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cylinder head surface
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Author:  Sahig131 [ Thu Jul 02, 2009 6:15 pm ]
Post subject:  cylinder head surface
hi guys,
just a quick question,

I hooked up my radiator yesterday and filled it with coolant. This morning i noticed that there was coolant in all 4 cylinders, it had leaked! argh
so Ive taken off the head.

after getting the head back from being milled a couple of months ago i noticed that the surface wasn't smooth, it has concentric grooves and feels a bit like 800 grit sand paper. I was told at the time that this is fine and it was from the old machine they were using...just wondering if this is the case.

thanks,
steve
Author:  Wombat [ Thu Jul 02, 2009 6:37 pm ]
Post subject: 
I think that sound too rough - I'd prefer it to be dead smooth
Author:  BALLISTIC [ Thu Jul 02, 2009 6:59 pm ]
Post subject: 
Yeah should be smooth.
Author:  Convertible Mini [ Thu Jul 02, 2009 7:44 pm ]
Post subject:  Rough surface.
What did they surface it with ? An angle grinder ? Take it to someone with a proper machine and that preferably knows what they are doing when it comes to Minis.
Author:  drmini in aust [ Thu Jul 02, 2009 9:57 pm ]
Post subject: 
You can mill em or surface grind em, either way the head must finish up flat all over and have a decent finish.
I mill them, GR does too.
Author:  mini_mad_matt [ Thu Jul 02, 2009 10:05 pm ]
Post subject: 
The following method was featured in a car magazine technical section i read once.

To surface the cylinder head, get a rear wheel drive car with an open diff.

1. Jack one side up so one wheel is still on the ground.
2. Wrap sandpaper around the tyre that is in the air.
3. Place cylinder head under said tyre.
4. Start car up and put in gear to spin said tyre up.
5. Lower the car until the tyre comes into contact with the cylinder head and move the head forwards and back until the desired amount of metal is taken off.
6. Job done!


Ok so the technical section was just a joke, but it was a really good read. It also had some interesting techniques for decking the block and some other things. :D
Author:  Tombo [ Thu Jul 02, 2009 10:06 pm ]
Post subject: 
Easy way to check, put a quality steel rule on it's edge across the face, no light should get through. When i was doing engines the finish was more like 2000 grit, no problems (we had a good mill)
Author:  TheMiniMan [ Thu Jul 02, 2009 10:28 pm ]
Post subject: 
ha,,, that`s nothing , you should check out Spag-dot-com,,, he ground down the bottom of a rover V8 block by stting on it & dragging it along the concreat footpath with a motorbike towing it along ,,, true!!!! :-)
Author:  mini-dunger [ Fri Jul 03, 2009 12:26 am ]
Post subject: 
if your in SA...... bring here, me fix
Author:  TheMiniMan [ Fri Jul 03, 2009 7:47 am ]
Post subject:  Re: cylinder head surface
Sahig131 wrote:
hi guys,
just a quick question,

I hooked up my radiator yesterday and filled it with coolant. This morning i noticed that there was coolant in all 4 cylinders, it had leaked! argh
so Ive taken off the head.

after getting the head back from being milled a couple of months ago i noticed that the surface wasn't smooth, it has concentric grooves and feels a bit like 800 grit sand paper. I was told at the time that this is fine and it was from the old machine they were using...just wondering if this is the case.

thanks,
steve


Jut as a side note,,, What type/brand of head gasket was used??? Some of the early "monotorque" head gaskets (sivler with the blue lines) had an issue where the thickness of all the blue sealing lines varied greatly & lots of them leaked watwer out the sides

Another thing to look out for is to make sure that (sometimes) after heads have been machined "too much", & while tightening it down, the thread bottoms when the cyl head nuts on the studs (or bolts) & obviously then it wont be pulling the head down any further & may not be actually clamping the head down enough to seal,,, check thread depths & head thickness & add hardened steel washers if need be to combat that problem

I really don`t mind a swirly machined surface,,, it helps the gasket bite,,, just has to be clean & flat is all
Author:  DOZ [ Fri Jul 03, 2009 8:02 am ]
Post subject: 
I use a surface grinder on both the block and head for a smooth and flat/level finish. The engine is turbocharged, never had a problem and I have reused the head gasket 3 times without tearing it (Metro Turbo Group A).

Daniel
Author:  Sahig131 [ Fri Jul 03, 2009 5:53 pm ]
Post subject: 
Quote:
Another thing to look out for is to make sure that (sometimes) after heads have been machined "too much", & while tightening it down, the thread bottoms when the cyl head nuts on the studs (or bolts) & obviously then it wont be pulling the head down any further & may not be actually clamping the head down enough to seal,,, check thread depths & head thickness & add hardened steel washers if need be to combat that problem


another problem solved, thanks :D
gonna start it up tomorrow, should be fun :P
Author:  drmini in aust [ Fri Jul 03, 2009 7:11 pm ]
Post subject: 
Related to the post above, pull all the studs out of the block and wire wheel the top threads. Otherwise, when you tighten the (now thinner) head down, the nuts can bind in the old paint/rust/crud left in the previously unused threads.
If you don't want to pull all the studs out, run a 3/8" UNF dienut down them to clean the threads.
Author:  Sahig131 [ Fri Jul 03, 2009 7:44 pm ]
Post subject: 
done and done
cheers :)
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