Advice needed re. Slidebars

I have now temporary fitted the weighshaft onto to boiler and with regard to the alignment of the slide valve assembly it is absolutely perfect, I had to get STW to remove 2.5 mm from the base of the weighshaft which was exactly the correct amount, I just had to turn a couple of the jacking screws up about 1/2 a turn to get the final adjustment. My kits arrived with me a few years ago and it is only now with the lockdown that I have had time to continue this build (one or two builders had the same problem - LynnR I think, but it only affected a few weighshaft castings)

I am now having difficulty in getting the slide bars to align up, so that the Cross Heads slide up and down the slide bars. No problem with the vertical misalignment because I can use the shims provided and also I have made a few thinner ones but the Cross Heads are very tight due to a the sideways misalignment. I have attached the Cross Heads to the piston (tightly but without the rings fitted but have not done the grub screws up yet) but I have fitted the piston rod bush (BS 41304) but not the packing or the piston gland (BS41305). Originally I very lightly filed and polished the slide bars so that the Cross Heads moved perfectly freely up and down, maybe I need to give a little more clearance on these to allow a very small amount of misalignment? Does anybody think I should open out the piston rod bush (BS 41304) a little because I am sure this would greatly help the problem.
Any advice would be much appreciated.
Charles

Hi

You must get the pistons to run true in the bores. Otherwise you will get premature wear. You can elongate the holes in the cross slide bars to allow sideways movement. This will allow the bars to be set correctly with the bore of the cylinder and piston. Then shim / move the crank bearings to get the crank in line with the cross slides and piston bore.

So you need to do all the adjusting at the weighshaft end and towards the crank. The bushings on the piston rod need to be kept a close fit as they help to align the piston in the bore and stop it colliding with the cylinder wall.

Yes I used a grinder to adjust the saddle on Crystal.

Hi Charles,

I had exactly the same issue and ended up machining material off the side of the bar to allow it to move to one side and also slot the retaining hole. I reckon I took about 1.5 mm off all 4 bars so it all fitted nicely. The other thing to check is the straightness of the slide bars as the first set I had were bent along its length.

Regards,

Neville

Hi Neville
Thanks for that advice, I will go and have another look at my slide bars.
Kind regards,
Charles