modern starter drives

[Rob Doe]

Y, I noted that I had read the information. My old ring gear was trashed at the time, but it was definitely chewed up some. The starts were violent. I have no idea what the quality of the bendix was.

An additional piece of information that I did not mention was that the hard hits might play a role in bent shafts over time, which I checked for on the work bench.

Actually, my experience with the modern bendix seems to support your position. A lot of Model A's won't see 17000 miles in a man's adult lifetime. The information I quoted did come from experienced people on another forum. Please note posts #7 and #9.

Thanks for the picture. Looks like you're in good shape.

 

[Bob C]

Below is an old post that sheds some light on the engagement of the modern drive, maybe they have been corrected by now.

12-20-2013, 02:49 PM #6 MikeK
Senior Member



Join Date: May 2010
Location: Windy City
Posts: 2,919

Re: What's wrong with this starter drive?
There is nothing wrong with the barrel-drive starter in the picture, other than the inherent design flaws and slight mis-application.

They all freely drift forward, unlike the original Bendix design which incorporates a small ball with spring which locates in a detent to retain the drive in a retracted position.

The barrel design relies on the incline of the engine in the drive train (3 degrees in an "A") to offer slight resistance to forward drift. Unlike the original bendix, they can and do drift and occasionally 'ting' the ring gear, especially on long downgrades greater than 3 degrees. This seems to be of no damaging mechanical consequence, other than making an almost undetectable occasional zzzztt noise driving down steep ramps.

There are three different manufacturers of the drive sold for the A, and all have idiosyncrasies. I have had failures with two, and disassembled all three types.

Although similar in outer appearance, two have 1/8" less 'throw' and will never achieve more than 60% gear engagement. In all cases, comparing the travel of an original bendix, with it's wide pinion gear that over-travels the width of the ring thus maintaining 100% contact, the barrel drives will not achieve full tooth contact if mounted using the original set-screw hole on the starter shaft.
The only realistic fix is to machine a new woodruff slot and screw spot 5/32 closer to the starter body. If done 180 degrees opposite the original locations, the shaft will be able to properly accommodate the bendix and all three barrel drive types with 100% tooth engagement. Some people, upon doing a grease pattern and learning of the partial engagement, resort to shimming of the starter mounting face. If you do this, you lose the positive location ring on the starter and the whole thing is located by the sloppy bolt holes. There are also many people who happily motor along with a barrel drive that has only partial engagement.

One maker uses an internal elastomer that swells if exposed to oil, causing it to stick and jam. One had a glass-brittle helix that shattered, causing a jam.

Original type drives got a bad wrap for two reasons: 1) Poor quality knock-offs (repops) of the original Bendix, some eliminating the retraction detent and ball/spring, others with inferior bolts, springs and retainers. 2) People experiencing kick-back from starting with too much advance. If anyone thinks the barrel drives will stand up to repetitive kickback, think again. The very thin investment cast helix is much weaker than the stout design of the Bendix. The barrel relies on hitting its forward elastomer travel limit to relieve shock to this part. A kickback slams the weak barrel drive helix directly, and it unwinds the spring in a Bendix, but the very robust helix of a Bendix does not fail. No drive will last forever if abused.

 

[Terry Burtz Calif]

Below is an old post that sheds some light on the engagement of the modern drive, maybe they have been corrected by now.

12-20-2013, 02:49 PM #6 MikeK
Senior Member



Join Date: May 2010
Location: Windy City
Posts: 2,919

Re: What's wrong with this starter drive?
There is nothing wrong with the barrel-drive starter in the picture, other than the inherent design flaws and slight mis-application.

They all freely drift forward, unlike the original Bendix design which incorporates a small ball with spring which locates in a detent to retain the drive in a retracted position.

The barrel design relies on the incline of the engine in the drive train (3 degrees in an "A") to offer slight resistance to forward drift. Unlike the original bendix, they can and do drift and occasionally 'ting' the ring gear, especially on long downgrades greater than 3 degrees. This seems to be of no damaging mechanical consequence, other than making an almost undetectable occasional zzzztt noise driving down steep ramps.

There are three different manufacturers of the drive sold for the A, and all have idiosyncrasies. I have had failures with two, and disassembled all three types.

Although similar in outer appearance, two have 1/8" less 'throw' and will never achieve more than 60% gear engagement. In all cases, comparing the travel of an original bendix, with it's wide pinion gear that over-travels the width of the ring thus maintaining 100% contact, the barrel drives will not achieve full tooth contact if mounted using the original set-screw hole on the starter shaft.
The only realistic fix is to machine a new woodruff slot and screw spot 5/32 closer to the starter body. If done 180 degrees opposite the original locations, the shaft will be able to properly accommodate the bendix and all three barrel drive types with 100% tooth engagement. Some people, upon doing a grease pattern and learning of the partial engagement, resort to shimming of the starter mounting face. If you do this, you lose the positive location ring on the starter and the whole thing is located by the sloppy bolt holes. There are also many people who happily motor along with a barrel drive that has only partial engagement.

One maker uses an internal elastomer that swells if exposed to oil, causing it to stick and jam. One had a glass-brittle helix that shattered, causing a jam.

Original type drives got a bad wrap for two reasons: 1) Poor quality knock-offs (repops) of the original Bendix, some eliminating the retraction detent and ball/spring, others with inferior bolts, springs and retainers. 2) People experiencing kick-back from starting with too much advance. If anyone thinks the barrel drives will stand up to repetitive kickback, think again. The very thin investment cast helix is much weaker than the stout design of the Bendix. The barrel relies on hitting its forward elastomer travel limit to relieve shock to this part. A kickback slams the weak barrel drive helix directly, and it unwinds the spring in a Bendix, but the very robust helix of a Bendix does not fail. No drive will last forever if abused.

Bob C,
Thanks for posting that from Mike K.
Additional problems occur when the main bearing thrust is not in the correct place and the starter motor has excessive end play.
The "Barrel Drive" is used on tractors and is not a direct replacement for a Model A Bendix.

 

[30Murray]

I have been having some problems with my starter engaging properly and when I removed it, I couldn't see much difference between the 10 year old modern drive and a "new" made-in India one I was given. After comparing the fit of the two plus the old bendix drive, somehow I lost the woodruff key. It was driving me nuts looking everywhere until by chance I tapped the old modern drive and something rattled inside the big end. It must be the key, but there is no way to get it out. I guess its complete junk now so I'll just refurbish the bendix drive. I wonder if this is a common fault in the way the slot is cut?

 

[nkaminar]

I had to take my starter out today to change the brushes. While it was out I looked at the ring gear and the pattern on the modern drive. The modern drive I have is making full engagement with the ring gear. It is working well. I am very happy with it. See photo.