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Rephased stock engine, lighteniing the crank ?
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Srinath
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PostPosted: December 23, 2009, 10:02 am    Post subject: Rephased stock engine, lighteniing the crank ?

I am doing a 277 rephase but am not boring or doing much performance mods. The idea is longevity useability and refinement. Of course doing top end work is a lot easier than opening the bottom, so anythign on the crank that will make it better to set it for a later wild motor gets a thought.

So having said that, does any one know how to lighten the crank.

The piston that is about to stop is balanced by the other piston that is flying in the other cylinder. So I am thinking a chunk taken out of the opposite side will help, but can anyone tell me where and how much to take out.

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xsjohn
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PostPosted: December 23, 2009, 10:55 am    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Lightening will increase ratcheting and don't relieve the crank anywhere......it will vibrate beyond comprehension.....
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Srinath
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PostPosted: December 23, 2009, 11:23 am    Post subject: Re: Rephased stock engine, lighteniing the crank ?

What do you mean by relieve ?

I dunno how to explain it, but the weights on the crank are intended to keep the piston moving up when they are both moving up at the same time.

I am thinking I should take out 1/2 the weight of the each piston from across the rod pin. But well, I am thinking that may be too crude or ... wrong.

I am hoping someone can tell me something like, punch a 3/4 inch hole across from the rod pin.

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yamaman
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PostPosted: December 23, 2009, 12:03 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Ok then, punch a 3/4" hole across from the rod pin. Mr. Green

Interesting read here:

www.victorylibrary.com...-bal-c.htm

And here:

www.brufnut.de/SS100/E...alance.htm

www.offsetcrank.com/thefirst.htm

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Srinath
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PostPosted: December 23, 2009, 12:15 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

If I knew how to make sense or even calculate any of those ... you think I'd sit at a desk all day pushing buttons ? ... OK fine I will, but ...

I dunno much about balancing nothing.
I also am not spending much more than the 30-40 I am in already ... potentially with another 20-40 to go ...

Ergo too cheap and too stupid.

So a location and hole diameter are what I would need. Or a rough picture ...

But if you were serious about that 3/4 inch across from the pin ... I'll take it ... unless too many people say no ... it is a democracy y'know ...

Yea dont talk to an injun about democracy, we spell it as Demo - Crazy.

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gordo
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PostPosted: December 23, 2009, 7:43 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

srinath, usually machine shop's near airport's that have allot of smaller plane's do balancing on the rotating mass. In Bedford Mass, there is a shop well known for their balancing, called Lindskog Machine. Balancing is very important, as your rephase is for a smoother running engine,right? As far as John's statement, it means removing metel off the crank.
Balanceing need's to be done by someone with the proper tool's & knowledge to do it. Cannot just tell some drill a hole here & all will be fine.

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Srinath
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PostPosted: December 23, 2009, 8:01 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Thanks for the idea gordo, but I tend to think outside the box in a lot of cases.
This is my case for why I want it done the way I do ...

From crank to crank, yamaha didn't make any differences.
I have seen other bikes too and they all have crankshafts that look the same as each other.

So If I built a stock XS650 and say I had a crankshaft machined out of bare metal I could drill the same things the same way as yamaha did and have a new result that is the same.

So I am trying to copy a stock piston fitted, stock bore all otherwise stock XS650 motor with a 277 rephase. Of course it may be a rareity cos everyone is boring theirs. I mean you have the crank lying in pieces on your and floor and several other places ... and what is a bore and a larger cyl and a head and this or that.

I effectively want to study the 277 vs stock ... now of course when you say that one can promptly say then you ahve to use it as it is, to shich I would counter ... I want to do wha tyamaha would have done in this situation ...

One of the aussies is doing this, and he's said he will post when its done. But I fear I would re assemble it before he does.

There is another aussie who said that yamaha should recall all the stock XS650's and replace the motors with 277's and send them back with an apology. They were supposedly that good.

