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Hello,
I have an '80 GS750ET. 40k miles. It's broken. I'm about ready to put it back together, but the cause of failure is still not definite enough for my comfort.
I was driving on the highway and started hearing an increasingly louder loose valve clearance noise, which turned out to be the left side intake (letter C) cam caps coming apart. Before I could make it to a rest area, the cam broke and the bike shut down. I'd say it went 2-5 miles making noise before the end. Bike ran great up until that point.
I've pulled the head and found no evidence of valve to piston contact that might indicate timing chain slip. Can't say too much about clogged oil passages as there was a lot of debris in the head when I opened it.
I partly suspect bad wrenching by a previous owner. (I've had the bike for just under 1k miles.) The mating surfaces on the head and jug look like they were cleaned with a bad razor blade, leading to some slight oil seepage at the front of the head gasket. Someone who would perform work like this may not torque down a cam properly, either.
The oil level was just at the top of the sight glass. I have normally kept it there due to the oil leak. Possible issue?
My oil pressure light sometimes comes on under deceleration and at low rpm. (It was not on when the engine failed.) Is this abnormal? Reading about it in one of the 4-valve manuals seemed to indicate that the oil pump is a sealed unit and a suspect one should be replaced. Are there clearance specs somewhere?
The bike has had a slight high rpm vibration since I started riding it. I was previously not very concerned with it. Normal? I suppose it could have been a bent cam.
The cam cap bolts were all tight when I removed them. The middles of the caps were pushed up and they came apart in pieces. The cam broke just to the right of the drive sprocket, opposite the carnage. Valves are straight.
I have a lower mileage head to put on, but I'd like to be fairly certain I'm not putting it back together with a problem inside and I'm new to these bikes. Any insight is much appreciated.
-Jeff
I have an '80 GS750ET. 40k miles. It's broken. I'm about ready to put it back together, but the cause of failure is still not definite enough for my comfort.
I was driving on the highway and started hearing an increasingly louder loose valve clearance noise, which turned out to be the left side intake (letter C) cam caps coming apart. Before I could make it to a rest area, the cam broke and the bike shut down. I'd say it went 2-5 miles making noise before the end. Bike ran great up until that point.
I've pulled the head and found no evidence of valve to piston contact that might indicate timing chain slip. Can't say too much about clogged oil passages as there was a lot of debris in the head when I opened it.
I partly suspect bad wrenching by a previous owner. (I've had the bike for just under 1k miles.) The mating surfaces on the head and jug look like they were cleaned with a bad razor blade, leading to some slight oil seepage at the front of the head gasket. Someone who would perform work like this may not torque down a cam properly, either.
The oil level was just at the top of the sight glass. I have normally kept it there due to the oil leak. Possible issue?
My oil pressure light sometimes comes on under deceleration and at low rpm. (It was not on when the engine failed.) Is this abnormal? Reading about it in one of the 4-valve manuals seemed to indicate that the oil pump is a sealed unit and a suspect one should be replaced. Are there clearance specs somewhere?
The bike has had a slight high rpm vibration since I started riding it. I was previously not very concerned with it. Normal? I suppose it could have been a bent cam.
The cam cap bolts were all tight when I removed them. The middles of the caps were pushed up and they came apart in pieces. The cam broke just to the right of the drive sprocket, opposite the carnage. Valves are straight.
I have a lower mileage head to put on, but I'd like to be fairly certain I'm not putting it back together with a problem inside and I'm new to these bikes. Any insight is much appreciated.
-Jeff
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