New rings and honing

[dohnjoe]

hi

next week I'm having a car coming most probably for rings change.

I say 'most probably' because I only had a brief moment to check the compression.

compression was 10.5, 12, 11, 11.5 (bar)

there is high oil consumption, blue smoke out the tail pipe only after the engine gets warm.

I had not the opportunity to do a cylinder leak down test, but I'm pretty sure it's only the rings.

the car has 180,000 km, it's a 1.3 l engine.

 

my question is about honing (deglazing) the liners.

when new rings are fitted on old pistons, is honing mandatory?

please explain.

any other tips, tricks, questions are welcome.

if you know any thorough guide about changing the rings on Felicia 1.3 please point me the link.

thanks

[TeflonTom]

Honing and deglazing are not the same thing, honing is done after a cylinder block is bored, which finishes the bore to the correct size as well as adding a cross hatch pattern and also it ensures the bore is perfectly round.

as the bores wear they get polished by the old rings, they become semi smooth, using a glaze breaker clears baked on carbon deposits and also roughs up the surface to assist the new rings to properly bed in.

it can be done with the liners still in the block if you are careful to not let them move, possibly you could find a small piece of plate with a hole drilled in it to use to bolt bolt the liners using the cylinder head bolt threads, also make sure you stuff some clean rags at the bottom of the bores to protect the crankshaft from dirt ingress, use plenty of clean brake fluid as a lubricant for your glaze breaker, also you need to go up and down with the tool fairly rapidly as it turns, always stop the drill turning and release the tension before you remove it from the bore to avoid vertical scratches. Plus keep the up and down motion going all the time until the drill is stopped.

the other time consuming job is cleaning the ring lands (grooves) in the pistons, there are proper tools for this but I find a good cleap alternative is to snap one of the old rings so it leaves a point, then use this to scrape the mucky oil and carbon deposits out of the ring lands.

new rings must be fitted the right way up, often if they are marked top on one side, or more commonly for vw group parts it will say oben (German for top), if they are not marked then it might have a dot printed or painted on one side or a part number printed denotes the top facing side, a piston ring spreader tool is an absolute life saver when fitting new rings to avoid breakages, but you can do it without if you are very careful (thy are very brittle) use a pair of feeler blades to protect the edge of the piston when the gap in the ring is and spread with your fingers, the compression rings must have the ring gaps offset too, ie when you look down on top of the piston try and have a ring gap facing at least 60 degrees away from each other, the oil control ring is made of 3 seperate components if I recall, 2 very thin rings and a serrated bronze alloy ring, normally serrated one fits first, then the thin ones go either side

when inserting the piston/rod assembly into the liner use some fresh clean engine oil on the skirt of the piston, a pistons ring compressor tool is required, the best type is the metal strap type which you tighten up with a 1/4" drive, once tighten onto the rings place it onto the liner and use the wooden handle of a hammer to tap the ring compressor tool to ensure it is fully flat against the liner, once it's flattened, use the wooden hammer handle to tap the piston into the bore, the arrow on the piston crown points towards the timing chain.

[dohnjoe]

thank you for your extensive answer.

I was misled by almost all American youtube videos that say deglazing = honing (ie https://www.youtube.com/watch?v=zvr1bJ9Kjuc)

just to be sure I got it right, I have a few more questions.

 

1. is deglazing done also in factory when liners/pistons/rings are fitted for the first time?

2. how much wear is allowed on liners before a new boring is needed?

3. assuming the old liners are still in specs, doesn't deglazing adds to their existing wear?

4. I couldn't find a reasonable logic explanation for deglazing = better sealing. is there one?

5. how many more miles lasts a well done rings only change?

[TeflonTom]

1. No, the bores are machined to a size which is a tiny bit smaller than the finished size, normally by Cnc milling machines, different manufacturers have different methods, but honing is probably done by hand in most cases. It's kind of like a big drill hanging on an elastic strap which aids it's up and down motion, this honing leaves a crosshatch pattern which after cleaning is ready for the new rings to go into. The other reason for honing is to minimize the minute tooling marks left behind after milling.