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xsjohn
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PostPosted: December 23, 2009, 8:29 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Any place that I know of that balances these takes them apart removes the rods and places dumb weights on the big ends then reassembles.....then they only spin them at 500 rpm and balance by grinding here and there until the operator is satisfied it is better...the dumb weights are kinda of a guess figuring what ever overbalance they decide...the rods and pistons are balanced......made the same ........when I had mine done 10 years ago it had virtually no vibration at 1200 but still vibrated at 3800 like it always did...and it s*** the bed after 10K because we didn weld it....actually the 2nd stock crank that I have in there now at 8-1 is far smoother than all that money I spent on that first one......the whole frickin thing is just far better.....all that was a waste that I could have done for nothing if someone had told me.......but everyone is on the stupid ass hop up thing..or just rides the vibrating thing as is.....duh.........so I just sit here thinking that no one is listening now either....no skin off my ass.... Laughing

xsjohn
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Srinath
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PostPosted: December 23, 2009, 9:52 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

That 8 to 1 is somehting I am thinking of too. Its rephased, and 8.7 to 1 isn't that high. That is what is preventing me from doing it. Plus my rephase cost me so right about wha tthat second head gasket is likely to cost, unless you stuck that told one in there. Of course mine I believe is torn in 2-3. So I need 2 new ones.

OK and 500 rpm is bogus for most any bike. On an XS I'd shoot for a 3000 rpm or so. I once ran a GS500 (180 crank, counterbalanced motor) balanced by spears enterprises in CA after pulling its counter balalcer out - it ate those bearings and they were impossible to get in any size other than stock. They balanced that for 7K if I recall. That motor spun up so quick it was scarcely believable. Especially compared to stock. It was bored to 569 CC from 487 and had a list of hop up's enough to put Casey Stoner's ducati to shame.
But it was barely rideable under 6K, it was smooth as butter between 6 and 9K, past that it vibrated a lot less than a stock one at 10K (redline for stock GS), and it revved to 13K or so ... Ofcourse for a race bike it worked great, till it was redlined for almost 1/4 mile and blew itself up.
Yea the rider had no idea of what it meant to shift.

Anyway if I dont find that ... drill here with this size bit, I am walking over that stem and moving on.

I'd say for right now, I am in for about as much as the extra head gasket cost on yours (assuming you put a new one on).
Definetly it will have more $ in it, mostly cams and the botch job ignition I will do ... but. lets see where it takes me. I should get the cams done for under 100 ... hopefully under 50.
Ignition - I am working on carting that out of a seca or a similar 4 cyl ... or 2 cyl with 1 coil and 1 pick up per cyl. Like a virago 535. A 75 twin ... maybe close enough to my 83 ... :-((
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yamaman
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PostPosted: December 24, 2009, 8:27 am    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Srinath wrote:

But if you were serious about that 3/4 inch across from the pin ... I'll take it ....

Nah, sorry mate, that was my sense of humour! Surely you've seen Get Smart..........."Awwww I asked you not to tell me that"

For sure, nobody is going to give you a magic number. If you want it balanced, then you either learn, or trust someone else to do it right for you! So, as you said not at cost, no cost is nothing, so your free from that now, carry on.

I hope you've been taking some pics & will post them. While a lot of what you say seems far fetched, still be good to see the progress & results, be they good or bad.

Sounds like your enjoying it all though, so keep at it & have a great christmas, cheers

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Srinath
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PostPosted: December 24, 2009, 9:41 am    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Looks like I wont be doing that. My goal is to get it for as cheap as possible.
People think a rephase has to cost whatever 2-3G.
I have some tools I have made for this purpose, I'd be loaning it out when I am done (like the pin pulling tool etc) and I'm trying to get the rephase itself for under 50 or so, in effect its a lot of labor and depends on where you live literally cos shops work at different rates.
Let me see where it goes. I have 20 bucks in tools maybe so far. Had to buy a bearing puller that I didn't have. Also had to buy those crazy 5/8th bolts and coupling nuts and cut them etc. I dont actually count tools as part of a modification, cos it is useful in many other cases. Parts and $ paid to others for work I cannot do cos I dont have the tools+knowlwdge+experience is my benchmark.
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Tomterrific
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PostPosted: December 24, 2009, 12:04 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

The rephase has an unequal time between firing impluses. To make a comfotable rephase idle smoother and not stall on take-off the idle speed needs raised or the flywheel effect needs to be increased. For racing, the easiest way to lighten a flywheel is to pull the rotor and run constant loss ignition. Pull the rotor to see what a lighter flywheel will be like. I think the 90° engines use a text book 50% balance factor unless testing proves otherwise.

Tom Graham
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Srinath
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PostPosted: December 24, 2009, 12:39 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Yes I have read that 50% balance factor.
So I need a heavier flywheel ? or does that mean I have to drill the holes on the area near the pin ?
OK then what is a stock XS's balance factor - 100% ? - if so, that would imply we remove the 1/2 of the rotating assembly weight from the opposite side of the pin would it ?

