Tech Tip #171: Deutz Head Gaskets: Composite or MLS

Deutz diesel engines, like any engine, can be frustrating to work on at times and parts help can be hard to find. At Foley Engines we have both the knowledge to help you through those tough times, and the parts to make sure you get it done right the first time.

This Foley Engines Tech Tip discusses Deutz cylinder head gaskets and which type to select, multi-layer steel (aka: MLS) or composite, when servicing an industrial engine such as a Perkins, Deutz or John Deere. While we discuss this in the context of Deutz diesel engines the principles apply to all industrial engines.

What Types Of Head Gaskets Are There?

When ordering a replacement head gasket for a Deutz engine, you might be asked if you have a “composite gasket” or” MLS”. This is an important question and fortunately arriving at the correct answer is very simple. Here is some background to help you out.

1) Multilayer steel head gaskets have been used for years in internal combustion engines. They have as many as 3, 4 or even 7 layers of steel with the outer layers usually composed of “spring steel” to achieve a positive seal. A thin coating of Viton or nitrile rubber is often used between the layers of steel as well as on the external surface to help the gasket seal better. The MLS gasket is a rugged gasket, used very frequently on high horsepower, big bore engines. If properly installed, it will not “blow out” very easily.

The challenge is that a multilayer steel head gasket needs to be installed on a smooth surface, at least 40 Ra (“Rough average”) or smoother, if it is to hold a good seal. It is best if you can get the surface down to 30 Ra (or lower). Another way of measuring smoothness is Rz, which is a better indicator of the texture across the complete head surface. Rz is the average difference between the peak height and valley depth across the head surface and an Rz of 180 or less is the goal to get a good seal with an MLS head gasket.

2) Composite gaskets are a recent innovation in head gaskets. They are far more forgiving of rough surfaces or blocks with protruding liners and hold better on a rough surface. In fact, they need a surface roughness of Ra 40 (or 240 Rz) or higher to seal well. The general maximum surface roughness that a composite head gasket can handle is 100 Ra or 600 Rz. Not only do they seal well on less-than-ideal head surfaces, composite head gaskets cost a less than an MLS head gasket.

Which One Should I Use?

If you are doing a total overhaul of your Deutz engine (and will have the head resurfaced as well, as the top of the block “decked” you probably want to Make sure they know what gasket you have purchased for your engine. If you have an MLS Gasket and they finish the surface for a composite gasket, you may run into troubles down the road.

If you are the average guy, with a Deutz powered stump grinder or aerial lift, you are pressed for time and need to go right back to work, this might help you in a pinch. While it is always best to go with the gasket type originally specified for your engine, in certain cases you can use either. If you have an engine with an MLS head gasket, and need to replace your head gasket, you can typically use either the composite or the MLS versions. But note, this does not work in the other direction; If you have a composite gasket, you should not use a MLS gasket unless it was originally specified for your engine or your head and deck surfaces have been reconditioned to the appropriate level of smoothness.

Let’s Not Forget …

Cylinder head bolt hardware is important. Cylinder head bolts perform a tough job and shouldn’t automatically be re-used. They endure many temperature cycles and over time will stretch, fatigue, and lose their clamping ability. No amount of head bolt over-tightening will overcome this. While you could invest in a head bolt gauge to measure head bolt stretch, it is less expensive (and easier) to simply replace the head bolts. To help you put on the cylinder head so it stays on, we stock new head bolts for all Deutz diesels.

Summary

Head gasket selection is an important part of the overhaul of a Deutz engine. If you are not going to resurface the block and head, we recommend a conversation with your machinist to make sure you are getting the right work done and using the right gasket. In any case, whichever gasket type your engine may use, we strongly suggest not overlooking replacement head bolts. We also suggest the head bolts be torqued correctly to achieve maximum sealing and with a Deutz head, this is a slightly complicated, multi-step process that is outlined in the Deutz Workshop Manual for your engine.

We hope that this Foley Engines Tech Tip is helpful to those working on Deutz diesel (and other) industrial engines. To support people like you, we stock over 20,000 square feet of Deutz replacement parts, turbos, Workshop Manuals, etc. If you are interested in learning more, some of the following tech tips may also be of interest to you: