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Old 05-01-2018, 08:16 AM   #151
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Square tooth Gates belts are readily available in the USA and we stock them for $34.
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Old 05-05-2018, 07:25 PM   #152
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Quote:
Originally Posted by ROG100 View Post
Square tooth Gates belts are readily available in the USA....
I checked quite a few websites without finding it. All my faves (928 Intl, Pelican, Vertex, RM European) plus a half-dozen other Porsche and 928 vendors.

$29 through eBay, delivered.
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Old 05-05-2018, 07:48 PM   #153
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Default Intake tube polishing

Here's a few pictures and discussion on polishing the intake tubes.

This picture shows the first set of tools used on the tube. They're in order of use, left-to-right.

The first tool is a eye hook on a rope that drag either a Scotchbrite pad or rag through the tube. The trick is two large washers that force those against the sides of the tube. The tube is a bit more than 1 1/2" and the washers are 22mm.

With some mineral spirits on the scratchy pad, the inside of the tubes got fairly clean. Then the rag gets the solvent. When I first tried the sandpaper flap, it got gunked up really quickly and the working part had to get cut off. That's OK but I was going through the paper pretty quickly. Cleaning it first worked well.

The second step was to use the wire wheel on the ends. The wheel is 1 1/2" and fit the tube well. Lightly pressing up/down/left/right and the ends got nice and shiny. The nose of the drill fit into the tube so it'd get 4" in from the end.

Then comes the sandpaper flap. That's a "locally sourced" tool. The spring shaft is from a magnetic pick-up tool. With a finishing nail pressed into the end, it could get clamped tightly in the drill chuck. The sandpaper is a 1" wide sanding belt cut in half. Then the belt gets duct-taped to the shaft and it's ready to go.

I fed the flap in a few times from each end and worked in back-and-forth a lot. After each of the first two or three cycles the end needed to be cut off but after that it wasn't getting clogged with oily dirt. I was surprised how much gunk was inside the tubes.
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Old 05-05-2018, 07:49 PM   #154
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Default Tube polishing, cont'd

The next step is to grind the inlet end. The tools are used left-to-right. The half-moon file was rarely employed but helped where the casting line was especially thick.

Which reminds me... I'm curious as to how the tubes are made. I always thought they were cast and there were mold separation lines. I'm starting to think they were cast in two or more parts and then welded together. From the inside, it looks like it may be welded. That'd explain why the "casting lines" are so thick. It might be cheaper to make that way, too. Anyways...

The goal of the grinding was to make the inlet end more circular and wider at the mouth. The tubes don't all line up with the plenum right and opening up the tube and rounding off the lip should help air flow.

The main tool is the barrel grinder. Using that, the inlet gets shaped more into a "V" or maybe a tulip shape. Takes a good while to do especially to make it circular and clean up the two weld/casting lines.

The ball grinder cleans up any unfortunate gouges and bumps deeper in the inlet. It's also good for smoothing down the bends right after the inlet.

The cone grinder is used to smooth the inside after it's been cut back and to shape the lip. The tube, as made, has a fairly square lip and a few passes at different angles makes it a quarter-round.

The rotary sander (110 grit) bit takes out a lot of course grinding marks. It's also good for reaching down the tube to the first bends.

Finally, some sandpaper (220 grit) is used to get the surface smooth. That pie-shaped piece is a section of self-adhesive sanding disk. Quite handy as I'd stick it to a gloved finger and could get some good action with it. All the preceding tools are rotary and this one goes across those. I'd do it on the inlet and then on the outlet where the wire brush left some scratching. The ends are nicely smooth to the touch afterwards.
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File Type: jpg PolishingTools2.jpg (139.3 KB, 0 views)
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Old 05-05-2018, 08:11 PM   #155
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Default Tube Polishing, Cont'd

This pictures show the before and after. The first pic is the inlet after cleaning with the eye-hook thing. Note the thickness of the lip and how square it is. The surface feels rough.

The second and third pics show the results of grinding and the flapper. The pics were taken before cleaning the tubes out with the eye-hook, clean towel sections and lacquer thinner. I'll clean them again and blow them out to ensure not grit gets sucked into the engine.

The texture is really exaggerated in the pics. Might be the lighting or smearing of the metal. (Check the bits on the grinders) It's a little "dimply" but very smooth. The third pic shows the inside and you can see the flapper has cleaned up the tube.

The tube inlet is about 1/2 as thick after the grinding and is rounded. The thinner lip blends smoothly with the rest of the tube about 2" in.
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File Type: jpg TubeOriginal.jpg (168.1 KB, 0 views)
File Type: jpg PolishedTube1.jpg (146.5 KB, 0 views)
File Type: jpg PolishedTube2.jpg (133.3 KB, 0 views)
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Old 05-05-2018, 08:23 PM   #156
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Default Tube polishing, cont'd

This is the debris that came out. The black pile is from using the wire wheel and the sandpaper flapper. Maybe 2 tablespoons of crud. The initial scouring took out most of the oily dirt. Note the sparkles of Al in the pile as those tools do work the surface back a bit and take off the tiny nubs from the casting.

The silver pile is the aluminum taken off in grinding. It's 1-2 teaspoonfuls.

The whole operation took almost an hour per tube. Maybe not the most valuable use of time. I've been mulling this over since I started modifying the 928 so 15 years. "Can ya port that intake manifold?" Just had to give it a whirl.

A friend asked how much power it'd yield. I had to be honest: "Something between 5 hp and 0.5 hp." I don't have high hopes but if it's 5hp, I'll be super happy. Assuming 300hp a 1% increase in air flow would net 3hp. Then again, I'll never know.

Just a few more pre-build things to get done, like fix the wiring harness, and it'll be assembly time.
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File Type: jpg TubeDebris.jpg (153.0 KB, 0 views)
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Last edited by GlenL; 05-06-2018 at 07:47 AM.
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Old 05-07-2018, 03:54 PM   #157
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Quote:
Originally Posted by GlenL View Post
I checked quite a few websites without finding it. All my faves (928 Intl, Pelican, Vertex, RM European) plus a half-dozen other Porsche and 928 vendors.

$29 through eBay, delivered.
http://shop.928intl.com/Timing-Belt-...28-105-157-00/
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Old 05-21-2018, 10:26 PM   #158
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Moving along towards assembly. The block went back on the stand today.

Here's a couple of pictures showing how the block was drilled to allow use of a later oil pump. This '89 pump (discussed previously) has a different oiling path that pumps oil through the bearing and, from there, it drains back into the pan. Early pumps draw the oil from behind the seal and may suck in air through the seal. This is better (or simply "better") and the pump itself, although used, is likely tighter than the original one.

The first pic shows the drilled hole and the inside view of the pump. The drain is the oval area. The second pic shows marking the drain area on the block.

I also used Plastigage to size the rod journals. Using one rod and an old bearing, I checked the clearance each journal. All were in the range 0.045mm to 0.075mm which is in-spec (0.02-0.07) or real close to it. Considering the old bearing is a bit worn, it looks really good. This gives reassurance that the rod journals aren't worn and some guidance if the new bearings are too tight or too loose as to where to move the bearings to get a better fitment.
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File Type: jpg OilPump2.jpg (233.4 KB, 0 views)
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