I have very little idea of what I am talking about. I am talking about something I dont understand in terms of somethgin else I dont understand but it is quantized. As in, We have this lump here. No clue what it is or how much there is, but we need 1/2 that lump out from over there. OK great. I'll get 1/2 of it removed. That way.

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xsjohn
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PostPosted: December 24, 2009, 1:32 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Don’t remove anything or you will be looking for another crank….plain and simple……
The bob weight for a stock xs650 crank is 538 grams……if you arbitrarily remove or add any weight to the crank you will have a vibrating nightmare…balancing is a black art and should be left to professionals……doing it yourself would be a total shot in the dark……..to say the least…….I speak from experience on this subject…..

The one thing that we can do to improve balance is to get both pistons to the same weight……using a gram scale measure both pistons……then remove weight (inside on the pin journal) so that the heavier piston (if one is heavier) is the same weight as the lighter piston….

And an 1/8” or so of retard will help start off’s and smooth out the lower rpm cruise…

Cam timing is critical as I have said before……..any more advance in the cam than factory will create artificial leanness as the intake valve closes too soon not allowing the cylinder to fill completely……these cams are already advanced to the “absolute limit” and even 2 degrees “will definitely” cause artificial leanness………raising the head to lower the compression means you will have to retard the cam about 2 degrees (which puts the cam back to stock configuration) or the above situation will “definitely” occur and it will be impossible to tune and run clanky like a crappy 2 stroke…and both cylinders (when the cam is changed for the 277) better have the right cam timing or you can have one running different that the other……for you guys that want these to run smoother and with less vibes the 8-1 CR configuration on a stock engine that I have described many times is the simplest and easy way to go……..and it will run like an engine is supposed to and without engine noises……what would I know after 40 years of this stuff……..

xsjohn


Last edited by xsjohn on December 24, 2009, 1:40 pm; edited 1 time in total
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Srinath
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PostPosted: December 24, 2009, 1:39 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

I am still working on it ... 538 grams you say for a bob weight. Ah ha ... so 50% of that will need to be the balance factor weight.
Next it to decode the location ...

I know black art and I do a mail in mail out service on it ...

I am wondering that also with the 8-1 ... cam chain length, timing etc etc ...

Compression is not even 3-4 on the list of mods for power. Flow, displacement, rpm etc all beat it hands down. And they are more reliable too.

Anyway 8-1 may be in the cards if I am willing to gamble the chain will fit.

Hey I should put up pics of this stuff so I can ask if some stuff is beyond use limit.

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xsjohn
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PostPosted: December 24, 2009, 1:55 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Falicon said 538.........so they placed the bobweights on the crank big ends and spun it to ballance...grinding off some here and there I guess.....that cost me 400 dollars and it was a waste of money cause it still vibrated on the express and drove me crazy.....I used 2 gaskets and moved the cam and now it is right for no money...with a stock crank....duh......and a new camchain won't fit on the 8-1 I'm afraid.....I collected slightly used chains ........one guy used a 2K used chain and said it went on........tight but it went on.............

and the ratcheting is all but gone so the engine should last a long long time and also the cam chains....ratcheting is what beats out the cam chains always changing dirrections (snatching).....for example my sons xj650 had 60K on the stock chain when we changed it and it was almost the same length as the new chain we put on.......as compared to an xs650 that can eat a cam chain in 20K or less.........and smooth the outside of the cam chain (and master linl) so it doesn't eat the guides as fast or at all......

xsjohn



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Srinath
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PostPosted: December 24, 2009, 2:47 pm    Post subject: Re: Rephased stock engine, lighteniing the crank ?

Yea ratcheting, I now believe that was wha tlead me to conclude that the 82 motor was bad and pull it out and split it.
See if you turn off the key and the pistons are on the way up ... they will never make it up, they will promptly drop to the bottom. That may have bunched up my loose cam chain, and that created the grinding noise I heard as I turned it by hand.
It was perfect when I opened it. I think the 277 rephase will all but eliminate ratcheting cos 90 twins dont ratchet. On a 360 crank compression even if its 8 to 1 causes massive slow down. You just have less of it than the stock 8.7. However with a piston flying up the cylinder on the exhaust stroke or with the piston flying down on the intake is a natural resistance to ratcheting. However odd power stokes are the payback.
Let me see what it works to be.
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