77 XS650 - Cylinder Temps Uneven.. Cracked Head? Gasket Leak?

[Prescottrogers]

Hi Everybody,
(You can skip straight to the problem below if you don't want the back story)

I acquired a 77 Xs650 about a year ago. The PO had installed a 750 Kit because during an engine rebuild he f'd the end of one of the original cylinders. The bike looked and seemed turn and go. Opposite of ratty. Said he'd used it as a city A-B bike. The bike had lots of new parts, and he said he had thoroughly cleaned up the motor, including cooling fins with a dremel, cleaned and polished the heads, new cam chain, lapped the valves, gaskets, seals, etc. Seemed like it was all rebuilt and ready to go. Anyway, he said he hadn't got the carbs in sync.. Which was fine, I had a carb sync and the bike seemed to run healthy.

Got it home, rode it around during the season, but occasionally it would just quit at a light on take off or sometimes sitting, I wasn't sure why, thought maybe it was just me getting used to the bike. Maybe took it out a total of 15 times.. Then I noticed the #2 cylinder was WAY hot not long after starting it up, riding for a minute.. Worried me.

-Problem-
-Skip Here -
While working on it, I couldn't get the carbs to sync and noticed #2 cylinder ran hot pretty quick, while #1 was cool. Compression test: #1 was about 120psi, #2 was about 140-160 (This thing is a beast to kick.. Electric start not hooked up yet.) Then I did a leak down test with about 20-30psi and heard leaking in the head and the case through the oil cap.. on both sides. Did not hear anything from carbs or exhausts. I'm wondering if anybody's had the same thing, or if anybody knows something I don't..

I figure it's probably either a broken/leaking gasket by the cam chain or a cracked head.. and lastly, scored cylinder walls from a botched installation or something.. So any suggestions, help etc. is what I'd greatly appreciate before I take the engine out and tear down the head..

Thanks!

 

[XSLeo]

These engines do run a bit warmer on the right side. We think it's because the right side has the primary drive, this tends to add some heat but more provides less cooling. Some where around 20 degrees.
On your compression the #1 as you call it at 120 is low. the #2 is fine. The book calls for 145 lbs. with 10% difference between them. One side 140-160, lets call it 150, the other at 120 leaves 20 difference, that 20%, twice the spec.
Just reread your post, my 750 kitted 75 got around 195 psi. On the engine stand, full of assembly lube. No carbs just using the starter. Haven't checked it since, but it's more than stock. I have the 750 kitted 75 and a stock 81. The 81 I can kick over easily, the 75 not so much.
Most of us do a head retorque at least once, often several times. Try that and set the 8 big head nuts to 30 ft.lbs.
I set the torque, let it set ove night, retorque, install, The next day retorque, start up, let warm up a few minutes, let set over night retorque. At this point you should not really turn the 8 large nuts to set the torque.
I then run it for about 50 miles then check torque. During this first fifty miles I get it up to around 35 then use a fairly firm roll on up to around 50 mph the back of to coast down 35, then roll on the 50 and back of. do this as much as you can during the first few miles. This help seat the rings.
Then during the spring wake up I recheck the head torque.
Leo

 

[scabber]

I wouldn't trust anything a PO says as fact or his mechanical ability. Since it failed leak down and compression parameters. Fix it now or run it till quits your call.