Subaru rear main thrust conversion

[AC sports]

As some may know the early flat 4's have centre main thrust washer location.
We are looking at adding an additional rear thrust surface at the back of the case halves.
Has anyone done this? How would you do it? I'm thinking case half on a mill bed. A right angle cutter on the mill. Cutter same diameter as thrust washer. Mill away one case half at a time to the correct depth.
Ideas welcome.
Thanks

[Curtis Mc]

Paging MotionMachine (Dale)

Here is his video>> https://www.youtube.com/watch?v=oNuTxfXy8sg

[MotionMachine]

As some may know the early flat 4's have centre main thrust washer location.
We are looking at adding an additional rear thrust surface at the back of the case halves.
Has anyone done this? How would you do it? I'm thinking case half on a mill bed. A right angle cutter on the mill. Cutter same diameter as thrust washer. Mill away one case half at a time to the correct depth.
Ideas welcome.
Thanks

Quite honestly, this job should be done on a purpose built fixture with the case halves bolted together so that all machining is done referenced from one datum location. There are 2 datum holes on the pan side of a Subaru but I've probed some that were not in the same X location. If you do the halves separately using 2 different datums, it's highly unlikely that the thrust faces would line up exactly. And there is not a lot of room for error. The datum hole is the only reference to establish the location of the thrust, so you'd have to come up with a way to set your tool height at the center of the datum hole. I can probe it and use my optical tool setter to get my zero set. I also see a lot of stack up error... your 90 degree adapter not exactly square to the table, tool not exactly square in it's holder, mainline not dead square, interrupted cut, etc. Having said all that, if you really want to pursue this, on the next one I do, I can measure the distance from the original center thrust face to the new rear location. This spec obviously is not on any factory blueprint as the blocks only had one thrust but it would be accurate.

[modok]

Either make bushings and line bore it, or stand it up on a big bed mill.
If you don't have any line boring tools nor a large bed mill,....then, well, you might consider making some line boring tools, since you have a mill and lathe, then you can make them.

if you have enough spacers maybe could do it in a bridegport, expanding facing head would be nice.

[AC sports]

Appreciate the replies. I don't have the luxury of a cnc mill unfortunately MM. It will need to be done either on a line boring machine with special tool or the mill manually as Modok suggests I guess. I'll see how everything lines up and secures on the bed first.

[MotionMachine]

That would be a challenge on a traditional line boring machine. I've line bored Subaru's on my line bore previous to doing them on the CNC, and would think it'd be very difficult to accurately cut the thrust, especially the inside surface. I forgot that I still have the first test block I converted so I've measured the distance from the rear side of the center thrust to the rear of the rear thrust at 115.75mm. The rear thrust width spec is 19mm, not 18mm like the center. Depending on the brand of bearing you use, they will either be tight or loose in the block at 19mm because the bearing width between the flanges vary brand to brand. Your best bet is to just shoot for 19mm. On a side note, one major bearing maker came out with an o.s. thrust for Suby's. All they did was move the flanges away from each other, not make them thicker. So the bearing itself flops back and forth in the block! This was early on in production, hopefully they fixed it.
Here's a video on cutting the bearing tangs after the conversion. You must be sure to not totally cut away all the material at the center location as that will give you a direct internal oil leak. This is a danger on blocks that from new have a wider than normal chamfer on the center thrust.

https://www.youtube.com/watch?v=JlEYaZGyXnw

[AC sports]

That's great information. I didn't even consider the bearing / tang mod.
I'll take another look at it after the weekend when my head is clear.
Appreciate the reply.

[modok]

Five years later....now I get a request to do this job.

BIG THANKS to MotionMachine for measuring and posting it here for future use.

[MotionMachine]

I'm going from memory but am pretty sure that if the block is standing on it's nose on a mill table, the distance from the center of the rear datum hole to the rear thrust surface is 6mm. I made a plug that fits snug in the datum hole, touched off on it with the probe, then calculated the tool height from there. You could get close enough probably by just touching the tool to the plug and finish the cut at -.236". Cutting the inner thrust is the challenge if you don't have the right tooling or fixturing but I'm sure it can be done with some other method.

[modok]

I'm thinking stand it up and use automatic facing head, but I may also just tell them to go away depending on how I feel about it tomorrow.
I see no performance benefit to doing this.
Nice to see you are still here.
What happened to your precision ground subaru "post" fixture? did you sell it?

[MotionMachine]

All my Subaru tooling/fixtures/programs are going to another shop who just took delivery of a new RMC V40. They do Subaru work now but this will greatly expand their capabilities.

[modok]

I DID IT
With a bridgeport, and an enco automatic facing head.
Came out very nice indeed