Upping the compression

oldkarkid · Posted: December 16, 2009, 9:33 pm Post subject: Upping the compression

I am looking to up the compression on my hammer to around 10-1 to 10.5-1 and possibly 11-1. The heads are already ported, I am running a performance cam, and I have a good exhaust. Just curious if I can get this accomplished by having the heads milled down a little bit. Any info is would be helpful, including how much to take off. Thanks fellas.

xsjohn · Posted: December 16, 2009, 9:54 pm Post subject: Re: Upping the compression

Popup pistons most likely to get that high..........but you will be sorry if you ride it much.........

xsjohn

dpmphoto · Posted: December 17, 2009, 12:30 am Post subject: Re: Upping the compression

I read somewhere in that xs650 manual the old yamaha tuners where selling that too much compression in the xs can actually hurt performance/power #'s. could this be true??

oldkarkid · Posted: December 17, 2009, 12:31 am Post subject: Re: Upping the compression

John, can you give any details?

xsjohn · Posted: December 17, 2009, 12:58 am Post subject: Re: Upping the compression

There are some wizzards on the garage site on that subject.....don't know how long that stuff lasts if that matters....I used to build all that when I worked for yamaha when it was necessary for racing.........but never chose that route for my bikes on the street.........I ride too many miles and the extra compression just causes to many problems.........heat ....broken parts......less longivity..........ratty running for cruise........engine "noises"......to list a few..........a bigger bike would be a better investment....then you would have 2.....many would dissagree I'm sure....

And there is something to be said for a nice ride without all that thrashing going on down below.......hate that............mine has absolutely none of that and I love it....all I hear is the exhaust after 75 thou...and I get home just as fast......

And I spent my time in the sh#t before I figured that one out myself too......I boutht a few hopped up pieces of crap too over the 45 years that shi# the bed......and drove me crazy.........don't waste your time........and money.......

xsjohn

oldkarkid · Posted: December 17, 2009, 1:45 am Post subject: Re: Upping the compression

xsjohn wrote:

a bigger bike would be a better investment....then you would have 2.....many would dissagree I'm sure....
xsjohn

Haha I actually have 3 bikes. I will use my Harley for eating up the interstate, and the Yamaha to get me to work in a hurry when I choose to push the snooze button on my alarm clock one too many times Embarassed

. I figured the 40 bucks the machine shop needs to do it wouldnt be too bad. Would 9-1 be a better range? Or just flat out not at all? Im mostly just curious, but I would like a little more juice, and I really dont mind the noise.

xsjohn · Posted: December 17, 2009, 1:59 am Post subject: Re: Upping the compression

Have you considered a diet..... Laughing

.. since food doesn't stick to me I can fly on a moped.......sh#t I hated 8.7-1 after all was said and done.....guess I shouldn't have got into this post.........think you would notice a bit of boost at 9-1......can lower the deck which most do ...20 thousands for that to get to 9-1....20 thousands shouldn't effect the cam timing much and it would be towards the retard which may even help the high end.....would loosen the cam chain though.....where as going any farther toward advance by raising the head to lower the compression you have to change the cam timing or it won't run right..........hope this helps....see grisld1 on the garage ......he knows all that hop up stuff on the xs's well as where I know how to trim them out for less vibes and thrashing for the long run........ .........xsjohn

oldkarkid · Posted: December 17, 2009, 9:20 am Post subject: Re: Upping the compression

hahaha! I am already skinny! Thanks for all of your input John. I wont be jumping into this right away so I may continue to tinker and research. I like the idea of 9-1 more than 10. but, who knows, i may continue to ride the pee out of it as is.

Srinath · Posted: December 17, 2009, 12:13 pm Post subject: Re: Upping the compression

For performance its actually more important to flow than compress.
It may help, but I'd almost bet flow first, displacement second (a distant second) and compression third.

Its possibly cheaper to get compression than displacement.

And you will need to cool the motor when you touch any of the above.

And on an xs you have to watch the vibration and ratcheting (thanks xsjohn).

He did it with an extra head gasket, a dimpling of piston skirts etc, but the other way to get that is to rephase the pistons so they both dont stop at the same time. I am going that route ... may also do a double head gasket and dimpling of pistons though.

And I've heard, just a rephase is supposed to let it run so much harder cos its not shaking itself it bits and ratcheting itself out ...

