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Unread 08-02-2019, 09:32 PM   #211
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Default Leak down percentages

Got the leak down numbers which are paired with the compression number:

Cyl PSI LD %
1 140 10
2 140 12
3 130 16
4 150 10
5 145 11
6 145 8
7 140 12
8 130 18

The correlation on the graph is really clear. The leak down percentages don't mean anything as far as leakage except for relative amounts of leaking.

I had a craptastic "Pittsburgh" tester kit on the shelf and it was a mess as many Harbor Freight tools are. I couldn't make sense of the reading which would snap to new values on each test of a single cylinder. It took a while to get something repeatable out of it. The first step was to open the "percentage" gauge and re-adjust the scale.

Inside the gauge, which is pretty standard, there's a Bourdon tube that's connected by an arm and gear to the needle. The calibration is by bending a little arm to read higher/lower. (There's no zero and span, just zero.) I twisted it so the gauge read 90% at atmospheric pressure and that pulled the bottom up, too.

The real problem is the pressure regulator. On each use it'd pick a new applied pressure and wouldn't be repeatable even under identical conditions. It also did a craptastic job of regulating the pressure at all. The more flow; the lower the pressure even with a much higher input pressure than output.

So... What I'd do is to readjust the regulator on each cylinder until the measured percentage was stable and the applied pressure was 1 Bar. And tap on the gauges so they weren't stuck. This gave repeatable results going back to prior holes for a check.

If you haven't checked one out, a leak down tester is pretty simple. There's a regulator with its output measured by a gauge and then the air goes through a tiny orifice. After the orifice is the "percentage gauge." Then the air runs through a hose into the cylinder. What you're supposed to do is run the pressure with the outlet capped and adjust the regulator to make that read zero percent leakage. (Makes sense.) Then the second gauge shows the lower pressure proportionate to how much air is flowing through the orifice. But! The regulator is crap so each run would have a different zero and a different reading. Sometimes by 10 to 20 percent. Useless!

1 bar was often close to zero and seemed usable so I adjusted the applied pressure to at least be consistent. While hard numbers are appealing, relative numbers and consistency are good enough.

The final analysis is that #3 and #8 are worse but not terrible. I'm not convinced the rings are broken although that's a likely problem.

I really wish I'd have checked the gaps of the top rings after installation. I sized the rings and bores and put rings into specific holes to compensate but didn't measure the gaps on each hole. It'd be interesting to see if that top ring gap correlated at all to the leakage and compression numbers.
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Last edited by GlenL; 08-03-2019 at 10:48 AM..
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Unread 08-28-2019, 09:27 AM   #212
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Default Pressure brake-bleeding

No progress on the engine problems. Pull it, take it apart and see what's what? No rush to take on that work right now.

I did resolve a mushy brake pedal. My assistant (kids) are grown (mostly) and at least less available for brake bleeding. To get it done, I grabbed a vacuum pump/bleeder and used that for some bleeding and flushing. That moves a fair amount of fluid but I'd notice at some times it'd be foamy. I chalked that up to air leaking in around the bleed screw. Nope. It was sucking in air through the seals.

That turns out to have been a big mistake. An ex-Porsche tech finally told me that the vacuum bleed will suck air in through the caliper piston seals and seems he was right. After first doing it, I'd try some pedal-pumping bleeding when I had help which would make it better and then I'd vacuum bleed it which would be no change, or worse. (Duh!)

At the track, the ex-mechanic told me about problems with vacuum bleeding and a guy offered to use his pressure bleeder on the car. That was a clear improvement.

Back home, I got a Motive Products Power Brake Bleeder model 0100 for European brake reservoirs. It's the cap to the reservoir that makes the difference between kits. I ran a quart through, drove it, and then did another quart. Now the brakes are fairly decent.

So... Don't use the vacuum bleeder. I got it to test vacuum components and help tune vacuum-advance distributors. That's all it's good for.
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Last edited by GlenL; 08-28-2019 at 01:26 PM..
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Unread 09-21-2019, 11:26 PM   #213
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Default Bad ignition switch

I've been working on electrical gremlins lately. Warm evenings and baseball on the radio lend themselves to mild puttering.

Learning a lot about the wiring system on the 928. Some people have these things memorized but I'm getting there that bus 30 is unswitched battery, 31 is ground, X is accessory and 15 is run.

