Piston rings

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DefenderScout

DefenderScout

Member
Posts
31
Location
Slovakia
Hello,
I have a s3 with only 20k on clock but stood for a while. The engine wont start because the compressions are low. I have fuel in the system and I already fixed the saddles on valves.

Tried leaving diesel in cylinders over night. In the morning diesel was gone. I am about to take out the pistons.

0F92CDF2-E89A-4805-9A56-0D2C0450C841.jpeg


Now the question is - would you replace the rings with a set of new or just unstuck and reuse the old genuine one as they werent used a lot?

Thanks
 
I think on balance I would use new rings, but it probably wouldn't matter too much. Don't forget to change the oil now that it has diesel in it.

Col
 
How do you know compressions were low ? Did you do a compression test with a compression gauge ? Problems with low compression are more often the result of wear/corrosion of the valves and their seats in the head. Do not know what you mean by " saddles" on the valves. Do you mean valve clearance?
If engine is genuine low miles but has sat some time I would think the diesel soaking would free any stuck rings. How do the bores look? Any steps near the top ? Can you see crosshatching ?[ fine diagonal lines around the bore ]
 
There's no point in chaging the rings unless you intend to fit new big end shells and ideally main bearing shells. Its worth doing but its a lot more work as getting the pistons off means sump off, big ends off, which means new big end bolts and shells and you can't be sure of those until you get the size of the old ones in case its undersize. Unlikely but sods lawy etc. So the choise is:
head gasket, valve grind and back together
or
that plus big ends, mains, crank seals, rings and bore hone (in situe).
The latter is more than double the work but it will give the engine a longer life. It also reaquires a lot more cleaning and care and unless you take the engine out a lot of the work is underneath.
 
tottot said:
How do you know compressions were low ? Did you do a compression test with a compression gauge ? Problems with low compression are more often the result of wear/corrosion of the valves and their seats in the head. Do not know what you mean by " saddles" on the valves. Do you mean valve clearance?
If engine is genuine low miles but has sat some time I would think the diesel soaking would free any stuck rings. How do the bores look? Any steps near the top ? Can you see crosshatching ?[ fine diagonal lines around the bore ]
Click to expand...
I didnt do a compression test with a gauge, but the engine has hard time starting and diesel in cylinders was gone very quickly after soaking.
By saddles I ment seats, sorry. So I meant that I grinded the valves and valves seats. This was done probalby good, as I tried soaking diesel over night (head upside down) and it stayed there until morning.
The bores look great, no lines at all. Looks like new.

rob1miles - thanks. I will take the easier option as this I am not very skilled and dont plan to take the engine out. Its really an low mileage engine, so I would prefer keeping it as genuine as possible.
Maybe a silly question, but why do I need to fit new big end shells and bolts when removing pistons?
 
steve2286w said:
Are the heater plugs working ok and no air I fuel lines and injectors working ok with correct spray pattern
Click to expand...
Heater plugs are new and working. No air in fuel system. Spray pattern, ehm. Not so sure about the spray patern, but ai tried instaloing injectors from a car that starts and runs well.

jamesmartin said:
no point in fitting new rings unless you hone the bores, removing head etc is an odd place to start for poor starting
Click to expand...
Well, the engine wont even start on start spray and it was resting for about 25 years. On start spray I dont even get coughs, nothing..
 
There should be lines visible in the bores. If the bores are just smooth it could be that you have what is known as a "glazed" motor . This is often the result of an engine that has only ever been driven lightly doing short runs or spent a lot time ticking over and hardly ever gets to full operating temperature.
What happens is the diesel combustion is incomplete at those low temp/revs and the resulting residue is sticky and can cause rings to stick. As a result of that hot gases pass the piston baking the residue on to the cylinder wall. That is the glazing and it is hard. Engine will now tend to burn oil making it worse. Compression drops and it just gets worse until the motor will hardly go. Low mileage engines treated " kindly" are the worst case's.
If this is the case and as your engine is already in bits then pistons out and " hone " the bores to clear the glaze.
 
Wow that’s a long time standing , if the injectors are removed but connected to pipes then turn it over and a nice fan shaped spray comes out , is Diesel getting to injectors
 
Re new big end shells: The pistons come out the top but to get them out you have to take the sump off and undo the big end bolts. The bolts (or nuts) are often single use and so it is recommended to fit new each time. On my current engine I re-used them becuase I could see they were in good condition, I fitted new big end shells.. It is not usual to re-fit the same big end shells as they are cheap and they wear. If you do this you must put everything back the same way, same piston to cylinder, same way round and same big end shell same way round.
When someone asked about the cross scoring this is a good thing, it is the marking from when it is machined, if it wears off to a smooth shiny surface it has more wear. The step at the top of the bore where the rings stop will tell you how worn it is.
 
