OK so the dreaded miss fire problem on the 1.2 engined fabias crops up fairly often on here so I thought I would share a couple of pictures from one I am in the middle of repairing now.

If you have a miss fire code that keeps returning usually at low rpm this is the problem 95% of the time.

This engine had a miss fire on cylinder 3 that stayed with the same cylinder after swapping coils,plugs and injectors around. A compression test showed 180 psi 1st time around then 150 psi 2nd time. A leak down test is temporarily better way of testing them but my tester got borrowed and never came back!.

Anyway removal of the top cam cover revealed a few exhaust valves that could be physically moved sideways with the tip of a screw driver so off came the head.

This is the valve guide removed from the head..

This is the guide with the valve inside it to show the amount of wear

As you can see this one was pretty bad but still ran fine just putting the engine management light on occasionally.

We have a local guy who fits the guides for us and reseats the valves etc so I didn't get any pics of the valve seat damage he had to recut etc. Anyway hopefully these pics will help people understand a bit more of the problem and the work needed to make good again.

Wow, waggly!
Was that a 6v or 12v? Age/mileage?

Edited 10 June, 201610 yr by Wino

It's not just wear, they weren't machined correctly in the first place.

Cheap yellow bronze valve guides, cast iron guides are far more tolerant and much tougher but more difficult to fit. Soft bronze guides can be pressed in then reamed whereas cast iron guides need to be cryo-cooled first then honed.

What size hammer did you use to do your thumb? 

@techie don't know about that the inlets always seem OK, my head guy recons maybe something to to with sulfer in the burnt gasses but not my dept lol..

Wino.. dropped a press plate on it from about 5 inches.. invented some new swear words lol

We used to get service kits for them, a new head a manifold/cat and all the nuts, bolts and sealers required as they knew in a given engine range they had issues.

OK so the dreaded miss fire problem on the 1.2 engined fabias crops up fairly often on here so I thought I would share a couple of pictures from one I am in the middle of repairing now.

If you have a miss fire code that keeps returning usually at low rpm this is the problem 95% of the time.

This engine had a miss fire on cylinder 3 that stayed with the same cylinder after swapping coils,plugs and injectors around. A compression test showed 180 psi 1st time around then 150 psi 2nd time. A leak down test is temporarily better way of testing them but my tester got borrowed and never came back!.

Anyway removal of the top cam cover revealed a few exhaust valves that could be physically moved sideways with the tip of a screw driver so off came the head.

This is the valve guide removed from the head..

This is the guide with the valve inside it to show the amount of wear

As you can see this one was pretty bad but still ran fine just putting the engine management light on occasionally.

We have a local guy who fits the guides for us and reseats the valves etc so I didn't get any pics of the valve seat damage he had to recut etc. Anyway hopefully these pics will help people understand a bit more of the problem and the work needed to make good again.

Bad construction. Sad things... Had the same on mine, after 130 000 km, but not so much.

It's a sign of excessive lateral thrust on the valve stem due to the geometry of the valve train, you don't see it in direct tappet head designs because the follower itself absorbs any lateral thrust without transmitting it to the stem tip.

On ‎12‎/‎06‎/‎2016 at 13:25, sepulchrave said:

It's a sign of excessive lateral thrust on the valve stem due to the geometry of the valve train, you don't see it in direct tappet head designs because the follower itself absorbs any lateral thrust without transmitting it to the stem tip.

 

Agree, but that's not the whole story in my opinion. 

I think oil degradation is an important factor that could be crucial with this design of valve actuation.

 

As far as I can see from a mixture of SSP reading and looking at real bits, the oil feed which ends up lubricating the contact between the tip of the valve stem and the rocker finger might easily be badly affected by 'past-its best' oil. 

 

The feed comes in from a gallery in the head into the side of the 'hydraulic support elements', does its job of taking up the lash in there, then emerges out of the top end of the element into the space inside a ball-and-socket joint with the rocker. At an angle in that socket there's a tiny oil squirter jet, somewhere in the region of 0.3mm diameter. You have to move it all around at different angles against a torch or something to even see that there's a hole there. I tried to photograph it without any success.  That squirter lubes both the cam lobe/roller interface, and I think the rocker finger/valve stem tip interface.  This latter one will tend to drag the valve stem sideways more and more, the worse the lubrication of that interface is. The underside of the finger has a curved surface that looks like it's meant to 'roll across' the end of the valve stem as it describes an arc and the valve goes straight up and down. If well-lubed, that shouldn't result in much lateral force, I don't think. If poorly lubed, it'll tend to drag the tip of the valve instead. 

 

Some pics:

 

 

 

 

The tiny dimension of the oil squirter jet makes me think they could easily get partially blocked by build up/condensation of solids within the oil, if it is allowed to deteriorate excessively.

Higher temperatures won't help, I don't think, so there could be a vicious circle of poor oil, more friction, more heat, even worse lubrication, maybe..

