[DHABHAR.BEHRAM]

Originally Posted by ilangop

Sir, can it leak from the mechanical pump if the diaphragm ruptures? Because I don't see any possibility of fuel finding its way into crankcase, from the carburetor side. My 118 has got an electric fuel pump and if above can happen, I am saved.

Dear Ilangop - yes, you are correct, over time, the fuel pump diaphragm "perforates", mixing the fuel and oil. In cars having the fuel return line, this problem gets aggravated more, as both fuel and oil get contaminated. Now tell me, how to find out and pinpoint this (besides smelling the oil which will smell of fuel also). This is the interesting part. Go for it! .

Best regards,

Behram Dhabhar

[ilangop]

Originally Posted by DHABHAR.BEHRAM

Dear Ilangop - yes, you are correct, over time, the fuel pump diaphragm "perforates", mixing the fuel and oil. In cars having the fuel return line, this problem gets aggravated more, as both fuel and oil get contaminated. Now tell me, how to find out and pinpoint this (besides smelling the oil which will smell of fuel also). This is the interesting part. Go for it! .

Best regards,

Behram Dhabhar

This is my hypothesis. Could be wrong also.
Engine oil and petrol get mixed inside the pump and flows till the carb. Part of the oil sucked into the intake is burnt and let out as black smoke and eventually foul the spark plugs. In this case all sparkplugs will have almost same amount of soot unlike 1 or 2 plugs with a burnt valve seal.
The rest of the fuel returned to the tank contaminates pure petrol with some engine oil. Now the pump is sucking oil + petrol, adds some more oil leaked into the diaphragm and sends it to the carburetor. And this cycle continues.

[DHABHAR.BEHRAM]

Originally Posted by ilangop

This is my hypothesis. Engine oil and petrol get mixed inside the pump and flows till the carburettor. Part of the oil sucked into the intake is burnt and let out as black smoke and eventually foul the spark plugs. In this case all spark plugs will have almost same amount of soot unlike 1 or 2 plugs with a burnt valve seal. The rest of the fuel returned to the tank contaminates pure petrol with some engine oil. Now the pump is sucking oil + petrol, adds some more oil leaked into the diaphragm and sends it to the carburetor. And this cycle continues.

Dear Ilangop - you are correct, because this is the logic with which this defect will continue to spoil both the petrol and the oil. My question is, in a garage, how will you find out? What are the misleading and the concluding symptoms? . The answer is absolutely fantastic, and hats off to the analytical capability of the person who showed this to me 20+ years back!

Best regards,

Behram Dhabhar

[autocrat]

Originally Posted by DHABHAR.BEHRAM

Dear Ilangop - you are correct, because this is the logic with which this defect will continue to spoil both the petrol and the oil. My question is, in a garage, how will you find out? What are the misleading and the concluding symptoms? . The answer is absolutely fantastic, and hats off to the analytical capability of the person who showed this to me 20+ years back!

Best regards,

Behram Dhabhar

Dear Sir, What if we dip newspaper / blotting paper / filter paper in the fuel? If its pure petrol it will evaporate, if it contains oil it will remain on the paper.

[KkVaidya]

Originally Posted by ilangop

This is my hypothesis. Could be wrong also.
Engine oil and petrol get mixed inside the pump and flows till the carb. Part of the oil sucked into the intake is burnt and let out as black smoke and eventually foul the spark plugs. In this case all sparkplugs will have almost same amount of soot unlike 1 or 2 plugs with a burnt valve seal.
The rest of the fuel returned to the tank contaminates pure petrol with some engine oil. Now the pump is sucking oil + petrol, adds some more oil leaked into the diaphragm and sends it to the carburetor. And this cycle continues.

I still do not understand how the fuel pump is responsible for mixing of engine oil and fuel! As far as I know, it gets mixed due to blow-by in the crankcase.

[DHABHAR.BEHRAM]

Originally Posted by KkVaidya

I still do not understand how the fuel pump is responsible for mixing of engine oil and fuel! As far as I know, it gets mixed due to blow-by in the crankcase.