DefenderScout said:
Heater plugs are new and working. No air in fuel system. Spray pattern, ehm. Not so sure about the spray patern, but ai tried instaloing injectors from a car that starts and runs well.


Well, the engine wont even start on start spray and it was resting for about 25 years. On start spray I dont even get coughs, nothing..
Click to expand...
i think one of your biggest porblems is you dont know what your doing,lets have some good pics of bores
 
rob1miles said:
Re new big end shells: The pistons come out the top but to get them out you have to take the sump off and undo the big end bolts. The bolts (or nuts) are often single use and so it is recommended to fit new each time. On my current engine I re-used them becuase I could see they were in good condition, I fitted new big end shells.. It is not usual to re-fit the same big end shells as they are cheap and they wear. If you do this you must put everything back the same way, same piston to cylinder, same way round and same big end shell same way round.
When someone asked about the cross scoring this is a good thing, it is the marking from when it is machined, if it wears off to a smooth shiny surface it has more wear. The step at the top of the bore where the rings stop will tell you how worn it is.
Click to expand...
Interesting, I will take head off and inspect bores one more time.

jamesmartin said:
i think one of your biggest porblems is you dont know what your doing,lets have some good pics of bores
Click to expand...
You are right, I am newby to the engine department. I have a good mechanic in the shop, but I try to work alone on this one and learn. I will take head off and post pictures of bores
 
DefenderScout said:
Interesting, I will take head off and inspect bores one more time.


You are right, I am newby to the engine department. I have a good mechanic in the shop, but I try to work alone on this one and learn. I will take head off and post pictures of bores
Click to expand...

Always a good way to learn I hate spending money at garages
This should help , the official work shop manual , as said before if the bore is worn a lot you will see a wear ridge at top or if you have an internal micrometer that will
be useful

http://www.retroanaconda.com/landrover/manuals/series3wm/2_engine.pdf
 
Here are detailed pictures of all bores. What do you think?
 

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re-bore and new piston now youve got that far, its worn out but id think there were other issues causing not starting,id take block to local machine shop to get measured and new piston size determined so they can be bought and block bored/honed to suit
 
jamesmartin said:
re-bore and new piston now youve got that far, its worn out but id think there were other issues causing not starting,id take block to local machine shop to get measured and new piston size determined so they can be bought and block bored/honed to suit
Click to expand...

Thank you for opinion. Where exactly do you see the wear?
I would actually just like to get it started, not planning to do a full rebuilt. The car will be driven occasionaly for few miles.

Sorry for a rooky question, but where would you suggest to find the source of starting problem? I got fuel at the injectors, tried different injectors, valve seats are grinded and heat plugs are new - NOS type
 
The bores look very worn, we are looking at how soomth they are, they should be slightly rough to hold the oil, all of that has worn off. We are also looking at how big the step is at the top. the bore above the point where the rings stop wears very little so it give a measure. The bores also wear oval, more side to side than front to back because the con-rod/crank angle pushes the piston to the sides. If you get a inside caliper and some feeler gauges you can measure it. Clean the top 5mm of the bore and set the calipers to that, then move them down the bore and use the feelers to measure how much bigger it is. Remember it all started the same size. The rings will be very worn and not springy so there will not be enough pressure to fire the diesel. With a petrol it would run but burn a lot of oil. You may be able to fit new rings, but if you do you MUST cut back the ridge at the top - get a "ridge reamer" from an engine repair shop. If you do this you will need new rings and new big end shells, its the cheapest fix for an engine to keep it running. If you do not cut back the ridge the new rings will hit it and break. The vidoe of the measuring has a fancy tool but old fashioned calipers and feeler gauges work ok.

 
DefenderScout said:
Thank you for opinion. Where exactly do you see the wear?
I would actually just like to get it started, not planning to do a full rebuilt. The car will be driven occasionaly for few miles.

Sorry for a rooky question, but where would you suggest to find the source of starting problem? I got fuel at the injectors, tried different injectors, valve seats are grinded and heat plugs are new - NOS type
Click to expand...
cranking speed and pump pressure a worn pump can often not reach injection pressure at cranking speed,timing etc ,did you get any smoke from exhaust
theres a defined ridge were rings reach the top of the stroke and you can see were 2nd and finishes and bores have that extreme polished look ,ive done enough of those engines to tell just by looking
 
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