Audi A4 new engine or just cylinder head?

[iandandav]

My timing belt went while driving down the motorway and engine died. I decided to take the cylinder head of to check the damage. Spent ages trying to get the right size bit that was also long enough to reach the head bolts.

Finally got the spline bit to take off the head today (£24 with postage, what a rip off) could only find one supplier in the UK after two days of browsing the internet.

As expected the valve stems are bent and as a result the head is siezed, cant turn it easily as the valve stem wont go up into its bore (sorry dont know the terminology).

The pistons look ok, I turn the crank shaft with a spanner and they rise and fall, when two are up the other two are midway. There is some stiffness as I turn and it goes slack when the pistons reach the top of the cylinder (from what I remember from working on my Ford many years ago this is normal?). The seals appear good as some coolant water fell into the cylinders and it stayed there without seeping down between the cylinder and piston head.

The only problem I can see with the pistons is the valves when they hit left a semicircular impressions on each piston. These marks are the shape of the valves and about 0.5mm deep at their deepest part.

Finally my questions to those who know a bit about motors, do you think the engine is ok to keep and just replace the head?
Will the impressions on the pistons adversly affect the running of the engine, is it vital to replace or resurface them, or can I leave them?
Also is it OK to reuse the gasket and head bolts as I want to spend as little as possible if I can help it?

Thanks in advance
Ian
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[Burnerman]

In my experience, the pistons will be ok, but clean all of the carbon off to make sure.
when the valves bend, they often take the valve guide with them - either cracking the guide or gouging a groove out. Your head may not have separate guides. Sometimes the valves are so slightly bent you can hardly tell.
So, if you can get a hold of an exchange head, then great - failing that the old one can be refurbished by yourself, using pattern parts.
You must not use the old bolts or head gasket - both will fail.
If your engine has wet liners, do not turn the engine over - if you must, bolt a bar across the top of the block to keep the liners down.
Check the camshaft for a buckle - it should rotate perfectly when the valves are out. If it doesn't, then scrap the head.
Wishing you good luck on this one!
John

 

[iwaters]

You haven't mentioned which engine you have so I can't check but are the dents definaltey the result of the damage and are not just original relief shapes?

If the pistions are damaged there are two likely problems, one is that they have been weakend and might not be able to survive the forces they are subjected to. The other problem is the changed shape could cause hot spots in the engine and change the way the flame front passes through the cylinder, resulting in loss of performance or worse detonation.

The workshop manual state that all bolts and gaskets should be replaced.

If the pistons aren't damaged then it might be cheaper to get the head reconditioned, I have checked the price of new heads in the Audi parts catalogue and believe me you don't want to know.

 

[Burnerman]

If its a diesel engine, the piston crowns are really thick aluminium - they'll be ok I should think.
I can't see many breakers splitting a head from a good engine - they'd want to sell the lot. As you say, genuine Audi bits will make a nonsense of the repair. Maybe an outlet such as Eurocarparts could supply the valves and head gasket plus oil seal set, together with the new stretch bolts......and then the Autotrader beckons!
John

 

[fushionjulz]

To make a descision as to whether the head is scrap or not requires you (or your mechanic) stripping down the head...

If it were me, I'd strip the head completely..than take the bare head with components to a machine shop and ask them to:
a) crack test the head
b) crack test the cam shaft
c) check all the valves for straightness
d) check all the valve seats
and rectify as appropriate...

Obviously if the head has cracked or the valve guides and seats are damaged then it is probably past recovery and you need to have a scour of eBay (eBay.de is good for stuff like this if you can speak German)...

Then rebuild the head and clean the pistons...so long as there is only superficial marks, they should be OK...

 

[iwaters]

If you fancy stripping the head yourself I have the workshop manual which details the process. Just need your engine code (which can be found on the white sticker in the spare wheel bay) and an email address (which you can send me by PM).

Euro car parts do the valves, the exhaust valves are £20 each though (for my engine anyway) and depending on your engine you could have between 12 and 24 of these, if you have a 5V head.

They also do the gaskets, oil seals and head bolts.

The only one you will have to get is the cam tensioner gasket (if you engine has one - most of the petrol Audi engines do, certainly the ones around the 1998-2005 era, and possibly the new ones). It is not strictly necessary to replace this but it is a common source of oil leaks so might be worth while if the head is in bits.

