vintage David Bradley saws question: gear drive vs. direct drive

[davidbradley360]

I have a number of David Bradley gear drive chain saws 1950's vintage, but have none with direct drive. My questions are:

1. What was the purpose of the gear drive ? I found data on the net that stated it was to maintain constant rpm while cutting through large diameter trees- which makes sense- when I think of gearing anything down, I think of putting my 4-speed F-150 in granny low- slow but tons of torque to pull a house over with. Was that the general idea with the gear drive ?

2. Taking into consideration #1 above, what about the direct drive David Bradley saws ? Logic would dictate that the actual chain and/or chain sprocket speeds should be higher rpm and faster, than the gear drive saws. Is this true ? I'd assume the engine rpm would be the same on both types- but engine rpm being the same, wouldn't the direct drive saw cut through a smaller log faster, due to faster chain speed ?

any opinions or hands-on experience welcome, help me sort this one out. Because I've seen both 4.7 cubic inch direct drive, and 4.7 cubic inch gear drive, and just wonder why they'd slow the cutting speed down on the saw in a case like that. What's the advantage ?

thanks in advance for your replies

 

[no longer collecting]

Personal opinion,
Gear drive equals old heavy engines with long stroke that could achieve a max rpm of 4,000. The technology was simply not there. Those saws were running 3/4, 9/16, 1/2 pitch chain that needed more torque than speed.....from the late forties to the mid sixties. The ratio 3 to 1 was the ideal combination to get this fairly fast and efficient cut.

Only the 1/2 pitch barely survived the test (except for hotsaws on short time run) with the direct drive and was downgraded to .404 which proved to be the most popular pitch for speed and wear effects.....is is now 1965.

On today's saw if you try to run a 9/16 pitch with a modern saw, I don't think the clutch would last for long and would probably smoke and burn.

Bob McCulloch tried that in 1962 with the BP1 at 12,000rpm governed and the saw would burst causing injuries to the operator. They were recalled and destroyed.

Alain,

 

[Work Saw Collector]

Personal opinion,
Gear drive equals old heavy engines with long stroke that could achieve a max rpm of 4,000. The technology was simply not there. Those saws were running 3/4, 9/16, 1/2 pitch chain that needed more torque than speed.....from the late forties to the mid sixties. The ratio 3 to 1 was the ideal combination to get this fairly fast and efficient cut.

Only the 1/2 pitch barely survived the test (except for hotsaws on short time run) with the direct drive and was downgraded to .404 which proved to be the most popular pitch for speed and wear effects.....is is now 1965.

On today's saw if you try to run a 9/16 pitch with a modern saw, I don't think the clutch would last for long and would probably smoke and burn.

Bob McCulloch tried that in 1962 with the BP1 at 12,000rpm governed and the saw would burst causing injuries to the operator. They were recalled and destroyed.

Alain,

Rep sent thanks.

 

[heimannm]

Corporal has it, most of the early chain was pretty large pitch and the saws were underpowered, best way to make them work was gear reduction. Remember that chain was not as sophisticated as it is today, slower chain speeds would reduce the heat and even with the somewhat softer material the chain would last a while before sharpening was required.

The McCulloch D-44 was an early direct drive saw, same engine was also put on the 55 with a gear box. I think my 55 with 9/16" pitch chain will keep up the D-44 fit with .404 pitch chain. Guess we may have to test this theory in Darlington next weekend.

Mark

 

[smilin possum]

Hey guys I have 2 sears u-drive gear saws and can't find 1/2" chain around here. Any ideas or help on this would be great.

