Restoring OEM Stitch Length on Singer 29K70

[Snakeoil]

I decided to pull the head on my 29K70 to inspect, clean, and restore the stitch length if possible. I've learned here that wear on the tip of the bell crank is the most common cause for reduced stitch length.

First, off with the head. Four screws on the wheel side of the head mounting face is what keeps the head mounted to the top arm. Before removing the head, drive out the pin that connects the piston to the needle bar.

Remove the four screws and the head should come off. If it is stuck wiggle it a bit or give a tap with a dead blow or rawhide mallet to free up whatever gum is holding it in place.

Here is the head end of the machine with the head removed. A little cruddy, but not too bad. My head needed a wiggle to get off, by the way. The large round disc with the cam groove in it is the Feed Motion Cam Wheel.

Here is the inside surface of the head, as it came off my machine. See that little roller to the right of the head on the bench. That roller rides in the Feed Motion Cam Wheel and mounts on that pin at the bottom of the crud patch on the Slide Bar. At this point, remove the foot and the Stitch Regulator (clamp). You can also pull the needle bar out in either direction.

 

Next is removing the Revolving Bush Handle along with the bell crank. Two screws hold the Handle to the Revolving Bush. In the photo below, one screw is already removed. The other screw is at about 1 o'clock in the photo.

Here is the Handle with Bell Crank Lever still attached.

Continued in next post due to attachment size limitations.

[Snakeoil]

With Bell Crank accessible, remove the two Screw Studs (I cannot find these called out on the 29K70 parts diagram so I'll provide a photo. They are basically the pivot shafts for the Bell Crank Lever that hold it in the Handle.

Here is what those screws look like once removed. Screw driver slot is on the right end.

With the Bell Crank Lever removed, Here is what I found for wear.

Top side of tongue.

Bottom Side of tongue

According to Constabulary, the spec for the thickness of the tongue when new is 5mm or 0.197". This tongue measured 0.1895" or 4.82mm. So, my tongue was 0.0075 worn. I confirmed this by inserting the tongue into the ring on the sliding bar and was able to get a 0.007" feeler gauge in there with some drag.

This is a good place to discuss what the theoretical max stitch length of this machine would be given the dimensions for the existing bell crank lever. I measured both legs of the bell crank. The short leg, which is the tongue measured 1.312" from the center of the pivot hole to the center of the wear spot on the tongue. The long leg measured 2.035 from the center of the same hole to the bottom of the leg. With the bell crank in the machine and the foot down, the distance from the bottom of the long leg of the bell crank to the bottom of the foot was 0.710". So the effective long leg length was 2.745". Basically, a 2-3/4" leg.

If we do the arithmetic, the ratio for the Bell Crank is 2.745/1.312 = 2.09. So, for every thousandth of an inch the tongue moves due to the motion of the sliding bar, the foot moves 0.00209 inch. So, for what I was finding with my machine, for the stitch when set at 5 SPI and getting 8 SPI, my tongue would have had to have been worn 0.036". And we know that it wasn't. So there is more in play here.

Let's get back to the head in the next post.

[Snakeoil]

Before you and finish stripping the head, you have to remove the Foot Bar from the Foot Bar Revolving Joint Bearing. This is done by driving out the 1/16 pin at the top end of the Foot Bar. Here's a photo of that pin. The foot bar is not hardened and will bend. This pin is a bit of challenge to remove. You might bend the foot bar. Check it. If bent, carefully straighten and check with a straight edge. The dental pick is pointing to the pin in the photo below.

Another spot that made me a bit nervous was the Lifting Lever Shaft Lever, which is clamped to the Lifter Lever. I'm sure there is a procedure for setting the position of this lever. But since my machine sewed fine, I decided to scribe a line with a carbide scribe so I could reposition it where it was during reassembly. Here is how it looked with the line scribed in line with the split in the lever.

With that done, I stripped the head the rest of the way down. I cleaned and inspected parts in prep for reassembly. The topic for this post was restoring the OEM stitch length so that is where I will now go.

With wear on both sides of the Bell Crank Lever tonque, I chose to braze one side only. Reason being is the steel will wear slower than the brass and if the tonque only wore 0.007" in 40 years of service in a shoe repair shop, Having brass on one side and steel on the other should last longer than me.

Here is the tongue with the braze applied.

I then dressed down the braze material with small files and crocus clothe until I achieved the 5mm OEM spec. I used the slide bar ring as a gauge, checking my progress. When I got to 0.197", which is 5mm, the tongue was a nice fit into the ring groove. Here's the finished tongue. And that's not a flat spot. That's the light giving that impression.

This is another good place for a minor tangent. I read in a thread here that someone wondered if the Bell Crank they had was bent or if some of Bell Cranks Lever Legs are not made at 90 degrees to each other. I checked mine and the legs are set at 92 degrees. So don't think yours is bent if it is not square and you own a 29K70.

I put the head back together and mounted it to the machine, oiling everything with Break Free along the way. I did not mention this, but I did find some very hardened crud inside the head. Some of the crud had to be chipped away with dental instruments. But there was no appreciable wear seen anywhere inside the head, other than a slight groove made by the thread in the needle bar and the wear shown on the Bell Crank Lever.

