.png "Powered by vBulletin")
Hi yall,
I bought this '79 750 after it had been sitting outside for 10+ years (according to the previous owner's son). When I got it it had 30-90psi compression that would go up to 60-120psi with a teaspoon of oil in the cylinder. I got it up to 120 psi in all 4 after doing a cylinder hone, valve lapping, and valve clearance adjustment. In retrospect, it probably just needed the valves adjusted to run, but the pistons and valves were really gunked up so I just went for it. That and some carburetor fixes had it running.
Now around 100 miles later I'm back down to 60-80 psi in 3 of the cylinders. I did compression tests with oil and this time there was only 5-15psi change. I double checked the valve clearances and only found one that had too much clearance. While I had the plugs out I got in there with a borescope and the cylinder walls do look fresh. The exhaust valves seem pretty good as well, but the intake valves maybe not so much.
I think this means I probably messed up the valve job since the oil didn't help this time. This was my first time lapping so there's certainly a chance but can anyone give me a second set of eyes on these? Here are the borescope pictures: https://imgur.com/a/gs750-100-miles-later-X2wmwgG
Also, when I tear it back apart, am I gonna need to get a new headgasket even though this one is only 100 miles old? Will I also need valve stem seals if I take the valves out?
I bought this '79 750 after it had been sitting outside for 10+ years (according to the previous owner's son). When I got it it had 30-90psi compression that would go up to 60-120psi with a teaspoon of oil in the cylinder. I got it up to 120 psi in all 4 after doing a cylinder hone, valve lapping, and valve clearance adjustment. In retrospect, it probably just needed the valves adjusted to run, but the pistons and valves were really gunked up so I just went for it. That and some carburetor fixes had it running.
Now around 100 miles later I'm back down to 60-80 psi in 3 of the cylinders. I did compression tests with oil and this time there was only 5-15psi change. I double checked the valve clearances and only found one that had too much clearance. While I had the plugs out I got in there with a borescope and the cylinder walls do look fresh. The exhaust valves seem pretty good as well, but the intake valves maybe not so much.
I think this means I probably messed up the valve job since the oil didn't help this time. This was my first time lapping so there's certainly a chance but can anyone give me a second set of eyes on these? Here are the borescope pictures: https://imgur.com/a/gs750-100-miles-later-X2wmwgG
Also, when I tear it back apart, am I gonna need to get a new headgasket even though this one is only 100 miles old? Will I also need valve stem seals if I take the valves out?
Comment