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xs650 > > Motorcycle Systems > > Engine > > Top End


Top End
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bkmarsha
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Joined: Aug 02, 2008
Posts: 87
Location: Indiana

PostPosted: December 27, 2009, 7:22 pm    Post subject: Top End

Just finished up tearing down the top end of the bike and had a few questions before i got much farther. The reason for my tear down was a hole in the top of my piston.

I feel that i am going to go to an oversize piston because of wear and minor damage to the cylinder. Is there anything else that need to be done besides bore and hone when doing this work.

Is there anything else that i should look at and consider while i have the top end apart.

Is there any reason to tear down the bottom end if there has been no apparent problems.

Thanks for help any pointers or tips will be appreciated.

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dpmphoto
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Joined: Apr 18, 2007
Posts: 485
Location: syracuse NY

PostPosted: December 27, 2009, 7:54 pm    Post subject: Re: Top End

just a port and polish.No need to tear into the lower end there pretty tough.
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bkmarsha
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Location: Indiana

PostPosted: December 28, 2009, 2:11 am    Post subject: Re: Top End

what about the valves is there any thing that needs extra attention

i assume the machine shop that i have do the bore and hone can probably port and polish too?

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Pamco Electronic Ignition
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Srinath
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Joined: Sep 10, 2009
Posts: 343
Location: Charlotte NC

PostPosted: December 28, 2009, 3:58 pm    Post subject: Re: Top End

I'd like to add though, I was able to get my crank out and rephased for very cheap. It may be a worthwhile mod. Cams are all that I have not done, and they can be $ or maybe I will figure out a less $$$ way for that too.
Also if you fit bolts instead of the studs for holding the cyls on, you can pull it wihtout removing it from the frame next time.

Cool.
Srinath.
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tonyc2me
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Joined: Aug 19, 2009
Posts: 23
Location: BAKERSFIELD CA

PostPosted: December 28, 2009, 8:55 pm    Post subject: Re: Top End

What about a;; the debris from the piston that may have entered th oil pump and lower gears? Just a question. I know on BSA's if you hole a piston you better check out the lower end. TC
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bkmarsha
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Joined: Aug 02, 2008
Posts: 87
Location: Indiana

PostPosted: December 29, 2009, 1:02 am    Post subject: Re: Top End

is there a post on here somewhere to put in bolts in instead of studs

is there any recommendations or risks on doing oversize pistons i am thinking second oversize is what i am going to have to do

is rephase done at a machine shop too

_________________
1978 Yamaha 650 Special
Emgo Pod Filters with modified extensions
MikesXS Performance Oil Filter/ Cooler
Pamco Electronic Ignition
Green Monster Coil
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Photo Gallery
Srinath
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Joined: Sep 10, 2009
Posts: 343
Location: Charlotte NC

PostPosted: December 29, 2009, 11:14 am    Post subject: Re: Top End

A rephase is a press out job and past that its a little bit of welding and some crank truing work.
I have some equipment I have made for this that is actually easy for anyone to make but the first crank I pressed out I did it with a 5/8th bolt and a coupling nut.
This is a good illustration - and I think he used 3/4 bolt with fine thread.

www.650motorcycles.com...oltNut.jpg

It also shows a rephased crank.

Its best given to a bike shop that can weld and true a crank.
I have heard you cannot destroy the crank ... they are that tough, but watch out for the bearings etc and welding it has to be done carefully and after that it has to be shaved etc perfectly or it wont fit. I guess that way you can ruin it.

Cool.
Srinath.
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bkmarsha
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Joined: Aug 02, 2008
Posts: 87
Location: Indiana

PostPosted: December 29, 2009, 2:07 pm    Post subject: Re: Top End

what is the reasoning and advantages to doing a rephase and are there other modifications that have to be done
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1978 Yamaha 650 Special
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MikesXS Performance Oil Filter/ Cooler
Pamco Electronic Ignition
Green Monster Coil
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650skull
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Joined: Jul 19, 2007
Posts: 1186

PostPosted: December 29, 2009, 4:59 pm    Post subject: Re: Top End

The reasoning is to remove the vibration.........The advantages are the smooth ride and less stress and if you want to race it then it will rev higher..........The cam lobes have to be reground and built up to move the lobes to the 270/277 rephase, ( or buy a premade one), Cutting and turning then welding the cam for a rephase is not very reliable

Welding the crank is a preference rather than a given, if the standard motor is regularly reved for periods at 7.5 and higher mark then the pressed crank will separate.....the crank can be disassembled and assembled a couple of times before it needs to be welded...........A rephased crank does not have to be welded if you are not going to over rev the engine but it is important to have a good rev counter to keep in the safe zone.

If the crank is good and does not require a weld then it can be built again biut once it has been welded i think it is near impossable to rebuild
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Srinath
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Posts: 343
Location: Charlotte NC

PostPosted: December 29, 2009, 5:17 pm    Post subject: Re: Top End

Correct 650skull. And he's not even touched the ignition part.
Though I must say, the welding is done after trenches are cut in the pin and crank cheeks. No reason it cannot be ground again and pulled apart if needed, of course it will be very very painful. So there you're on your own.
Cool.
Srinath.
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