compression test results - thoughts appreciated

1982 xj550 seca. 18,000 miles.

Just made my valve clearances spec. 6/8 were a wee bit tight with the lowest reading on cylinder 4 (intake at 0.4 mm)

Cold compression test results (airbox removed, tci disconnected, all 4 plugs removed)

#1 - 157. Wet - 161
#2 - 145. Wet - 155
#3 - 145. Wet - 150
#4 - 150. Wet - 155

I am wondering if I should think about replacing my valves before a long trip in a few weeks. Any suggestions greatly appreciated!

 

Not surprised if the valves had never been touched.

What were your compression test results? For a 550, 100psi is "minimum" 120psi "normal" and 135psi "maximum." No more than 14psi difference.

 

Sorry see edit.

 

Why would you "replace your valves" on an apparently pretty healthy 18K mile motor? That's rather major surgery and shouldn't be necessary at this point.

Those results, if anything, are a bit (ok, way) HIGH. Before doing anything TOO drastic, I'd borrow/rent another compression gauge.

You can leave the air box installed; disconnecting the TCI is a good idea; and be sure the throttles are held wide open. Be sure the motor is slightly warmed up, not hot. And no real need for a "wet" test, there was nothing alarming about the first set of numbers you got (except for being a bit too high for a 550.)

Put a few miles on the bike (to clear out the oil in the cylinders) then test again after it's fully cooled down then been warmed up slightly. My 17K miles 550 Seca pushes 130~132 across the board.

 

I'm with bigfitz on this one. Your gauge must be a little off-unless someone has done major work to the motor but even then I don't think it would post those #'s. My 550 was in the 127-136 psi range and it runs like it was new-can't tell that it ever burns oil and it seems as fast or faster than my previously owned 650 shafty Honda.

Keep in mind that many modern car engines will have much higher compression #'s. Like 190psi or even higher, but that is a design feature of those motors and your XJ motor is perfectly happy and generating tons of power at the lower psi, although I would consider anything lower than 120 less than ideal. If you can't borrow a gauge from a friend go to Autozone and ask to use their 'loan a tool' gauge, just a deposit on a CC and when you bring it back a full refund.

Just for clarity it's better to create a new post when you add info like that, so the thread makes sense-on the plus side you will gain posts and can move up in your lore.

 

You noticed that too? My third ex-wife had a 650 Nighthawk, an '83 IIRC (might have been an '85) and despite a similar redline, the XJ550 is definitely quicker.

Back to the original question; I think we're all in agreement that the original compression test needs a "second opinion" but it smells to me like a healthy motor.

Re-sync the carbs because of all the valve-adjusting that happened, and ride. Keep a monitor on your fuel economy and an eye on your plugs. If the bike goes like stink and idles like a sewing machine while getting 52~56 mpg, you've nailed it.

Commence traveling.

 

Ok. I put some miles on it, rented the autozone compression gauge, and did the warm test and these were the results:

1 - 148
2 - 138
3 - 135
4 - 142

I actually had myself thinking that the valves were getting damaged because I rode this bike as a daily rider without mufflers for 8 months. Someone mentioned to me that the valves will sometimes burn without mufflers, but I guess these numbers are ok, right?

I've been lurking and soaking in information since January but for the future I'll definitely create a new post MercuryMan.

BigFitz thanks for the write up on valve adjustment. Not sure if I would have been able to do it on my own without it. I'll definitely be attempting to sync those carbs and keeping an eye on the mpg. Hopefully I'll be sewing my way down the road shortly.

 

If 135-psi is your LOW number, ... you're in good shape.