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How to remesh the sump strainer

Relevant to:

  • 9000 B204/234 engines (made after 1994)
  • NG900 B204/234 engines (all)
  • 9-5 B205/235 engines

The strainer featured in the article is from a 9-5 B235 engine but the proceedure applies to the 4 cylinder 9000 (after 1993), NG900 and 9-3 (up to 2002). Please note that each variant has a slightly different shaped strainer and that strainers are not interchangeable between models.

The strainer must be able to pick up oil freely from the sump to prevent oil starvation damage to the crankshaft, shell bearings, pistons & cylinder bores, balance shafts, camshafts and turbo charger.


Kit required (assuming that the sump is already removed):
Pliers
Chisel
Ball pein hammer

Materials required:

20 mesh woven wire mesh
Sump washer
Strainer oil seal: SAAB oe part # 9138009
Disposable gloves
Deagreaser or other cleaning agent

Oil absorbing granules or sawdust

Estimated time required:
0.75 hrs (assuming the sump has been removed from the engine)


Background

The phenomenon of particles accumulating in the sump and eventual blocking of the oil pick up pipe sump strainer causing oil starvation on 4 cylinder engines is commonly referred to as sludging (see related article). Readers who are concerned about sludging or potential sludging and the attendant engine damage should drop the sump to inspect the strainer. Our own cars invariably have this done as a matter of course, along with draining the oil cooler but we also change the mesh in the strainer from a design having 30 holes per inch to one that has 20 (this is 20 mesh). As well as increasing the open area across the strainer 'mouth', this allows the passage of soft sludge through the mesh -instead of blocking it- and into the oil filter where it will be trapped.

The author acknowledges the work of retired US aircraft engineer D.O.Shultz, who applied his aviation experience to the sludging problem within SAAB engines. Realising that the mesh in the SAAB engine was finer than that required within an aeroplane engine with which he had many years knowledge, he saw no good reason why the same mesh could not be fitted within the car engine. More than that, a set of calculations were performed to work out the open area of the mesh and the effect on the passage of material through the mesh. By changing to a type of mesh with a greater open area, more smaller particles could pass through the mesh, while at the same time significantly reducing the risk of the strainer blocking.

Standard and modified strainers compared

Method

Poke a hole through the old mesh with the chisel and prise out as much of the mesh as possible.  Next, start levering the peened over retaining ring at the edge.  Typically, engines made before 2000 will be easier to treat because later engines are fitted with a strainer that has 5 small spot welds (a severe case of over-engineering!). These small welds are broken with the chisel to allow the retaining ring to be levered fully back. 

Prepairing the strainer to accept a new mesh

Remove any loose particles and clean the strainer thoroughly. We tend to immerse the strainer in an old oil container with one side removed that we have filled with a suitable cleaning agent. In the photo (below) cleaning is only half complete. It is important to clean inside the pick up pipe - we often use a cork to seal the end and leave the pipe to soak before using pipe cleaners and compressed air to finish off.

An old oil container and toothbrush come in handy for cleaning the strainer and the price is right

The next stage involves pressing the strainer into a piece of paper to make a template for the new mesh. We sourced our mesh from Inoxia, a Chemical Supplies Company. We are very pleased with the quality of the product.
http://www.inoxia.co.uk/rw/product/product.aspx?ID=135

Press the strainer into a piece of paper to form a template for the new mesh

You will need shears or very sharp scissors to cut the mesh.  It is easy to replicate the domed effect of the original mesh by gently pressing in the centre when fitting. This is NOT a job to undertake in an hurry and it is essential that no stray pieces of wire are left that could be sucked into the engine.

Take care when fitting the new mesh and press the centre in to replicte the domed effect of the original

When you are happy with the shape and fit of the new mesh, fold the retaining ring back by degrees carefully, working gradually all the way around. Use pliers and a small pin hammer for the task. The secret is not to attempt to fold the metal back in one go but to do it gradually. Don't worry too much if the strainer looks a little deformed - it is easy to press back into shape.

Always use a new seal on the sump pick up pipe, because they become brittle in service and cleaning with solvent will tend to make them split. Remember that the seal is there to make an airtight seal - it is plain daft not to change the seal. This is OE part # 9138009

When you are happy with the look of the strainer, lubricate the seal with silicone spay and push the strainer pipe into the recesss in the sump. This may take some effort (normal). Next, tighten the torx type screws that secure the strainer to the vase of the sump and refit the baffle and its screws. Voila! Job done.


Not convinced?

Altering the design of an engine component may seem like a radical step but bear in mind that SAAB's own engines prior to 1994 were fitted with 20 mesh strainers! Other automotive (and some aircraft) engines have used 20 mesh without any problems but the author would like readers to know that we have modified at least 50 cars and operated them over time and some considerable distance without incident. Of more releavance, a number of these modified strainers have been fitted by technicians to their own SAABs.

The author has to admit, however, that on one or two cars, owners have reported that the engines seem a little less oil-tight than before. Since the strainer has no bearing on whether an engine is oil tight or not, we suspect that what is actually happening is that modified cars have (predictably) greater oil throughput (about 10%) and consequently run at higher oil pressure than before because a restriction has been removed. In short, we think that the modification may expose pre-existing conditions that were not noticed because of low oil pressure. The attention of readers is drawn to SAAB Technical Bulletin 210-2417 ed.4 (April 2006). Due to copyright restrictions this cannot be reproduced here but the gist is that affected cars should be fitted with Crankcase ventilation renovation kit 55 561 200 and (if required) hose-sump pipe 55 560 445, camshaft cover pipe 55 560 463 (a MUST, according to us!) and the check valve with hose 93 99 973.

From our perspective, the conversion reduces the risk of a blocked strainer and the resulting oil starvation. We believe that a magnetic sump plug is another worthwhile modification. For those wishing to follow this up, we can advise that the thread is the same is that fitted to most Fords (Escort, Mondeo), Honda and Mazda.

June 2011: additional comments

During the last month, the author was contacted by a reader who had read somewhere that the best way to prevent oil starvation and sludging was to fit a bigger oil filter. Unfortunately this well-meaning advice is incorrect due to a logic error (please refer to the oil circuit schematic provided below). In the B2x4 & 2x5 engine, oil is sucked up by the oil pump through the mesh of the sump strainer and if this gets blocked, the size of the oil filter fitted is irrelevant because oil cannot reach it! In more than ten years experience, not a single SAAB engine has been seen with a blocked oil filter. That said, it would be wrong to dismiss the idea of looking at the oil filter entirely, as it is generally accepted that oil does not wear out so much as require replacement due to a build up of contaminants and with that in mind, superior filtration (by use of finer filtration medium) is desirable.

SAAB B2x4/2x5 oil circuit schematic

 

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