Exhaust Valves

[Bogdanbonea]

Hi guys,
I just bought a GL1000 1975 (65000 km on the odometer) and when I measured the compression of the cylinders I found out that one of them had only 5 Bars. The others had 8, 9 and 11. Interesting thing is that both the front cylinders (1 and 2) were in better shape than the back ones (3 and 4). This is my first question to you: this has a logical explanation or it is just a coincidence?
After dismantling the cylider heads I found out that all the exhaust valves have some play in the guides, and the one corresponding to the cylinder 4 (the one which had the lowest compression) has a huge play in the guide compared to the other three. No play at all in the guides though for the intake valves. Can anybody tell me why all the exhaust valves have play in the guides whereas there is no play for the intake valves? Is this something specific for the boxer engine? And what could be the explanation for the exhaust valve of cylinder 4 having so huge play in the guide compared with the others? Somehow I would like to track down the reason so if there is any specific cause I can try to eliminate it. Many thanks, Bogdan

[WingAdmin]

Hi guys,
I just bought a GL1000 1975 (65000 km on the odometer) and when I measured the compression of the cylinders I found out that one of them had only 5 Bars. The others had 8, 9 and 11. Interesting thing is that both the front cylinders (1 and 2) were in better shape than the back ones (3 and 4). This is my first question to you: this has a logical explanation or it is just a coincidence?
After dismantling the cylider heads I found out that all the exhaust valves have some play in the guides, and the one corresponding to the cylinder 4 (the one which had the lowest compression) has a huge play in the guide compared to the other three. No play at all in the guides though for the intake valves. Can anybody tell me why all the exhaust valves have play in the guides whereas there is no play for the intake valves? Is this something specific for the boxer engine? And what could be the explanation for the exhaust valve of cylinder 4 having so huge play in the guide compared with the others? Somehow I would like to track down the reason so if there is any specific cause I can try to eliminate it. Many thanks, Bogdan

Valve guides do wear, and when it comes to valve wear, exhaust valves always wear before and more than intake valves. Exhaust valves are subjected to 1500+ degree gases which softens metal and embrittles seals. Not just on boxer engines, but on ALL engines.

[Rambozo]

Even though liquid cooled, the rear cylinders might run a touch hotter than the fronts. Just a guess.
Exhaust valves have a tough life. You have to go to great lengths to get them to last as long as intake valves. In some engines they are sodium cooled with a hollow stem, and many engines give them a larger stem diameter to achieve a longer life.

[Bogdanbonea]

Thanks for the answers! My real concern is why this happened at 65k km? And why cylinder 3 is in a very bad shape compared to the others? I also have a 1981 CB750C at 105k km. and all the cylinders have the same compression, no problem at all. I thought "the king of the kings" shoud have a more reliable engine...

[Rambozo]

It all depends on how it was used and maintained.