Burnt valve, what heads will fit

76xs · Posted: March 23, 2007, 9:48 pm Post subject: Burnt valve, what heads will fit

I have a 76xs. The left side has a burnt valve. Compression is 70 left side 90 right side. I adjusted the valves, and squirted oil in the cylinder and no change. It still backfires out the exhaust. There are no bike shops within 100 miles of where i live, so i was thinking if i could get a complete head off ebay that would be the way to go. Do all 650 heads interchange? Also it looks like I can remove the head without removing the entire engine. Can I? Thanks for the info MIKE
P.S. The odometer reads 15,000 miles. Is it normal for a motor with miles that low to have a burnt valve?

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

When you do a compression check,you need to hold throttle wide open and have the slides propped fully open. What this does is allow the motor to draw in as much air as possible to apply pressure on the backside of the rings to fully seat the rings against the cylinder wall for maximum sealing to build pressure. Also check point gaps and timing............Jack

beys

76xs wrote:

... so i was thinking if i could get a complete head off ebay that would be the way to go. Do all 650 heads interchange?

Take care to buy the rocker cover with the head! There is no gasket in between and they should match!

76xs wrote:

Also it looks like I can remove the head without removing the entire engine. Can I?

No. There is not enough place. taking the motor out of the frame is no big deal, it takes 1 1/2 hours. First of all, download the workshop manual as pdf-file here:
www.xs650.de/phplm/index.htm
Go to "Technik" in the chart on the left side, then to "Werkstatt-Unterlagen" The 9 links on top is the manual in three languages.

Strip off foot pegs, shift and brake lever, comlete exhaust tubing, alternator cover, wiring. Take off all engine bolts and brackets exept of the lower, long one. Bend the engine to the front as possible and stripp of the carbs. Take out the lower bolt (a second person would be helpful, the engine weights about 100 ibs) an take out the engine to the left side.

76xs wrote:

P.S. The odometer reads 15,000 miles. Is it normal for a motor with miles that low to have a burnt valve?

No question of distance but riding, I think. I killed my first (and only) XS motor at 9k miles back in '82 Embarassed

royfisk

If and when you want a head e-mail me I have them reasonable

76xs

I'll check the timing but if i do need a head will one from any year work?

qferret

I believe 74-79 all had the same motor.

Also, if you don't want to pull the engine all the way out, you don't really have to. By the time you get that far, it's not that much more work to pull it, but with my limited work area, I have a tendency to "tip" it at an angle so the head will clear the frame. That way it's still sitting someplace easy to work without needing extra workbench space.

76xs

Thanks for the info. You guys are great!

jayel

just be sure to get the matching cam/valve cover they were made as a set

beys

jayel wrote:

just be sure to get the matching cam/valve cover they were made as a set

As I said in my posting.
eanwhile the guys at XS650.de were discussing the same problem here
They say that its enough to put head and cover together on the working bench, put cam bearings and cam in, tighten it all at torque required and check if the cam turns easily. If so, you can use head and cam cover together, even if the numbers dont match.

royfisk

A old mechanic fronm the 70's told me that same thing along time ago, He claims that the japaneese machineing is so close tollarances that even the best machinest's wouldnt be able to find but mayby a couple thousants differance. He also said you had a better chance of over torking one a few pounds and distorting the thing then you had problams interchangeing the machined pieces. I dont know cause I have never tested the theory and I dont use or sell miss matched pieces, but who knows?

What Happened to 650rider.com?

Yamaha xs650