Replaced cylinder head, but now runs rough and wont even idle :-(

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flanagaj
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Joined: Sat Apr 13, 2019 6:29 pm
Drives: MK6 1.2 (VAG BMD 3 Cylinder)
Location: United Kingdom

Replaced cylinder head, but now runs rough and wont even idle :-(

Post by flanagaj »

I have a 1.2 (engine code BMD) and the EM light came on and it would then go into limp mode. A local garage did a compression check and said that compression was down on 2 cylinders and with 55k on the clock it was most likely valve stem seals. As I am rather skint I tackled the job myself.
Having removed the head I turned it over and the valves looked fine so I filled the concaves with water and left it. 2 of them had emptied completely and only one was still full.

I took the head to a cylinder shop who fitted new stem seals and and refaced the valve faces and skimmed the head. I fitted a new gasket and timing chain and also used the special tools to ensure that the timing was correct. I was already for the eureka moment, but when I turned the ignition it still runs lump and now won't even idle.

I had to reset the timing and did use the special tools to ensure the crankshaft and camshaft were locked correctly so that seems correct.

Any pointers as to what I can do now as I am feeling rather deflated given the amount of time I have put in to try and fix the car?
Lester
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by Lester »

What DTCs do you get when you scan the car?
flanagaj
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Drives: MK6 1.2 (VAG BMD 3 Cylinder)
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by flanagaj »

I get a 16687
Cylinder 3 misfire detected
DTC Status
sporadic


I just tried to a compression test, but I can only think the compression gauge was not sealing on cylinder 2 as I was getting the readings below

Cylinder 1 - 14 bar
Cylinder 2 - 0 bar
Cylinder 3 - 8 bar

I am thinking of getting a mobile mechanic out to perform a leak down test as I am totally miffed.
Lester
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Drives: 2008 Polo 9N3 1.4 BUD
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by Lester »

Have you tried doing a wet compression test on cylinder 2? This is done by putting oil in the cylinder which is supposed to seal the piston rings. If the compression improves, you might have a bad piston ring. If not, it could be the valve seal. What is the mileage of your car?
flanagaj
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Drives: MK6 1.2 (VAG BMD 3 Cylinder)
Location: United Kingdom

Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by flanagaj »

I haven't tried a wet test as I was really surprised to get a 0 bar reading. The car has done 55k and has full service history. It basically started playing up 3 days after we bought it. The EMS light would come on periodically when stuck in traffic and a local garage did a compression test and said that based on the mileage and the fact that valves are a common failure point that was the problem.

I should have done the leak down test before doing any work, but I had no reason to question the local garages knowledge.
RUM4MO
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by RUM4MO »

I'm amazed that the workshop that "repaired" this cylinder head only replaced the valve stem seals as well as recutting the seats and grinding the valves in, I would have thought that there would have be excessive wear in the bores in the head where the valves pass through, so they would have needed to get a machine shop to open them out and fit sleeves in these bores, very confusing and annoying for you!
flanagaj
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Drives: MK6 1.2 (VAG BMD 3 Cylinder)
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by flanagaj »

Also charged £280 for it (That included the gaskets and bolts).
RUM4MO
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by RUM4MO »

Bother Bother!
flanagaj
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Drives: MK6 1.2 (VAG BMD 3 Cylinder)
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by flanagaj »

I was in a rush to get the head repaired and on reflection I do feel like I have been stitched up. Trouble is, I'm not sure how to proceed. I have the kit to do a leak down test, but so far I haven't been able to find the compression stroke on cylinder 2 :-(

Cylinder 1 is fine as I can feel the pressure building up, but on 2 I get nothing when I turn the crank by hand and put my thumb over the hose from the leak down kit.

Any thoughts?

Starting to think I wish I'd just sold the car on ebay advertised with a misfire as with timing chain kit and head I am up to £400 and that was doing it myself.
RUM4MO
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by RUM4MO »

As long as you know the firing order, and have proved from that that you know when relative to the crankshaft rotations that cyl 1 and cyl 3's compression stroke starts and ends, you should be able to work out when to expect cyl 2's compression stoke to be starting - with a bit of care you can insert something long strong and thin down the spark plug hole and prove that you have got it right?

I can't honestly say that I would have been able to know when to stop with this job, you have started and should hopefully now you should be able to "locate" what is wrong, fix of get it fixed and get this car on the road.

As always, GOOD LUCK!

Edit:- I would not expect the valve stem seals to do anything to promote better compression, their job is to stop cam chest oil getting down into the combustion chamber.
flanagaj
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Drives: MK6 1.2 (VAG BMD 3 Cylinder)
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Re: Replaced cylinder head, but now runs rough and wont even idle :-(

Post by flanagaj »

I have dropped the head back to the company who were very forthcoming to help rectify the problem. Having taken the head off I was going to test the cylinder block for flatness, but wanted to ask whether it is possible for this to be out as I don't have an accurate straight edge. Haynes state a maximum of 0.05mm discrepancy.
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