MSS wheels not suited to tight radii on Peco track

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CSL
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MSS wheels not suited to tight radii on Peco track

Post by CSL » Tue Sep 05, 2017 8:39 am

Update on the Dream Steam webpages for MSS locos and wheelsets:

"Please note: If running this product on Peco track, its tyre and flange profile means it requires a minimum radius of 3 foot 6 inches to avoid binding. This issue is not evident on the MSS or Mamod 2 foot 6 inch fixed radius track."

Direct relevance to another thread I started! Is this a known phenomenon on this forum that I had missed?

(Query to Moderators: should this sub-forum be renamed "Mamod and MSS" as there is so much crossover?)

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Re: MSS wheels not suited to tight radii on Peco track

Post by Soar Valley Light » Tue Sep 05, 2017 10:14 am

It seems strange that the problem goes away on a tighter curve. This suggests to me its something to do with the track construction.

A fairly brief on line search has revealed non of the construction details for Peco SM-32 track I was looking for - but then I am technologically challenged! :?

My first thought is that Peco may be inclined in at 1 in 20 - which Mamod/MSS track certainly isn't! This shouldn't affect the gauge, which should be the same in both cases at the gauge corner of the rail head, however, the 'running table' (i.e the top of the rail) would present a very different profile to the wheel tread. My other thought was whether there was any physical clash between the bottom of the flange and the rail fastenings on Peco. I'd expect to see evidence of the rolling stock 'bouncing' over the fastenings if this was the case but if it's 'only just' foul then that might not be obvious.

I would expect 'flange bind' to be the main problem though and this is almost a pure function of wheelbase against radius - the tighter the radius or longer the wheelbase the greater the friction between rail and wheel. This may be linked to the first point above but I can't see it myslef. Hopefully someone cleverer than I (and there are many :oops: ) can shed some clearer light on the problem.

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Re: MSS wheels not suited to tight radii on Peco track

Post by Big Jim » Tue Sep 05, 2017 2:44 pm

I have never had a problem running mamod SL1s on peco track even with very tight radii. Whether the set track is different I don't know but on older flexible there are no issues that I have seen.
I don't know about MSS wheel sets but I thought they were the same as Mamod.
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Re: MSS wheels not suited to tight radii on Peco track

Post by tom_tom_go » Tue Sep 05, 2017 3:18 pm

CSL wrote:
Tue Sep 05, 2017 8:39 am
(Query to Moderators: should this sub-forum be renamed "Mamod and MSS" as there is so much crossover?)
I would need people who know more about these brands to confirm if this is the case as I understand Mamod and MSS are different companies making different engines?

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Re: MSS wheels not suited to tight radii on Peco track

Post by CSL » Tue Sep 05, 2017 4:55 pm

tom_tom_go:

The MSS loco and rolling stock *are* the old Mamod products with a few minor changes (including the dome and the wheels - see my next post!). If I've understood it correctly, at some point Mamod lost or sold the rights to their traditional designs, and now offer a new range.

This explains why replacement parts for my old Mamod are from MSS - because the loco design is no longer Mamod's.

As well as this crossover, both MSS and Mamod's cheaper products are "entry level" garden railway/live steam equipment so it seems to me that this subforum covers them both and ought to be titled accordingly.

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Re: MSS wheels not suited to tight radii on Peco track

Post by CSL » Tue Sep 05, 2017 5:21 pm

To clarify, the issue is that MSS wheelsets will negotiate the fixed curves from both MSS and Mamod which are 2'6" radius, but will bind on Peco SM32 flexitrack at less than 3'6" radius.

My old (c.1990) Mamod SL3 is quite happy with its original wheels on my Peco flexitrack bent to 3' radius , but when I fitted new MSS wheelsets (because the original wheels are loose on the axles) it would bind. No binding occurs on any other stock tried, including a Bertie, which has a longer wheelbase than the Mamod. There is no flange tip/rail fastening contact (except with Hornby O gauge stock, but that's another story!).

