2.5NA Headgasket keeps blowing...

[pat_pending]

To sugest that leaving the head gasket for two weeks before starting the engine, stopped it from blowing for 7000 miles is frankly nonsense. You have a fault with the engine or your method of assembly and you need to get to the bottom of it.

Another thought, when the head was skimmed was it done with the pre combustion chambers fitted? If not they will stand proud by whatever ammount the head was skimmed by when fitted.

Again, can you post some pictures? What was the final torque you did the bolts to?

[zeerover]

If the cylinder head gasket is leaking, you should see this. I do not think the seal is the cause for this engine. These are pictures of two different engines with a blown gasket.

[RustyNissanPrairie]

"Head bolts were always torqued in the order found in the workshop manual and in 3 increments, the last increment being the final torque"

NA head bolts are tightened in one single stage to 115-130NM IIRC and in the specific order.

Your not using the tightening sequence for a Tdi engine are you or getting NM mixed up with ft/lbs?

I did mine using an Elring gasket about 10months ago when I fitted my new gas flowed/Ricardo head, its also running a huge Donaldson air filter housing to help it breathe and has the fueling turned right up, sucks in loads of air, pulls like a train, and no problems with it.

edited to add;

have you compression tested it at any point both to determine if the combustion chamber is to small from block decking/head skimming or to determine where exactly the gaskets where failing?

[crusader]

To sugest that leaving the head gasket for two weeks before starting the engine, stopped it from blowing for 7000 miles is frankly nonsense. You have a fault with the engine or your method of assembly and you need to get to the bottom of it.

I would tend to agree with this statement, but with both the head and the block definitively eliminated as the culprit, that leaves only the mating of the two as the source of the leakage and I'm at a loss to explain it otherwise.

Another thought, when the head was skimmed was it done with the pre combustion chambers fitted? [/Quote]

Yes--Brand new hot spots fitted then head was surfaced. Interestingly, the hotspots were tight when I got the head back from the machine shop originally. When I pulled the head off for the first blown head gasket at rebuild+7000mi, the hotspots were pretty loose in their seats and a couple of them fell out when the head was separated from the block. I don't think this is an issue though, as the workshop manual says to use a smear of grease to hold the hotspots in place if they are loose in their seats during engine assembly.

Again, can you post some pictures? What was the final torque you did the bolts to?

Final torque was 95 foot-pounds. Pics below, though I don't think they tell too much. The block was cleaned and checked so the surface is...clean. The photos of the head are as-removed following the most recent (10-15 minute) run when the leakage occured. The head gasket is the one that was on for that 10-15 minute run. The light gray areas are where the gasket bonded to the block & head and left some gasket material on the head & block when separated.

NA head bolts are tightened in one single stage to 115-130NM IIRC and in the specific order.

Your not using the tightening sequence for a Tdi engine are you or getting NM mixed up with ft/lbs?

Nope. No Tdi's in the 90/110 workshop manual I was using. The Torque specs in the WSM say 115-130Nm or 84.8-95.8Lbf ft.

...have you compression tested it at any point both to determine if the combustion chamber is to small from block decking/head skimming or to determine where exactly the gaskets where failing?

No...I wish I could--don't have the equipment to compression-test this engine. In fact, I don't think I've ever seen anything that'll do it, so I'd probably have to assemble it and drag it down to a local diesel repair shop on some sort of a test stand and have them check it. I imagine it there is some sort of adapter that fits in place of the injector to enable compression testing...

Pics:

[TheHarv]

I bought a cheap compression tester off ebay which came with the right adapter for the glow plug holes (iirc anything that says it will work on a Merc should work on the Rover engines - M12x1.25?)

It was this one I think --> http://cgi.ebay.com/...=item588dbae001

I used cotton swabs to absorb any liquid in the bolt holes. I didn't chase the threads with a tap or anything--they didn't look fouled or corroded. I ran a 2mm wide bead of oil down the threads before installing the bolts on the last 2 attempts. I used red loctite thread locker instead of oil on the initial rebuild (the one that lasted 7000 miles before leaking.

I have no way to explain the loss of 20 to 25 foot-pounds of torque, except that perhaps the composite head gasket is compressing? They're brand new, genuine head bolts, so how faulty could they be, I wonder?

I'm definitely no expert but isn't that rather a lot? my understanding is it should be no more than a wipe of oil on the bolts

[Les Henson]

First TD head gasket that I did blew within 70-miles It turned out to be the torque wrench. I found out because I'd coincidentally bought a new one and I tested the head bolts before stripping it again.

