KZ750 "twingle"

Hi ! I am planning on having a set of cams for my 750 twin re grinded/modified so both intake and exhaust lobes are in the same position and not 180' apart. I know it has been done before but do anybody here have any experience with is KZ750 twin running as a double thumper ? I'm told these engines are strong but will it ruin the crank ?
Some talk about the extra load on the cam chain by having to open 2 valves at a time but I run standard springs so it won't be to bad I think. I'm not really interested in if you think I'm ruining what Kawasaki designed the bike to be but I am very much interested in experiences and pros and cons !

Simon, Denmark.

It has a counterbalancing system. I'd think vibration would be a major factor.
Steve

Structurally speaking the engine was not designed to function with both cylinders firing at the same time. I suspect there would be crankcase and crank stress issues, plus a significant increase in vibrational forces as well.

Oh yeah vibrations..... you think the added ignition and compression stroke will knock everything out of balancing ?
But I'm pretty sure it's done on these bikes before but I have no idea if they did anything o the bottom end.
I still think it would be fun to try that kind of torque but I do like the bike and do not want to blow it up. I own a Yamaha SR500 so I am not afraid of a little shake

I know you're looking for some feedback on the KZ750 specifically, but plenty of guys have done it with all manner of bikes - none of which were really designed for it.

I'm not saying I'd do it, or that it's even a good idea, but since the cam is the only thing you're changing, it shouldn't drastically throw off the engine balance or anything like that. I'd guess it would sound odd (maybe really cool), have a ton of torque, and probably shorten the life of your engine one way or another.

It was used in racing back in the 70's with the XS650 and some Brit bikes.
I've seen some dyno sheets of a XS650 "twinkle" and torque looked insane! The balance of the engine will remain the same yes. And I know nothing is free, the extra torque will be harder on the engine but it will not be as "high" reving as with the 360' cams....

Mk2Rookie wrote: ...... The balance of the engine will remain the same yes.....

Depends on what you consider "balance." The weight of the parts and their relationship to each other may remain the same, so if that is what you consider balance the statement is true. However, if you take into account the idea of having double the force driving the pistons down together and a longer interval between firings you may consider there are other factors involved when considering balance. Ed

650ed wrote:

Mk2Rookie wrote: ...... The balance of the engine will remain the same yes.....

Depends on what you consider "balance." The weight of the parts and their relationship to each other may remain the same, so if that is what you consider balance the statement is true. However, if you take into account the idea of having double the force driving the pistons down together and a longer interval between firings you may consider there are other factors involved when considering balance. Ed

Sure there is a difference in balance from the two firing orders and that is what I am worried about. But will it be too much?

I guess there's only one way to find out for sure. The good news is that as long as you keep a stock cam on the shelf the change can be fairly easily reversed if you find vibration to be a problem. Ed

thexscafedotcom.wordpress.com/2011/10/27/xs650-twingle/

No eBay APP ID and/or Cert ID defined in Kunena configurationIf the crank has opposing throws, it shouldn't be too bad. My 350 Honda had that. I suspect the KZ 750 does not thus the counterbalance mechanism. Some big "thumpers" have a compression release for startup.



Not sure how well it would work.
Steve

My Yamaha SR500 has a decompression lever but is not too bad to start without it. Can you explain more about why the balancing shafts will make it worse ?