Head trials and tribulations
Posted: Jul 24, 2021 9:31 PM
Replaced my cylinder head with a brand new one this spring due to cracks found in the old one during my covid engine refresh project. I somehow needed valves and springs too, even though valves were only 20k miles old and springs were checked when I did a Paul Burke head refresh. Machinist said valve float is the cause of what he saw, which was all the valve tips pounded into a mushroom, preventing him from removing them from the guides. An over rev I guess would have been possible the few times I let shops have it, but seems unlikely. So new b36 springs, new supertech valves.
Intake supertech valves only come in the long version. Machinist said he didn't have the tools to grind them all down a few mm required to get them to the same height as the old valves. He also warned me that valves are only hardened on the tips, and that grinding them down past the hardened part can ruin them. I called supertech, the told me there was 5mm of hardness and I only need to remove 3mm. $200 later to a different machinist and the valves are the right height.
I've driven it maybe 300 miles since being back together, signed up for a one hour track day on Thursday, and did a valve adjustment right before driving to the track just to make sure wear was as expected. All of the exhaust valves are the same as when assembled. Half of the intake valves have larger clearances than when assembled, a few of them out of spec, so I correct all but one that still has 330 clearance, since I don't have the right shim.
45 minutes on track, I notice a new noise when pulling off. From listening as closely as I can, it sounds like it's coming from the intake side of the head, and that it's too frequent to be bottom end:
https://photos.app.goo.gl/5fP1AaijP3dYGGgN9
Checked valves clearances. All but one intake valve is too loose, a few of them 380 (so more than a whole shim worth of wear after 45 minutes of hard driving). All of the exhaust valves are as I measured them before.
Any other takes on this? Should intake wear at a different rate than exhaust? Seems especially fast wear to me, and fits with the warning from the machinist. Also surprised just how bad it sounds from being one shim size out of adjustment, has anyone ever heard an s38 sound this bad from loose valves?
Car feels ok , can't feel any noticeable difference in driveability.
Intake supertech valves only come in the long version. Machinist said he didn't have the tools to grind them all down a few mm required to get them to the same height as the old valves. He also warned me that valves are only hardened on the tips, and that grinding them down past the hardened part can ruin them. I called supertech, the told me there was 5mm of hardness and I only need to remove 3mm. $200 later to a different machinist and the valves are the right height.
I've driven it maybe 300 miles since being back together, signed up for a one hour track day on Thursday, and did a valve adjustment right before driving to the track just to make sure wear was as expected. All of the exhaust valves are the same as when assembled. Half of the intake valves have larger clearances than when assembled, a few of them out of spec, so I correct all but one that still has 330 clearance, since I don't have the right shim.
45 minutes on track, I notice a new noise when pulling off. From listening as closely as I can, it sounds like it's coming from the intake side of the head, and that it's too frequent to be bottom end:
https://photos.app.goo.gl/5fP1AaijP3dYGGgN9
Checked valves clearances. All but one intake valve is too loose, a few of them 380 (so more than a whole shim worth of wear after 45 minutes of hard driving). All of the exhaust valves are as I measured them before.
Any other takes on this? Should intake wear at a different rate than exhaust? Seems especially fast wear to me, and fits with the warning from the machinist. Also surprised just how bad it sounds from being one shim size out of adjustment, has anyone ever heard an s38 sound this bad from loose valves?
Car feels ok , can't feel any noticeable difference in driveability.