sandblasted cylinder heads

alfaomega · 12-11-2014, 12:31 AM

Hello I hope you can help, I've got my cylinder heads back from the machine shop, and they have been sandblasted, can you tell from the picture whether they are ok to use on my 1986 3,2 as they are ?

Raceboy · Raceboy's Garage

The contact surface between the head and cylinder should be machined mirror flat, it will leak the way you have it now.

alfaomega · 12-11-2014, 01:15 AM

ok thanks
what about the upper contact surface, between the head and cylinder camhousing? on the Camhousing it is allso mirror finich

Raceboy · Raceboy's Garage

Yeah, but you use Loctite 574 there and there is no pressures involved, just sealing for oil.

Lapkritis · Lapkritis's Garage

X2 on the contact surface with cylinder... way too rough. I prefer a little Permatex copper spray on that surface even when smooth.

JFairman · 12-11-2014, 10:52 AM

If you lap the cylinder to the sealing surface of the head by putting some valve grinding compound on the sandblasted sealing surface and then rotate it around and around and back and forth by hand with only the weight of the cylinder head for pressure on it until it's smooth it may seal and work alright.
Machining it would probably be better if the cost isn't a problem.

For the head to cam tower surface Hondabond or Yamabond sealant works just as well. It cost a lot less from the motorcycle dealers or Amazon and it cleans up easily with laquer thinner or acetone.

cgarr · cgarr's Garage

If it was sand and not bead I would machine the sealing surface. Bead blasting will not change the dimension.

alfaomega · 12-13-2014, 10:13 AM

I have Just talked to the shop, it was Bead not sand
he told that he made the surface that way on porpuse, that the rough surface will "crush", and seal just fine, ???
Does that make any sense?
(Sorry for my english)

Lapkritis · Lapkritis's Garage

No, doesn't make sense. This is a machined surface sealing against another machined surface of same metals. Make one side rough and it'll be unstable.

Edit: if this were crush seal even, compare it to a crush joint like a cis fuel distribution block or other banjo fitting. Are the surfaces rough or smooth? Those joints even have a sacrificial soft metal sandwich to help it close up.