A few things have eluded resolution along the way. The turn signal indicator light and engine temperature are intermittent. The speedometer doesn't work. The volt meter bounces a lot with turn signals and brakes.

I had cleaned the grounds previously and revisited that. No difference. So I started to check voltages and resistances in the system. I won't list them all but some things don't seem to follow what they should be. What really was interesting was that bus 15 was about a half volt less than bus 30 with the car running and no other lights on. Hmmm... That should be a direct connection with a negligible difference

So it was time to pull the pod and check the wiring to the pod and the ignition switch. And, look, the ignition switch is busted and the halves are separating. Got a used out of the spares box and Ohm'd it out. Should work fine.

Hopefully this'll be the start of getting it all working. I'll be fixing that tang for the horn contact that broke off. Two steps this way, one step that way, it's inevitable.
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Unread 10-13-2019, 09:56 PM   #214
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I've put the electrics to right...at least mostly.

The problem with the speedometer was the speedometer itself. With the instrument cluster out, I could compare the resistance into the speedo to anther unit. Swapped in another speedo and now it works.

The connector for the coolant temperature is still a little fussy. Needs a wiggle to make it work, sometimes.

The voltage measurement seems better but the gauge still drips too much when the turn signal goes on. What helped with that was cleaning the power feed from the jump post. There are three heavy gauge wires that run from the post and plug into the front of the fuse panel.

Something I found was that the wiring diagram doesn't completely match the wiring diagram. Something that really stymied me is below. Schematic Part IX shows that the "right side" connector to the pod has a wire between 7R and 11R. 11R connects to the ground for most of gauges and the wire from it runs, eventually, to the speedo pick-up. Measuring the speedo pick-up wire in the fuse panel to ground showed like 7 Ohms when according to the diagram it should be zero.

With the pod removed, I could measure that 7R was not connected to 11R. I expected a wire crimped into both of the pins. Looking at a spare harness (save everything!) it wasn't connected either. Eventually, what I found was that 7R and 11R were connected as a clean short in the pod. Argh...

But, now the speedo works. The turn signal light works all the time. The horn tang is re-attached. The intermittent wiper works. All the pod lights work.

But, that gear for the odometer was broken on the old speedo and just crumbled on its replacement. Next time...

I was at the track, BIR, last weekend for one final time this year. Had some issues with oil ejection and brakes but still had some good runs. With the speedo working, I could see the car posting 150 mph going into turn 1. I've often thought The Zombie had more power than my other 928 and, it seems, that's true. The other car will typically post nearer 140.

Now to get the engine fully sorted and see what the lap times are.
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Unread 07-16-2020, 12:04 AM   #215
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It's been a while since I've had something to post on this car.

My other 928 has, meanwhile, gotten head gaskets, a new transmission and bearings on the torque tube. A bit of WYAIT madness but that all worked out fine.

So here's The Zombie at the track. Had a good day at the Brainerd International Raceway "Competition Course" that everyone calls the "Short Track." It's 2.5 miles and 14 corners. More technical than the 3.2 mile, 10 corner regular track.

Had a good day and the engine ran great. Very little oil used and almost nothing in the catch can. It's showing some drips after sessions so I should check for a leak.

The driving was good and the car is well balanced. I'm using Hankook competition tires this year and they're good.

The car drives a lot differently on a technical track compared to my other 928 as the transmission has a lower final drive (2.2 vs. 2.75) and the torque peak is a bit higher (3700 vs. 3500). That means grabbing 2nd out of a few corners instead of 3rd to keep the RPMs up. It's fun.

The car does well against the P-cars that seem to populate PCA events these days. I was getting passed by a parade of high-end GT-whatever cars. Often not well driven but with that much power, handling and PASM they go fast.

The event ended early when I found that I had only 1st gear before a session. I'd notice some difficult shifting, like not finding 3rd, on the track but this hint told me the day was over.
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Unread 07-16-2020, 12:17 AM   #216
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The shifting problem was pretty obvious and it was the shifter cup. THe plstic liner had cracked away and the cup had, eventually, come completely off the ball.Gotta kick myself for not replacing this when the whole drivetrain was on the floor of the garage. Fortunately, I had a new one (spotted it cheap on eBay) and could actually find it.