Les.

[zeerover]

I don't think it's the gasket but the head.

[pat_pending]

Might just be the photos but I can't see where the gasket is blown as all the fire rings seem to be intact!

So, wich of the following applys?

1.The head gasket has clearly blown from one or more cylinders to either a coolant passage or oilway or pushrod tube.

2.The head gasket has not blown at any cylinder however it has leaked across between an oilway/coolant passage/pushrod tube.

3.There is no sign of the gasket having failed but there is coolant geting into the oil or oil in the coolant.

Answer that and we may get a bit further.

[crusader]

Might just be the photos but I can't see where the gasket is blown as all the fire rings seem to be intact!

So, wich of the following applys?

1.The head gasket has clearly blown from one or more cylinders to either a coolant passage or oilway or pushrod tube.

2.The head gasket has not blown at any cylinder however it has leaked across between an oilway/coolant passage/pushrod tube.

3.There is no sign of the gasket having failed but there is coolant geting into the oil or oil in the coolant.

Answer that and we may get a bit further.

Perhaps "blown" is the wrong term. "Failed to provide a seal" is more accurate.

Addressing the above 3 choices:

1) No-the head gasket has not failed in an obvious manner--no burned-through bits or missing pieces.

2) I can rule this one out as there was more than just an oil-coolant problem, as evidenced by the half-quart of grey oil deposited in the oil filter via the breather. So I would definitively say that compression is escaping along with coolant into the oil. Where this is happening is not obvious. When the engine was split and the head gasket removed it was difficult/impossible to tell if oil in the area of the coolant + oil passages + lifter holes was the result of gasket failure or just the result of oil leaking down from the rocker area during head removal. Believe me, I unsuccessfully attempted to make this determination immediately after splitting the engine.

3) The most correct choice, in my opinion, though you must add "compression pressure into the crankcase" to the symptoms. Bear in mind that the head and block have both since been magna-fluxed and pressure tested by a local machine shop and found to be free of defects (or so they tell me).

I have come up with a plan of action to resolve (or at least positively identify) the problem:

I will clean and reassemble the engine using new piston rings (again).

This time I will chase all the head bolt threads with a 1/2-20 bottoming tap before assembly and use either a hint of oil or some loctite on the bolt threads (not the 2mm stripe of oil I used on the last attempt). This should eliminate any lingering procedural errors that could be causing my problem.

I will use a different torque wrench to tighten the head bolts in order to verify the accuracy of my current torque wrench.

After assembly, I will do a leak-down test on each cylinder to determine a)if there is any unacceptable leakage and if so, b)where the leakage is occuring (crankcase, intake, exhaust or coolant passages) using a stethescope. I'll have to keep in mind that there will be new piston rings that have not been broken-in yet.

After engine installation, I'll use a diesel compression tester to determine cylinder pressures. (I found a suitable diesel compression tester at my local tool store). If my math is right I should be seeing pressures right around...umm...14.7 x 20=294...so right in the neighborhood of 300 psi or a little less, I believe. If it's much higher than this I'll have to mathematically figure out what sort of cylinder volume I need to add by way of a thicker head gasket, to get into cylinder pressures into the correct 20:1 range.

[western]

When the existing piston rings were fitted were the ring gaps all in different positions or lined up,

IIRC the ring gaps should be fitted so they do not align with any other ring gap.

[crusader]

When the existing piston rings were fitted were the ring gaps all in different positions or lined up,

They were all staggered and away from the thrust side of the piston. Except for the chasing the threads for the head bolts, the Workshop Maual was followed pretty religiously.

I noted that some of the upper compression ring gaps had migrated around to the thrust side of the pistons on a a few of the pistons, though I doubt there is any significance to this.

[Les Henson]

Ring gap mis/alignment wouldn't blow the head gasket. In fact - if they were in line with each other - they would only lower compression.

half-quart of grey oil deposited in the oil filter via the breather.

Don't you mean the air filter?

I've never come across water/oil mixture (known as emulsion) in the air filter. I would guess that the mix has ocurred outside of the engine (condensation).

300psi is ok (but not a rebuild expected reading).

I would suggest you leave the block/pistons/rings/etc, well alone, and look at the head gasket and above. As far as rings are concerned - this would not cause the head gasket to blow (or a leak associated with it)

The head is a big lump of iron, and in my experience, the head doesn't bend, crack, or anything else. The deck is much the same, so usually just needs cleaning when the head gasket is replaced. I have, however, had bubbling from the head bolts on the manifold side of the engine, and a bit of a tweak with a torque wrench - beyond the recommended maximum, has cured that.

