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· The Suck, Squeeze, Bang, Blow Moderator,
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I've done a few engines now where I've upgraded the 97 engine into the later and stronger TLR cases and also simply converted a TLR engine into the TLS configuration.

The 98> and TLR cases basically are the same (there were some minor changes to the sump depth etc) straight from the cast.

Both cases have the TLS Oil Cooler Bosses cast on, only the TLS has these drilled and tapped out, so I'm going to explain how to convert a TLR case to a TLS case. This can be done with the engine assembled but the problem of swarf and machining flat surfaces for the banjo bolt washers is an extra headache so I would recommend stripping the engine.

The TLS has an oil gallery blanking plug fitted to divert the oil from the pump out of the right hand boss, through the oil cooler and then back in via the left hand boss. There is a small bleed hole in this plug btw.

Firstly you need the oil gallery blanking plug and oil filter mounting spigot from your old TLS cases, they can be made from scratch but first method is easier. To remove the oil gallery plug make sure you have a nice tight fitting allen key and apply heat to the plug and surrounding alloy before trying to screw out as it's loctited in and will round the allen socket if you don't heat it.

For the oil filter spigot I wrap a piece of 3-4mm rubber around the freshly washed (petrol or thinners) spigot and clamp with mole grips. It's not loctited and usually comes undone quite easily.

The oil gallery blanking plug is a 1/4 BSPT thread but if you need to make your own then I suggest converting to metric, ie M12 x 1.25

To make your own start with an M8 Stainless socket head bolt and cut the M12 thread on it, then drill the 3.68 (or 3.5mm) hole in the centre before parting it off etc.

Next you need to drill & tap the oil gallery in the case to suit either the stock plug or the new metric plug, if using a stock plug then you need to drill to 11.8mm before tapping, if using the M12 plug then you don't need to drill as the gallery is approx 10.5mm dia

You can use either a bottom tap or taper but you want to end up with the plug flush when it goes tight. Use loctite when fitting but don't fit until you have done the bosses otherwise you'll end up with trapped swarf etc.

Next are the oil cooler line bosses. Although the bosses are flat topped it's best to mill about 0.25mm off them to create a nice flat seat for the alloy washers to seal on.

The bosses need drilling/milling out to 12mm. The right hand boss is drilled until it breaks into the gallery and the drill point touches the opposite side of the gallery to ensure a full bore hole. The left boss is drilled until the drill touches the centre casting around the oil filter spigot boss.

Next tap the holes with an M14 x 1.5 tap to the top of the threaded flutes on the tap to ensure the banjo bolt doesn't bottom out. I always start the tapp off on the mill to ensure it's square and finish by hand. If the hole isn't tapped square you will have a nightmare getting the banjo washers to seal.


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