Coupling rods Binding

[John LintornParticipant @johnlintorn87585]

[John LintornParticipant @johnlintorn87585]

Hi guys!
This is a weird problem! My coupling rods on my Tich are binding in places. Now I would understand this if they were doing it in the same place all the time, however, some times they run free as anything, and then suddenly they will come up againstwhat feels like a brick wall!
Any suggestions guys?

[Jeff DaymanParticipant @jeffdayman43397]

Are your axle bearings / hornblocks secured in the frames? If they have too much play the coupling rod centres distance could become different than axle to axle centre distance and cause a jam.

The other thing I would check is that the rods are not fouling a pin end, link or something in the valve gear somewhere, as the engine rotates. On other types of machines I have seen bent over cotter pin ends rotate into and out of the path of nearby components intermittently. If you have any cotter pins it would be wise to check that the pin ends can't foul anything. Is the engine Walschaert's gear? JD

[John LintornParticipant @johnlintorn87585]

Yes it’s Walschaerts but I have stripped the valve gear and connecting rods off so that literally all that is left is the coupling rods.
Surely if the hornblocks were moving it would allow more play for the connecting rods or does it not work like that?

[Jeff DaymanParticipant @jeffdayman43397]

My thought was that there may be a condition of fits where the axle bearings are too far together or apart and are stuck there, with a centre to centre distance bigger or smaller than a coupling rod.

If you have all the valvegear off then that system isn't the issue. Are the rods well clear of the crosshead guidebars and motion bracket at all points of rotation/axle travel?

If all is clear then I would take one rod at a time off the engine and see if it is one or both binding.

It is possible for a wheel to slip on an axle and lose quartering, unless you pinned or keyed them in place.

Also check the rod retaining washers and bolt head undersides for galling or burrs, and that there is side clearance for the rods. In theory the crankpins could slip in or out of the wheel too, depending on how they are held in place or if they have a shoulder.

Just some thoughts, hope they help. I can only encourage you to be patient and remove a piece at a time to find the binding by process of elimination. JD

[John LintornParticipant @johnlintorn87585]

No I have checked and nothing is touching.

The bind occurs when the crankpins are at 45degress to 135 degrees and at 225 degrees to 315 degrees. Does this mean i should check the quartering of the wheels?

[Ady1Participant @ady1]

I was about to say.

Wonky wheels/axles??

[John LintornParticipant @johnlintorn87585]

It will all have to be set in the lathe with the old DTI and checked eh… It will be interesting to see where I have gone wrong. If the wheels do need re-setting, any suggestions on how to get them off the axles as they were a press fit and they are cast iron and obviously I don’t want them cracked?

[Jeff DaymanParticipant @jeffdayman43397]

hi John,

What did you find with the DTI? did you find the binding source of trouble?

Re if you need to get the wheels off – heat around the hubs (applied fast as possible) and an improvised puller jig similar to a gear puller to concentrate the force at the hub close to the axle as possible would be my best recommendations.

It might be possible to make a two plate puller , one plate behind the wheel and the other plate with a central screw to push on the axle centre – but be sure to use a spacer between screw and axle to prevent marring the axle. The plates would be bolted together outside the wheel max OD.

Don't pull on the wheel rims, or the web of the wheels – especially if the wheels are spoked. JD

[John LintornParticipant @johnlintorn87585]

It turned out that that my front wheels were 30 minutes out of 90 degrees while my back wheels were dead on. I managed to clamp the front wheel in the vice and luckily, my 16 year old self had not quite pressed them on tightly enough so I was just able to correct the angle. I have now pinned all 4 with M3 grub screws so they won’t be moving again. The chassis now runs perfectly! Now just to build everything back up! Thanks for the help guys!
Thanks for all your help!

[Jeff DaymanParticipant @jeffdayman43397]

Good news that you found and corrected the trouble. Well done! JD

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