Torque monster(?)

[treedragon]

Okay here I go, bound to stir some responses on this one............... :-)

I have previously mentioned my friend the bike engineer/whiz/Ducati specialist, highly biased towards XZ 550 motor but has nothing nice to say about the bike, friend of mine........... and one of his tuned XZ’s that I rode. It was a torque monster, (ahem..... relatively speaking for a 550 and compared to a standard unit).  Well I have been slowly weaseling out of him what he had done to it, bear with me on all this because I am extracting info at a glacial pace as the only time we get to talk is late at night when he is freed up a little........

Fact: first off the bike sounded different, something I had put down to the obviously home made exhaust. Well that’s a judgment I know but it looked home made to me and wasn’t one my friend had made, but the noise said freer..........
Fact: what he had done was change the timing, via the cams, so that it was as near as possible to firing as a single.

“Bang bang” to quote him, he had also junked the flapper valve in the airbox, and retuned the carbs.

I AM going to have this done to my bike, I will report when it’s done, but don’t hold your breath I need to find the funds for a new exhaust first.

My subjective view of how that machine went may be pertinent here  ;D
The relatively short time I used it was two up riding with the combined weights being getting towards the weight of the bike, ( oooohhh  I’m dead if “She reads this”) and yet it performed just like I would expect a modern grunty mid range bike to perform. You opened the tap and it went. Now at the time I never gave it a second thought as I had come off a tweaked FZ1000 and relatively speaking it was great, it wasn’t until I got on a standard model ie: my current bike, that I appreciated how well the other went.

My pillion who is a motorcycle illiterate made the comment “Doesn’t go as well as the other one...” and “But I’m glad you got this one because you could hardly pull up outside a restaurant on that other............... scraggly looking thing”.

[Extent]

I'm fairly certain that the cam thing is called twingle, and Tdub had that going on for the vision flat track racer a while ago.  You should be able to search up some of his discussion on it.  Or maybe he said Big Bang, but that I usually hear associated with I4s, I suppose the effect is similar.

[Superfly]

I twingled my eninge once.  It was ok, soundeded way different, but I eventually went back to the stock setting.

[williamruck]

so what would be the advantage of "twingling" my engine?

[Walt_M.]

None! The firing alterations are to improve rear tire traction under racing conditions. It would likely have no effect on a Vision and would probably reduce engine performance slightly.

[treedragon]

Twingling refers to a two stoke engine with two pistons, one for inlet and one for exhaust but sharing a common combustion chamber and sparkplug as I understand it.......

The bike I am referring to just had the cam timing adjusted so that the two cylinders fired as near as possible to a big bang scenario. It was part of a package that included free flowing exhausts, (standard headers), an opened up airbox with a tuned standard carb (no stumble), done by a pernickety specialist in this sort of thing. I am not aware of anything else done to it but haven't confirmed that yet. I have only ridden that one bike tuned in this way and two up (read heavy) it easily matched or out performed my current bike one up. Chalk and cheese as they say.

It was particularly spectacular (relatively speaking), pulling out of corners and appeared to have more top end but as it wasn't my bike so I didn't "enquire into the matter".  ;D
When I rode it with a view to buying it had been like this for many thousands of kilometers completely hassle free. The bike itself was a dog to look at so I hesitated I'm pleased to say as it was the disapointment on my face that prompted my friend to find me this bike.

Obviously the timing itself is only part of the story so what I am thinking is that before replace the exhaust I will have the timing redone just to see..........
Results will be very seat of the pants I know but none the less I will be able to give some feedback.

[Rick G]

The two stroke your refering to is the Puch (Allstate) twin piston single . The pistons were in line with the bike , not side by side.  The intake ports and transfer ports were controlled by the rear piston , the exhaust  by the front piston. The rear connecting rod was attached to  a journel  on the back of the front rod . Both pistons arrived at top and bottom dead center togeather , but the exhaust  and transfer/intake timing was staggered. They were trying to get the same effect as an expansion chamber , long before that theory was known. One side effect of this type of engine,  was the vibration, which had to be experenced to be believed!!  I  had a '56  "Gelandesport" 250cc , which had won the Catalina Grand Prix that year. It had two carbs, one on each side and if you opened the throttle when the engine was at rest , top dead center, you could see all the way through the engine and out the other side!

There were a few triumph  500 twins at Ascot in Gardena CA.  that  had the valve timing set so that both cylinders fired togeather, in an attempt to duplicate the success of the BSA Gold Star. Must not have worked that well , as it did not catch on.

[arfa vmax]

rootes motor group made a 2 stroke supercharged diesel engine called the ts3.It had 3 cylinders horizontaly aranged like a bmw k engine.The crank ran below the cylinders with con rods connected to rockers at the ends of each cylinder.Another set of rods connected to 2 pistons per cylinder,the pistons came in from the ends of the cylinders and met in the middle so no cylinder head,the inlet and exhaust ports were opened and closed by the pistons.Low pressure super charger was used to help scavenge the inlet.The exhaust had to be in tip top condition and the manifold had to be removed regularly to decoke the ports,this extra work made it unpopular.

[jasonm.]

some call it harley tuning. Meaning the front and rear intake and exhaust timing are the same with the only difference being the degree of the "V". In this case 70 degrees. So you get a power stroke on the rear cylinder followed 70 degrees later by the front cylinder. Which in real time is not that far apart.  ONE BIG negative...this can cause some increased vibes and possibly limit high rpm power.  TO do it ...you retime the cams and possibly the trigger on the flywheel .

[Rick G]

The Roots engine sounds much like a Fairbanks Morse Opposed piston Diesel. It had a crank on the bottom and on the top, so that a 6 cylinder was actually a 12 cylinder engine . They were used in submarines and other marine applications during WW2 and were tried in Railroad applications in the 50's . They had cooling problems, when the were no longer using the ocean as a cooling source. That and the Westinghouse electricals doomed them. The railroad OP engines were rebuilt and put into marine service.

[williamruck]

like a Fairbanks Morse Opposed piston Diesel

Dude, the Fairbanks headquarters is in my home town. Beloit, Wisconsin. But anyways, I digress, back to the topic at hand . . .

[Rick G]

Beloit , heaven to the FM OP fan. But I digress too ! So what's new ! ;D

[pullshocks]

In the latest Cycleworld mag the always interesting "TDC" collumn, mentions something about altered timing

"In 1992 when two-stroke 500cc GP engines were given traction-boosting close firing order (firing all four cylinders within 70-90 degrees, letting tire grip recover for the remaining 3/4 of a revolution), lots of teams had to resort to changing primary gears every day.  Otherwise they broke unpredictably from the higher peak toque loadings.  The parts that have been removed in such programs look perfect, but their stress history makes them untrustworthy.  The more cyclic loads resemble impacts, the more metal resents it.