 

I reckon a clean-out of those holes would be part of my refurb procedure, but not sure what I would use. Even the smallest of those TePe Interdental brushes is too big to fit at 0.4mm, I just tried...

Edited 31 January, 20197 yr by Wino
Fixing pics

We used to get service kits for them, a new head a manifold/cat and all the nuts, bolts and sealers required as they knew in a given engine range they had issues.

Did the new head include hydraulic tappets and rockers, can you remember, or did those get re-used from the old? Presumably it didn't include the cam-carrier and cam(s)?

Did you have any feeling for how the 6v and 12v engines were relatively affected?

Nah, the oil filter traps solids down to micron scale, it's the cheesy soft yellow bronze valve guides that are quick wear items, not much lateral thrust is needed to wear them out, as stated cast iron guides wouldn't wear like that but they're tricky to fit and rely on the valve stem being stainless so it doesn't wear instead.

I agree that the short follower doesnt help things but the 1.4 16v motors use the same setup and they dont seem to suffer from the same problem?

I agree that the short follower doesnt help things but the 1.4 16v motors use the same setup and they dont seem to suffer from the same problem?

 

They don't have valve guides made of Brie.

Nah, the oil filter traps solids down to micron scale, it's the cheesy soft yellow bronze valve guides that are quick wear items, not much lateral thrust is needed to wear them out, as stated cast iron guides wouldn't wear like that but they're tricky to fit and rely on the valve stem being stainless so it doesn't wear instead.

Yeah but even if the teeny hole doesn't get reduced by debris, the lubing of the finger/valve end contact zone will surely be adversely affected by poor oil quality. And doesn't the oil filter have an emergency bypass that lets unfiltered oil go through if it gets too blocked?

They don't have valve guides made of Brie.

 

Still bronze though, aren't they?

Yeah but even if the teeny hole doesn't get reduced by debris, the lubing of the finger/valve end contact zone will surely be adversely affected by poor oil quality. And doesn't the oil filter have an emergency bypass that lets unfiltered oil go through if it gets too blocked?

 

The lubrication is a red herring, it's a quality control issue with the valve guide material. Lateral thrust is unavoidable due to the valvetrain geometry.

 

 

Still bronze though, aren't they?

 

Yes, and they wear, but nothing like as badly because they're harder, the valve springs are softer and the valves smaller and lighter.

Your opinion is noted. Could well be a material quality issue, but without evidence it's just speculation

 

Valves are same part number between the 12-valve 3-pots and the 16v heads.  036109601AD inlet, 036109611K ex. Also springs same 036109623R

 

For obvious reasons the 6-valve valve-heads are a tad bigger at 34.5 inlet against 29.5, 28 exhaust versus about 26 on the 12/16v; same stem size, same length give or take 1mm...6-valve springs are a different part number so you might be right about them being stiffer, don't see why they'd need to be much different though.

Edited 12 June, 201610 yr by Wino

Your opinion is noted. Could well be a material quality issue, but without evidence it's just speculation

 

Valves are same part number between the 12-valve 3-pots and the 16v heads.  036109601AD inlet, 036109611K ex.

 

For obvious reasons the 6-valve ones are a tad bigger at 34.5 inlet against 29.5, 28 exhaust versus about 26 on the 12/16v; same stem size, same length give or take 1mm...

 

Not really speculation, I've seen it many times before on different heads, all with rocker arms.

As techie said, Skoda provided a complete new head casting as part of a kit to address the issue, that new head will have different guides in it than the original.

We had a batch of small block Ford V8 racing heads all go after only one race because the guides were a bad batch made of Chinese cheese, cost us a fortune to rebuild the whole lot with pukka phosphor bronze guides after which we had no further issues.

I prefer cast iron guides because they conduct the heat better, hold the oil better and don't wear but they are much harder to fit, you have to heat the head casting in an autoclave, then cool the guides in liquid nitrogen before smacking them in quickly with a soft brass drift, once they're all in properly you have hone each guide for a perfect fit. It's a far better solution though, bronze guides shouldn't be needed in a production engine these days, robots can push the cryo-cooled guides straight into hot head castings in moments.

Also thinking of the direction the oil is spraying off the rollers.. the inlets throw oil towards the valve/finger tips where the exh side would throw it away ? Which is the primary source of lubrication for the finger/valve contact as no way is a jet getting there from the tappet end.

I wonder if the 12v has a more aggressive cam profile to the 16v which makes it worse maybe.

I reckon it just must drip along the downwards slope of the finger body after the cam/roller contact area, but you're right; on the exhaust side, the cam would be flinging the oil back towards the jet. By the same token though, the bottom of the roller would be flinging drips towards the finger 'tip' area I guess?

 

Was the engine in your pics above a 6v or 12v? I have a feeling 6v are worse affected, but that's only based on a hunch really. Any thoughts?

 

Not sure on cam profiles, I've got a spare set of 12v ones I can look at, but no accessible 16v ones.

Edited 14 June, 201610 yr by Wino

It was a 12v one mate.