Head Gasket Retention

Better life through machine work……

Here we go again….. Another day, another customer with chronic head gasket problems on a big bore that was built by yet another “pro” :confused: What was the answer? Studs, copper head gaskets, O-rings, and copper spray?

So let’s dive into engine building 101;
Everything on an engine needs to work as one harmonious system. The cam should be balanced with the intake and exhaust for best power, easy enough. Sealing combustion promotes maximum efficiency, while minimizing combustion by-products in the crankcase that cause engine component deterioration. This is all basic stuff.

Head studs and so forth do have their place, but are rarely needed. Studs using high torque values will absolutely pull a cylinder out of round causing increased blow-by, thereby increasing engine and/or ring wear. Ring wear in turn will eventually lead to more blow-by, power, and effiency losses over time.
The best studs will fully bottom out in the factory holes to distribute the added load over a broader area.

Copper gaskets are notorious for “cold weeping”, where the gasket will leak coolant around the outside of the head until it gets warm enough to expand and seal. They are usually made of a thicker material, and will require extra machine work to get the piston to deck clearance back where you want it. They usually require more torque to do the job (see studs).

O-rings? Every O-ring setup I have seen on an ATV engine is grooved on the cylinder side only……. This absolutely defies any logic I can muster, so I won’t even comment on it, except to say that turbo race cars use a receiver groove in the head.

So what is the answer?
Have the head and cylinder machined flat and as smooth as possible, just like you would for any decent rebuild. Use a flat piece of thick safety glass or granite that is nice and flat. Use a piece of wet/dry paper on the surface (I use 3M spray adhesive), and “lap” the head until it is smooth. I recommend a minimum of 400 grit final finish (600-800 is even better). Even the best machine work is not always smooth enough for Cometic (MLS) gaskets, they are extremely sensitive to surface imperfections. Better safe than sorry.

The next step is to chamfer all bolt holes, which not only helps even out and spread the load, it also eliminates any “summits” that would pull up around the threads. Any type of riser around the bolt that would come with fastener torque, will lower clamping force across the rest of the gasket.

You will want to do this to the head and cylinder. What you’ll end up with is a better performing engine that lasts far longer for a few bucks worth of the right tools rather than a few hundred dollars worth of “band-aid” fixes.

This entry was posted on Friday, May 29th, 2009 at 3:36 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.