Tom's McCulloch BP-1

heimannm

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And the carburetor all together.

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In truth, I spent several hours on the carburetor today; I do like to pressure test a carburetor before installing them on a saw and this one leaked badly. My first attempt at the fix was to remove the seat body (again) and flip the rubber seat over and polish up the tip of the needle.

Still would not hold pressure...get out the spray bottle with soapy water and I found that the gasket between the primer and the fuel pump body was leaking badly. I took it all apart again and cleaned, cleaned, cleaned the surfaces, even resorting to flattening them on a granite plate with some emery cloth and despite all of my efforts is still leaked. I had another (used) primer on hand so I tried that one, still leaked...replaced the fuel pump diaphragm set and the primer gasket, still leaked...

Although it is against my principles, I was getting desperate at this point so I applied a very thin film of three bond on the primer gasket and low and behold, it held pressure.

There is an old, old thread over on AS about velocity stacks, air flow, velocity and pressure...reason I bring it up here is have a look at the throat on this carburetor, 15/16" bore.

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However, there is a "diffuser" installed in the inlet of the carburetor that reduces the opening by 50 or 60%???

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I have a spare diffuser on hand, just thought it might help to visualize if I threw it in this photo.

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Bottom line, the saw was running by the end of the day.

Mark
 

heimannm

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Randy - I have only seen maybe 7 BP-1 saws in person; my saw, AWOL's, James Shimniok (Baraboo), one in Indiana (ex McCulloch dealer), two that MWEBA and his buddy had, and this one. 5 of the 7 were definitely working saws that had run and cut a lot.

I have seen 4 or 5 Dolmar KMS4 saws, none appeared to have been run long or hard.

I have seen perhaps 5 or 6 Echo Twin saws, none looked like they had done a lot of work.

I have only seen two Solo Twins, both appeared to have been well used.

Point of this? The guys that had the BP-1 saws (and the Solo Twin) tended to use them and the saws were able to keep on going and going, and going...

Thanks Ross - I had to take some time off work this week to try and decompress a bit, time it the shop is a good prescription for that.

Mark
 

exSW

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Randy - I have only seen maybe 7 BP-1 saws in person; my saw, AWOL's, James Shimniok (Baraboo), one in Indiana (ex McCulloch dealer), two that MWEBA and his buddy had, and this one. 5 of the 7 were definitely working saws that had run and cut a lot.

I have seen 4 or 5 Dolmar KMS4 saws, none appeared to have been run long or hard.

I have seen perhaps 5 or 6 Echo Twin saws, none looked like they had done a lot of work.

I have only seen two Solo Twins, both appeared to have been well used.

Point of this? The guys that had the BP-1 saws (and the Solo Twin) tended to use them and the saws were able to keep on going and going, and going...

Thanks Ross - I had to take some time off work this week to try and decompress a bit, time it the shop is a good prescription for that.

Mark
I'm starting 16 days of decompression today.
 

heimannm

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The finished work.

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I was looking through the BP-1manuals and service bulletins today hoping to find some additional information on the carburetor but I didn't find anything more.

I did see an interesting note regarding the Auto Mac self sharpening chain. The rim of the grinding wheel was intended to contact the clutch drum to spin the wheel, you could tell if it was working properly by examining the pattern the wheel left on the cutting teeth of the chain.

A few observations on the BP-1. Although it was a short production run saw, my best memory says it was around 9 months, there were many changes and improvements made along the short way.

Mine has pinned rings, this one does not have location pins for the rings.

Mine has a vented fuel cap, this one has a non vented fuel cap and a vent built in to the tank.

This one has the improved stop switch with the plate attached to the dust shield, mine has the original design with a very small target for the contact.

Mine has the later "improved" throttle shaft with a positive stop, this one relies on the throttle butterfly contacting the diffuser in the throat of the carburetor to stop it in the wide open position.

I saw in the service bulletins that they redesigned the points cover from the round plastic version to a magnesium model with a flat top to provide more clearance for heavy gloves.

Progress, always progress with McCulloch.

Mark
 

heimannm

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How about two of a kind? Mine is currently equipped with the original Auto Mac self sharpening chain and a sprocket nose bar, I am pretty sure it is 1/2" pitch although Acres site calls it 9/16". Even though it is 1/2" pitch, the drivers are much smaller than other 1/2" pitch chain so you must have the special straight bore rime type sprocket to run it.

Both of these bars are have the "Speed Mac" feature with the oil channel directed to the nose of the bar rather that dumping in the top groove as per conventional bars.

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I set this one up with .404 chain since I don't have any 3/8" straight bore sprockets to fit the output shaft of the gearbox. If you work on many gear drive McCulloch saws, you need to make one of these handy gadgets to lock the sprocket when loosening or tightening the nut to change the sprocket.

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I cannot take credit for this device, I saw it in one of the McCulloch Service Bulletins a long while back.

Mark
 

heimannm

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BP-1 brochure showing the oil channels to the nose of the bar along with the other features, balance piston, self sharpening chain, etc..

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Warped5

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Mark, I'm enjoying this thread immensely.


..... but don't you think it's time for a bit of sleep?
 

awol

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Don't think I could bring myself to give 2750 for 346xp, but Id give 2750 for a NOS BP-1 in a heartbeat!
 

cat-face timber

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Mark,

I wanted to thank you for making this thread.
Your work is just amazing.
I love seeing a man that knows his stuff, use his knowledge.
WOW just WOW.

You kind sir have risen the bar on saw knowledge.

Thanks again!
 

heimannm

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This is one way we can all learn more about the things we are interested in.

I will add something on the gearbox and oiler once we are home again.

Mark
 

jacob j.

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IIRC, a 120cc McCulloch 77 gear drive was over $500 in 1957. That's a lotta loot...

I believe the last sales price on the 090AV at the local shop was around $1400 in the mid 80's with a 42" bar. A local ranch owner (Roger Hardy- Hardy Cattle Company) got the very last one. He still has it today and runs it on aviation gas. I guess if you want big iron you gotta pay big money.
 

heimannm

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Next up - the gearbox. I borrowed the next two photos from MWEBA, the engine with the gearbox attached. See how the clamp that holds the gearbox to the engine also has a locating tab to properly position the gearbox.

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The automatic oiler is a plunger in the end of the output shaft so the oiler only pumps when the chain is moving.

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I don't know how well is shows up but the hole in the shaft is slightly off center so that as the shaft rotates the plunger is worked back and forth against an adjustable swash plate.

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That shaft has a flat milled on it to form the swash plate, and can be rotated slightly with a thumb operated linkage. When the shaft rotates as the angle of the swash plate in increased the stroke of the pump plunger and so the output of the oiler increases with each revolution.

Mark
 

heimannm

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The clutch drum is connected directly to the pinion gear in the set. The opening in the side of the gear case exposing the clutch drum has a purpose...the grinding wheel was to be adjusted to just contact the drum and spin the wheel to grind the top chain.

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The red circle encloses the adjuster used to position the grinding wheel just right to spin it without wearing the clutch drum or rim of the grinding wheel too much.

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Here is a view of the original style Auto Mac self sharpening chain.

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Mark
 
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