 

[no longer collecting]

The 1/2 pitch chain is NLA for sure......They are so rare because they are used in hotsaws.....The one's i buy are chains used for hotsaw racing and that are no longer fit for that usage. The price may varry depending on the amount of wear. Usually there are 80% life left on them and they go for about $2- $5 a foot.
Only glitch.....you need to know a racer

Alain,

 

[davidbradley360]

thanks for the informative replies.


the statement about the older engines being underpowered is debatable IMHO- the old David Bradley 134 cc/8 HP saw has a more powerful engine than most on the market today. What it lacks is high rpm capability, lightness, and a modern chain- not engine power- the DB actually compares favorably with a modern Stihl saw in the horsepower and engine size specs, it just won't rpm/cut as fast as the Stihl, and the Stihl weighs only 22 lbs., while the old DB weighs over 35 lbs.- I found this spec link for a comparable new Stihl saw:

http://www.stihlusa.com/chainsaws/MS880.html


From your helpful posts, and my own research, its apparent there was a general downsizing of chainsaws from the 1960's onward (this occurred on just about all types of machinery)- to make them lighter/handier/safer/easier to use- that dictated a smaller chain, and less pitch, and higher rpm to make them cut faster- that in turn required a smaller engine with lightweight internal parts, to attain higher rpm capability. The newer engines aren't necessarily more powerful from the HP/torque aspect, but they do turn much higher rpm, which is what a saw chain needs to cut quickly. The saw mfrs. realized, chain speed is everything to attain a fast cut. Some net research turned up an informative patent on a hybrid chain, with longer pitch, but otherwise has size traits of a smaller pitch chain. I never realized the chains were so high-tech on the new saws !



http://www.freepatentsonline.com/3929049.html

"Whereas improvements have been made in chain saws to enable them to be made smaller, and because of the desirability in the market for smaller, easier handling, less expensive and faster cutting chain saws, saw chain has been required by the chain saw industry to be made smaller. The configuration of the cutting link of the saw chain has been designed over the years largely by trial and error. Thus, the configuration that has come to be standard in the industry is considered most suited for satisfying preference of chip size and clearance, endurance of cutters, ease of sharpening and manufacturing, etc. Thus, as the size of the saw chain was reduced, the configuration of the cutting link was maintained. The pitch of the saw chain is the average distance between the rivets. As pitch increased or decreased, so did all other dimensions. Because pitch is important to match saw chain to drive sprockets, pitch became the term used to measure saw chain size. Thus, whereas a number of years ago a popular sized saw chain for hand chain saws was 3/4 inch pitch chain, this was reduced down in stages, e.g. to 5/8 inch pitch chain, 1/2 inch pitch chain, 3/8 inch pitch chain and more recently to 1/4 inch pitch chain. This reduction in pitch has had a number of effects. A most significant effect is the increased number of parts required for the same length of chain. A foot of 1/4 inch pitch chain includes many more parts than even a 3/8 inch pitch chain and the cost of making the smaller chains has, accordingly, increased.

It is an object of the present invention to produce smaller size chain while maintaining a larger pitch and fewer saw chain components. It is a further object to increase stability of the chain and greater safety while maintaining or improving cutting efficiency."

 

[davidbradley360]

now that the Acres database is back online, I researched this topic more, and found that David Bradley made all 3 of their saws in engine sizes 4.7, 5.8, and 8 cubic inch, in both gear drive and direct drive models, during the same model years of the 1950's. In other words, the gear drive and direct drive DB saws were sold side by side- the direct drive wasn't a later development. The chain pitch difference was very slight, 7/16" vs. 1/2"



example: model 917.60011 used the big 8 CID engine, with a 7/16" chain pitch, and direct drive, at 4500 rpm

http://www.acresinternet.com/cscc.n...47ee6891e22cc2a788256bb7004da101?OpenDocument



while the 917.60009 used the same engine with a 1/2" pitch chain, and gear drive, at 4500 rpm

http://www.acresinternet.com/cscc.n...743185d8699941d688256bb7004d55e8?OpenDocument



the direct drive saw was 10 pounds lighter. This chain pitch difference is slight, the engine rpm on both saws is the same, so I was wondering, what gives ? Why did they even bother adding 10 pounds and all that extra gear drive stuff, for a lousy 1/16" larger chain pitch ? It hardly seems worthwhile.

then I compared the BAR LENGTHS used, and that explained it- the gear drive saw was available in 20" to 32" bar lengths

while the direct drive saw was available with only a 16" to 24" bar lengths

the major difference appears to be bar length capability- the gear drive torque was used with the 1/2" pitch chain, but could run a much longer chain and bar.