Dear KkVaidya - a mechanical fuel pump has a diaphragm. On its top is petrol, at its bottom is oil. When the diaphragm perforates, both fluids will mix with each other. Petrol will go in the sump and oil will go in the carburettor. On cars with fuel return line, this dirty petrol / oil mixture will then go in the tank and it will keep on circulating. The engine will miss and sputter as it cannot run on a mixture of petrol and oil!

Dear all - here's what to do to find out. Take a long garden hose (at least 4 feet or longer). Connect it to the engine top cover blow-by opening or positive crankcase ventilation opening, the diameter is almost the same. Start the engine, it will miss and sputter in idling. Try and keep it going for a few seconds by holding the throttle plate slightly open. Hold the open end of the garden hose vertically (be careful), take a match, strike it and hold it to the open end. If a flame continues to burn, petrol has mixed with oil. I saw this being done more than 20 years back. I have done it many times to determine the diaphragm perforation. .

You will not get this information in any Automobile Engineering forum or course. In my opinion, the person who showed me this is a genius. He is just a mechanic working in a garage, but I consider him as one of my gurus. His analytical capability is absolutely fantastic! We sit in the garage for hours, exchanging information on numerous things that we see happening to various cars. Hats off to him.

So, let me ask one more question. Brand new clutch assembly, completely destroyed in 2 kms of drive, 2 times on the same vehicle. What can it be? .

Best regards,

Behram Dhabhar

[KkVaidya]

Originally Posted by DHABHAR.BEHRAM

Dear KkVaidya - a mechanical fuel pump has a diaphragm. On its top is petrol, at its bottom is oil. When the diaphragm perforates, both fluids will mix with each other.

So this is not the phenomenon in an electric fuel pump? And is it that in old cars, converting from a mechanical pump to an electric is a life saver?

[dracul]

Originally Posted by DHABHAR.BEHRAM

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So, let me ask one more question. Brand new clutch assembly, completely destroyed in 2 kms of drive, 2 times on the same vehicle. What can it be? .

Best regards,

Behram Dhabhar

Crank oil seal may leak and oil will enter the clucth assy
and damaged the lining.

[DHABHAR.BEHRAM]

Originally Posted by dracul

Crank oil seal may leak and oil will enter the clucth assembly and damage the lining.

Dear Dracul - it is very good to know that you are analysing. Please read my question. The clutch got destroyed in 2 kms of driving, not 20, 200 or 2000 kms of driving. New clutch was fitted on the same vehicle, again it got destroyed in 2 kms of driving. Same specification clutch fitted in another car having the same specification as the first one worked perfectly for 86000 kms and beyond. Now, please re-analyse. There is so much to learn, it is so interesting!

Best regards,

Behram Dhabhar

[dracul]

I may assume the clutch plate, pressure plate and release bearing had changed. Only thing left is the flywheel, pilot bearing and clutch fork. May be the flywheel surface is uneven and unbalanced so that clutch plate cannot make a good contact with flywheel.
I am sure this is not correct but still a try.
OT BD sir I had missed the opportunity to meet you in Pune(Club sierra meet). Next time I will attend for sure.

[DHABHAR.BEHRAM]

Originally Posted by dracul

1. I may assume the clutch plate, pressure plate and release bearing had changed. Only thing left is the flywheel, pilot bearing and clutch fork. May be the flywheel surface is uneven and unbalanced so that clutch plate cannot make a good contact with flywheel. I am sure this is not correct but still a try. 2. BD sir I had missed the opportunity to meet you in Pune(Club sierra meet). Next time I will attend for sure.

Dear Dracul - my reply is as follows:
1. No. Clutch plate, pressure plate and release bearing had the same specification including part number in both vehicles. First scenario = failure in 2 kms (two times), second scenario = same parts running for >86000 kms in the same vehicle.
2. Always welcome, send me a PM so that I can arrange the formalities.

