E36 3.2 Headgasket DIY

[Henry]

So why did the car start. Surely if those valves were sticking and therefore not closing fully then that would account for lack of compression

[James_G]

I have nothing to add other than I am very much following with interest. Fingers crossed for you.

[richb10touring]

So why did the car start. Surely if those valves were sticking and therefore not closing fully then that would account for lack of compression

And it started first time like an absolute beauty. I am shrugging my shoulders here! I will get to the bottom of it eventually.

[richb10touring]

Finally got myself the bits to do an effective leak down test using Drew's home-brew tester - thanks again for the loan Drew, it worked a treat once I'd past a 1mm bit through the restrictor to clean it up and put a bit of PTFE tape on one fitting that was letting air by. Cams and lifters are removed and therefore all valves in theory closed tight by their springs.

Not great news...

The only cylinder that appeared to hold any pressure at all was number 6, which matches up with the earlier compression test. The rest were letting 100% of the applied air straight back out again. These leaks are very obviously via the inlet valves - a noticeable whistle from the inlet manifold where the throttle body bolts on (I'd taken it off already to make it easy to get an ear in the right place).

Causes seem to now be narrowed down to:

1. Although fitted in the right place with the timing blocks, I mis-timed the inlet cam by fitting the VANOS incorrectly, so that when I revved the engine it adjusted the inlet cam's timing sufficiently to knock the valves. This would explain why it ran OK and started first time until I gave it gas. Must've been gentle enough that I can't see any damage on my £20 boroscope, but hard enough to bend at least 5 of them a tiny amount. It wouldn't take much of a gap to lose all the compression.

2. The machine shop made an error when refitting the valves and they aren't seating properly - seems less likely than 1.

Whatever the cause is, that head is coming back off again and will need some valve work. Won't take long to do it now I know how is the silver lining, I guess?! Just need it to stop raining reliably for a couple of hours, and for the kids to learn the ability of self-entertainment

[simon13]

yes incorrect Vanos fitment could cause this, it can be tricky to refit correctly with the tool and the times i've done i've had to re time and do it again to make sure it went on perfect

Head off and some new inlet valves i'd say and check the guides while your there. ALthough sounds like they've only had a gentle kiss

[Drew]

Well at least you now know for sure what the next step is: head off. Not great news I agree, but it's all fixable, and if the valves only got a light tap then it should just be new valves required

[richb10touring]

Got the head back off again, amazing how much quicker it is when you've done it before. Almost disappointed to see absolutely nothing unusual - at least to my amateur eyes! With the cams off and the valves all in their 'closed' position, the inlets don't look any different to the exhausts, and the portions of the valve stems that are visible through the manifold ports look straight and normal. Some light scratching from where I'd struggled to locate the head onto the dowels when fitting it, but nothing significant.

IMG_1863.jpg (570.33 KiB) Viewed 1711 times

Piston tops look just as they were, not even the lightest of marks from a valve touch.

IMG_1864.jpg (538.15 KiB) Viewed 1711 times

A bit of coolant gunk, presumably from some mixing of different types - I'll need to flush the whole lot through.

IMG_1862.jpg (385.78 KiB) Viewed 1711 times

I guess it doesn't change much, next step is to take it back to the engine shop after Christmas and see what they can find with a pressure test.

[davettf2]

I'm following progress with interest.
Just a thought.
If the valves are slightly bent you may be able to find just by using a small amount of petrol or other suitable thin fluid poured into each port in turn. Its worked on my bikes when over revving has caused a minor touch. It might give an early indication of your issue.

[simon13]

whip the valves out and spin them up in a drill, you will soon see if they are true!

[richb10touring]

Now there’s a couple of very good and simple ideas! Cheers. Doubt I’ll get away with doing that tomorrow though

[Henry]

Just can’t see how the valves are bent if there’s not a scratch on the pistons.

[Drew]

I'm following progress with interest.
Just a thought.
If the valves are slightly bent you may be able to find just by using a small amount of petrol or other suitable thin fluid poured into each port in turn. Its worked on my bikes when over revving has caused a minor touch. It might give an early indication of your issue.

The tall chap from wheeler dealers did this by pouring petrol into the combustion chambers of a head with poor compression; showed up valve seat recession (poor valve seating/sealing) very well. Think it was a TR6 or similar. No loss at all from some valves, but one or two drained completely.

[davettf2]

Just can’t see how the valves are bent if there’s not a scratch on the pistons.

Good point, alloy piston and steel, or better, valve. The valve should leave a 'kiss' mark as a minimum.

Hope all is going forward.

Cheers
Dave

[richb10touring]

Managed to move on a stage today, and resolve the mystery of the zero compression inlet valves...

The good news is, no bent valves. The reason for the loss of compression was that the valves were being held open by accumulations of crud on the inside. The source of the crud was the inlet manifold itself, that I had had sand blasted and powder coated. I had given it what I thought was a decent cleaning out, but clearly not decent enough. The engine started perfectly but then as the crud was sucked past the valve, compression progressively got worse until it would run no more...

So, no errors on my part in timings or fitting the VANOS, but a very basic error of not being obsessive enough about cleanliness!

Machine shop have sorted the backs of the valves, given the inlet manifold a proper clean out, and also given the head a very mild re-face to clear up some scratches that it had picked up during installation/removal. They also sourced me a new Elring gasket for only £35 +VAT which was a steal. I'll put the Elring part numbers on a post in the Car Advice Info when I get around to it. Pressure tested and now good to go on again, this time with a helping hand to line it up instead of going solo!

Because the engine has ingested some sand (it hurts just to type that!), there exists a risk that any particles that didn't get burnt up or exhausted during the engine's short run could make their way to the piston rings and cause carnage. Because of this I'm going to do a very careful clean of each piston's perimeter whilst at TDC with an airline to make sure that they're perfectly clear. It'll also have a full oil change as soon as I can get it up to temperature.

[Henry]

Sure hope you get all the grit out, have you thought of making a funnel for a hoover lead as an added method even if it only pulls 1 bit of grit out. Glad you know the cause and good luck with the rebuild.