The 4.7 CID saws had similar specs, the gear drive units had a 1/16" longer pitch chain, and slightly longer bars.

 

[Mr. Bow Saw]

I like the David Bradley saws, I think there neat looking old saw.

 

[davidbradley360]

looks like a really nice minty or restored 4.7 with a really unique cutter on it- tell me about that cutter ! what is it, and what was it used for ?

what I like about the DB saws is they are so easy to work on (so far)- compared to the newer small chainsaws have everything crammed inside them close together

 

[Mr. Bow Saw]

looks like a really nice minty or restored 4.7 with a really unique cutter on it- tell me about that cutter ! what is it, and what was it used for ?

what I like about the DB saws is they are so easy to work on (so far)- compared to the newer small chainsaws have everything crammed inside them close together

The saw is restored, It has what is called a Bow bar on. There used
for pulp wood, Bucking up smaller logs.

You can read all abot them here.

History of bow Saws,
http://www.arboristsite.com/showthread.php?t=109002

 

[davidbradley360]

very interesting

 

[SkippyKtm]

I like the David Bradley saws, I think there neat looking old saw.

Man, That saw is a Beaut! Makes me want to find one on CL and restore it. I have a Homie 6-22 in restorable condition with owners manual too.

 

[sawbones]

Around 1964 Homelite built the stick shift so you could have the best of both worlds.

not sure how long it was made but they are hard to find today.

After this they made the C series convertible drives. c-5 c-51 c-71 c-91

You could change the clutch cover in 9 minutes for direct or gear reduction.

they also made a gear reducer to fit the XL 12. These gear units are also very hard to find now.

this is the dealer wall poster.

1963 dealer handout

another dealer brochure with spec sheet

 

[sawbones]

 

[davidbradley360]

gear shift chainsaws- now we're cookin' with gas !

 

[cheeves]

David Bradley

I just got a David Bradley (model no. 917.60051) that I just got as partial payment for clearing up some trees downed in Irene. I tried starting it, but there's no spark. I'm attaching a picture of it. Any input would be greatly appreciated. Thanks, Bob http://www.freelygiven.org/DavidBradley.jpg

 

[davidbradley360]

I just got a David Bradley (model no. 917.60051) that I just got as partial payment for clearing up some trees downed in Irene. I tried starting it, but there's no spark. I'm attaching a picture of it. Any input would be greatly appreciated. Thanks, Bob http://www.freelygiven.org/DavidBradley.jpg

about half the DB saws I've run across were sitting due to no spark. Without exception, every single one came back to life, after I removed the flywheel, and the points, and sanded the point contacts, and regapped them. The ignition on those saws is really simple and easy to set up.

The next most common problem with the DB saws is, the diaphragm carburetors go bad from sitting, and they need a kit. Also the fuel tank and lines need to be cleaned out and/or replace the rubber fuel line.

once the spark and fuel is taken care of, even a saw with a lot of miles on it, with less than top compression, will start and run. It also saves a lot of hassle changing the spark plug right off the reel.

 

[J.Walker]

Some shots of my David Bradley saw.

View attachment 197983

View attachment 197984

View attachment 197985



.

 

[cheeves]

about half the DB saws I've run across were sitting due to no spark. Without exception, every single one came back to life, after I removed the flywheel, and the points, and sanded the point contacts, and regapped them. The ignition on those saws is really simple and easy to set up.

The next most common problem with the DB saws is, the diaphragm carburetors go bad from sitting, and they need a kit. Also the fuel tank and lines need to be cleaned out and/or replace the rubber fuel line.

once the spark and fuel is taken care of, even a saw with a lot of miles on it, with less than top compression, will start and run. It also saves a lot of hassle changing the spark plug right off the reel.

Thanks for responding and help in getting this classic going again. I feel it is important to restore these old relics that are living history in the field that we so much love. You're to be commended! Take care. Thank you.