I really wonder why people don’t understand how critical the condition of the sealing surfaces of the deck of a block and the fire face of the cylinder head is to head gasket sealing. Old school engines used paper gaskets so you could get away with some flaws, but modern engines use metal head gaskets which require the block/head is 1)absolutely flat and 2)is free of flaws or defects. As you can imagine, metal doesn’t flex and fill defects like a paper gasket can. When I say free of flaws, I mean no scratches, nicks, and dents either. The more cylinder pressure there is (aka boost and horsepower) in an engine, the more critical flatness, surface roughness average, and perfection of the deck/head is. When you look at a factory manual and you see the spec of a block or head needing to be flat within .002″, that’s fine for factory horsepower levels. A quick rule of thumb I use is if you plan on doubling the horsepower, split that spec in half. So for example if a factory 280bhp RB26 has a spec of .002″ for flatness, then it needs to be .001″ for 560bhp. Triple the horsepower and it needs to be absolutely flat. 800+bhp is no laughing matter and the deck/head must be ABSOLUTELY flat and free of ANY defects. The surface roughness average should be also be at least half of stock. When it doubt, have the block and head lapped for the ultimate in sealing force.
The reality is that people often ignore how critical the deck and fire face are. If an engine is loosing gaskets, here’s a list of potential problems:
1. Warped head
2. Warped deck of block
4. Lifting of the head due to detonation and/or weak head bolts
5. Flaws on deck of block or fire face of head
6. Too much horsepower (you need bigger or higher grade studs)
7. Poor surface preparation (see below)
If you are suffering from #6, chances are you already know what I’m writing about here. I am writing this for those people who buy a brand new quality head gasket from HKS, Tomei, Cosworth, Apexi, Greddy, etc., loose a gasket, and then foolishly blame the gasket like a fucking dumb ass. The reality is that it is YOUR fault for not properly preparing the block for your horsepower level. People also like to blame head studs and of course its NEVER their tuning, but come the fuck on: how come the pros can do it right? Detonation and knock can destroy a head gasket real quick; especially if you have all forged components.
Anyhow, before I go off on a full on rant again, here’s a quick tip on how to clean up the deck of a block or a fire face of a head. If the block is not flat or the head is warped, you will have to remove the engine, disassemble it, and take it to a machine shop. This tip is only for cleaning the surfaces up or repairing a minor flaw. It also works for cleaning up the deck if you’re changing a head gasket with the engine in a car. You can also flatten a head if you have more time than money since aluminum is softer.
Get yourself a block of steel (thicker and heavier the better), some 400 grit sandpaper, and WD40. You’ll want to take the block of steel to a machine shop to have them grind and/or lap one surface flat. GRIND, not cut. I did capitalize GRIND.
Wrap the 400 grit sandpaper around the steel block and use the ground surface against the deck of the block or fire face of the cylinder head, spray a shitload of WD40 on the sandpaper and surface to be flattened/repaired, and go at it with smooth strokes along the entire length of the block or head. You will also need a straight edge and feeler gauges to measure for flatness. This picture was taken for illustration only. You’ll want to remove the dowels from the block before sanding so you can sand the entire surface.
That’s it. As with any kind of engine building or assembly, it always takes time or money to do it right. Skipping steps will result in disaster. Pay attention to the details and you will be rewarded with an engine that performs when you need it to. Almost every engine and head built at Cosworth is done this way and trust me, we don’t do it because it’s fun.