Monday, December 14, 2020

Winter Projects 2019/20 - Part 3 - Front of Engine cleaning and Throttle Body rebuild

 

Cleaning the front of the engine

January 1, 2020 - I realize that two consecutive blog posts focused on cleaning a greasy engine is not very interesting to read about, so I'll try to be as brief as possible here. Being tedious, repetitive work, I found I often put myself  "on autopilot" as I cleaned.

During this mindless activity I was able to get acquainted with everything installed in that engine bay, assess the condition of the hardware, the wiring, hoses and anything else that was subject to wear, weathering, incompetent mechanics, and aging. The pictures below show various stages of before and after.

 

You can see the results of the upper balance shaft seal failing in the upper third of this picture. This is where the majority of the oil that was all over the timing belt came from. The gear you see is the timing belt drive gear located on the crankshaft snout. The bare threaded studs are where the timing belt auto tensioner was installed.



To make enough room to get at the engine front, I first removed the cooling fans. The radiator was left installed, but was covered with a 1/4" thick styrofoam panel to protect it. 

I used the same cleaning process - spraying  Simple Green Aircraft cleaner onto small areas, scrubbing the grime loose, and cleaning with a rag - on the front of the engine as I did on the driver's side. Above is a shot of the oil pump and crank shaft area. The oil pump is located on the crankshaft snout in this engine. Almost all the grimy sludge to the right of the crank was oil that leaked from the upper balance shaft sealing o-ring which had failed. That to the left of the crankshaft had come from the lower balance shaft which is just out of view at the extreme left. There had been little or no oil actually leaking from the front main seal, the oil pump, or the oil pan gasket, seen along the bottom curve of the engine.


Lower balance shaft on the left, crankshaft on the right. The empty holes in the oil pump are for the two lower belt cover mounting bolts.


While cleaning the engine I had plenty of opportunity to identify hardware that would need to be replaced, like the hose clamps. Some were the wrong type and others way too big for their hoses. Bel-Metric (www.belmetric.com) has the correct European hose clamps, yellow zinc plated metric hardware, correct fuel and brake line fittings and more. They are Gretchen's favorite hardware supplier!


The belts, pulleys, and rollers had come off easily and were cleaned in a manual parts washer. 


This is a balance shaft drive gear, flange, and washer in the parts cleaner


To fix the upper balance shaft seals, the cover and balance shaft were removed. The seal at the rear of the shaft had also failed, and was leaking not oil, but false air, and very badly. Air would enter the block at this point, go through the crankcase, out the air-oil separator, into the intake duct, and then enter the idle control valve air stream, without being metered by the air flow meter. This helped contribute to the very lumpy, lean idle. 

The blue masking tape covered the intake ports so that dirt and other foreign matter was prevented from entering the engine. The plastic bags were used to stuff in the gaps around the engine when I wasn't working on it, to keep the cat out! You'd be amazed how hard it is to keep cat hair out of openings in the engine!

The front section of the balance shaft housing (not shown) which contains the forward bearing slides off the end of the shaft and is sealed to the main part of the block with an o-ring. The front of this shiny section is exactly where the o-ring is located. You can see the groove for it in the lower picture. The balance shaft cover contains the other half of the groove.

The more or less clean engine. Some of the oil stains wouldn't come off using the cleaning method I used; if I had the engine out of the car and completely disassembled, the block could have been cleaned in other ways and would have ended up looking brand new. This may happen at some point in the future.


Once the front of the engine had been cleaned and the new oil seals installed, I worked my way around to the passenger side of the engine. There is very little access on this side, unless you remove the exhaust and frame crossmember underneath the engine. That work hadn't been planned for in this phase, so I just cleaned what I could get access to. 

The blue silicone you see above has been applied over the rear seal on the lower balance shaft; it was leaking false air just as badly as the upper shaft on the other side of the engine. This Mickey-Mouse temporary repair should last a year or two until I can pull the engine and replace the lower balance shaft seals properly.

View of the oil pan sump showing the drain plug and oil level warning sensor. Also just visible at the right edge of the picture is the crossmember. This ties the two front frame rails together, and the engine, steering, and front suspension are all mounted to it.


The exhaust comes down right in this area as well. The wires you see just beyond and below the pipes are for the starter, which you have to remove to take the timing belts off the engine. Once the starter is out you mount a locking device on the flywheel; this prevents the engine from turning as you to loosen the bolt on the front of the crankshaft to remove the timing and balance shaft drive gears and harmonic damper assembly.


The freshly cleaned oil pan front and AC compressor


The cleaned engine from underneath/front. The plastic bag over the crank snout was to help reduce the possibility of rust forming on the exposed machined surface, and to keep any dirt away from the new oil seal.

This is a view of the lower balance shaft with its new oil seal installed. The surrounding reinforced areas are where the power steering pump, balance shaft tensioner, and balance shaft idler roller all mount.
 

 

 Cleaning and rebuilding the throttle body

I cleaned and rebuilt the throttle body at the same time I was cleaning the engine. I purchased the $20.00 rebuild kit from 944Online and went to work.

 

First I disassembled the unit as far as possible, and then cleaned everything with Simple Green Aircraft Cleaner. The throttle body itself was actually not very dirty, but the throttle position sensor (or TPS, pictured above) attached to the end of the throttle shaft was full of the oil that had been sucked out of the air-oil separator, courtesy of the air leaking through rear seals on both balance shaft housings. 

The TPS contains two switches that signal the DME (engine computer) when the throttle is completely closed (at idle) and when it is completely open (actually 2/3 or more open), so the DME can make proper fueling and timing calculations. 

Since the TPS is located underneath the throttle body when installed, and because the throttle shaft seals were completely disintegrated, this is where a lot of oil ended up. The result was that the wide-open throttle (WOT) switch was intermittent due to oil all over the contacts. The idle position switch was less affected because it's a sealed microswitch, as opposed to the completely open construction of the WOT switch. The TPS is a very overpriced part, and so I opened it up, cleaned it out, applied a high quality contact cleaner to the WOT contacts, and resealed it.

View of the back side of the throttle body. The groove is where the sealing o-ring is located - there is no other gasket between it and the intake manifold. 


This picture shows how disintegrated the shaft seals were. It took a fair bit of careful cleaning and a magnifying glass to get all the old seal debris out without damaging or dislodging the needle bearings. This was the first time I had ever seen needle bearings used on a throttle shaft. The old marketing slogan rings true - There is no substitute!

These leaking seals were another big source of false air contributing to a rough idle.

The 944Online kit contained all new throttle shaft seals, new main o-ring for the base of the throttle body, and all new stainless hardware. I didn't use the stainless mounting screws; stainless steel fasteners are not compatible with the magnesium intake manifold on the 944S and would cause accelerated corrosion of the threaded mounting holes. Instead, the original steel fasteners were installed with zinc anti-seize. This is a far less reactive combination of dissimilar metals.

 

There was a bit of wear in the throttle bore, creating another less than ideal situation for idle quality. I just hoped the impact would be minimal. There should be as close to an air tight seal as practical when the throttle is closed. But this is exactly the kind of thing the Motronic Adaptive Idle system was designed to compensate for; hopefully it will cope with the air leak this is going to cause.


Here is the finished unit, ready to install.


Next time, Fresh paint and some reassembly

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