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March 22, 2016

Oil Filter Adapter

[Click the pics for a better view]

TR6 cars still retained the old-fashioned canister oil filter arrangements.  While they were effective full-flow filters, they tended to be messier to replace than more modern spin on filters.  They also lacked the anti-drainback feature of many spin on filters.

To remedy this situation, many TR6 owners have bought and installed spin on adapters for their cars.  There is one ubiquitous model of adapter that is widely available.  It mounts in place of the canister filter and provides the right angle bend to allow attachment of a spin on filter in a vertical orientation.

I bought one of these adapters, and soon realized what others already knew:  the adapter can't be installed with the filter vertical because the filter fouls the clutch slave cylinder.  The adapter has to be installed with the filter at a pronounced angle.

Now granted, this is not a big deal in terms of filter effectiveness, but it looked tacky to me.  It somehow offended my inner sense of righteous design.  Was this just lazy engineering?  Was it a good design that was borrowed from another application, even though the fit was imperfect?  I didn't know, but I reflexively started looking for ways around it.  I found some very short filters that would fit the adapter vertically, but the clearance was still sort of tight, and I was a little concerned about using a filter with less than half the filter media area.

In the end, since it looked like we were going to have another few weeks of chilly weather here on th plains, I decided I might have time to make something from scratch.  Having built an oil filter adapter for my Triumph motorcycle a few years ago, I thought I understood the basics, so I got busy.

I stared with a puck of aluminum big enough to fit the original filter cover groove.

I machined a lip around the circumference to fit the groove, and a circular recess to hold a square section O ring (size -227).  That O ring presses against a flat feature on the block, and it keeps the oil going to the filter and the oil from the filter separate.  The store-bought adapter has this seal feature spring loaded, surely to accommodate variations in dimensions on the block.  Since I wasn't worried about portability on my adapter, I just machined it so that when the adapter was torqued down to spec against the outer sealing ring, the inner O ring was compressed by a few thousandths.  I certainly didn't want the inner seal to bottom first, and prevent the outer seal from seating fully.  A little weeping past the inner O ring wouldn't be a big problem.  Besides, the pressure difference across that inner seal is not system oil pressure, but just whatever the pressure drop across the filter is.

So much for the block side of the adapter.  Now for the spin-on side.

Started with a raw chunk of  aluminum, squared it up, drilled and tapped for the filter nipple, and drilled the inlet and outlet oil passages.  Because the adapter block is fairly shallow, the filter nipple bottoms in its hole, so it has to have a relief drilled for the oil outlet.  This implies that I had to take care when installing it that the nipple cutout aligned perfectly with the oil passage.


Did some shaping to make it more pretty, and drilled matching oil passage holes in the block side of the adapter.  I couterbored those passage holes for some square O ring seals (size -013).  If I were doing this again, I might consider making the entire adapter as one piece, which would eliminate the need for these seals.

From the start, I had planned to powder coat the adaptor, but at the last minute decided to anodize it instead.  I though briefly about red or blue, but in the end, landed on boring black.

Installed the filter nipple with red Locktite, and staked it all around.  I don't want it turning.  Then installed the seals and fastened the two parts together.

Installed on the block.  The unit is held to the block with a 7/16 socket head cap screw with a copper crush washer to seal it.  The washer, actually more of a gasket, is a common aircraft part, designated AN900 (AN900-7 for the 7/16 size).

Plenty of clearance now.

Here is a smaller filter that gives even more clearance.

This was probably more of a machining project than an automotive one, but the weather here has been more conducive to shop time than garage time.  Total cost was around $40 for materials, and at about $1/hr for my labor, I came in under the cost of the commercial unit.  But at least the filter now is dead vertical.

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