Stuart victoria

[Arthur GoodwinParticipant @arthurgoodwin45738]

Piston stroke

[Arthur GoodwinParticipant @arthurgoodwin45738]

Hi all

I have just got to the stage of doing a trial assembly of the engine (photos to follow) and have come across a big problem.

On the out stroke the slide bearings hit the back posts and on the instroke the bearings are 7/16 off the front posts and the piston is the same distance short of its "full" return position.

Its almost like the con rod is 3/8 short between centers.

I have double checked my dimensions and they are spot on

My question is would the engine stroke under pressure with the piston not getting back to the end of the cylinder.

Thanks in advance

Art

[Howard LewisParticipant @howardlewis46836]

It sounds as if your diagnosis of the the con rod centres being too small is correct.

Effectively the piston and cross head need to be moved forward, relative to the Crankshaft bearing saddles.. To my mind, the distance should be such that if the engine is double acting, the clearance at inner and outer dead centres should be equal.

To avoid damage, I certainly would not apply air, or steam, pressure until the situation has been rectified

But I am not a steam man, so others may give different advice.

Howard

Edited By Howard Lewis on 06/02/2021 12:52:15

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Ramon WilsonParticipant @ramonwilson3]

Hello Arthur,

Given that the cross head slide bars are at their correct location and I'm sure they are then the issue has to be either the conrod or the piston rod length. As previously said at mid piston stoke the cross head should be equally spaced between the ends of the cross slide. (The crank will not be vertical at this point)

I would look at the piston rod length between C/L of piston width and C/L of cross head pin again as I think this is where your problem may lay

Regards – Tug

[Arthur GoodwinParticipant @arthurgoodwin45738]

Hi

Thanks for your advice. Will look at tugs suggestion.

Have been unable to upload any pics. Keep getting "memory low" error.

Does anybody know what the max resolution/ file size is.

Thanks again

[Jim NicParticipant @jimnic]

As I see it given that the crank bearings and the slide bar mountings are located on the engine bedplate and thus likely to be correctly positioned, then the crosshead should not impact the slide bar posts if the conrod is the correct length regardless of the piston position. Disconnecting the piston rod from the crosshead would eliminate it, or not, from the equation.

Jim

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Arthur GoodwinParticipant @arthurgoodwin45738]

Hi

Thanks for your advice. Will look at tugs suggestion.

Have been unable to upload any pics. Keep getting "memory low" error.

Does anybody know what the max resolution/ file size is.

Thanks again

[SillyOldDufferModerator @sillyoldduffer]

Posted by br on 06/02/2021 13:32:04:

Posted by Arthur Goodwin on 06/02/2021 13:22:46:

Hi

Thanks for your advice. Will look at tugs suggestion.

Have been unable to upload any pics. Keep getting "memory low" error.

Does anybody know what the max resolution/ file size is.

Thanks again

So waste of time sending my reply so best I delete it then .

br

Edited By br on 06/02/2021 13:34:28

Gosh, you're quick on the draw this afternoon br!

Art may not have responded (yet), but I'm sure others would have taken note! Don't forget forum threads are read by many interested people, most of whom never comment.

Dave

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[JasonBModerator @jasonb]

No limit on what you can upload as forum software will resize it but must be a .jpg image file.

Agree with Dave, some people are not just sitting in front of their screen and may take a while to read a reply, if OP said his sizes on the drawing are correct I doubt posting yours presumably from the drawing would have helped anyway.

As said by others check piston rod/piston/crosshead assembly to make sure that is not overlength but if it's hitting the posts rather than hitting the end of the cylinder sounds like something else.

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[SillyOldDufferModerator @sillyoldduffer]

Posted by Arthur Goodwin on 06/02/2021 13:43:38:

…

Have been unable to upload any pics. Keep getting "memory low" error.

Does anybody know what the max resolution/ file size is.

Loading a big photo into a forum album automatically reduces it to 1024×768 pixels (I think), but the process is prone to misbehave if you have a big image and a slow internet connection or the server is busy.

When I had an 8Mb/s link it was worth reducing photos at my end with an image editor to 1024×768, but I've not bothered since upgrading to 40Mb/s. However, for taking internet pictures I set the camera to low or medium resolution, because small pictures are less likely to cause trouble. At high resolution my SLR camera creates gigantic jpegs, and I'm not sure this poor old forum could suck them up without gagging.