The issue appears to be that the MSS wheels are machined with a flange that doesn't taper to the tip (it is visibly thicker at the "point"), and this interferes with the Peco rail profile - but not with MSS or Mamod rail profiles - at radii less than 3'6". The original Mamod wheels do have a tapered flange and so have no problem on the Peco track. MSS wheelsets have noticeably less lateral play between the rails than other types, too.

To summarise, it seems that you will can expect problems if you try to run an MSS loco (or original Mamod SLx loco fitted with replacement MSS wheels) on Peco track at less than 3'6" radius. I am rather surprised this hasn't been noticed earlier - presumably other owners of Mamods with dodgy original wheels have more railway space in their gardens than I do and lay their curves accordingly!

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Re: MSS wheels not suited to tight radii on Peco track

Post by Soar Valley Light » Tue Sep 05, 2017 7:31 pm

Thanks for the additional information. thicker flanges could, theoretically extend the wheelbase slightly - and it wouldn't take much to cause the problem. It also sounds like the back to back dimensions has increased and that could have the same effect.

Your advice is very useful. This sort of freely shared information is one of the best features of this forum. :thumbup:
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Re: MSS wheels not suited to tight radii on Peco track

Post by Big Jim » Tue Sep 05, 2017 8:05 pm

That is rather interesting. Thanks for the information.
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Re: MSS wheels not suited to tight radii on Peco track

Post by Chris Cairns » Tue Sep 05, 2017 9:22 pm

It is interesting, but I cannot understand why there is a problem with Peco Flexi Track? Does the same occur with Peco Setrack?

I have just compared some Mamod/MSS track with some Peco Flexi Track and the profile of the part of the railhead which will be in contact with the wheels are very similar, with similar measurements between the rails.

I already mentioned on your other Topic ( viewtopic.php?f=44&t=11255 ) that MSS flanges can be too thick so even with the correct back to back measurement they will be wide to gauge. This is confirmed with your statement above -
MSS wheelsets have noticeably less lateral play between the rails than other types, too.
So is your Peco Flexi Track actually at the correct width between the rails where you are having these binding problems?

Mamod wheels varied between production by the 4 different owners in the 1980s. Some had 90 degree straight flanges whilst others had tampered flanges. Just checked two Mamod loco wheelsets. Set on an old SL3 have 27.5mm B2B with 30.5mm between the tapered flanges. Unused set have 28.5mm B2B with 31.5mm between the straight flanges. There were also variations with the mazak cast Mamod/MSS track - we had some on a portable layout that were less than 32mm between the rails on a troublesome curve.

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Re: MSS wheels not suited to tight radii on Peco track

Post by CSL » Tue Sep 05, 2017 9:54 pm

Chris Cairns:

Thanks for your past and present responses to my posts.

"Does the same occur with Peco Setrack?"
I don't know. My garden track is a circuit of Peco flexi only apart from a single Peco point, which if memory serves has a 3'3" turnout radius (and causes less of a problem than the 3' nominal radius curves elsewhere).

"So is your Peco Flexi Track actually at the correct width between the rails where you are having these binding problems?"
I would have thought that if this was a problem then I would have found binding with other types of wheelsets, notably the longer wheelbase Bertie. But it doesn't occur, and there is no visible sign of gauge distortion.

I believe that Dream Steam have conducted their own experiments before amending their website, i.e. they have independently validated the binding phenomenon that I had experienced.

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Re: MSS wheels not suited to tight radii on Peco track

Post by tom_tom_go » Tue Sep 05, 2017 10:20 pm

I remembered this evening I had a MSS loco visit my line years ago when it had a continuous run and it did not have issues running on Peco ST-605 curves:


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Re: MSS wheels not suited to tight radii on Peco track

Post by CSL » Wed Sep 06, 2017 7:26 am

(Off topic) Wow - raised track, tight curves, no side fencing and a manual MSS loco. Not sure I'd be so brave!

(On topic) It's curious, but as I say, Dream Steam must have amended their website for a reason.

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Re: MSS wheels not suited to tight radii on Peco track

Post by CSL » Mon May 07, 2018 4:39 pm

Just to close off the main subject of this thread, I have now fitted Roy Wood wheelsets with success (details on the thread about running MSS locos on 4' diameter curves).

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