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ALFAcentro T E C H Q & A
Tech QuestionsOctober 2002 Tech Q & A

Answers by Technical Editor Rex Chalmers

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October Topics:

Enlarged 1600 Pistons | Broken Alternator Stud | Street Headers | Milano HVAC Fires
Reverse Clunk | Steering Wheel Removal | Prop Shaft Dissasembly | Axle Limit Straps
Battery Drain Diagnosis | Cam Timing

Enlarged 1600 Pistons : question by Frank | Duetto 1600

Will appreciate your comments on the following. I discovered that my duetto with the 1570cc engine had been modified by the previous owner about 10 years back where he had replaced the original 78mm bore piston and steel liner for thiner liner and 80mm bore piston thinking that it will change the engine into a 1750 engine. I do not think he had changed the cam shaft either so it is still 1600 stock cams. The thing is he didn't realised that the stroke difference between the 1600 (82mm) and 1750 (88.5mm) is 5.5mm! So now I have an engine that is about 1642cc being 80 bore and 82 stroke. My question is that since the bore and piston is now effectively 80mm while the combustion chamber in the head is still stock 78mm and not enlarged, do you think it is a problem since the piston cylinder is now 2mm wider then the combustion chamber now. I had just recently acquired the car, it starts immediately even when cold (I now live in the tropics) but I am worried about the long term effect (as if it is not already too late after 10 years of driving).

I am thinking about putting back the original 78mm bore piston - that is if by using 80mm I will continue to damage the engine. also with the presumably out of shape combustion chamber, is it likely to lessen power and torque output then the original? As I have never driven any other duetto apart from the spider 2000, so I have nothing to compare what I have now and what is stock!
Answer : No worries Frank, just use a 1750 head gasket. The reason for this is that the gasket needs to have proper seal to the cylinder bore. Regarding your question concerning any damage you may be doing to your engine, I’ve used the 80mm bore for many street and time trial engines with great success. I’ve also built more than a few “1600” race motors with 80mm and larger bores and have never experienced a problem due to the bore size. It is actually a very nice upgrade for a street and race engine alike. The increase in HP and torque is quite useful and generally produces a wider power and torque band.. You won’t do any damage to your engine if the modifications were done correctly. As far as which cylinder head to use is concerned, if you are going to have porting done go with a small port 1600 as this head has a very thick casting and provides the best palate for the head porting guru. If you aren’t going to port, either a large port 1600 or a 1750 would be your best head choice.

Broken Alternator Stud : question by Jeff Nantais | ’88 Spider

The other day I heard a rattling noise when I pulled out of the garage. Whe I opened the hood I noticed the alternator was vibrating as though the sliding belt tensioner was loose.

When I shut the car off, I grabbed the alternator a moved it back and forth - the stud that mounts the tensioner bar to the water pump had sheared clean off! Glad I didn't ignore the rattle. So I've got the bar removed, and now I've got two questions:

How do I remove the remaining "root" of the stud from the water pump/block (it's sheared flush - nothing to grab), and how would this have happened?

I assume that I can use a shortened spare exhaust stud - once I get the root out of it's firmly planted position...
Answer : The best way to remove the broken stud in your water pump is to replace the water pump. Due to the position of the stud, it is necessary to remove the water pump pulley to drill the stud. Unless you have an Alfetta pump with a bolt on pulley, you will have to press off the pulley to get a perpendicular angle with your drill. After removing the pulley center drill the sheared stud and use an appropriate extractor. If necessary drill completely out, re-thread or install a heli-coil. In my 30+ years of working on Alfas, I have seen this failure only one or two times. As I recall, the cause was traced back to a loose lower mounting bolt, causing excessive vibration and stress on the adjusting bracket. This cause appears to be backed up by your statement that you could move the alternator back and forth. If the lower mounting bolt had been tight, you could never have moved the alternator by hand.