Cool.
Srinath.

xsjohn · Posted: December 17, 2009, 4:09 pm Post subject: Re: Upping the compression

My take is the bearings aren't stone tight in the bearing support (cases)......guess I could measure that.....

ay loose some bottom end torque with the rephase..........lowering compression requires the cam to be moved a bit .......I have been dimpling the pistons for 40 years....xsjohn

Srinath · Posted: December 17, 2009, 4:32 pm Post subject: Re: Upping the compression

I've never pulled a engine apart and put it back together - yet. But the mods for holding oil and there is a bunch of them, they do that with tappets, starter nose holes in virago outer cases which actually are best fitted with teflon bronze oil light bushings and others.

I'll check if the bearings are tight in the cases.

BTW I totally made a mistake on the 6306 bearing, that is the outer most one, that is the one you like to replace. Not the inside ones.

I may replace the inside ones if its inexpensive. I am getting it all welded. The $$ is adding up, I think I would have 50-60 bucks by the time its rephased, and that not even counting gaskets and what not.

Now I can see if we took out rotating weight how it will lose torque.

I am only making one piston stop and reverse direction at one time. I dont see how it would lose low end.

As you've noted, a stock XS spends most of its energy trying to shake itself to bits. Ratcheting is an indication that its not got enough power to get out of its own way ... it wants to stall all by itself. Lower compression is one way to reduce ratcheting yes. Its pushing a less heavy load ... but when one piston is pushing the load the other is flying at a good clip is the theory behind rephasing.

I will fit it back together, invent the ignition system for it (thinking of a crank fired 2 coil system ... by cannibalising a 4 cyl yamaha's vital parts.

Lets see.

Cool.
Srinath.

xsjohn · Posted: December 17, 2009, 4:43 pm Post subject: Re: Upping the compression

Think....not sure......the 360 may have exhaust on one side and compresson the other....rephase may have some compress and fire happening at the same time.....if so that would hurt low end..?....surely someone that is into this would know for sure......you never commented of 2 magnets on TCI.....sometimes neat stuff happens if dicked with..if so I would dig the existing magnet out annd use 2 small magnets of the same strength measured and glued in....like I said we know that a magnet can be glued into an old rotor for tci already found that works......

xsjohn

dpmphoto · Posted: December 17, 2009, 4:53 pm Post subject: Re: Upping the compression

I would just port the thing properly,buy a decent cam, get the best free flowing exhaust you can 1 5/8 for 650,throw on a good oil cooler system and spend hours tuning it.I have owned several xs's but I have never strapped a 750 on it or gone with high performance pistons et unless I was building it for someone else, it's just not worth it unless the xs is your bike of choice for vintage racing. These bikes are 30 something years old and running it hot will just keep your fingers greasy and your wallet empty. It's much easier to go buy a rd or an sr and build some crazy pipes with big expansion chambers and what not and go screaming down the road on that.Or buy a cb 750 throw some 1000 pipes on that and the rest of the goodies.A wicked hot xs650 or 750 is good for a few things, selling it,riding to bike night,going to buy a pack of smokes,or racing it on the weekends then tearing it down for next week.Listen to john he knows his stuff

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

I have thought about the pick up on the TCI for a rephase.

Surely if another pickup was put on the stator at the correct position then it could have a separate circuit, same principal as the points set up for rephase here www.650motorcycles.com/277ign.html

replacing one bearing would be like replacing one piston

Srinath · Posted: December 17, 2009, 5:12 pm Post subject: Re: Upping the compression

xsjohn wrote:

Think....not sure......the 360 may have exhaust on one side and compresson the other....rephase may have some compress and fire happening at the same time.....if so that would hurt low end..?....surely someone that is into this would know for sure......you never commented of 2 magnets on TCI.....sometimes neat stuff happens if dicked with..if so I would dig the existing magnet out annd use 2 small magnets of the same strength measured and glued in....like I said we know that a magnet can be glued into an old rotor for tci already found that works......

xsjohn

OK In some ways the pistons being at the top of the compression stroke and 83 degrees down on the same stroke ... aka an 83 motor instead of a 277, is supposedly good for torque, its called a big bang motor. It will actually cause the least ratcheting if I imagine it right. Problem is ,it horrible for almost everythign else, including starting it. That is however an 83 degree crank and I am not building that.

