Seiko STH-8BLD-3 - Help diagnosing noise at low speed

[pgc]

Hi! I have a Seiko compound feed (STH-8BLD-3). I’ve been using it for about one year making backpacks (not leather).

The problem - At low speed, the machine intermittently makes a low pitched rattle/groan.  I cannot hear the sound when I turn the machine by hand (with or without the belt on the pulley). The sound goes away as soon as I speed the machine up.

Here is a short video with sound. https://imgur.com/a/XNju9LX

The sound really comes through in the video. It’s not quite that bad in person, but it’s bad enough that I don’t want to use the machine until I fix it.

Background - I tuned it when I got it and lubricate it regularly. I don’t recall when it started making this sound. Maybe it happened gradually.

I lubed it the first time I heard it, and it didn’t help. I’ve now removed all the covers, checked everything for loose parts, removed the hand wheel and remounted it, removed the needle position sensor, etc. I swapped the servo motor with another machine and replaced the belt. Nothing helped. The machine still sews very well.

It seems like the sound is coming from the middle of the machine, in the enclosed area to the left of the upper oil reservoir. But it is hard to know. I tried a mechanics stethoscope, but the noise is so loud that I can’t pinpoint anything.

There are no sewing machine mechanics in my area except one shop with a really long waitlist, so I learned to fix all of my machines. But I’ve spent a couple nights on this and I’m stumped. I’d really appreciate any suggestions.

Thank you!

Phil

 

[pgc]

Here is the video on YouTube (in case you don’t use Imgur): https://youtube.com/shorts/yIBxxLMi13w?feature=share

[pgc]

Found a suggestion to loosen belt. I thought it was plenty loose, as it had almost 1” deflection. Loosened it significantly and the noise is gone. fingers crossed it doesn’t  come back. 

[Wizcrafts]

9 minutes ago, pgc said:

Found a suggestion to loosen belt. I thought it was plenty loose, as it had almost 1” deflection. Loosened it significantly and the noise is gone. fingers crossed it doesn’t  come back. 

The belt may be bad. Try another belt.

[pgc]

3 hours ago, Wizcrafts said:

The belt may be bad. Try another belt.

Thanks! It was the belt. It was too tight. I loosened it and it is running very smooth now. So nice to have it quiet again. 

Edited May 10, 2021 by pgc

[Wizcrafts]

8 hours ago, pgc said:

Thanks! It was the belt. It was too tight. I loosened it and it is running very smooth now. So nice to have it quiet again. 

I would still replace the belt.

[pgc]

3 hours ago, Wizcrafts said:

I would still replace the belt.

Will do. I’ve been using an automotive belt. I’ll search the forum for thoughts on sewing machine specific belts and go from there. 
 

Thank you! I’m a moderator on Reddit Make Your Own Gear. We often refer the really difficult machine questions to this forum. Thank you for being a great resource!

Edited May 10, 2021 by pgc

[DonInReno]

That’s great news the sound has subsided.   You can still buy sewing machine belts at the auto parts store of your choice.    They are labeled 3L followed by the length in inches.    For instance a 30” long belt is a 3L30 or 3L300.   A 30.5” belt is a 3L305.    Not every auto parts person knows about the 3L belts since they are not associated with a car, but most chains stock them.

Ebay or Amazon are probably the easiest and least expensive option.

For some strange reason a google search for a specific 3L belt turns up a bunch of crappy suggestions, few of which are anything close to a basic 3L belt.   A search on Amazon, eBay, Napa, grainger, etc. will give better results.

[Wizcrafts]

FYI, a type 3L v-belt is 3/8 inch wide at the wide top side. Most auto belts are type 4L, which are 1/2 inch wide. There is a big difference in applied pressure between the two sizes. With the proper length 3L belt you can probably tighten it back up to 1/2 inch deflection.