3/4" pitch chain

[Aviacs]

Very fortuitous to ask here and have you reply - I'd probably have broken something eventually.
The hub does have to come off first.
Then the woodruff key ("1/2 moon key") should be removed.
If the entire unit was pulled using arm pullers over the "case", the bearing in the "case" would likely ride on the woodruff key, still retained by the hub, and make a mess of the key & shaft.

I made a simple little puller for the hub, and a center stud to bear on the shaft while pulling.
After getting it off, removing all the plates, and then pulling the basket (the "case") with a 3-arm puller, It occurred to me to wonder what the 2 setscrews were for?
They unscrewed easily, and as my son has reminded me in the past "Light dawned on marble head".
IOW, if the puller had been made longer, the basket could have been pulled with the same shop made tool, moving the screws to an outer position.
I hope this may be useful to the next person who has to investigate a clutch on one of these saws.

My intention had been to just machine a new basket and retain the old one as a spare. However, the center bearing is notchy, and the sprocket is worn quite badly.
All the parts are riveted together including the bearing in the center, so it is useless as is. New plan is to remove the rivets, and build a new sprocket onto the old basket.
Some of the dimensions don't look ideal, but close enough to keep going.

 

[Aviacs]

Here's comparison of the chains.
Disston L ("scratcher"), Disston chisel, and .404 harvester.

.404 on actual harvesters is run with center drive sprockets (example included in photos, not correct tooth count, though)
.404 is run on manual saws with spur drive.

Spur drive allows the chain to find its own axial center to align with the bar.
Center drive needs to be precisely aligned with bar. (This is not a problem)
However, it seems spur drive would be a little more tolerant of flex in the bar or other anomalies in use.

The concern here is safety.
Any opinions as to whether spur drive or center drive would be better for the Disston 2 man saw?

Also, 13 tooth .404 sprocket is going to be very nearly the same as the pitch line of original Disston 3/4 pitch 7 tooth.
However, to put the side links in the same place might require 15 T .404.
Diameter over tips of Disston in unworn area is 3.125" - 3.126" Nose entry at bar is a little less defined but around 3.030"

I've searched most of the online mfg'rs guides and have not found a system to size the sprocket to the bar by dimensions of the entry to the bar.
the sprocket needs to be smaller so the chain does not throw, but too small and it wears at that area of the bar. Any math derived charts, formulas, or advice?

Thanks!
smt

 

[Skeans]

Here's comparison of the chains.
Disston L ("scratcher"), Disston chisel, and .404 harvester.

.404 on actual harvesters is run with center drive sprockets (example included in photos, not correct tooth count, though)
.404 is run on manual saws with spur drive.

Spur drive allows the chain to find its own axial center to align with the bar.
Center drive needs to be precisely aligned with bar. (This is not a problem)
However, it seems spur drive would be a little more tolerant of flex in the bar or other anomalies in use.

The concern here is safety.
Any opinions as to whether spur drive or center drive would be better for the Disston 2 man saw?

Also, 13 tooth .404 sprocket is going to be very nearly the same as the pitch line of original Disston 3/4 pitch 7 tooth.
However, to put the side links in the same place might require 15 T .404.
Diameter over tips of Disston in unworn area is 3.125" - 3.126" Nose entry at bar is a little less defined but around 3.030"

I've searched most of the online mfg'rs guides and have not found a system to size the sprocket to the bar by dimensions of the entry to the bar.
the sprocket needs to be smaller so the chain does not throw, but too small and it wears at that area of the bar. Any math derived charts, formulas, or advice?

Thanks!
smt

Newer 404 the 19hx can’t be run on a spur sprocket it must be run on a rim same as 11BC or 11h 3/4 chain. One thing to remember is this is hydraulic fed chain it might be more aggressive and with your concern being safety why mess with harvester chain?
Also take a real good look at the drivers on harvester chain it’s different then saw chain as well.


Sent from my iPhone using Tapatalk

 

[Aviacs]

I really can't see a functional difference in the shape of .404 H Stihl chain, and say, .375 other than size?

We both know the key question is, "with a 1.5mm depth gage, will the saw pull it?"
Original Disston chisel chain looks to have over 1mm at the depth gages, and the teeth and offsets are much bigger. I had a spec on original, but regrettably did not save it.
If the saw's HP is biased (gear reduced) at the bar to favor torque over speed, it might be a wash.

Have not verified kerf of original, looks "much bigger" than Stihl .404H
Finally found factory spec on Stihl .404H = .350" kerf with new chain

I have not verified whether my saws are 3:1 or 2.57:1 gears.
At 3:1, chain speed is only 1,047fpm
at 2.57:1, CS = 1,222fpm

Safety: are your concerns regarding reports when it first came out, that Stihl .404 80ga sometimes broke new out of the box? Or is your concern regarding something else?

So far, everything that i can see or measure makes .404H look better than original; except some reports that it was breaking new, out of the box when tensioning and run up before use. There don't seem to be recent notes on that. It is also not clear to me if that was the .063 ga., which has been discontinued. This app uses .080 ga.

