side slap on rods

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: cbrew, Harold_V

Post Reply
trainman154
Posts: 6
Joined: Fri May 28, 2021 9:23 am

side slap on rods

Post by trainman154 »

Hi I recently acquired a 7.25 inch gauge model locomotive project that somebody started but did not finish. The entire running gear of the locomotive was machined by the previous owner and as I was inspecting it I noticed that it has quite a bit of side slap on the main driving rods. So my question is how much side slap should a model locomotive of this size and wheel arrangement have?


IMG_20210525_195655_599.jpg
IMG_20210525_195655_584.jpg
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: side slap on rods

Post by NP317 »

I think the answer would depend partially on how much lateral motion exists in the three drive axles.
I prefer to allow more lateral motion in the front and rear axles and keep the drive rod axle fairly tight.
Then the drive rod side motion can be minimal to reduce wear, while the engine can still negotiate tight radius (relatively) curves.
Just my thoughts.

Looks like a fun project.
RussN
User avatar
LVRR2095
Posts: 1688
Joined: Sun Mar 04, 2007 6:50 pm
Location: Maine, USA

Re: side slap on rods

Post by LVRR2095 »

What do you consider “Quite a bit” to be?
Can you measure the clearance?

Keith
User avatar
Bill Shields
Posts: 10460
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: side slap on rods

Post by Bill Shields »

#1 If it runs over rough track and does not bind and sounds good with steam cylinder oil in the rod bearings..then it is just about right.

#2 If there is a lot of travel in the cross head pin..then maybe it needs attention.

#3 If you take out 'slop' in the rod bearings and it begins to bind...see #1

What one person considers slop may be needed to make up for manufacturing tolerances.
Too many things going on to bother listing them.
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: side slap on rods

Post by NP317 »

I see answers to two different definitions of "side slap on rods."
Are you referring to sideways motion of the main rod bearings on the drive pin, perpendicular to the track rails?
Or fore/aft motion between the drive rod bearing and the drive pin, parallel to the track rails?
RussN
trainman154
Posts: 6
Joined: Fri May 28, 2021 9:23 am

Re: side slap on rods

Post by trainman154 »

I am referring to the sideways motion of the main rod bearings on the drive pin, perpendicular to the track rails.
User avatar
Bill Shields
Posts: 10460
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: side slap on rods

Post by Bill Shields »

Ah...well that is probably not a problem.

Move front and rear drivers to the left limit..center drivers to the right. Repeat in opposite direction.

How much side to side movement do you have on any rod?

Any binding...do any of the rods prevent axle motion?
Too many things going on to bother listing them.
Post Reply