+1 on Gilbertd's view.
Worth measuring first, to make sure they've got a skim left in them though, as you've no idea how many times they've been through the mill before.
If skim required is in excess of that, you're in rocker shim territory or, in extremes, the head will require a lot of additional work to combustion chambers etc.
At first sight it looks like these heads had a very different combustion per cylinder, for sure leaking gaskets or maybe a failing valleygasket too.
In the bigger circle, is that a trace of detonation? How is the pistonhead in that cylinder? The smaller circle, is that a damaged inletvalve?
The other bank has a more equal combustion so to see with brownish inletvalves.
I should give these heads a good service, skimmed for sure and the valves grinded, then a pressuretest.
Ferryman wrote:
At first sight it looks like these heads had a very different combustion per cylinder, for sure leaking gaskets or maybe a failing valleygasket too.
In the bigger circle, is that a trace of detonation? How is the pistonhead in that cylinder? The smaller circle, is that a damaged inletvalve?
The other bank has a more equal combustion so to see with brownish inletvalves.
I should give these heads a good service, skimmed for sure and the valves grinded, then a pressuretest.
Big circle is on the cylinder with the exhaust leak to atmosphere.
Re equal combustion, does the gems ecu have the smarts to adjust fueling on a per bank basis? If so it would probably have been running this bank out of kilter due to the misfire/blow.
Will have a closer look at the heads later.
Everyone here seems very trigger happy about skimming. Surely if an engineers straight edge shows they aren't warped, skimming is an unnecessary expense (ignoring other damage that might give reason to do it)? I'll check them later, but I'm quietly hopeful that they won't be, there were no cooling issues with this engine, just the blown head gasket, which I reckon is down to old age - the gaskets were genuine LR, so most likely on there from new. 150k miles on them seems reasonable.
I wouldn't consider re-fitting an alloy head without skimming it, particularly not one that has had a blown gasket. The erosion and weakness at the point where the gasket went is going to be right where the fire ring needs to seal so it will stress at that point and burn through in exactly the same place.
GEMS can adjust the fuelling per bank so that would explain the black on one head. No firing on one cylinder would mean the air and fuel intended to be burnt in that cylinder isn't. The lambda sensors can only detect the air and not the fuel so too much air in the exhaust will make the ECU think that bank is running lean and richen the mixture giving you the black, sooty look.
I'm with Tony on this, that does look like a chunk out of the inlet valve too.
Really, you are looking at the do it right, do it once scenario. Skim the heads, lap the valves, new valve stem oil seals, replace anything that looks even slightly suspect and put it back together with a stud kit instead of the stretch bolts. That way I'll last for another 150,000 miles rather than needing the heads pulling off again in a tenth of that.
How much are reconditioned heads going for these days, then? As I will be > 200 quid for skimming on these before I do anything else.
Cost varies, as you'd expect, but from a reputable builder like:
http://www.v8developments.co.uk/products/heads/standard_4.0_4.6/index.shtml
Many cheaper back-street alternatives are available from eBog and the like, but you get what you pay for!
Of course, if you go down this road you'll want to do the rockers, if you do that, may as well do cam and followers, which, of course will need new timing chain/ gears and, while you've got the cover off, a new oil pump. If that far into the engine, new shells and, as you're there, may as well drop in a new set of rings...
That's actually not a bad price for a pair, about the same or maybe even slightly less than I ended up spending by doing my own heads while the block was at V8 Dev having the top hat liners fitted. I had both heads skimmed (my local place charges £45 per head but curses for hours as he has to set the machine up with an angled support for the heads), new valve guides, valves, seals and the valves lapped in and pressure tested. Get those heads from Ray at V8 Dev and you know that they will be perfect.
I was also thinking that the price was good and I wouldn't be able to do much cheaper than that if I did all of the messing around and sourcing bits (apart from the machining) myself.
Shame I don't need new heads- this week anyway!
Orangebean wrote:
Shame I don't need new heads- this week anyway!
Humour is all that keeps us going!
Humour is all that keeps us going!
Humour, duct tape and cable ties anyway!
You've had your share so far I think...
Heads disassembled and cleaning commencing. Hopefully they will be sufficiently cleaned by Monday to go to the machine shop.
I did a quick petrol-in-upturned heads test. On the good head, valves held it pretty well. On the bad one, no real surprises that the blowing cylinder leaked away fairly quickly. One other cylinder on the bad head also leaked away a little quicker than I'd like.
With the valves out, they all look pretty good. Will need to see how they look once cleaned up, but valve stem seals/stems appear to not be excessively worn - they all passed the 'pop' test on removal.
Sounds positive, although the pop test isn't a great indicator on an engine with as many miles as yours. The valve tops tend to mushroom slightly over time. That, combined with carbon build up in the guides, will pop, even on badly worn stems/ guides.
Time to get the micrometer out! Dimensions/ tolerances are page 7 Overhaul manual- Cylinder head.
Where do I find the overhaul manual?
http://www.landroverresource.com/
I use sometimes the Disco II manual as it is more specific when it comes to machining measurements.
http://www.landroverresource.com/40_46_V8_overhaul.pdf
Cheers Ferryman, will peruse.
RAVE also available here:
http://rangerovers.pub/static/rave.zip
Ta.
Ignorance is bliss OB.. :| Either my micrometer is knackered, or I'm looking at replacing valves + valve guides now.
Mic up the unworn part of the valve. Top bit inside spring is good. Then you'll know how knackered your micrometer is :)
You don't have to fit new valves/ guides. As long as faces/ seats can be lapped together without completely buggering up the seat angles and valve doesn't slap around the guide too much, you could just stick on a new seal and be done with it!
Depends, I suppose, on what you want from the car. As I illustrated above somewhere, the ripple effect kicks in and you end up completely rebuilding the engine- a spendy process, just ask Marty and Ferryman!
Looking at how little protrudes past the stem seal, I wasn't able to find a decent reference point at that end.
Gordon: got a calibrated micrometer?