Spark knock with rebuilt head on 2F (1 Viewer)

[85roktoy]

New to me rig. PO had the head rebuilt due to a broke valve and worn valve guides. Runs great and is punchy but has a pretty substantial spark knock. I haven’t messed with the timing yet but is this common with having a head rebuilt? Compression is high in 175’s across all cylinders. I was going to run 93 to see if that helps. Will it harm anything driving like this until I address it?

 

[Mark Jennings]

Chances are, timing to far advanced. Hopefully the timing advance didn’t hide other issues.

Also, take the plugs out and roll the engine so each position is at the top of its stroke and inspect the top of the pistons. If there is a lot of carbon, that may cause it to knock also. The P.O. May or may not have cleaned the piston tops when the head was rebuilt.

 

[Mark Jennings]

Also at 175 psi on each cylinder, looks like the machine shop overdid it if they shaved the head to make it flat....compression should be in the 150 range.

 

[Mark W]

I expect to see 175 on a fresh build, higher if the compression is bumped up. Toyota says 149 is nominal and 113 is minimum acceptable. I have never seen a fresh engine read that low though.

Mark...

 

[85roktoy]

Yes I believe the head was shaved when it was rebuilt.

 

[John Smith]

Yes I believe the head was shaved when it was rebuilt.

Then run the 93 octane with normal timing and you should get rid of the knock.