Center drive sprocket would certainly be a whole lot easier to make, and probably more stable in heat treat. My concerns are along the lines of will it clean as well, and how will it tolerate minor but inevitable flopping the bar around when the bar is laid flat for ripping cuts? (sawmill)
What, in your mind, makes center drive superior to spur drive for the proposed app? I'm open minded, and fully aware that in any design field there are small subtleties that amount to big "gotchas". This is a real question, not argument, i want to know what you know, so long as it is based on technical foundation.

Look - fundamentally, this is a quick and easy experiment to try - so long as there is not some accident profile i'm overlooking at first test?

Thanks!
smt

 

[Skeans]

I really can't see a functional difference in the shape of .404 H Stihl chain, and say, .375 other than size?

We both know the key question is, "with a 1.5mm depth gage, will the saw pull it?"
Original Disston chisel chain looks to have over 1mm at the depth gages, and the teeth and offsets are much bigger. I had a spec on original, but regrettably did not save it.
If the saw's HP is biased (gear reduced) at the bar to favor torque over speed, it might be a wash.

Have not verified kerf of original, looks "much bigger" than Stihl .404H
Finally found factory spec on Stihl .404H = .350" kerf with new chain

I have not verified whether my saws are 3:1 or 2.57:1 gears.
At 3:1, chain speed is only 1,047fpm
at 2.57:1, CS = 1,222fpm

Safety: are your concerns regarding reports when it first came out, that Stihl .404 80ga sometimes broke new out of the box? Or is your concern regarding something else?

So far, everything that i can see or measure makes .404H look better than original; except some reports that it was breaking new, out of the box when tensioning and run up before use. There don't seem to be recent notes on that. It is also not clear to me if that was the .063 ga., which has been discontinued. This app uses .080 ga.

Center drive sprocket would certainly be a whole lot easier to make, and probably more stable in heat treat. My concerns are along the lines of will it clean as well, and how will it tolerate minor but inevitable flopping the bar around when the bar is laid flat for ripping cuts? (sawmill)
What, in your mind, makes center drive superior to spur drive for the proposed app? I'm open minded, and fully aware that in any design field there are small subtleties that amount to big "gotchas". This is a real question, not argument, i want to know what you know, so long as it is based on technical foundation.

Look - fundamentally, this is a quick and easy experiment to try - so long as there is not some accident profile i'm overlooking at first test?

Thanks!
smt

All my experience is with GB 404, Oregon 18/19hx, and Oregon 11 series chain. The 18 series Oregon and the GB will work on a spur sprocket since they run more of a traditional chain driver, were the 19 and 11 series run a harvester driver that doesn’t have a tang on the bottom of the driver. My harvester has a few different saw motors available for it a 19cc is the smallest with up to a 30cc to run the 19hx it takes some horsepower to turn the chain a cut plus it’s very aggressive well cutting.


Sent from my iPhone using Tapatalk

 

[Aviacs]

I think i see what you are saying, but can't capture one of the clear drawings/photos online to show it here. (Stihl probably protects them)
IIUC, it appears the bottoms of the drivers with 18H (& Stihl .404H) is the same as the bottoms of the straps, with a little central notch, that would allow them to ride over a spur uniformly.
With 19H, the notch is not complete under the cutters, and the chain would bump along and wobble side to side as it was forced over spurs?

So far, looks like Stihl .404H will pass on that requirement.

Further, with the depth of cut these things pull, it makes sense to support the sides with a full circle rim. Spurs would probably wear too rapidly in actual harvester use & jam the chain.
OTOH, at my age, will probably only rip a few more logs and store the saw again.

I'd be happy to make a full circle rim - easier than spurs by a lot. Just have to get comfortable the chain won't runoff with the bar set horizontal.

 

[Aviacs]

How important are the clean-out reliefs in the side of a full circle sprocket?

Thought i was settled on full circle/rim support sprocket.
Still would need to make it myself, for reasons shown including rivet spacing..
However, big issue is sawdust clean-outs at base of sprocket..

Clutch is outboard of chain, so the only exit for packed sawdust in such a sprocket would be to dump sidways out the thin flange, against the frame of the saw.

Seems like this might have to be a spur sprocket, to avoid sawdust packing.
Or is that not a problem?????

 

[Aviacs]

Decided that due to possible issues with shedding compacted sawdust in a full circle drive in this app, that an open sprocket is a safer way to go.
Though it might not be as durable. Then again, how many more logs will i saw in play mode?

Been pecking away at the low hanging fruit.
Trepanned out the clutch back to save the center for measuring and reference, then bored the rest, drilled & pressed out the rivets through the rim, and pressed the remaining ring out.
Made new blank for back, and for inside flange.

Mocked up sprocket in Al to test profile and dimensions. It needs loosened up a little bit, and the radius at the back of the tooth should be greater.
Real sprocket will be A7 and then heat treated. It's too expensive to test with. Or i should say the cutting charge and shipping on small pieces is about 3x the material cost, so using what is here and hope not to have to order more.