This absolutely unique clutch case happened in the year 2000. We (my engineer colleague and I) took 4 days to solve it, it was complete mental and physical torture for both of us for 4 days because we did not do anything else, but in the end it was worth the effort. We showed the result to our boss, all 3 of us will never forget. Sadly in today's corporate world, those glorious days are gone, forever. Sad!

Best regards,

Behram Dhabhar

[dracul]

Sir, I cannot think anything other than I said earlier. Please enlighten us.

[DHABHAR.BEHRAM]

Originally Posted by dracul

Sir, I cannot think anything other than I said earlier. Please enlighten us.

Dear Dracul - fyip. .

Best regards,

Behram Dhabhar

TEST CASE STUDY: ANALYSIS OF CLUTCH FAILURE:
Identification of defect: What is the defect? Screeching noise heard as soon as the clutch pedal was operated. Transmission gears not engaging in any gear. Clutch pedal free play increased to more than half pedal travel within 2 kms of run.

What happened when the defect occurred: The vehicle could not be operated, as the transmission gears did not engage in any gear with the engine running. The transmission gears were engaging in gear with the engine not running. Attempt to shift into gear with the engine running produced a small movement of the vehicle, without the gear lever actually slotting into its place.

What do the above observations indicate: The clutch is NOT disengaging. The thrust bearing is not returning to its initial position after the actuation process is completed (when the pedal is released).

Analysis of defect, how many parts are involved?: The following is the COMPLETE list of parts, which were analysed to identify the root cause of the above defect. Clutch pedal assembly / Clutch pedal bush / Clutch pedal pivot bolt / Position of the clutch pedal with respect to the B&C bracket in fully engaged and fully released position / B&C bracket assembly position in the vehicle / Orientation of the clutch pedal-mounting bracket on the B&C bracket / Clutch pedal-mounting bracket itself on the B&C bracket / Clutch cable / Clutch cable orientation and clamping on the B&C bracket, body, chassis and transmission / Clutch cable assembly with it’s corresponding arm at the transmission end / Outer cable holding bracket on the transmission / Orientation of the clutch operating arm on the transmission with it’s outer cable holding bracket / Length and offset of the clutch operating arm / Perpendicularity and interference of the splines of the clutch operating arm with it’s shaft / Clutch operating fork / Tolerance on fork OD to transmission housing bush ID / Centrality of the clutch operating fork with the transmission drive shaft / Matching of the clutch operating fork with it’s corresponding dimension on the thrust bearing sleeve / Clearance on the ID of the thrust bearing sleeve / Built up dimension of location of the thrust bearing face on the transmission assembly / Pressure plate locating finger dimension from the flywheel / Bell housing depth / Location, orientation and tension of the clutch fork return spring / Location, orientation and tension of the thrust bearing return springs / Pressure plate assembly / Driven plate assembly / Flywheel assembly.