A true 277 will be @ TDC on compression on left and 1/2 way down suction on the right, and when the right @ top of compression left is 1/2 way up the exhaust stroke. That will make for a very smooth motor which would nto ratchet, fill and scavenge both its cyls well, and effectively not be lacking anything. It should be almost as much torque as the standard 360, power pulses are a bit staggered, but really not enough to hurt anything, power pulses only contribute to vibration a very small amount, its the reciprocating weights that make it vibrate. The odd thing is, even 180 parallel twins vibrate less, a lot less but they do need balancers.

Anyway a 277 mainly should vibrate like a 90 degree V twin, make the power and torque of a normal xs and run a even cadence at almost any rpm (AKA less ratcheting). Maybe I'll run a digital tach to check it out of it as an experiment.

I would experiment with both the big bang and the normal 277 if I were to have the $$$ and time. However the XS will prolly get sold in a few weeks, then I get to fiddle with it as he gets it customised and then I pretty much will be left with a 277 motor ... though I suspect he is angling for that, my idea is to weld the crank up and refit that in the case and leave it in a box for now. I would decide what else after that when he makes a decision. Of course if he bails on it, I am building the 277 and riding it so I can compare to stock xs.

Cool.
Srinath.

Srinath · Posted: December 17, 2009, 5:22 pm Post subject: Re: Upping the compression

650skull wrote:

I have thought about the pick up on the TCI for a rephase.

Surely if another pickup was put on the stator at the correct position then it could have a separate circuit, same principal as the points set up for rephase here www.650motorcycles.com/277ign.html

Shaadup and stop giving away my secrets ... (I am kidding, its hard to tell tone of voice in text).

Anyway, a vision or seca or virago TCI will support 2 coils. There is extensive research and circuit diagrams etc done on the vision unit, and a seca and a virago one is awfully close.

So we have an extra set of leads out of the TCI for runnign the other coil.
An extra pair of wires for the triggers to plug in.
I'd place the triggers on the case @ the right location, wire it into the TCI, then all I have to do is run an extra set of leads for the second coil.

On the XS TCI there are 7 wires, I suspect its like this ... though before shooting my mouth I should look at the wiring diagram but ... I like to live dangerously ...
3 from the trigger.
2 to the coil.
1 is the power.
1 is the side stand/neutral/clutch/your's neighbors girlfriends aunt's brothers grand mother in law's cut off.

On a seca TCI I believe there is 9 wires. Or maybe 10. I suspect its a 4 and a 6 plug wiht 1 pin missing in the 6 so its 9.
The 2 extra are for the second coil. That is it. Couldn't be simpler ... clear as mud.

Again I should verify this before shooting my mouth off ... but I wont.

Cool.
Srinath.

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Check these out from the XS650 club of Aus. Diagrams and dissections of the rephase

www.xs650.org.au/repha...0angle.htm

www.xs650.org.au/smoothness.htm

An extract from Dave Bath who has the 750 rephase with a 10.25:1 The first thing that can be noticed when the engine is idling is the slightly different exhaust beat, rev the engine to 3000 / 3500RPM and the amount of reduction in engine vibration
www.xs650.org.au/270.htm

Srinath · Posted: December 17, 2009, 5:52 pm Post subject: Re: Upping the compression

OK a seca 82 550/650 has only 8 wires out of the TCI.
There is the 4 from the 2 pick up coils.
There is an orange and a grey to the left and right coil respectively, and a R/W that splices into 3 and one to TCI and 1 each to the 2 coils.
Then there is a ground.
I think its a easy splice into the XS ... The side stand cut out be damned.

The vision turned out to be too different.

650skull dude - I will check them video's out but I have seen them before I believe.

Cool.
Srinath,

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Srinath, The information is for every one to use but it is oldkarkid's thread and i posted for him in answer to his original question...........the thread has been kinda hijacked........

Srinath · Posted: December 17, 2009, 6:25 pm Post subject: Re: Upping the compression

Right 650skull ... please

Pardon the interruption guys, as you were now ...

Cool.
Srinath.

oldkarkid · Posted: December 17, 2009, 7:41 pm Post subject: Re: Upping the compression

hahaha you guys are funny sh*t!!! I dont mind, hell, this is how I learned most of what I know (which is never nearly enough), by just hanging out in the shop listening to whats being said. A good shop conversation always has a few twists and turns in it, but is all good information. I think I am going to leave the head alone and maybe play with the pipes just a little more. I know she's got it, I've just gotta find it.

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Yamaha xs650