Street Headers : question by Jeff Nantais | ’88 Spider

I just recently aquired a Spider with dual webers and standard converted electronic distributor. My plans are to put on headers and a after martket electronic distributor with a little abit of fire behind it. The reason I want a different distributor is to get rid of the chessy vacumn that is installed with a mechanical type a different type setup as a kit. My question is as follows: 1. Where do I find a inexpensive headers? 2. What diameter pipe do I use for the exhaust? I was thinking about 2.25 - 2.5" but I am afraid to have too little back pressure.
Answer : As far as vendors for inexpensive headers is concerned, I would try our friends at International Auto Parts, Centerline, Vick Autosports, or Alfa Ricambi. I am sure that there are other Alfa parts purveyors who can supply headers as well; these are the ones I am most familiar with. For a basically stock engine a 2 1/4” outlet pipe seems to be the best compromise for a street power band.

If any of you are looking for Competition headers, give
Sperry Valve Works or Paul Spruell a call. Sperry Valve Works makes a set of competition headers that start out at 1 3/4” and taper out to 1 7/8”. They have found that these headers give the broadest power band for competition Alfa race engines. The outlet pipe for this application is 2 1/2’. I just talked to Stuart at Sperry Valve Works and they are currently developing a “tri Y” header for Alfa, initial dyno results look promising.

Milano HVAC Fires : question by Phil Waldrop | ‘87 Milano Platinum

The HVAC blower motor control resistor ignited an accumulation of South Georgia pine straw and burned the motor and/or the adjacent wiring. My shop manual does not say how to get at that stuff, and I don't want to tear things up.

Answer : Unfortunately your smoldering wiring event is not an isolated event for a Milano HVAC system. Once we get you into the bowels of your blower give building a shield for the resistor serious consideration. To access the blower motor and resistor, you have to remove the blower motor. It is located just to the East of the gas pedal. Unplug the wiring, remove the drain hose, and screws holding the fan into it’s housing. Then remove the fan assembly. The resistor is now revealed. I’ve been told that it is impossible to remove the fan assembly without removing the dash. I agree that it is tight, but if you are patient, it can be done.

Editor's Note: It is also highly advisable to fashion a screen to cover the cabin air intake located uder the hood near the windshield wiper motor. This will prevent any such episodes in the future.

Reverse Clunk : question by Stephen Hinchliffe | ’66 Duetto

When the car is put into reverse and the power applied there is a clunking sound coming from the rear end. It sends a shuddering feeling down the car. As I seldom use the car I can't say precisely when this occurred. Also the front suspension appears uneven. The car seems a little lopsided. I can't tell you the cars history prior to my ownership but the guy was a D:I:Y freak although I expect his skills at auto rebuiding may be questionable.
Answer : Most likely suspect would be one of and / or several of the components of the drive shaft. Starting at the front, check the flex disc for cracks, dry rotting or other signs of wear. The next suspect in the line is the center bearing and support. The support can be torn, dry rotted or the mounting bracket may be loose. The center bearing is best checked by removing the drive shaft and feeling for play, wear or bearing failure. The next items to check are the drive shaft U-joints. The best way to check U-joints is to remove the rear section of the drive shaft and make sure that they are not seized or are too loose. If all of the drive shaft components check out, there is always the possibility of the cause being a malfunctioning clutch.

Steering Wheel Removal : question by Dom | ’92 Spider Veloce

I'd like to change the present steering wheel on my Spider with a wooden version. I unbolted the main bolt, however, cannot pull out the present steering wheel. Is there a trick to it?
Answer : The only trick, if you can call it that, is to own or have access to Alfa special tool puller A.30451. Since you don’t have one, I would contact your local AROC chapter. Many chapters have some of their own special tools to loan out or at least will try and help you locate the tool you need.

Please take note: DO NOT use a jaw type puller on this wheel; you will do irreparable damage to it.

I believe that your wheel is equipped with an air bag. I do not believe that removal of the air bag is a legal operation. Aside from the legal implications, you should consider what the insurance ramifications would be should you or someone else be injured in an accident in your vehicle.