With the machine back together, I ran a sheet of paper thru it with the stitch regulator set at 5 SPI and I got 6.5 SPI. I did it several times and each time got 6.5 SPI. That is a slight improvement over the 8 SPI I was getting before. But, I was not content. I wanted to know where the rest of the missing stitch length was going. Having had the head apart, I have a pretty good idea.

 I measured the moving of the sliding bar ring with a dial indicator. The ring moves vertically 0.139" with repeatability. If I take my Bell Crank leg ratio and multiply it by the ring movement, I get a stitch length of 0.291". A 5 SPI stitch should measure 0.200". So, Singer obviously accounted for the required operational clearance in the machine. But with my bell crank restored to a nice tight fit, where is my stitch length going.

I'm pretty sure it is the play in the foot bar at the Stitch Regulator Gib. I measured the amount of free play in the Foot Bar and got 0.030". If you take a 0.200" stitch (5 SPI) and take 0.030" out of it you have a 0.170" stitch length. That equates to just under 6 SPI. But I'm getting 6.5 to 7. So, there is wear elsewhere and could be in the Motion Wheel Cam, the mating roller or both.

So, If I either buy a new Stitch Regulator and Gib or fix mine so have near zero foot bar movement fore and aft, I'll gain 0.030 in stitch length. Using my 6.5 SPI that I measured after restoring my Bell Crank, that would result in my getting about 5.4 SPI with my machine, max case. It will reduce as the material being sewn, thickens.

I hope somebody finds this helpful. I learned a lot about how the machine works today. Hope this helps pay back the help I've received here since first getting this machine a month or so ago.

regards,

Rob

[mikesc]

Thankyou :) Superb thread / posts :)

[Bert51]

This needs to be placed in a safe place where it can be found easily, if any one wants details on restoring their 29 head, I think this information is invaluable.

But this is only my opinion.

Bert.

[Constabulary]

Great read!

If it helps, the diameter of a new cam roller (# 1816) is 10mm and so is the width of the cam track of the feed motion cam. I have replaced all rollers on my 29K71, except the large one that runs on the inside cam on the top shaft.

Regarding Lifting Lever Shaft Lever - I once discussed the setting of this lever with Wiz because I have a fairly high foot lift on my machine (I´m able to sew 12mm thick material) and I took some measures of the Lifting Lever Shaft Lever in relation to the lifting lever (which rides on the roller of the feed motion cam). I took measures with the lifting adjuster in position H, M & L.

This may or may not work on your machine but these are the measures that work for my machine w/o any binding. It may also depend on some other settings of parts. If you set the lever to low (for higher lift) the machine will bind!

Edited February 16, 2020 by Constabulary

[Snakeoil]

Thanks Constabulary. That's good input. I figured there was a spec for setting this hidden somewhere. But Heaven knows where. I will check my settings and compare to yours.

I tend to use the K71 Parts Diagram because it is more logically laid out and the parts list is so much simpler to use. But I've found several "improvements" on the K71 that don't appear on the K70 machine.

I think I'm just going to make a new gib for the stitch regulator and sew what I gain in stitch length. But you are right, changing the rollers might gain me a bit more as well.

It is amazing how much quieter the machine runs after going thru the head. I suspect the play in the bell crank tongue was one of the "clicks" I heard before and which has now become silent.

[Constabulary]

The measures are nothing official, it's just how I set the lever. The click could also be the thread when slipping around the shuttle and passing the the ball tip spring of the shuttle carrier. But similar machines can sometimes produce different sounds.

[Snakeoil]

Following up where I left off, today I made a new gib for the Stitch Length Indicator clamp. I had measured 0.030 of Foot bar movement due to wear in the existing components.

A spare Indicator came with the machine. No SIMANCO markings or numbers, but identical and virtually new. So the new gib was all I needed.

Here is the new gib along with the original Singer gib. Note that the wear on the original gib is at the top and bottom edges. I'm thinking that the gib was not truly worn very much. I'm now suspecting that the wear was in the Foot Bar where it contacts the Gib and Indicator. But I made the new gib anyway and this tightened up the Foot Bar to near zero play fore and aft, which still allowing free movement. Note that on my new homemade gib, the relief cut for the Foot Bar is minimal.

I ran a few test stitches down a sheet of paper. I got just under 6 SPI. Might call it 5.9 or 5.8 SPI. That was less than I had expected with the elimination of the Foot Bar play. I was expecting about 5.4 SPI. So, I took the foot off and put a dial indicator on the Foot Bar and measured the movement now that all the play was removed. I set the Indicator at 5 SPI. The Foot Bar moved 0.185" with good repeatability. That length equates to 5.4 SPI, which is what I was expecting. So, my guess is this could be a bit of slippage due to the foot teeth being worn and slipping a bit.

I'm probably going to leave it as it is for now. I might buy a new foot and maybe a new roller or two for the head internals. But rather than beat this stitch length horse any further, I'll address the wear in the Carrier Drive Pinion first and try to restore that back to zero play.

regards,

Rob

[Wizcrafts]

On 2/16/2020 at 1:17 AM, Constabulary said:

If you set the lever to low (for higher lift) the machine will bind!

That's not all that can happen if the clearance is zero. I actually broke one of these lifting blocks on my Singer 29k71. Had to get a replacement machined locally.