How many items did we zero in on during our analysis?: The following is the list of parts, which we analysed, to identify the root cause of the above defect. Clutch pedal assembly, dimension X on layout checks Y mm. Dimension X checks Y mm, THIS AFFECTS THE CLUTCH PEDAL RATIO AND THUS AFFECTS PEDAL TRAVEL / Clutch pedal bush / Lot of side play observed, THIS PREVENTS FULL MOTION OF THE PEDAL TO BE TRANSMITTED TO THE CABLE, THUS REDUCING CABLE MOVEMENT / Clutch pedal pivot bolt very loose in the bush – THIS PREVENTS FULL MOTION OF THE PEDAL TO BE TRANSMITTED TO THE CABLE, THUS REDUCING CABLE MOVEMENT / Position of the clutch pedal with respect to the B&C bracket in fully engaged and fully released position / No stoppers provided in the part – THIS LEADS TO EXCESS TRAVEL AND TOTAL BEARING AND PRESSURE PLATE FAILURE. DRESS LEVEL OF B&C BRACKET NEEDS TO BE DEFINED – DIMENSIONS OF X AND Y MM NEED TO BE MAINTAINED / Orientation of the clutch pedal-mounting bracket on the B&C bracket, this affects clutch cable orientation, it’s operating radius and also it’s design length. DIMENSION X MM CHECKS Y MM / Clutch cable / Clutch cable orientation and clamping on the B&C bracket, body, chassis and transmission / Inner to outer cable orientation is important to operate the system / Inner cable angle with the clutch pedal and the transmission lever is important to determine clutch pedal effort, cable thrust and therefore it’s life / Outer cable support and radius are important to prevent loss of movement on the inner cable, due to flexing of the outer cable / Clutch cable assembly with its corresponding arm at the transmission end / No free play is permissible as it reduces the effectivity stroke of the clutch cable / Outer cable holding bracket on the transmission, this defines the orientation of the centre of the clutch cable with the clutch actuating lever on the transmission. Loss of orientation leads to loss of cable movement and rubbing of the cable with the outer sheath / Orientation of the clutch operating arm on the transmission with it’s outer cable holding bracket / Length and offset of the clutch operating arm / This should be at 90 degrees, otherwise, thrust is generated on the lever / Large offset is not advisable / Clutch operating fork dimension found undersize, leading to interference / Tolerance on fork OD to transmission housing bush ID / The fork gets jammed in the housing bush, so clutch does not operate / Matching of the clutch operating fork with it’s corresponding dimension on the thrust bearing sleeve / Interference was observed. This leads to jamming of the sleeve during return / Clearance on the ID of the thrust bearing sleeve / Lot of interference was observed, along with ovality. This has led to jamming of the bearing during return. Built up dimension of location of the thrust bearing face on the transmission assembly / This defines clutch pedal free play and is very important to maintain for getting full disengagement / Location, orientation and tension of the clutch fork return spring / Tension was observed ZERO (spring totally free) CANNOT WORK AT ALL / Location, orientation and tension of the thrust bearing return springs / Tension not available as the spring ends expand during fitment / operation and do not return to their original position, thus increasing free play.

What was done to solve this problem?: a lot of rework, including fabrication of brackets and local welding was done to make parts confirm to specifications. After thorough study and step-by-step analysis as above, vehicle is made operative. After correction, same vehicle ran for 86000 kms with one clutch.

How much time did this take?: 4 full days of doing little else.

[dracul]

Thank you sir. That is a huge amount of work. Now I know why companies spends millions for the development of a car. BTW Which car is that?.
Sir, what will happen if one bolt is missing or loose in the bell housing mated to engine?.
Is it possible a faulty clutch assembly results in crankshaft problem?

[DHABHAR.BEHRAM]

Originally Posted by dracul

1. That is a huge amount of work. Now I know why companies spend millions for the development of a car. BTW which car is that? 2. What will happen if one bolt is missing or loose in the bell housing mated to the engine? 3. Is it possible a faulty clutch assembly results in crankshaft problem?

Dear Dracul - my reply is as follows:
1. Yes, that is a lot of work which brings out the importance of using product clarity, simple logic and a little bit of common sense. We (my colleague and I) did nothing else except this analysis for 4 days. As expected, very few people understood what we were doing, from others, we got huge brickbats, because we were always in the workshop, most of the time below the vehicles, which is not considered nice! . At the end of 4 days, we found the solution. Then everybody came, because they wanted to take the credit! . See the spread, 2 kms on one clutch to 86000 kms on one clutch!
2. If you are meaning the M8*1.25*30 mm long bolt securing the Premier Padmini bell housing to the cylinder block, most of the mechanics don't fit this one bolt on the bottom LH side because it is very difficult to access. Cars have run for years like this without the customer even knowing, but technically this is incorrect.
3. Generally speaking, yes. If you have a specific case, please mention.

I cannot disclose the name of the vehicle on which this clutch exercise was conducted. I was the chief engineer for the project. The vehicle sold in huge quantity, decimated the competition completely and created a huge quantity of new user segment, which is doing very well now. The first prototype was built in record time. For me, there was huge learning from a classic case of "CUSTOMER-CENTRICITY IN ACTION". It also proved that millions of rupees are not required to achieve product success in the marketplace out there!

Best regards,

Behram Dhabhar