head rebuilding tips?

[zooky]

rebuilding a 1.6TD head and have a few questions:

1. I can get a 'O' drill bit (.316) into the valve guides, but nothing bigger, is that acceptable?

2. If not, can I change the guides myself?

3. If I knock the precombustion chambers out to clean in there, can I reuse them or do they need to be replaced?

4. I searched for porting tips but didnt find much details, is it worth the effort on these heads? I plan on fuel and boost mods if that makes a difference.

This engine is going into something heavier than a VW, probally a 2WD Toyota Pickup (3000 lbs?? or so) so I need to get what I can out of the engine. Any other tips or advice would be helpful

[tylernt]

1. Bentley lists .315 to .316 as the spec for new guides. No wear limit is listed that I can see, though.

2. Yes, if you have (access to) a hydraulic press. Not sure how many tons you need, though, probably a lot. You can also test for guide wear by putting a valve in and seeing how much it rocks side to side. Wear limit is .051 for exhaust and .039 for intake valves.

3. Dunno.

4. I plan to have the ports polished on a spare head I have. I'm not planning on porting it though. VW diesel heads are famous for developing cracks between valves, and I'm afraid that removing any more material will lead to catastrophic failure. I don't know that much about it though, maybe you could just remove material from the manifold end of the port and be fine.

People have put diesels in Vanagons which are pretty heavy (and have a lot of wind resistance). Engines tend to last only 100,000mi in this heavy-duty usage though. How much HP depends on how much $$, really. Turbocharging up to 30psi is possible, and with the fuelling mods to go with it you can get 100-150HP or more.

[935racer]

Check the valve guides for wear using a dial indicator and rocking the valve side to side as shown in the bentley. Yeah you can change the guides yourself if you have a press. You cna pretty much quarantee they will need to be replaced though, vw guides suck big time.

AS far as porting go's if you don't know much about it dont take out too much material. Dont try and polish the ports, keep the surface a bit ruff but get rid of the castings ridges. Porting isn't gonna make the cracks between the valves better or worse.

[tylernt]

Dont try and polish the ports, keep the surface a bit ruff but get rid of the castings ridges.

I know that the surface of the gasoline intake ports should be a little rough to keep the air/fuel mixture turbulent. But exhaust ports and diesel intake ports only flow air, so wouldn't a mirror smooth polish reduce friction and improve HP?

Just curious. I've often wondered about this.

[935racer]

You would think but the answer is no, air actually flows better over a slighty rougher surface than completely smooth, about 120 grit works really nice for intake and exhaust ports. I've done mirror polishes and it actually hurt the flow, the head porter that showed me the ropes said the air "sticks" to
completely smooth aluminum. I am gona try cermaic coated ports sometime soon and see what that does...

[Fisher]

The Head Shop I go to in Seattle uses Cast Iron Guides on rebuilds, better for Diesel, they come Knurled, they take the heat better.