Propeller Shaft Disassembly: question by Jani Hartikainen | ’71 Spider

I am in the process of replacing propeller shaft intermediate bearing. This seemed quite an easy task, but separating the flange from the front propeller shaft has been impossible - so far (I haven't tried TNT yet). I have owners workshop manual from Brooklands Books, but it is missing one tiny detail: how to open keys locking the flange to the front propeller. Any help in dismantling the propeller shaft is appreciated.
Answer : Once you have the lock nut and the main nut removed, screw the main nut back on until the shaft is flush with the top of the nut. Now for the magic. Place the shaft in a press, yes a press. The flange is held on by means of a keyway and a tapered shaft, it is not coming off without judicious application of several tons of direct force. Now support the flange in the press, I suggest use of 2 1/2 circle plates. Believe it or not, I have actually seen flanges bent in the press, so proper support of the flange is essential. Heating up the flange for several minutes with a propane torch will also help reduce the amount of force needed to achieve separation of the flange from the shaft. I don’t recommend the use of pullers, as it is difficult to achieve enough evenly placed force to get the flange to separate.

Axle Limit Straps : question by Tim Crowell | ’69 Spider

I noticed two canvas straps, approximately 2" in width, on the left and right side of the rear axle. What is the purpose of these, and where can I find replacement parts?
Answer : These straps are commonly referred to as limit straps. Their function is to limit the travel of the rear axle. If these straps were not there the only thing holding up the rear axle when rear suspension travel reaches its limit would be the shock absorbers.

Battery Drain : question by Nicole | ‘91 Spider

I recently purchased my spider. I replaced the battery shortly after because the car would not start. I then continued to have problems getting the car to start. I figured out that the radio was not turning off, I replaced it and a fuse as to not continue to drain the battery. I thought for sure that I had found the problem, but turning the key still gives no indication of juice. No lights, no sound, not unless I jump it. I have multi metered the connection at the battery but I am unsure as to where to go from here. Any thoughts as to what I may want to check next. This is the beginning of a new project for me and I do have the workshop manual, however it does not have a lot of troubleshooting. Thanks for any information.
Answer : The standard procedure for tracking down a battery drain requires that you have a fully charged battery and a multimeter. Disconnect the negative cable of the battery, set the meter to mA/A dc, and connect the positive cable of the multi meter to the negative post of the battery and the other to the negative cable. Note the amount of voltage draw. Most ECUs will draw 10mA or more continuously. Some ECU draw is normal, if you want to take the ECU out of the equation, Disconnect the main cable from the ECU so you can see how much errant draw there actually is. Now pull down the fuse box and disconnect the first fuse, and note the draw. If the draw drops you have found at least one source of your voltage draw. Now repeat the procedure, removing one fuse at a time. By the end of the fuse pulling party, you will hopefully have found your voltage draw. If not, you will have to manually disconnect the 12V leads to the non-fused accessories on your vehicle one at a time.

Cam Timing : question by Thomas | ’85 Giulietta Nuovo

I want to change my cam timing to something better. Currently my cams on the 2.0 liter alfa is inlet opens at 23 degrees btdc & closes at 42 degrees abdc. The exhaust valve is the same opening at 42 and closes at 23. For both the inlet & exhaust that is a duration of 245 degrees. Now to work out the MOP I halved 245 by 2 = 122.5 less the 23 btdc gives me a MOP of 99.5. I want to make the MOP about 110. Timing now will be about inlet opens at 13 degrees btdc and close at 52 degrees abdc.

The question is, is this a good move and what can I expect performance wise by making the overlap smaller. In South Africa BMW brought out a 333i with the same duration and stroke with the MOP been 110 degrees and that car, whilst the engine is bigger, goes very well with a MOP of 110 degrees.

Answer : In general the power band is moved up in the rpm range and low-end torque is reduced by moving the lobe center higher. The engineers at Alfa have set lobe centers on specific models for reasons specific to the character of each application. By that I mean, some cars require optimal performance in high rpm ranges, for others economy is the main requirement, low end torque for some, emissions for others, etc., etc.,etc….

Most 4cylinder Alfas of all flavors that are not equipped with variable cam timing respond very well to lobe centers around 102 degrees. To optimize the power band for any given combination of engine components, dyno testing is by far your best solution. Also, bear in mind that the cam timing marks on Alfa 4cyl. Engines work on the same theory as the Alfa oil pressure gage; it is an indication of the cam timing, not an exact measurement. At my shop, I use a degree wheel to setup cam timing, most owners would be fairly concerned if they knew how far of most of the cam timing marks actually are. Use of paper templates to adjust cam timing not only assumes that the original mark is correct, but also assumes that the new mark is scribed in an extremely accurate fashion.

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