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Discussion Starter · #1 ·
I have a few different sets of heads for my xcr 800 and want to find out if I have the ccing process down and measuring the squish band ok here's the info I have so far installed ccing starts out with leveling the motor,top dead center the piston, pull the heads rub a small amount of grease around the edge of the piston and the cylinder to make a seal for the water install head to torque specs pour water to the top of threads for the plug while measuring the amount of water.Uninstalled pull head install plug take plexiglass with a hole in the middle and place it over the head and measure the water it takes to fill it just to the plexiglass. Squish band take some solder (i don't know what size yet)make a hook lower the piston putt it in plug hole pto to mag side rock motor back and forth to smash the solder and measure with a caliper both mag and pto results. Any info on the proper procedure would help.

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who cares about cc's, not being rude but whats it matter? for a trail engine cut about .010" and run it. any more and you risk detonation from bad gas. if you are mixing race gas to assure qaulity, then take more. .060-.065" is trail safe squish. some guys run tighter but then they reshape the head and change the angle of the squish. but there you are getting into engineering at that point you are better off to send them out and have the companys with experience simply reshape them for you and set them for your application.
 

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Discussion Starter · #3 ·
Im trying to figure out the ccs because the new motor I picked up from a storage unit auction has several different heads.It is a union bay motor Doug Ruth porting, 40mm bored carbs with union bay's power jets. I call Fastrax and they talked to Doug and he recalls the motor being race trail ported but have three different head options 14.1,13.1 and 12.1 so they asked me to cc them to find out the difference between the heads. The plate has allot of advancement now so I think I has the 14.1 now. Im just trying to dail it in for trail use.
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ah, then flip them upside down with the spark plug in them and measure the water that they hold. to me that would be the head volume.
how you sealed up the rings with grease, that would be chamber volume.
if you know chamber volume at tdc and chamber volume at port closing then you can figure your own ratio. with the piston rings at the top of the ports just closing them. if you held 10 cc's of water, then at tdc you held 1 cc of water that in theory would be a 10-1 ratio.
 

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madcow said:
ah, then flip them upside down with the spark plug in them and measure the water that they hold. to me that would be the head volume.
how you sealed up the rings with grease, that would be chamber volume.
if you know chamber volume at tdc and chamber volume at port closing then you can figure your own ratio. with the piston rings at the top of the ports just closing them. if you held 10 cc's of water, then at tdc you held 1 cc of water that in theory would be a 10-1 ratio.
That seems like the easiest and most accurate way of doing it[thumb]
 

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Discussion Starter · #6 ·
Thanks for the great information Madcow. Unoin bay(fastrax) had me doing some crazy science project.What is the measurement on a stock xcr 800 head I guess I could caliper them to find out.You said .010 is trail safe how much stator plate advancement do they like .
40mm bored carbs, V-force threes,HTG's edge/xcr pipes ( I dont know what rpm's they are)htg can, gutted slp box , 128 1 inch hack saw (firecat track) (edge skid modded to fit)wahl racing big wheel kit,primary 63 gr tuck 140-330 almond spring shimed for a 115 belt,secondary dalton 50-34 brz/blk spring hole 3,chaincase 23 40 74 196 1.7 roetin hornets.
This is how I bought this sled last year late in the season with a Htg/flannery motor but the cylinders where on the low side on the bore gauge, crank needs a rebuild and this new motor came about for great price.Had it apart it looks great,new pistons,rings,new crank bearings,welded pins (ultra crank)dont know why,cylinders perfect,porting dont know exactly what I'm looking at ,newer v forces,black slides in the carbs (new),power jets. I just what to dail this sled in as much as I can on the bench.
I need some help with this sled I'm new to the xcr 800s. Madcow pm me with your shop number and lets talk about a game plan at hourly or flat price for tech support from what I read on the site your are the xcr 800 guru

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that sounds like a real close setup to what everyone else is running.

give a call any evening

320-629-4889
 

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compression ratio is calculated by swept volume plus chamber volume all divide by chamber volume. madcows example would be 11:1 compression ratio.
 
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