Head trials and tribulations

Specific conversations and info for the BMW E28 M5 and M535i.
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Randomg
Posts: 443
Joined: Jul 12, 2007 3:12 PM
Location: Seattle

Head trials and tribulations

Post by Randomg »

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.
m535is
Posts: 1314
Joined: Feb 12, 2006 1:00 PM
Location: Greenville SC
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Re: Head trials and tribulations

Post by m535is »

My experience with this head, as the system wears, the clearance between the cam and shim gets smaller, especially after doing major head work, as the valves wear in the seats. So much so that on a fresh head I set the valves on the loose side because I know they will tighten up. For you to be getting a larger gap means the shim, bucket or valve is getting shorter. I hate to say it but I think your original machinist was correct. There was not enough hardness in the valve to take off that material. Unfortunately the only way I can think of to tell is to pull the cam tray off and inspect the tops of the valves.

Regards,
Rob
Randomg
Posts: 443
Joined: Jul 12, 2007 3:12 PM
Location: Seattle

Re: Head trials and tribulations

Post by Randomg »

Late update on this one. Took off the cam, top of the valves looked okay. Readjusted the valves and hoping that I don't see clearance increase further. I Right as I was getting it all back together I noticed two loose bolts on the fan pulley on one side, so I suspect the terrible noise might have actually been the loose pulley.
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