The back was made about .003 larger than the rim (.001"/in. dia) and pressed together with loctite.





Oddly, the old rim rivets were totally random, and 2 on one side nearly together, 2 others spaced widely but randomly elsewhere. At least they were radial so drilling them did not require weird angles.
I added one new rivet (5 total) where a couple of the old ones were quite far apart.


Nailing it together.



After cleaning up the rivets on the lathe. First knocked the excess length off and peened, as per original, then turned flush with basket OD.

 

[Aviacs]

Here's one more of sprocket shape.
Again, this is just a test for dimensions.
Needs some tweaking, and OD needs to be about .015 dia smaller.


smt

 

[Aviacs]

Had to take a break for finish to dry on my furniture project, so worked on the sprocket today.



It's ready for heat treat; ran out of time tonight.
There is oversize allowance on ID & OD & thickness for grinding, in case of minor distortion.
Photo tells me the boring bar withdrawal scratch ought to be polished out first.

smt

 

[toadman]

Had to take a break for finish to dry on my furniture project, so worked on the sprocket today.

View attachment 831647View attachment 831648View attachment 831650

It's ready for heat treat; ran out of time tonight.
There is oversize allowance on ID & OD & thickness for grinding, in case of minor distortion.
Photo tells me the boring bar withdrawal scratch ought to be polished out first.

smt

Beautiful...

 

[Aviacs]

Thanks!

Fingers crossed for a "stress free" heat treat.....

 

[Aviacs]

Reverse designing stuff does have its pitfalls.
I probably erred on the side of conservative with heat treat.
On one hand, "very hard" is desirable.
On the other hand, non-distortion or size change during heat treat, and maximum toughness in use are preferable. Especially with complex thin sections with lots of potential stress risers.
Anyway, this seems plenty tough, (or at least used the most conservative heat treat profile) however. Probably did not attain much over Rc55 if that. Plenty hard for hobby use, would have preferred more.

first photo, right out of heat treat




grinding the OD




Grind ID:

 

[Aviacs]

More or less finished up.
Need to wait for a new bearing which i neglected to order until today. Also, have no one to help on the other end when saw is completed, so not sure what the next step is.
Not getting a strong sense this is interesting. However, hopefully, documentation will help the next person as a possible option to replace 3/4 pitch chain as it becomes less & less available in safe condition. Of course that is not really known until the assembled saw can be tested.

The pair of 1/4" - 20 threaded holes in face of clutch, outside the sprocket drive circle, are for pulling the clutch, as per original.
The dowel holes are reduced so they cannot work into the clutch (inside) but the reduced hole was made through, so they pins could be pressed/punched out if necessary.
Regretfully, I forgot that the thin flange was to be reduced on the side closest to the saw frame casting. I did leave the dowel holes stepped to prevent working through. Too late realized that the .112 step cut that part off. Will have to use loctite on at least one end of the dowels. Or punch over the flange. Or both.

To make another sprocket, i would probably use A8.
It has very good toughness, is stable in heat treat, gets harder and has intrinsically more wear resistance than S7
That said, using S7 for all it's toughness and shock resistance is not really a choice i regret for a first prototype. Will be interesting to see how it wears.

 

[cbfarmall]

Outstanding.

 

[Aviacs]

Thanks, cbfarmall!
Your drawing was key to getting this project underway.

smt

 

[ML12]

This is incredible. Thanks for posting all the photos. Your machine work is great!

 

[Aviacs]

In case anyone wonders, saw has been back together for a week.
It was always hard to start, but ran fine before the machine work began.
Since, can't get it to fire at all. I know - nothing really changed except the clutch and chain.

Anyone have a tutorial on how to remove the magneto? Manual states it can be done, leaving the rotary center part in the block. IOW, remove the magneto case from around it?
No pix, no clear instructions in the book.

Advice so far is "magnets might be weak",
or "needs new coil."

I timed it by removing the coil wire, since no change in continuity occurs, points open or closed, with it in place.
However, with bent wires in the plug wire sockets, there is a weak blue spark to ground over about 1/16 to 1/8" gap.
With plug wires in place and connected to spark plugs laying on top of cylinders, weak orange-reddish spark.

Knowledgeable advice welcome.

smt

 

[cbfarmall]

I'm not much help here, only have the section from the tech manual and the IPL image.

One day I want to get back into by KB7 and completely restore it. I changed the transmission seal and stopped the motor from sucking oil in but it isn't perfect.

 

[cbfarmall]

Regarding your weak spark, always start with cleaning the points. Next most common thing is a failed condenser and they can behave in all sorts of weird ways. It could be the coil depending on the condition of the insulation. The old lacquer coatings will badly deteriorate over time. You may be able to press the core lamination out of the old coil and sub in a new one. I don't know where the magnets are on these, maybe in the rotor but you can check that with a screwdriver, I suppose. They can be re-magnetized. If this were a tractor magneto, you'd need to check the impulse mechanism but I don't believe these saws use those.

Chris B.