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Norden mill engine

Errors on assembly

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Jim C02/09/2019 13:17:17
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Hi. Just wondering if anybody has built this engine or is in the process of building it? I am a good way through the project and today had a trial assembly of cylinder, piston, connecting rod and crank. On assembly I found that the cross head travels almost outside of the guide bars by about 1/4 inch at the extremity of crank stroke!! I also left the guide bars slightly over length and am confident that I have all the contributing lengths to drawing size. IE, table legs at 4 7/8 inch long and at 8 degree angle. Suggestions as to what to do now would be very welcome, like maybe try to extend the guide bars? Neil, any drawing errors known of. Many thanks, Jim.

Former Member02/09/2019 13:28:24

[This posting has been removed]

JasonB02/09/2019 13:31:31
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Jim, can you post a photo of yours, may be able to spot something obvious. Neil's photos of his look to have plenty of room for the crosshead to stay within the guides. I did check through his drawings before publication but nothing on the list that would affect your situation.

What length did your guide bars come out as as they are a "check on job" item.

Edited By JasonB on 02/09/2019 13:34:00

SillyOldDuffer02/09/2019 13:51:31
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The plans are on Neil's Stubmandrel website here if anyone fancies some detective work.

Looks as if the height of the table legs on Sheet 4 have to be inferred from the drawing and their length derived from an angle. It's the sort of calculation I always get wrong but scaling the drawing off-screen with a caliper gave me 4.9" which is close to Jim's 4.875" value for legs at 8°.

I've failed to explain the problem!

Dave

JasonB02/09/2019 13:59:43
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Dave, the legs have the 4 7/8" dimension on them

Jim C02/09/2019 14:03:16
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image.jpg

Jim Nic02/09/2019 14:20:50
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From your photo it's plain to see the problem at the top of the guides, what's it like at the bottom? If the crosshead has 1/4 of an inch to go before the bottom of the bars the problem could be in the length between the centres of the connecting rod. If the crosshead goes too far down as well as too far up then I would be looking at the throw on the crank.

Jim

Edited By Jim Nic on 02/09/2019 14:21:38

JasonB02/09/2019 14:23:41
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Does look something amiss

Adding up the vertical length of the legs ( 4.827),  table thickness and bearing pedestal height I get a crank Ctr of 5.52"

If we then add the crank throw to this the pin when at TDC will be 6.07"

Less the conrod length of 2.125" gives the middle of the cross head at 3.95".

 

Now add up the cylinder height, cover thickness, guide and foot and you get 3.626" to the top of the guide Though that is a check on job dimension.

Two options but best wait for Neil to comment first as he has a Model to check sizes from.

 

Edited By JasonB on 02/09/2019 14:27:32

Edited By JasonB on 02/09/2019 14:28:26

JasonB02/09/2019 14:42:10
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Doing what we should not do on the general arrangement drawing the legs look like they should be a lot shorter than the 4 7/8" , more like 4 1/4"

SillyOldDuffer02/09/2019 14:48:03
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Posted by JasonB on 02/09/2019 13:59:43:

Dave, the legs have the 4 7/8" dimension on them

Doh, drawn in the top right corner. I see it now.

Ho hum, I not only failed to answer the question, I misread the plan as well.

Sackcloth and ashes for tea...

Dave

PS I'm going to make a rattle damper this afternoon. Milling and turning to my very own design. What could possibly go wrong?

Jim C02/09/2019 14:55:15
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Firstly, apologies for posting a photo with no additional notes.!! To Jim Nic...when I was initially assembling the engine, I set the cross head at the bottom to gauge the piston rod length. There is lots of clearance at the bottom. It was only when I took the cross head to the top that I realised that the guides where too short. ( I even left them a bit over length !) Hi Jason, thanks for your comments and numerical input. Yes it would also seem to me that the legs as dimensioned could well be over length as you infer. Hope Neil is around soon to put a rule on his model and shed some light on the issue. It may just be possible to cut off the tops of the legs and re solder the table on ? Cheers all.

Maurice02/09/2019 16:55:53
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Hi Jim, just caught up with the posts. I thought that I would just point out that the crosshead should just overrun the ends of the guides by, In full size, about 1/4". This is to prevent the wearing of a step where the crosshead travel ends. Likewise, the leading edge of the piston rings, going in each direction, should over run the bore a little, into the counterbore that should be at each end of the cylinder bore. This is what is recommended in text books on full size engines. Whether it is worth while on a model depends on how much actual running it will get, and how authentic you wish to be.

Maurice

Neil Wyatt03/09/2019 15:32:04
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Yes, I'm afraid the legs are too long high - they are angled at 8 degrees.

They are about 4 3/16" high so should be made 7 1/4" long, I have no idea why the plan give the wrong dimension as it was auto dimensioned and is drawn the right size.

Sorry about this - the best solution is probably extending the connecting rod by, say 3/8".

I'm surprised this hasn't been noticed before although only a few appear to have been built.

I'll change the plans.

Neil

Jim C03/09/2019 17:06:23
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Hi Neil. Thanks for getting back to me. Today I decided I would increase the length of the guide bars. They still might be a tad over length but can shorten if needed. Cheers Jim.f76abaaa-1b75-4bdf-a5a1-556d83135044.jpeg88eb163a-60dd-4305-824b-01aa1e25fcd8.jpeg

Neil Wyatt03/09/2019 17:19:06
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Thanks Jim,

You are doing a nice job. Looks neater than mine.

Neil

Jim C03/09/2019 17:50:25
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Cheers for that Neil, I’ll keep on at it and when finished give it to my grandson to look after and run, hopefully ?

Then I’ll get back on with the Wyvern, which I shelved because I found the carburetor a really tricky job and put it on the too hard shelf !!

Jim.

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