360 to 180 degree crank

[G-Man]

Steve

My buddy had a CD175 which definitely had a 360 crank. He ran it on open meggas and it sounded unbelievable and could be heard for miles. My brother's CB250K0 also had meggas and sounded pretty nice as a 180 motor.

My Guzzi V twin gets the best of both worlds by having a cool sound and a perfectly (almost) balanced motor with the 90 degree angle.

G

Sound was very important. I remember back in the early 1970s my friend Alans CB160 sounded quite powerful for its size. It was a very cool bike. He had a single seat, a sissy bar and a Captain America tank. So did snotty Gregs SL175, thinking back on how it sounded it must of also had a 360 crank. Having only owned singles up to that point I didn't know about type 1 verses type 2 motors. I knew Ralphies 305 Scrambler sounded flat out mean, but I thought that was due to its straight pipes. I think this is kind of funny, but until I got into restoring old Hondas I didn't even know Scramblers came with a muffler. The owners must of removed them as soon as they got them home.

[Steverino]

Snuff-or-Nots were manufactured here in Oregon. They were very popular out here, but maybe there were makers of similar devices everywhere.
Snuff-or-Not Ad by stevesteverinomeister, on Flickr

[teazer]

Get your hands on a copy of the factory service manual and it shows more power and higher revs from the 180 crank versus the 360 degree crank - with the same cams.

Think of it as being the first approach at a crossplane crankshaft (R1) or Big bang race motor.

It just works.

[G-Man]

Teazer

Nice to hear from you. Both cranks are still flat plane with no advantage from inertia optimisation, like the R1, so still difficult to fathom.

The pistons are still speeding up and slowing down at the same parts of the stroke whether they are going in opposite directions or not. Maybe the 270 crank engine is the answer.....

I can understand the different 'feel' of the engines leading to different performance on the road. The better primary balance and 'lazier' exhaust note of the 180 will encourage higher revs, as well.

G

[teazer]

I remember trying to rationalize it years ago and decided that why it works is less important than the fact that it works.

One could always build a twingle and fire both at the same time with a 360 crank - just to be different.

I have a CL175 sloper motor here that the crank has been re-phased from 360 to 180 and of course the cam needed a little twisting to get all the bits to work at the same time. Those small motors really do not like to rev and peak at about 10,000 even with a hot cam.

I'm looking for 30 HP and 12,000 plus but for that it needs different pistons and better control of the cam chain. and a few other small mods.

[G-Man]

Teazer

I can never resolve why those little engines have such long inlet tracts compared with a CB72 engine. The single carb heads have very short inlets and the twin carb versions have giant inlet spacers. Have you done something different on yours?

G

[pcmenten]

The reason for the 180 vs 360 crankshaft is the head and the carb(s).

Although I'm new to these bikes, I think figured that one out. If the engine had a 180 crank and a single carburetor, the carb would see two pulses of air, one at 0 degrees and the next at 180 degrees, followed by a long pause at 360 degrees and 540 degrees. That ragged firing order would probably cause significant problems with metering air/fuel for a single carb feeding two cylinders.

When they went to a more open framed bike, they could fit two carburetors, one for each cylinder, and could balance the crankshaft. I don't think you can fit the two-carb head to the Dream because the carburetors will foul the bike's frame.

I also suspect that the Dream engine feels smoother at lower RPMs with the 360 firing order; bang-pause-bang-pause for the 360 vs. bang-bang-pause-pause for the 180. At higher RPMs the needs of mechanically balancing the engine becomes more important. The forces increase at the square of the speed, so the higher performance, high RPM bikes get a 180 crank and dual carbs.