750 or Stock?

[Dunc]

Going through all the bits & pieces to put an engine together & there's 750 pistons/barrels with low usage, a stock set with pistons & another set of barrels. Do I fit the 750. stock or bore & fit o/s new pistons? I'm trying to keep it as original as I can apart from some reliability upgrades.

 

[Jan_P]

If i get this right 3 possibility's
a ) --> 750 pistons/barrels with low usage
b ) --> a stock set with pistons
c ) --> another set of barrels.

I usually like stock ..But I don't like costs either b ) is a bit " Worn " and c ) Requires some work
Installing worn parts b ) ..don't like that
Buying pistons and perhaps bore c ) .don't like that

Provided b ) is more worn than a ) I would go for a ) even though I would prefer stock
having a solution already in house.

No experience of 750 in XS and it depends if this a bike for riding or other.
But I personally would look into keep it simple and cheap --750
Trying to measure it first

 

[650Skull]

Is the 750 kit a standard set of barrels with 750 liners bored for 750 pistons to suit??????????? If so what are the 750 pistons. Make.

Is the standard set a drop in or do the barrels need to be honed and new rings or is it new and ready to go.

just a set of barrels..........Cheapest good quality pistons from Cruzinimage will set you back $100 US then the barrels need to be bored. Locally it costs me $90 per barrel as long as it is one oversize per cut...........That's $300 at least.

If the 750 set up was a standard barrel set up, it is going to look standard and no one will know or notice it isn't standard. Not going to have any hidden costs as the carb set up is the same for 750 as the 650. Nothing wrong with a slightly used set as long as the pistons are in spec. The bore may only need a light hone and at worse the pistons could do with a set of new rings. Cost minimal, again crusinimage rings are cheap, a set + postage will still be cheaper than 1 set of rings for 1 piston from GeofsXS.

 

[Dunc]

Re-sleeved & 80mm bore size with Wiseco pistons. A quick hone of the bores & a set of rings would be OK.
I have a mate that could do a bore job if I go new 650 pistons.
He could also mic up some used barrels/pistons as well.
AlI I need to buy for the 750 would be rings as there's some new gudgeons in the box of bits.
Just checked conrod small ends & they're worn.
Looks like a crank rebuild.
Probably the reason it was pulled apart as PO was told it had a gudgeon rattle.

 

[jay760]

If you have the 750 kit, I would go with the 750 every time, that little extra power is so much fun

 

[Dunc]

Re-sleeved & 80mm bore size with Wiseco pistons. A quick hone of the bores & a set of rings would be OK.
I have a mate that could do a bore job if I go new 650 pistons.
He could also mic up some used barrels/pistons as well.
AlI I need to buy for the 750 would be rings as there's some new gudgeons in the box of bits.
Just checked conrod small ends & they're worn.
Looks like a crank rebuild.
Probably the reason it was pulled apart as PO was told it had a gudgeon rattle.

Found a crank that's OK! In the box of new bits there's 2 gudgeon pins & circlips as well.

 

[Jan_P]

OK I see now i was to slow post it anyway

Not knowing your financial situation--- but a top job and bottom job And we are quickly up in the 4 digits US Dollars range
Cranks can be found in Exchange Programs in Europe
But 2 x freight can be costly --> https://www.heidentuning.com/xs650-...ings/crankshaft-447-type-exchange-detail.html

If there is a usable crank in the crate with parts that can be a good thing.
I am not saying it is a bad idea some people does it .Otherwise it would not be up for sale.
But it can be regarded as " Taking a Hit " on / for some Bikes

triple g Gary have cranks sometimes from Barn finds that can be an alternative. perhaps. Or finding one elsewhere.

 

[grizld1]

Dunc, the answer to your original question is this: measure twice, assemble once. You'll find plenty of information here on measuring bores and pistons to determine clearance. Hone the bores. Then if your bores and pistons fall within an acceptable range, you're good to go. What that acceptable range is will depend on whether your pistons are cast or forged. Forged pistons expand more and need more clearance. A quick search or two will give you the range. If you don't feel comfortable doing the job yourself, a machine shop won't charge a lot to hone and measure.

With a 750 big bore (or any performance mod, really) it's a good idea to have the crank pins welded; flywheels in these motors have a nasty habit of walking.