Dave

[JasonBModerator @jasonb]

Just looked at the two sets of drawings that I have, the older ones have the conrod ctrs at 6 1/32" and the newer ones at 6 1/4,

Horizontal distance between crankshaft ctr and ctr of guide bars is also 6 1/32" so would suggest the older sizes are correct and the new ones not

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[SillyOldDufferModerator @sillyoldduffer]

Posted by br on 06/02/2021 13:57:58:

Dave yes you are right – having a bad day today.

Fed up with having to get rid of the Mydford and mill etc because of this arthritis in my hands so unable to persue the hobby as I would like to.

Fed up with trying to help members and not even a thank you.

br

Don't let the lack of obvious approval put you off – I think most forum contributions drop silently into the pool!

I'm guilty too – I often see marvellous photos, smart ideas and clever techniques without commenting. I get more out of the forum than I put in, and it's thanks to blokes like you. Keep up the good work! I'm reading your posts…

Dave

[Arthur GoodwinParticipant @arthurgoodwin45738]

Hi thanks to all

Re jasons post. As i said my con rod centers are 61/32 bu my crankshaft to center of guidebars is just over at 63/64 not enough to creste my problem.

Im thinking the pads on my baseplate are out and will speak to stuarts tomo sbout it.

Once again thanks to all

 

Edited By Arthur Goodwin on 06/02/2021 14:45:14

[Arthur GoodwinParticipant @arthurgoodwin45738]

[roy entwistleParticipant @royentwistle24699]

Looking at your photos I feel that your con rod is short. I fail to see how the pads on the base casting can be wrong

Roy

[noel shelleyParticipant @noelshelley55608]

From the photos it appears the con rod is short. Noel.

[JasonBModerator @jasonb]

Back in from the shed and I've looked a bit deeper, there are also differences in the bed, figures are conrod length followed by guide bar ctr to crank ctr

1976 drawing 6.25" and 6.156"

1993 Drawing 6 1/32" and 6 1/32"

Princess Roya; 6 5/32" and 6 5/32"

Only the last two will give equal travel 1" either side of the guides mid point, if positions have been tweaked to get the parts to sit nicely on the cast bosses then crank will need the same adjustments.

[Arthur GoodwinParticipant @arthurgoodwin45738]

Hi

Thanks for your comments.

Will phone stuarts on Mon to verify the correct distance between centers

Regards

[Ramon WilsonParticipant @ramonwilson3]

Hi Arthur – just come in from the shid and seen your PM. Some others may benefit from these thoughts

I would agree with others but looking at the images it's likely to be one of several things.

Not in any order specific order.

The piston rod is too long – cross head hits rear post before piston is at bottom of stroke

Con Rod is too short (likely) or Crank throw is too big but if the latter the slide should move the same distance in the opposite direction (unlikely)

Main bearing position is wrong relative to length of con rod.

Cross Head slide is wrongly positioned.

Looking at your images you do not appear to have anything positioned wrong and you say you have checked the dimensions. Given that all is correct in layout dimensions – you need to evaluate what is causing the problem.

Ignore for the moment any drawing dimension of parts.

Concentrate first on being able to get equal movement of piston and cross head.

With the piston at mid stroke so should the crosshead be. If you can set the piston and cross slide in such an equal set up then you have the piston rod the right length – ie equal movement either side of mid stroke gives an equal gap between piston and cover and between cross head and end post. If you can't obtain that equal movement then the piston rod requires to be modified to give that situation. Once that is correct the rod length can then be looked at. Bear in mind at mid stroke the crank will be at an angle relative to the perpendicular position.

Always happy to add more if required but if you begin with trying this first I think you will soon see where the error lies.

Regards – Tug

[JasonBModerator @jasonb]

Arthur, did your drawings and the castings all come from Stuarts as one or have you bought drawings to complete an old casting set? The reason I ask is that from the photos your main bearing is overhanging the cast pad of the base front & back. The old drawings had a narrower bearing or at least the hole spacing is less no actual dims on the overall bearing size. So could it be you have a casting that needs the old drawings?

[Author]

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