TheSamba.com :: View topic - Someone explain to me cylinder head rebuilding please

Wed Jul 23, 2008 4:51 pm

I am assembling a 1600 out of good used parts, mostly just to learn how they work. This will be a spare engine in case the one in my car ever needs work.

Anyway, I have a set of cylinder heads that I was told came off a running engine. They do not appear to have any cracks, but it can be hard to tell with all the carbon on there. Let's just assume at this point that they're crack-free, for the sake of my understanding how you rebuild a head.

What does a full-on engine rebuilder do to rebuild a set of heads? New valves all around? New exhaust valves only? What else gets machined/replaced? And then, retrospectively, what would a prudent but cheap engine rebuilder have machined/replaced?

Thanks!
Zach

Wed Jul 23, 2008 5:19 pm

A top notch rebuild will cost as much as a new stock head.

Glass bead heads, replace all exhaust valves, replace all valve guides, flycut heads .010-.020 to clean up seating surface, grind valves and valve seats. replace any broken exhaust studs, replace valve springs.

Wed Jul 23, 2008 5:29 pm

I am (partly) in the same situation as you…

the main aspect to rebuilding stock cylinder heads is inspection/replacement of the valve guides (the brass things which the valves run up and down in, these wear and get sloppy), and also inspection/re-cutting/replacement of the valve seats… that’s the surface where the valve seats/seals inside the combustion chamber, which has a specific geometry. Those two jobs are best left to a competent machine shop. There are other things, but those two are the main issues.

The rest of it is cleaning, inspection and replacement of other items (valves, collets, springs etc) which may be worn… its best to have the heads bead blasted completely clean before you decide whether to rebuild them as there may be cracks - look very closely. The valves may be able to be re-used… a machine shop will clean up the angled surface on the back of the valve if it is out of spec.

A valve spring compressor will enable you to remove valves and strip the head completely so you can wash the heads at home and do an initial inspection. I have stripped my heads, intend to get them bead blasted and serviced at the machine shop (giving them the valves too) then I'm going to re-assemble at home and cut the new valves in (because I havent done this before).

I'm not an expert, hope this helps :)

Thu Jul 24, 2008 7:17 am

"The valves may be able to be re-used"
NEVER---- NEVER ever reuse exhaust valves ever, and only on the most cheap arse rebuilds consider reusing the inlets ,