Issue with R3986 9F connecting rod

[DarkRedCape]

I’ve gotten round to installing another HM7000 into one of my new 9F’s, I’m just running it in and there seems to be an intermittent issue where the nut that holds the connecting rod to the wheel hits the connecting rod itself, locking up the wheels and bringing the loco to a sudden stop. It seems to be a random occurrence as my current layout is just a 3rd radius oval and it doesn’t do it in any one particular place.

I’ve taken the baseplate off and there seems to be a lot of side to side play in the axles. I know this is somewhat a feature of the 9F due to the wheel configuration.

The offending nut is on the second from front axle, right side, and seems to stick out much further than the nut on the first axle, so I thought swapping them round may solve this.

Does anyone have any experience with 9F’s and this problem in particular?

[What About The Bee]

Hi DRC

I do not own a 9F, nor will I ever. Swapping parts around may teach you something but is unlikely to solve the problem without understanding root cause.

Instead of looking at the connecting rod shoulder bolts on one side, comparing between two axles, document all 8(?) connecting rod shoulder bolts on all 4 axles. That longish shoulder bolt on interior axles may be deliberate, and will be obvious when all the shoulder bolts are examined. Perhaps to allow radius 2 turns.

The offending shoulder bolt may have a burr on the inside, that catches the rod. The offending shoulder bolt could be odd man out. The connecting rod may have a burr there. The problem may lay anywhere in that system. Resist the urge to just change something.

I hope this helps.

Bee

[Going Spare]

Other than on the centre wheels where a long crank pin is provided together with a different screw, all the other coupling rod screws should be the same. Swapping screws between wheels 1 and 2 should make no difference. You need to establish why screw 2 extends further out than the others. Has it not been screwed home fully or working loose? Is there something stopping it seating correctly?

[508006]

Hi DRC

Could you provide a picture please as this will help us to determine what the problem is and advise accordingly, thankyou.

[ColinB]

I don't know if this is of some help. I found that some connecting rod screws are not always the same size, I even put a post on the subject many months ago. So is your 9F new or secondhand, it could be that you are right that the one in question is bigger. I know I have sometimes swapped bolts around because the ones nearest the valve gear interfered with it because they were slightly bigger. The other thing to check is that the posts on the wheels are pushed in correctly from the back of the wheel. Sometimes on mine they move out so the conrod is closer to the wheel than it should be. I know you said one is sticking out further than the others but it could be that the one on the wheel in front of the one in question has pushed out.

[DarkRedCape]

I've tried to get some pictures directly from above so that the spacing between the nut and the connecting rod is accurate. The loco is brand new and I’ve only had it a month or so.

The first picture is the nut and the connecting rod at their maximum separation. It’s the middle axle.

The second picture is at their closest. There is a very slight overlap between the two that is causing the issue.

I didn't notice it before, but looking at the pictures, it seems like the connecting rod may have a slight inward curve to it. I'm not sure if this is how it's supposed to be, or if it's slightly bent.

[Going Spare]

In the lower photo, the lower centre driving wheel appears to have moved inwards an appreciable amount, pulling the connecting rod inwards in the process, whilst the wheel on the other end of that axle has stayed in line with the other wheels on that side. The screw holding the coupling rod to the wheel does not seem to be the culprit. Is the wheel on its axle correctly? If all appears correct there, I would put a very slight outward bend on to the connecting rod just sufficient to clear the screw head.

[What About The Bee]

This rod does appear bent inwards and is not a photo artifact

[508006]

I might be wrong here and if I am then fair enough but to me from the pictures, it looks like the wheel/s on axle 2 and possibly axle 1 aswell might still have some space left to be pushed onto their axles till they cannot go any further.

Also bending the connecting rods outwards a little aswell as changing the spacers between the coupling and connecting rods will potentially help to sort out the issue, this would simply require the spacers from an older 1990s hornby locomotive ( doesn't matter which as all the spacers used were the same size ) if you have any available in a spares box, it might be worth a try.

[atom3624]

Couple of questions:

1. Where the interference of the hex-headed screw with the valvegear is suspected, is the valvegear properly located onto the peg/spigot?
2. Has the valvegear been flattened slightly on that side, possibly by being gripped there to pick up the locomotive?

I've had a few locomotives where I've had to 'change the profile' of some rods - very slightly - to avoid this interference.

I've also had a few where I've had to crimp the tiny upper rivet of the valvegear as I've found this to be too 'sloppy'.

Al.

[DarkRedCape]

I don’t get as much time to tinker as I’d like right now. I had another batch of power banks turn up so I managed to get up in the loft and look at the 9F. After I put the power bank in and closed everything up, I very gently pulled the connecting rod outwards, the difference is barely noticeable, but I sent it round the layout for 30 minutes and I had no further issues. Seems like problem solved.

Thanks to all for your replies. Lots of useful answers that I’m sure will benefit me down the line.

[What About The Bee]

Hi DRC

I was hoping to hear an update and now it is apparently fixed. Hooray!

Bee