Not by much, and I suspect at least one wheel wasn't square on the axle.  This all amounted to putting the loco in a perpetual right hand turn.  The gauge realigned the wheel sets, I put the whole thing back together, and of it went, smooth as you like. 

 

Thank you !

[Chris Wood]

I recently picked up a secondhand P class for a reasonable price from a reputable dealer. Unfortunately when I tested the model it ran quite badly with a definite sticking point. At this point I probably should have packed it away and returned it to the dealer. However I knew I had no chance of getting a replacement, being both 2nd hand and the only one in the shop. I could have requested a refund but I chose to investigate further. Initially I thought the crank pins were catching the steps as they seemed to be very close. I tried to tighten the crank pins inwards to give further clearance but this did not improve the running. I eventually decided the issue was the wheel quartering as the coupling rods did seem tight in places. I persevered with this idea until I eventually succeeded. Now the loco runs exceptionally well. The pickups on the center wheel do look a little soft and not always in contact with the wheel, but while it is running so well I am reluctant to mess with it.

In my opinion the model, although not without floors, is an exceptionally fine example of modern RTR steam loco's and the main manufacturers would do well in using this as a benchmark. However, as with many RTR steam loco's quality control can be a little wayward (not sure how you'd get around this for the money).

[GreenGiraffe22]

I found if I pushed all the pickups back against the wheels they would slowly migrate away from the wheels over time , so the loco would run great to begin with that get increasingly worse as it went round the layout 

[Hattons Dave]

Hi Chris & GreenGiraffe

 

Thanks for the feedback about the locos.

 

Chris - Sorry to hear that the loco quartering was out but good to know you managed to fix it and it now works well.

 

GreenGiraffe - This is one of the compromises with the materials that I don't think anyone has quite mastered yet.  Too soft and it moves out of the way and sticks there but can be re-shaped over and over, too hard and it stays in contact but as it is moved by the wheels it becomes brittle and eventually shears off. I like to think we are almost there with the P and AB material giving enough robustness to not break combined with enough spring to not have to alter them too often.

 

Cheers

 

Dave