Does this knock sound familiar to anyone?


#1

Hey everyone. My spec e30 project is happily back off the back burner, trying to get it running right now. Unfortunately since buying the car, it has had a pronounced single knock or tick, half engine speed, every rotation, regardless of rpm or cold vs warm.
First thing I did after bringing it home was adjust the valves, with no improvement. Recently rechecked them to find still in spec
.
In the last month I did a new timing belt and tensioner(needed belt and suspected bearing was bad), water pump, rotor, cam seal. Knock still there.

Leak down test yesturday (engine cold), suspecting a bent valve, showed 0.5%-1.5% on all cylinders.

Ran the car today with no valve cover to hopefully catch something I missed or at least localize the sound but I’m still at a loss. Pushed on rockers, pulled plug wires one by one, was unable to change the knocking sound. I know it’s towards the front two cylinders. Is it still a bent valve closing slowly but sealing? Some kind of a worn rocker or cam bearing?


#2

I struggled with the exact same issue last year. After blowing a head gasket, I sent the head into the machine shop to get decked and rebuilt. Reassembled, then had almost identical knock. Tinkered and replaced a lot of valve train components, but ultimately discovered that the head was shaved just past tolerance and pistons 2 and 3 where kissing the head. Swapped in a thicker head gasket and knock disappeared. I have video of the knocking, PM me and I’ll send it to ya


#3

Interesting, thanks for the new place to look. Should be able to measure the head height while it’s still in place.


#4

Well, so I was able to get a decent measurement on the head height and it is factory original, unmachined.

Is it possible to have a slightly bent valve that may be slow to close but still seals well in a leakdown test?


#5

I would say probably not. The idea of “slow to close” sounds kinda unlikely. But a compression test would be a better check of your theory than a leakdown test. The former is nicely dynamic so should catch the “slow close”. A leakdown is too static.

Rich Bratton did a bunch of testing re. shaved heads. He found that shaving the head is a bad idea. The mechanical timing retardation that occurs costs you more hp then the compression you gain.


#6

Thanks Ranger, I was thinking I’d try a compression test next, see if it shows anything different. The head looks to measure unshaved. Haven’t found an easy way to measure the deck height of the block yet, but besides the noise, the engine seems to be proving more and more healthy with everything I check.

Is it normal for the rockers to move laterally on the shaft as the cam engages them? The #1 exhaust rocker moves maybe 0.050" front to rear every exhaust cycle.