2.specifically for the skoda ones I don't know off hand, it will be listed in the technical data books, it mentions a piston to bore clearance of 0.025mm, although bare in mind a piston is measured across the skirt at right angles to the gudgeon pin, a piston is not round, they are oval, plus the crown is generally a smaller diameter to the skirt... So this also means the bores will wear oval as well, so you need to measure them at various heights and at a few different angles when looking down. There may also be more wear on the thrust side of the rod ( ie the side which gets loaded when on the combustion stroke)

3. Yes, but you are talking 1000ths of a millimeter here,

4. It roughens up the surface to help the new rings bed in better, it also brings the bore back to a more uniform circle, in fact on a badly worn liner or bore you can sometimes see witness marks left behind which are polished in appearance where it has not been touched by the hone/glaze breaker.

5. So long as everything is clean, and everything goes back together ok, it will last the lifetime of the car

I notice that skoda do list oversized pistons in 3x 0.25mm steps as spare parts for the 135 and 136 engines, I should image this comes as a matched liner and piston assembly, probably in singles, but if used they must all be changed as a set..

[maroje]

hello,

 

I'm having the same problem, my compression test results are almost the same as dohnjoe's.

 

so I would like to ask if you could put photos and step by step guide on how to do this. Thank you!

[dohnjoe]

what special tools are a must for the piston rings replacement job from a to z?

[TeflonTom]

Piston ring compressor is probably the only one which is 100% essential! Plus a torque wrench for the big ends and cylinder head bolts on reassembly. the rest you can improvise or apply some lateral thought to, but a ring spreader is a massive bonus for installing new rings onto the pistons if you have access to one. Everything else is just your basic hand tools and common sense.

Cleanliness is king don't forget, make sure you are familiar with the timing chain setup and the timing marks if necessary, you may not need to take it off even but be aware of it anyway, you will need a new cylinder head gasket set, you might as well renew all of the seals etc whilst it's all apart. You might need a set of big end bolts for the connecting rods as well, I can't remember off hand if they are use-once only stretch bolts on those engines, but most vw group engines do need to replace the big end bolts every time they are undone.

when you remove any pushrods or other components like big end bearings make sure you keep them in the correct order so they can go back in the same installed position

the sump has to come off too, so you will need some suitable sealant to refit it, like silicon or instant gasket or whatever, whilst the sump is off is a really good time to clean out the gauze and strainer in the oil pickup pipe too.

[dohnjoe]

so no special tools to assess for wear?

[dohnjoe]

in previous reply I was thinking at micrometer for pistons wear, very fine feeler gauges for rings gap, dial comparator for bore wear, etc.

to me they are special tools as I have only a digital caliper in my garage.

 

 

one other thing before removing the head:

is it possible to have good rings but bad valve stem seals that leak 1 liter of oil / 1,000 km and drop the compression to such low values specified in 1st post?

I don't know how bad could valve stem seals leak compared to rings.

my impression is far less than rings on normal wear, but if they are totally destroyed...

 

can I install new valve stem seals without removing the head?

if I rotate the crankshaft till TDC, is it still possible to drop the valves too much and not be able to install the valve collets back?

[dohnjoe]

I will try to change first only the valve stem seals without taking out the cylinders head.

here is my plan:

• take off rocker arms shaft
• insert some 3 feet of thick cotton rope through spark plug hole leaving one end out
• raise the piston to TDC to press on valves from below
• take off valve springs using an improvised device (see photo)
• remove old valve stem seals and insert new ones using a long tubular socket

what do you think?

 

[TeflonTom]

There is a special air line fitting that you screw into the spark plug hole so you can use compressed air to hold the valves shut, I'm not sure about the cotton rope idea.

[Red Studio]

I've heard the cotton rope idea a few too many years ago related to the same job on Mini engines but never seen it used.

[dohnjoe]

these two jokers actually use the cotton rope with good results..