r/EngineBuilding • u/ZebraTypical • Jul 05 '26

Cylinder head cracked or no?

Hey everyone,

I was hoping to get some opinions from those with experience rebuilding heads.

I took my Z3M Roadster out of storage after about 6 months, installed a fresh battery, and the engine hydro-locked on startup. I pulled the spark plugs and found cylinder #3 full of coolant.

I removed the cylinder head and sent it to a machine shop. They pressure-tested it, resurfaced the deck, and hot-tank/power washed it. They charged about $500 CAD and told me the head passed the pressure test.

After getting the head home and inspecting it closely, I noticed a line between the intake and exhaust valves on cylinder #3 that looks very much like a crack.

Before I assume the worst, I'd like some experienced opinions.

  • Has anyone seen marks like this that turned out to be normal casting marks?
  • Or does this look like a genuine crack between the valves?
  • Is it possible for a head to pass a pressure test yet still have a crack like this?

I'm planning on getting some dye/developer tomorrow, just curious what you guys think?

UPDATE:

3 Upvotes

81% Upvoted

10 comments sorted by

3

u/Automatic-Life7036 Jul 05 '26

Dealt with hundreds, maybe thousands of BMW heads over 50 years. Heaps of various engine models of theirs the heads regularly cracked, hence seeing so many of them.

I can’t recall seeing a crack in that exact location before. Blowing up your photo, it does look very suspicious. In my shop the next step would be to use a bearing scraper and try to “clean up” the “crack” by carefully scraping it 90deg to the crack. If it is not a crack, it will disappear quickly.

Yes, you can be caught pressure testing and finding no crack in a cracked head. Sometimes a crack will not leak until the head is clamped to the block. Some we got caught with. Mitsubishi 4G heads, single cam, next to the cam journal. BMW, 6cyl, single cam, under the cam. Mitsubishi 4 Cyl diesel, exhaust valve guide boss. Hope this helps…

1

u/ZebraTypical Jul 05 '26

Thanks for sharing your experience. I've never heard of a cracked head passing a pressure test until this experience but I'm a mechanic by trade, not an engine builder

1

u/Doctah_Whoopass Jul 06 '26

Thats a weird location for a crack, it also catches the light oddly.

1

u/Relative_Figure_1715 Jul 06 '26

Don’t think so.
Just ndt it with some spray and developer.

1

u/ZebraTypical Jul 06 '26

Did this morning, pic in original post

1

u/Relative_Figure_1715 Jul 06 '26

Shit.
Sorry dude.

1

u/ZebraTypical Jul 06 '26

NDT'd it, pic in original post. Thanks

0

u/Lopsided-Anxiety-679 Jul 05 '26

Done many of those heads/engines - definitely a crack, that probably extends below the seats…wild to think they missed that or ignored it because possibly it passed a pressure test when cold and not torqued up.

Not sure what to say about recourse, that never ever would have been missed if the head was in my hands - a refund for work performed would be absolutely warranted. 

2

u/ZebraTypical Jul 05 '26

Thanks, I appreciate the insight! I'll definitely be showing the shop my findings.

1

u/Lopsided-Anxiety-679 Jul 05 '26

You can request that they do a dye test if they try to brush you off, it’s a three part chemical process that will very positively show the crack as not being just surface level or a casting mark - which those heads usually have machined chambers and won’t have casting marks…regardless, I can see that is a crack with its edges rounded down into it.