McCulloch BP-1 update

[catskinr]

Since I last wrote, I have gotten in alittle deeper than I had expected. While trying to get some spark out of the BP-1, I noticed that the engine began to lock up. It acted like it had something on top of a piston. A flashlight showed that the problem was deeper, so I proceeded to disembowel the sucker. The trouble turned out to be some sawdust that somehow entered through the muffler and made its way to the main bearings. I have flushed everything out with carb cleaner, and the bearings seem to be o.k. as they are smooth and quiet. I'm going to try to get it back together in the next week or so, then it's back to fixing the no spark situation. I took some pictures last night, I thought you might want to see what a BP-1 looks like inside.

Crank, Rods, Power piston (large), Balance piston (small), clutch, and flywheel:

 

[catskinr]

More BP-1 pics

Take a gander at the penny in the Carb throat. Remember, this is a 40 some cc saw built in 1963...

 

[catskinr]

More BP-1 Pics

The balance cylinder is mounted in the bottom of the saw, in fact you can see the housing around it from the bottom of the saw.

 

[catskinr]

More BP-1 pics

The power cylinder is not real special, Exhaust port looks a little small to me, but it will do.

 

[vw_motorsports]

Very cool

 

[Duke Thieroff]

Have you looked over at the McCulloch thread?


Mark over there just came across a BP1, what a cool saw.


CT

 

[funky sawman]

cool picts, I was always wondering what one looked like inside. Now if I can figure out how they work??

 

[Eccentric]

R. P. McCulloch was an eccentric genius. Some of his stuff worked brilliantly.......while others didn't quite make it. Those BP-1's are the "Holy Grail" of McCulloch collecting for good reason. Thanks for posting the pics.

 

[vw_motorsports]

When I need old vintage parts I go visit this old timer....he actually has one of the macs that has a battery operated starter...he showed it to me..the batteries are in the handle. I think built off the 10-10 chassis, I think that was the golden age of saws, because you would see so many really different designs.

 

[heimannm]

Thanks for posting catskinr, the BP-1 is one very interesting and unique saw indeed.

I picked up a well used unit a couple of weeks ago and haven't had a chance to do much with it yet. No spark when I got it but a simple cleaning of the points and spark was good. Low compression but I can get a pop if I prime it. I did find a set of rings as well as a few other items I was looking for. Check with Sherwood at Discount Marine as he has perhaps 15-20 part numbers for the BP-1 in stock including the fuel pump diaphrams for the carburetor.

Here's a photo of mine just the way I found it.

As I noted, this saw did get a lot of use, I guess that makes it that much more attractive to me.

vwms - there were three different models with the electric start, 3-10E, 5-10E, and 10-10E. I have a 3-10E working complete with a new battery pack. I also have a 5-10E that runs but needs a good clean up. I don't think I'll go the route of batteries for this one, just too much to spend for something I will probably never use. I did have my 3-10E out for the Iowa GTG the first part of November. I was pleased to find that even after setting for a year, with a little time on the battery charger I could start it using the electric start.

Mark

 

[vw_motorsports]

I am not a collector by any stretch...I just try to constantly upgrade. But, I would love to have a BP-1. The engineering that it had for it's day is impressive. The old timer stated that the BP-1 could go to 18000rpms. Maybe that's when they exploded?

 

[Wildman1024]

The BP-1 is really cool and I hope to see one in person some say but did anyone notice this thread was from 2003 and brought back today??? Even the orginal poster has not been on since june ROFL.

Aaron looks like you been had again

 

[Eccentric]

The BP-1 is really cool and I hope to see one in person some say but did anyone notice this thread was from 2003 and brought back today??? Even the orginal poster has not been on since june ROFL.

Aaron looks like you been had again

Dammit! Gotta get my observation skills tuned up.:hmm3grin2orange:

 

[chainsawwhisperer]

cool picts, I was always wondering what one looked like inside. Now if I can figure out how they work??

It's really a simple concept, but you have to think outside the box that is "conventional 2-stroke engine design"
As the power piston moves up, the balance piston (B/P) moves down, creating a negative pressure in the crankcase(just like a conventional 2-stroke, just with an extra piston sharing the crankcase) When both pistons approch TDC the bottom of the balance piston (B/P) slides past the intake ports opening them, at that point negative crankcase pressure draws in a new fuel/air charge. Continuing it's rotation, the crankshaft brings the B/P back up toward BDC closing the intake ports. Intake ports closed, both pistons moving toward each other, a positive pressure is created. At the point that the spent F/A charge is nearly exhausted out the exhaust port, the upper piston slides past the transfer ports opening them. The positively pressurized
F/A charge in the crankcase is forced up into the upper cylinder.

The balance piston is weighted to counterbalance the upper piston.

One bonus to this is the extra crankcase pumping effect from the balance cylinder changing the volume of the crankcase.
This forces more F/A charge into the combustion chamber than would be possible with just one piston.
Hope this helps.
Jim

 

[cbfarmall]

did anyone notice this thread was from 2003 and brought back today

Not only that, but it is titled as an update thread. Somebody go dig up the original!

Chris B.

 

[chainsawwhisperer]

The BP-1 is really cool and I hope to see one in person some say but did anyone notice this thread was from 2003 and brought back today??? Even the orginal poster has not been on since june ROFL.
:

June of '09 that is!

 

[funky sawman]

The BP-1 is really cool and I hope to see one in person some say but did anyone notice this thread was from 2003 and brought back today??? Even the orginal poster has not been on since june ROFL.

Aaron looks like you been had again

holy crap, that is funny, I didn't even notice this was an old topic ROFL ROFL ROFL:hmm3grin2orange:

 

[chainsawwhisperer]

Not only that, but it is titled as an update thread. Somebody go dig up the original!

Chris B.

http://www.arboristsite.com/showthread.php?t=11080&highlight=

 

[chainsawwhisperer]

Yes this thread is back from the grave. LOL
But if you search for threads about the BP1, there really aren't too many.
So if info can be added to an existing thread, I'm all for it!
This is my non-runner...low compression, but I did score a NOS pair of rings!

 

[chainsawwhisperer]

I have a FB page with pics and info.
http://www.facebook.com/pages/McCul...alance-Piston-Chainsaw/155055017865555?v=wall