How to read HG and engine internals?

MikeT · Post by **MikeT** » 23 Jul 2008, 14:14

If you've seen my latest blog post, you'll see the head is now off but I can't see anything wrong. My friend thinks the gasket is not original due to the way it easily came off in one piece and initial inspection has drawn a blank.

I can usually spot an obviously failed gasket but this isn't one of those. What should I be looking for exactly?

Post by **CitroJim** » 23 Jul 2008, 15:16

On a diesel Mike, it onlyy needs the slightest of tthe tiniest of leaks to pressurise the cooling system. You are very unlikely to see the point of failure as if I recall correctly you had just pressurisation. You just will not see a "blow" on the fire rings as so often seen in a petrol engine HG.

Don't try to read the HG but do measure the head for trueness. The head gasket may have been replaced in the not too far distant past but without having the head lightly skimmed to clean it up, if nothing else. This is very important and is money well spent as a good gas-tight seal is crucially dependant on having the head and block surfaces flat and spotlessly clean.

You can tell roughly how many times the head has been skimmed by the depth of the blind hole opposite the dowel hole on the head face. On a virgin, unskimmed head, this'll be about 30 'thou deep.

Get it skimmed, pop it back on and we'll see you on the road at the weekend, OK?

MikeT · Post by **MikeT** » 23 Jul 2008, 17:02

Trouble is Jim, I have a very inquisitive mind and would like to understand what I'm seeing.

These are the two centre bores, pistons at BTDC. What I was hoping to capture was the criss-cross honing marks and the white speckling on the crown. And what's with the vertical streaks and broken carbon on the rear side of the walls?

Xaccers · Post by **Xaccers** » 23 Jul 2008, 17:36

That doesn't look good to me.
Cassy's were practically spotless (apart from the slight valve impressions - will see if I can find the photos tonight), but then her HG hadn't gone, although saying that, her old head had been skimmed once before by the looks of it after we removed it.

citronut · Post by **citronut** » 23 Jul 2008, 18:49

that valve in the bottom picy looks like it might be bunt/burnning out, both picys look like there is something elss wrong, it is very important to have the head presure tested especialy as you cant see an obviouse gasket faliure, i susspect you are far to far away from ST LEONARDS ON SEA as i biult my own XUD presure tetting rig, down here if i had to go to get a presure test done it would cost around 40 squide

regards malcolm

ps.
it would be very interestting to see what is revealed when you take the valves out

Post by **CitroJim** » 23 Jul 2008, 18:54

I agree Malcolm and Xac, it does not look good in the pictures.

The white looks very much like coolant corrosion and doubtless the time spent as a "work in progress" has not helped

Don't dispair Mike, give it a clean up and see how it looks then.

Xac's new head was was pressure tested at the same time as it was lightly skimmed for just £24

jeremy · Post by **jeremy** » 23 Jul 2008, 22:18

Are those pictures of valves? - they look like pistons at the bottom of their bores to me - and the strange feint lines are reflections in the bores.

Still strange looking whiteish deposit to the left of the lower one looks like water corrosion to me.

Have a good look at the head for cracking - although this seems to be a BX problem and better design or metal eliminated this from Xantias.

I'd run a straight edge over the head face and see if I could see anything like indentations. I appreciate that with some gaskets its virtually impossible to get the head face clean enough to make this worthwhile (I've used oilstones in the past when I didn't want a skim taken.)

Post by **CitroJim** » 23 Jul 2008, 22:49

Mike,

Those streaks on the back of the bore intrigue me. Were you by any change running it on a high ratio of veg just before it was laid-up to do the head? And did you just start it up briefly to say, move it into position and did not run it long enough to get it hot?

If the answer to both questions is yes then maybe these streaks are nothing more than veg oil that has been injected and shot out of the prechamber and across to the back of the combustion chamber and has not been burned in the combustion chamber. I say this as if you look at the pictures of the head in your blog thread, you can see a corresponing dark mark from the prechamber of one cylinder across to the back.

A good deal of cold veg does not burn and remains a liquid in a cold engine and is the cause of polymerisation in a DI engine when it shoots out, remains unburned, slides down the bore, past the rings and ends up a gooey mess in the sump and gums up rings.

It's only a bit of speculation but it may explain those streaks. The head also suggests to me that it did not get at all hot the last time it ran on account of the black, fluffy soot present.

MikeT · Post by **MikeT** » 24 Jul 2008, 00:48

Thank you everyone for your comments and I apologise for the error - I meant the pistons are at bottom dead centre so yes, you are seeing the bores, and pistons at the bottom.

It's too late (gone midnight) to go into all of this right now so I'll just ask if those (combustion?) marks could be the work of easystart? It could be that each line represents each dose as I know the AA used it once and I may have done two or three before I fitted new glow plugs

MikeT · Post by **MikeT** » 16 Aug 2008, 17:14

citrojim wrote:You can tell roughly how many times the head has been skimmed by the depth of the blind hole opposite the dowel hole on the head face. On a virgin, unskimmed head, this'll be about 30 'thou deep.

Mine measures appx 5.2mm 5.3mm. How many times do you think this head has been skimmed before Jim?

citronut · Post by **citronut** » 16 Aug 2008, 18:47

your hole is miles to deep them Mike,
as 30 thou =0.762mm and
5.2mm = 204.72440945 thou

try this sight i found

http://www.kids4kids.biz/length-conversion.html,

ignore the kids4kids part, it was just the first site i found for conversions

regards malcolm

MikeT · Post by **MikeT** » 16 Aug 2008, 19:09

Wrong hole then Malcolm

. How does 0.62mm sound?

jeremy · Post by **jeremy** » 16 Aug 2008, 20:40

The marks on the bores - and the piston corrosion (second photo) concern me. If it were my engine I'd pull the pistons out to inspect the rings - as if they are in good order I can't see how the marks on the bores could stay there. Others may have better theories - but as they say 'I've never seen anything like it in my life'

I think the corroded left side of the piston in the second photo is evidence of water getting into the combustion chamber as indeed are the relatively clean pistons.

Broken rings could have contributed to starting problems - causing you to use easystart. I thought (not having considered the maatter in great detail) thet the problem would be the very loud knocking caused by 'Overfuelling' - which you can get with a poor starting diesel when it fails to ignite first time and when it does fire there is more than one charge in the cylinder - hence a very heavy explosion. In the case of easystart there would be a charge of fuel and a dose of ether which could cause a very large explosion.