What is Engine Back Compression

[shantanil]

I am new to this forum. Mods move this thread to the appropriate section if it does not belong here.
I have little knowledge of automobiles. But recently our Mahindra Bolero vehicle started suffering from reduced pickup and heavy lube consumption. The mechanic here said that the engine had gone into back-compression and the only way to fix this would be to get the engine overhauled. Now my questions are:
1. What is engine back-compression and how does it happen?
2. Does the engine really needs to be overhauled or is there some other way?
3. If the overhauling indeed needs to be done, what could be the costs?

I shall be grateful if some experienced members could answer my queries.

 

[Umang]

hi buddy, welcome to TAI. am not very techy guy but what i know is that overhauling costs very much. hope some tai experts like raj_5004, ilango, 350z can help you..search forum and maybe you will also get some answers. one member did engine overhaul himself - http://www.theautomotiveindia.com/f...0-engine-rebuild-project-post-2-lakh-kms.html

 

[avindu]

Hey Shantanil, just sharing these things with the basic things I'm aware of a diesel engine. First of all, a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency. (thats the air and fuel mixture)

So, the compression is normally between 15 and 20. So, if you see the engine drinking a lot of oil, thick black smoke emitted is probably due to deformed ead-gasket lead into crankcase, that affects the Engine oil's viscosity, thereby reducing the compression. I'm not sure of the exact technical term, however there are some compression tests available which might help you to identify the cause.

There are many other factors too, like piston rings losing there effectiveness or fried piston rings with engine temperature shooting up accompanied by smoke . Leaks in Cyclinder's allowing coolant to mix with air-fuel mixture during ingition are some of the causes for blocking the engine from functioning normally.

If yours is non-crde engine, which consists of mechnical parts, it might be little easier to identify the root cause but for a crde engine there is almost no way to find out, what triggered the issue.

 

[avindu]

I forgot to ask, how many kms have you done?

To add to the above, a crde engine consists of injectors which are more expensive than the mechnical injectors. Moreover, its hard to isolate if it is the turbo, the electronics part or the mechnical part that is causing the issue.

So my suggestion would be to get the car checked by atleast 2 or 3 different mechanics, which should give you a fair bit of idea, whether to go for a overhaul or not.

 

[anmol_1990]

engine overhaul is done after 1 lac KM , but yours is a diesel and i think the cost would be more than petrol engine.

 

[cooldhaya]

Hello Shantanil welcome to TAI buddy. First of all how much KMS has your car covered? If its more than 1Lakh KMSnthen maybe yes an over-haul is required!


Ilango again can provide the best answer!

 

[shantanil]

Thanks for all the answers. Yes the engine has just recently clocked 95K Kms.

 

[ilango[speed thirst]]

engine overhaul is done after 1 lac KM , but yours is a diesel and i think the cost would be more than petrol engine.

Before expressing my view for thread starter ,

No anmol , there is no hard and fast rules for engine to be overhauled at 1L kms.
Engine can be run without overhaul for so many lacks of kms.
cars that i have seen in real

Lot of qualis run till 4L kms.
honda city have driven till 3L kms
A good maintained indica till 2.5L kms , a bad maintained indica till 90K


A perfect functioning of engine with best output has good compression.
other than this its termed as engine loosing compression , may be refered as back compression too , but i am not sure.

Compression failure may be due to lot of reason .
But main one is improperly maintained engine.
no regular oil change , no regular inspection etc adds to it Improper cooling by coolant , no coolant etc cause them. This is early stage of engine cease.

Common heals that are followed
May be in your case , the piston rings change is enough - anything can be said only after a close inspection.
Valve door adjustment
valve replacement .
engine flush and engine oil change.
and after this whole cooling system check .

Engine overhaul is need maximum only if it cease ,
But not necessary , an uneven block wear , lines in block also need a over haul(In this case block and piston rings replacement is enough.)
check the connecting rod bearing etc too.

Also check is the air filter and the air passage are all sealed and in good condition , this one too may be root cause .

 

[samuel]

I am new to this forum. Mods move this thread to the appropriate section if it does not belong here.
I have little knowledge of automobiles. But recently our Mahindra Bolero vehicle started suffering from reduced pickup and heavy lube consumption. The mechanic here said that the engine had gone into back-compression and the only way to fix this would be to get the engine overhauled. Now my questions are:
1. What is engine back-compression and how does it happen?
2. Does the engine really needs to be overhauled or is there some other way?
3. If the overhauling indeed needs to be done, what could be the costs?

I shall be grateful if some experienced members could answer my queries.

Dear,
as far as i concern back compression means leakage of unburn fuel from engine cylinder through piston. it happens when the pistons rings are worn out or the piston cylinder. there is only option to remove from the back compression is overhauling. or if the only piston rings are found wear out. then we need to change the piston rings only. but first of all, we need to check up the pistons and piston cylinders.

 

[samuel]

Dear,
as far as i concern back compression means leakage of unburn fuel from engine cylinder through piston. it happens when the pistons rings are worn out or the piston cylinder. there is only option to remove from the back compression is overhauling. or if the only piston rings are found wear out. then we need to change the piston rings only. but first of all, we need to check up the pistons and piston cylinders.

 

[drifter]

Before looking at an engine overhaul I wouldmake a compression test.

High oil consumption might stem from wear of moving parts, but is in most cases a rsult of sticky piston rings, which is caused by the fuel or more precisely because of the additives in the fuels.

The best product to make piston rings free again is a detergent based engine flush additive, which can be run for several days to weeks without doing any harm.

This would be my first call.

If this is not the reason for the oil consumption it could be a leaking head gasket or a crack in the head other than wear. However wear does not manifest itself that quickly in terms of oil consumption.

 

[ilango[speed thirst]]

Dear,
as far as i concern back compression means leakage of unburn fuel from engine cylinder through piston. it happens when the pistons rings are worn out or the piston cylinder. there is only option to remove from the back compression is overhauling. or if the only piston rings are found wear out. then we need to change the piston rings only. but first of all, we need to check up the pistons and piston cylinders.

the term back compression is

due to wear and tear in block and picton/rings , oil and unburnt/burnt things that must be above the piston goes below the piston.
that is in the connecting rod areas.

while the piston moves up , pressure created and compression and regular process of explosion and power stroke take place , that is normal!

but when the piston returns back , say after a power stroke , pressure is created in its bottom side too.
the leaked oil/ fuel etc gets compressed . its back compression and pressure die to them is back pressure.

they hamper in free movement of piston , like some one holding the car

 

[codename47]

isnt this normal with Turbo charged engines if am not mistaken. or is that back pressure .

 

[ilango[speed thirst]]

isnt this normal with Turbo charged engines if am not mistaken. or is that back pressure .

be it NA or turbo engine , there should not be back compression.

 

[canani]

Hi, I'm new to the forum and just wanted to tell all of you that this forum has all the characteristics of becoming a great platform for automobile enthusiasts.

I have a question for the Diesel engine experts on the same topic..I have 4 yr old diesel engine (Logan 1.5 Dci) which has done ~60K. when I had gone to a local multibrand (non Mahindra Renault) car service station for a minor fix, one of the mechanic pulled out the engine oil dip-stick when the motor was in idle and commented that the engine has a 'back compression' as a little oil came out of the dip stick opening. Other than this the engine is absolutely smooth and makes great noise including the typical Renault diesel engine 'whine'. Mileage is great too and have not noticed abnormal smoke from exhaust.. is the 'dip stick' method a safe indication? is there a better way to know if indeed there is a 'back compression"??