Thought Exercise... Inline 4, double twin

Posted: Sun Apr 12, 2020 5:29 am

Just thinking out loud....

By just changing the cams (if such things were available), one could convert an inline 4 engine into a 'double twin' where 1 & 4 fired at the same time and 2 & 3 fired 360 degrees later. Maybe it would need a larger flywheel, and ???? Just wondering if anyone has ever heard of motor like that? Bet it would sound cool.

Posted: Sun Apr 12, 2020 7:24 am

Actually they don’t and will fire 180 deg apart so you would end up with a 180 -540 -180 - 540...... If you tried this on an F you would break cam chains in very short order due to the doubling of load across the entire range. The only way around this is an increase in chain size and spec similar to the Yamaha R1 cross plain (similar phasing) and this necessitates a different gear on the crank.
FYI this is very easy to do on my billet crank and I was considering this chain upgrade in the future.

Captain

Posted: Sun Apr 12, 2020 11:47 am

I would be interested in that as a future project

Posted: Sun Apr 12, 2020 3:01 pm

only 3rd hand info: have heard of folks flipping the cams on the honda VF 750 RC36 motor

Posted: Sun Apr 12, 2020 11:09 pm

What got me thinking of this was reading somewhere that someone made new cams for a parallel twin to turn it into a 'Twingle' (I know - not a real twingle).

Posted: Mon Apr 13, 2020 4:19 pm

What would be the advantage of making the bike a double twin?

Posted: Mon Apr 13, 2020 5:49 pm

Probably none otherwise somebody would have done it. Maybe more low end torque?

Posted: Mon Apr 13, 2020 5:58 pm

BlueThunder wrote:

What would be the advantage of making the bike a double twin?

If the result would be like the Yamaha R1, my understanding is the cross plane crank puts power down differently, in a way that allows the power strokes not to overwhelm the rear tire while accelerating.

I think the concept gained traction ( pun...yuk yuk)from flat track applications when putting power down on dirt is the difference in winning and losing.

Wasn’t aware the Honda Dohc engine had extensive wheelspin out of corners , that the cross plane crank offered substantial advantages for the trouble....maybe after you are 150+ hp?

Posted: Tue Apr 14, 2020 12:24 pm

On the CBX , the cams can be installed (by mistake) to actually do this and has been done due to a printing error in one of the FSM.

You'll get about 20 miles on the motor before the cam chain breaks then BAM all those tagged valves and broken guides.

Here's what a 4 cylinder might look like:

Posted: Wed Apr 15, 2020 8:57 pm

Holy shit. That's some printing error! How would one spot that they had a misprinted CBX FSM?

Posted: Thu Apr 16, 2020 11:59 am

PGSmick wrote:

Holy shit. That's some printing error! How would one spot that they had a misprinted CBX FSM?

You'd need to know what you're working on and recognize that something just isn't correct.