 

[iandandav]

Thanks for all the feedback.
The car is Audi A4 1996 (N) 1.8 ADR petrol engine. Cant get the number as its in a relative's garage ar the moment.

I dont want to remove and inspect the pistons that would be too much hassle. Could damage to the pistons be detected by turning the crank shaft and feeling and listening for anything weird like a scraping noise or a abnormal stiffness or that maybe the pistons are not inline with its neighbour as they move up and down? As I mentioned in my first post the pistons are all in the correct position relative to each other. They move smoothly with some stiffness and then the stiffness lets up when the pistons reach the top of the cylinders, This is this normal isnt it?

I dont think I will go through the dismantling of the head option, too much time too damn cold and I think with the testing and the new components maybe a complete second hand head wouldnt be more expensive. I think I saw quotes for them at around £200 - £300.

Anyone know of a honest reliable breakers (many send out items by courier now I beleive) or even a company offering reconditioned heads?

If I went for a second hand head (complete with valves cam shaft etc) what should I be looking out for to indicate its a good one, or more importantly if its a bad one?

 

[Burnerman]

I've had a few dealings with engines with dropped valves, and never seen anything so drastic as bent connecting rods - although that most definitely does happen with engines that have ingested water.
If I could get hold of a 2nd hand head, I'd put it on (new gasket and bolts) and say a few kind words in prayer. I'd probably pour some petrol into the inlet and exhaust ports just to see if there was any leak around the valves before popping it on though.
Heads from 'specialist' breakers could be ok - but as a precaution I'd have it skimmed by an engineering shop first....after all, the donor car could have popped a head gasket, and the head would be warped.
Also check for the usual dropped damage, stripped threads etc.
John

 

[iandandav]

You haven't mentioned which engine you have so I can't check but are the dents definaltey the result of the damage and are not just original relief shapes?

Its definately damage. I noticed the wedge shaped sections cut out at the edge of the pistons that are part of the casting. The damage is clearly the result of the valves impacting on them.

I have checked the price of new heads in the Audi parts catalogue and believe me you don't want to know.

Yes out of curiosity I asked them how much would a new engine cost, they quoted £4k. The car is probably worth less than a thousand, so a second hand head is probably the best way to go.

 

[iandandav]

Here are some pics of the valves, couldnt shoot the pistons as car at relatives

 

[Burnerman]

Nice pics, and thanks for that.
At least the valve faces haven't snapped off from the stems, so your task is, should you choose to accept it, is to either renew most or all of the valves, together with the oil seal on their stems, or track down a replacement head, as was said.
John

 

[iandandav]

Im assuming these valves should be set at an angle so they fit the reccess and they are horizontal because they have been pushed against the piston. Also are the valve stems supposed to have a bit of a bend or are they supposed to be perfectly straight? Is replacing the valves difficult requiring specialist tools or is it pretty straight forward one the head is off?

 

[Burnerman]

The valves must be perfectly straight, with the heads concentric on the stem....in fact in early engines the camshaft lobes were slightly off centre to allow them to rotate a little - not necessary now.
Taking the valves out is dead simple using a valve spring compressor - yours will likely need the deep recessed type that Laser tools do.
On top of each valve stem will be an oil seal that will need replacing - these are cheap enough.
If your tappets aren't hydraulic, the cam to valve clearance will need to be set too.
John

 

[iwaters]

The workshop manual suggests using a variety of specialist tools for removing the valve steam seals. Although the method they detail is for removing them with the head still attached so you should be ok with the laser tool suggested by John.

The valve stems must be perfectly straight but they are set at an angle in the head, the inlet and exhaust valves are set at a different angle - just to be annoying.

You have hydraulic bucket tappets so no need to adjust clearance, however the manaul states that once everything is back toegther you must leave the engine 30 minutes to allow the hydraulic components to settle. This includes the cam chain tensioner.

You must ensure that the cam chain tensioner and chain are installed correctly or you will wreck yor newely rebuilt head.

As I said previously I have all the info you need from the workshop manual and can email it over.

It is also worth renewing the camshaft oil seals, they are a pain to change with the cams in the engine but easy when they are out, they only cost about £3 each, they are another common source of oil leaks.

 

[Mursal]

A secondhand head will be the most cost effective approach, especially if
your pressed for time.

As already mentioned get it skimmed and a new head gasket. We have
reused the head bolts in the past without trouble. But might be best to
replace them if not to expensive?

Good luck