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Stuart victoria

Piston stroke

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Arthur Goodwin06/02/2021 12:30:17
63 forum posts
42 photos

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 Lewis06/02/2021 12:51:30
5545 forum posts
13 photos

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

br06/02/2021 13:06:43
697 forum posts
3 photos

Dims apparently not of interest so deleted.

br

Edited By br on 06/02/2021 13:07:05

Edited By br on 06/02/2021 13:33:51

Ramon Wilson06/02/2021 13:11:51
avatar
1205 forum posts
308 photos

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 Goodwin06/02/2021 13:22:46
63 forum posts
42 photos

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 Nic06/02/2021 13:26:17
avatar
358 forum posts
202 photos

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

br06/02/2021 13:32:04
697 forum posts
3 photos
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

Arthur Goodwin06/02/2021 13:43:38
63 forum posts
42 photos

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

SillyOldDuffer06/02/2021 13:48:03
Moderator
7690 forum posts
1697 photos
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

br06/02/2021 13:57:58
697 forum posts
3 photos

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

JasonB06/02/2021 14:04:18
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Moderator
21632 forum posts
2493 photos
1 articles

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.

br06/02/2021 14:07:37
697 forum posts
3 photos

Point taken Jason, seems mine was a pointless reply.

br

SillyOldDuffer06/02/2021 14:10:09
Moderator
7690 forum posts
1697 photos
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 1024x768 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 1024x768, 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

JasonB06/02/2021 14:13:39
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Moderator
21632 forum posts
2493 photos
1 articles

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

br06/02/2021 14:23:22
697 forum posts
3 photos
Posted by JasonB on 06/02/2021 14:13:39:

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

Well that is interesting, Jason

Mine is 6.25 inches, checked with a vernier, and was built by a well repected engineer on this forum who knows his stuff, and was bought from him as a completed and running item

The steel slide bars on the side where the brass bits slide in, when I move piston to full forward and then full back, the distance is exactly the sameeach end measured fromthe pillars.

Runs a treat .

br

SillyOldDuffer06/02/2021 14:32:11
Moderator
7690 forum posts
1697 photos
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 Goodwin06/02/2021 14:33:47
63 forum posts
42 photos

img_20210206_143709.jpgHi 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 Goodwin06/02/2021 14:47:51
63 forum posts
42 photos

img_20210206_143709.jpgimg_20210206_143700.jpgimg_20210206_143700.jpgimg_20210206_143647.jpgimg_20210206_143636.jpgimg_20210206_143624.jpgimg_20210206_140722.jpg

roy entwistle06/02/2021 15:00:48
1436 forum posts

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 shelley06/02/2021 15:20:40
861 forum posts
19 photos

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

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