Compression after rebuild

rowdyrandy

XS650 Enthusiast
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Fellas -

Just got done rebuilding my top end, thanks to everyone who provided invaluable advice along the way.:thumbsup: here's what was done.

-new cam chain
-new cam bearings
-smoothed out intake and exhaust ports
-lapped valves
-new 1mm over piston and rings + bore and hone
-new elephant foot adjusters
-valves guides, gaskets, etc.. other bits and bobs worth doing

My question is concerning what I can expect as far as compression goes. I know there's a million opinions out there on the right and wrong way to break in a fresh rebuild, so far I've been sticking to the leo method of rolling on and off, but I only got it started today and have probably only put a few miles on it. Anyway...my compression reads ~130 in both cylinders - is this a good starting point? Just want to see if I'm still on the right track, this has been my first rebuild and I'm just stoked it started and runs as well as it does.
 
Sounds like you're not seated yet. Gotta give everything time to settle in. I know nobody wants to miss something and wreck all that work, but be patient, and go with what Leo gave ya. One day does not finish a break-in.
 
After a few heat cycles, you'll need to re torque the head. You may need to do this a few times. Each time you do that you need to check the timing chain and valves. The new chain may also stretch a bit, so keep an eye on it. Should go to 150 - 160 warm once the rings bed (a tank of fuel), dont forget to hold the throttle wide open for the comp test. Well done on getting it all together, cheers

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Thanks guys - patience is going to be the biggest hurdle here, I would have rather not had to do this is the middle of summer but it hasn't run this well since I bought it, so I'm happy. What kind of riding can I really do? I've got a 9 mile commute to work consisting of longer stretches of road with mixed stop lights, never really getting over 45mph - would that work? Not trying to over think this one but I gots the itch and just want to make sure my whole fall wont consist of me just riding on/off, on/off, on/off up and down the same old service road.
 
You don't want to cruise at a steady speed and RPM. Vary both and do lots of engine braking. Don't baby it (cruise around at 3K RPMs) but don't beat it either (run up at redline). Grab big handfuls of throttle to load the engine and run it up to 5 or 5.5K, then let off and engine brake. The loading and engine braking force the rings out into the cylinder walls so they can seat.
 
The roll on/off only needs to be done in the very first few miles. After about 50 miles the rings are about as good as they get.
When I did the 75 as a 2nd over, on the engine stand, no carbs, fill of assembly lube. Cranking on the E-Start I got 165 lbs of pressure. I never checked it after I had it up and running. Should have I guess.
When that engine got the 750 kit, all the same concitions I got 195 lbs. The 9-1 gives you a bit more than the stock 8.4-1.
Haven't checked that one after getting it up and running either. I just know it ran well as a 650 and stronger as a 750.
I think your 130 is fine, as Yamaman said, did you hold the throttle wide open?
Leo
 
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