Replacing the shifter cup was fiddly and took about 5 hours. The critical part was getting the jam nut loose that's holding the cup to the rod. After 40 (?) years it could be corroded solid.

To get access, the exhaust system needs to be dropped and the forward heat shield removed. The shift lever needs to be released from both of the rods. THe the forward rod can be pulled to the side enough to access the cup. Not much room and hard to get leverage. With a vice grip on the rod and multiple attempt, the jam nut came loose. Luckily, the cup unscrewed without tools.

Getting the new cup on takes some luck to get the threads started. It's also important to measure how far to screw it in so the lever will be positioned right. Once the cup is back on, it'd be miserable to remove it.

With the cup on, it's time to reconnect the rods to the shift lever. I lubed the cup with white lithium grease. It took a while to get it positioned over the ball but then a crow bar levering against the top of the tunnel made short work of forcing it on. Done! Except for the rest of the reassembly...

Shifts nice. Maybe I'll stuff some GT3s at the next event. There's always hope.
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Unread 08-15-2020, 12:19 PM   #217
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Default Power Steering hose failure

I've figured out where the power steering fluid is going: straight through the hose!

I checked for leaks at fittings and around the pump but couldn't see where it was going. Idling it and looking for drips didn't help, either. I finally figured it out, unfortunately at a track day, as it got bad enough to really see.

It helped to idle the car while holding the wheel all the way over to create some back pressure. Then the fluid comes oozing right out to the hose. Not at the fittings; just straight through the hose.

I'm wondering if later transmission fluids, even though they says "Dexron/Mercon," are incompatible with the hose. Perhaps this was a defective hose in the first place. It was new three years back.

New hose on order. I'm planning to get this one re-lined as a back-up.
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Last edited by GlenL; 08-15-2020 at 03:34 PM..
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Unread 08-30-2020, 11:32 AM   #218
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I like pictures and, I think, most people do. I didn't take pictures of this one. Not much to see, though.

I had rebuilt all of the calipers and that seemed to be working well. "Seemed?" Yeah... I noticed some extra brake dust sticking to the right-front wheel and figured it was either brake fluid of dripping splashing up from the engine or catch can that's mounted nearby.

When swapping brake pads, the answer became clear: When using a big screwdriver to force the pads back, a few drops of fluid hit the floor. I like clear failures. The quick fix was to go to the box of calipers and pick out a decent-looking right-front with the thread-in hose. Swapped it in. Bled it. Seems to be working fine.

The question is why there was a leak coming from the piston. Disassembly didn't show anything wrong. The piston was clean and without corrosion. The seal was mounted right and not twisted or anything. So I rebuilt it again and it's now he back-up.

The interesting part was getting a new seal kit and new piston. Centric offers the right piston that's available from Rock Auto for $14.50 and the seal/boot for $1.50:
CENTRIC 14654042 Caliper Piston
CENTRIC 14345006 Caliper Repair Kit

The piston is correct except it doesn't have the notched section on the face of the piston. That faces towards the incoming rotor (down) to help balance the forces on the pad. In any case, good to know it's available as some pistons show pitting and flaking of the plating.
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Unread 10-10-2020, 09:18 PM   #219
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I took the car to a track weekend a couple of weeks back and learned a few things.

The oil ejection problem only happens on the long, 1-mile straight at BIR and only when revving the engine about 5800 RPMs. If shifted at 5800 RPMs, instead of 6300, there will be very little to no oil in the catch can. The amount ejected when running to the higher RPMs seems to be decreasing, too. I'm hoping that the rings bed in better and I can drive the car harder.

The low, low 2.2 final drive ratio is really hurting lap times. Coming out of most hard turns, the engine is turning 3000 RPMs in 3rd gear. That's well below the torque peak and the car accelerates slowly. The remedy is to grab 2nd a lot. That's fun and gets the car moving. I'm not happy with the extra shifting and it'd be faster to use 3rd from corner-to-corner like I'm used to.

The car has an '86 G28/11 "Borg Warner" transmission and I can update to a 2.73 rear for money and time. I figure that it's losing at least 2 seconds a lap due to this. It's a comparatively cheap way to gain back the time. Or just put in an old G28/05 after a rebuild.
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