1982 GS450TX No compression in Right Cylinder

[hockey911]

(obviously i know that i am going to need a rebuild)

bike has 28,000 miles on it, and sat for an unknown time when purchased ("not running")

Now here is where the fun begins, ive never been able to figure out why the bike runs just fine at rpm above 4k but it cant idle correctly....

Anyways ill go through how i figured this out...

Cleaned the carb (got high end perforance back)
Changed spark plugs(more high end)
Checked grounds (actually got it to idle for a time, probably not related)
Random symptom bike burns oil when coming to a stop at a light from the cylinder with 0 compression


After i ran out of things to check i pulled out my compression tester, cylinder 1 has 120psi compressoin and cylinder 2 has 0 psi compression :hypnotysed:

Anyways ill cut to the chase, what are the common causes of 0 compression in these bikes?

My guesses so far
Burnt Valve, Valve not closing or not sealing properly
Burnt Piston, or warped cylinder

And also what does a rebuild cost if i were to do it myself over a weekend? And what should i buy and lookout for


Edit: On the cylinder with 0 compression i can feel air rushing out of the spark plug hole, however with the compression tester on it i go to 0, (i can conclude the air is going elsewhere but not sure where)

 

[tkent02]

(obviously i know that i am going to need a rebuild)

bike has 28,000 miles on it, and sat for an unknown time when purchased ("not running")

Now here is where the fun begins, ive never been able to figure out why the bike runs just fine at rpm above 4k but it cant idle correctly....

Anyways ill go through how i figured this out...

Cleaned the carb (got high end perforance back)
Changed spark plugs(more high end)
Checked grounds (actually got it to idle for a time, probably not related)
Random symptom bike burns oil when coming to a stop at a light from the cylinder with 0 compression


After i ran out of things to check i pulled out my compression tester, cylinder 1 has 120psi compressoin and cylinder 2 has 0 psi compression :hypnotysed:

Anyways ill cut to the chase, what are the common causes of 0 compression in these bikes?

My guesses so far
Burnt Valve, Valve not closing or not sealing properly
Burnt Piston, or warped cylinder

And also what does a rebuild cost if i were to do it myself over a weekend? And what should i buy and lookout for


Edit: On the cylinder with 0 compression i can feel air rushing out of the spark plug hole, however with the compression tester on it i go to 0, (i can conclude the air is going elsewhere but not sure where)

Usually it's a lack of maintenance, have you adjusted the valve clearance? There can be no compression if the valves are not closing.
Of course if the valve isn't closing it will get burnt, so you may be right.

 

[Nessism]

Can't figure out why people don't adjust the valves. It's pretty darn easy. I wouldn't even bother to check compression before I verified the valves were okay.

BTW, you can do a quick and dirty top end job on that bike for cheap. Even if you need parts it won't cost you much to buy replacements on ebay. Most expensive things are gaskets and piston rings.

 

[tkent02]

Yeah, I bought a 500 piston and cylinders for $30, bolts right on, gives it a big power boost and it's running great. I think the gaskets were $20 or so also on Ebay or maybe Amazon.

 

[tkent02]

Yeah, I bought a 500 piston and cylinders for $30, bolts right on, gives it a big power boost and it's running great. I think the gaskets were $20 or so also on Ebay or maybe Amazon.

Top end is really simple and easy.

 

[hockey911]

probably a dumb question, before i go through all the work, can i take the head off the engine while the block is still in the frame?

 

[bwanna]

I did the same. Did you have any problems with the timing? the 500 jugs with gaskets is ever-so slightly taller than the 450. Had to adjust the spark timing to compensate.

 

[tkent02]

Nah, just slapped it together and it runs fine. The spark timing comes from the crankshaft, only the cam timing changes with the taller cylinder, the cams are advanced a tiny bit but it's not much.