Rephasing, What is it?

Good Luck in your dyno testing! It's all about changing the reciprocating masses at their maximum velocity points in assisting the opposing mass through it's cycle. Sorta like a see-saw balance effect,which in effect lowers the stress loads on the bottom end, vibration, allows much higher than normal RPMs and quicker engine response. Go to Britbike.com for some thorough discussions on this exact topic.

If we a starting a book on this put me down for 20 bucks that a rephase alone will produce ZERO increase in torque.

The seat of the pants is a known pathological liar.
 
Actually, I think you're both right. The engine doesn't produce more power: thermodynamically, it can't. BUT, more power gets to road because you're not pumping that energy into the vibration of the bike. So, the engine isn't more powerful in a thermodynamic sense, but since you've just improved the mechanical efficiency, you do get a lot more out.

you know, you might be on to something there, though a "lot" seems to be a stretch.
 
It should have the exact same rhythm as a 90 degree twin like a Ducati.

Rephased XS:
90 degree difference between crank pins
0 degree difference between cylinder angles

Ducati:
0 degree difference between crank pins (one pin)
90 degree difference between cylinder angles

Either way the two pistons are 90 degrees out of phase so you get the 270,540,270,540... firing interval.
 
It should have the exact same rhythm as a 90 degree twin like a Ducati.

Rephased XS:
90 degree difference between crank pins
0 degree difference between cylinder angles

Ducati:
0 degree difference between crank pins (one pin)
90 degree difference between cylinder angles

Either way the two pistons are 90 degrees out of phase so you get the 270,540,270,540... firing interval.


There are lots of crank throw angles used by various V-twins of course. The ducati 90 degree configuration is sometimes called an "L twin" since one jug is almost horizontal.

The re-phased XS motor sounds like a duck but doesn't always walk like a duck.

Because the splines on the crankhalves of the XS650 do not allow for an exact counter match of the crank throws most rephases set the throws at 277 degrees I believe. With more machine shop work you can bet 270, but most are of the opinion that the benefits do not justify the expense.
 

I don't know who ported yours heads but those exhaust ports volumes still appear to on the high side and the turns in the roof weren't addressed at all either,you can loose about 15 to 20CFM's just alone in the roof,not to mention lost velocity. ( you do not want to knife edge the guide boss, as it creates resistance that'll cause turbulence at that area) Don't mean to be a critic,just trying to pass along some valuable information.
 
The guy that ported it, has a pretty good handle on crappy ports. He's been making Harley s go fast for some time now.

Thanks for the input, appreciate hearing your opinion.
 
A Harley mechanic would not know about the XS650 Head unless he had owned one, (Even then 90% of XS650 owners don't know), or was involved in some XS650 Racing.

Some heads were cast so bad the ports have to be rebuilt to be able to rework them for improvments.

Do some research yourself on the topic and you may be surprised
 
Yeah, mine was cast quite bad. We put a good 3/8" of weld on the one side and an 1/8th or so on the other side of each port to fix the core shift. The port is now significantly smaller.

Keep watching the blog, we'll get it on the dynojet when its ready and we'll see if the "Harley mechanic" knows anything about air flow.

I have done a fair bit of research and Michael Morse provided us with a good bit of info from the XS650 - 750 engine modification guide. I think Jerry Branch, Shell and Lillie amongst others had some good success in the early years and most of that is written in this guide. If you don't have it, I highly reccomend contacting Michael and seeing about getting a copy.
 
Yeah, mine was cast quite bad. We put a good 3/8" of weld on the one side and an 1/8th or so on the other side of each port to fix the core shift. The port is now significantly smaller.

Keep watching the blog, we'll get it on the dynojet when its ready and we'll see if the "Harley mechanic" knows anything about air flow.

I have done a fair bit of research and Michael Morse provided us with a good bit of info from the XS650 - 750 engine modification guide. I think Jerry Branch, Shell and Lillie amongst others had some good success in the early years and most of that is written in this guide. If you don't have it, I highly reccomend contacting Michael and seeing about getting a copy.

Trust me when I say this, your head and the lilly head have nothing in common when it comes to yielding power and combustion efficiency. The key areas of the exhaust port is the roof and applying art work rather than addressing the ports issues is another thing when it comes abstracting power. The exhaust flow ratios needs to be kept in check when running extreme high lefts or over scavenging can become an issue,simply put you let the cam do the work,one area where the Lilly head was tuned for and the flow ratio was very low in comparison to my high velocity E/P's flow ratio but my ports are flow tuned to my cam,was your head ported to the cam?,mostly likely ported to resemble art because looks is what produces power like open headers:laugh: hope the pull produces positive results
 
I no longer disclose any photos of my exhaust port work to strangers cuz I have to much time and money invested for someone to copy my work. Don't be afraid to open the port volumes as choking can be just as harmful limiting any gain,you'd gasp at my E/P volumes but I get the results Im have after with proper balance of cfm's and increased velocity. My flow ratios average around 80 to 88% but these figures are based around using a reverse pattern cam and CR500 rods
 
I have a quick question on the crank phase of the rephase process. I went ahead and pressed apart my crank and moved the center pin three splines forward for a 277 degree setup. My question comes with a picture I drew to illustrate what I'm talking about.

Imagine the crank pin is facing you on the right hand flywheel. Two dots on the right is the starting point and the dot on spline #1 ended up on #3. Is this right for the three spline move? I put in an e-mail to Hugh at Hughs Hand Built last Sunday, but have got no reply. So I turn it over to all you knowlagable folks.

IMG_0306_zpsae489942.jpg


Here is the finished crank. It looks right from pictures I can find on the internet. But I have doubts I didn't go far enough.

IMG_0305_zpsccf63639.jpg
 
Right leads left by 3 splines, have you moved it 2 or 3 splines..? It should almost be a 90deg angle between the 2 crankpins.
 
^^^^^^^^
Yes, right leads left. But do I move the spline marked three forward counting the original position as one, or three splines forward not counting the original position? If it's the later, I need to go one more spline. If the former, then I'm alright.

I'm of the opinion I need to go one more spline. Just eye balling the rods extended straight out with a degree wheel, it looks like 69.5 degrees or so. I think I need one more spline to get the 83 degrees. Just looking for confirmation.

Hoping Hugh would speak up here since he is the guru. I went through his original post on 4x4.com, but it looks like he deleted some crucial pictures I remembered seeing.
 
Curious -why.? To compensate for In~ex flow differences.? or for high RPM work.?

In stock form and when ported,the exhaust port can exhibit flow ratios in the mid to high 80 % from lift ranges .100 to .400 given ideal conditions,on my proto D port head,I had near 100% from .100 to .200 which could lead to over scavenging. The 256 cam with it's reverse pattern cushion limits the duration time the valve stays off the seat allowing me to push the ratio a bit higher for my long rod motor without fear of O/S or power dropping off,at least that's what I'm hoping for.
 
OK thanks.

In stock form and when ported,the exhaust port can exhibit flow ratios in the mid to high 80 % from lift ranges .100 to .400 given ideal conditions,on my proto D port head,I had near 100% from .100 to .200 which could lead to over scavenging. The 256 cam with it's reverse pattern cushion limits the duration time the valve stays off the seat allowing me to push the ratio a bit higher for my long rod motor without fear of O/S or power dropping off,at least that's what I'm hoping for.
 
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