Method is - clean the deck with (if necessary), a brass wire brush in an electric drill - the same for the head face. Clean the threads of the head bolts if you are using the old ones, then run a head bolt down every head bolt hole in the block. As a rough check - measure the thickness of the head where one of the head bolts pass through, then screw a head bolt into the deck and measure the distance between the underside of the top of the head bolt and the deck. You will then be able to determine if the bolt is going in far enough to allow the torque to be applied correctly and not because the bolt hole is partially filled with debris.

Composite gasket is usual on this engine, which is not ideal, but equally is not a problem. If the deack and head have been skimmed, then an mls gasket would be preferable and better.

Les.

[crusader]

Don't you mean the air filter?

Indeed I did mean air filter not oil filter--sorry about that. Nothing strange about seeing oil in the oil filter.

The 300psi is low--That equation doesn't really work accurately, I know...

I'm confident that my problem will be traced to:

1) Improper clamping force due to improper head bolt installation,

2) Improper clamping force due to overskimmed head and block/bottomed out head bolts or

3) Overpressurization of gasses due to overskimmed head and block.

Good idea about measuring the working length of the head bolts, Les.

Unfortunately, I'm against re-using piston rings, even ones with only 7000 miles on them, especially since I had the shop lightly re-hone the cylinder walls when they tested the block a few weeks ago. In other words, it's too late to leave the bottom end alone.

[RustyNissanPrairie]

its not a cracked piston is it? I know that dosnt account for water/oil emulsion but it could account for over pressure of the bottom end when the engines warm.

[pat_pending]

OK, so you can't be 100% certain you have combustion gas entering the crankcase. I wouldn't take emulsion in the air filter as proof.

When coolant enters the crankcase of an engine it will primarily emulsify at the top of the engine, it will then block the breathers where it's forced by (normal) crank case pressure into the air filter.

From what I've seen, I think you have a coolant leak into the oil from elsewhere, not the head gasket.

Despite the pressure and crack testing you've had done' I've seen engines that held pressure but leaked only when hot, a fault that could not be reproduced and isolated when they were stripped and pressure tested.

So where might this leak be?

If the block has been sleeved then it's possible there is a crack behind one of the liners allowing coolant to pass between them and into the sump. If this is the case then I doubt if it would show up unless the whole engine was up to operating temp.

It's also possible it has a heat sensitive crack above one of the cylinders between the water jacket and the underside of the rocker shaft.

Less likely is one of the push rod tubes (these pass through the water jacket and are replaceable) has corroded and has a pin hole in it. I certainly would expect that to show up on a standard pressure test though.

How to proceed is a dilemma, in this country these engines are only worth scrap value and it would not be difficult to obtain another engine. I imagine it's different in the States.

Before you reassemble this engine there are some checks you can do to put your mind at rest about the whole block/head skimming/head bolt length issue, although I'm fairly certain this is not where the problem is.

Put the front cover back on, no need for a gasket, just a couple of bolts. lay a strip of card (cereal box type) along the centre of the block longways. then drop the head on and torque it up.

Check the underside of the stat housing on the head is not fouling on the front cover where the water pump lives.

Then remove the head and check the card has been compressed. It should be apparent as the strip of card will be untouched where it passes over the bores. If it has compressed that without the bolts bottoming it will certainly clamp the thickness of a head gasket.

If that proves OK then you're back to the crack scenario. It's possible you may never be able to prove where the leak is.

[crusader]

This headgasket issue was a blessing in disguise!!

I began preparing the engine for reassembly this morning. As I was cleaning and renewing the rings on the #1 piston, I discovered the following:

It seems that there was a casting flaw; A thin spot along the circumference of the skirt on this one piston, which caused a stress crack to form. In the last photo, you can see how thin the casting is on the left side compared to the normal skirt thickness on the right.

This cracked piston skirt would surely have lead to a catastrpohic piston failure, given enough time. It got this far in only a little over 7000 miles!

[Bowie69]

It got this far in only a little over 7000 miles!

Did it come in a blue box....?

[crusader]

Did it come in a blue box....?

Well...It wasn't BritPart, but rather Allmakes. I've used lots of Allmakes parts and I've only had one other problem with a part--The sepcial mainshaft nut on the back of a series transmission wouldn't fit the special tool used to tighten it.

[crusader]

RECAP:

After 7000 miles on my rebuilt 2.5 NA diesel, I began getting coolant in the oil. I suspected the +.020 in combination with a head/block overshave was casuing a headgasket failure. I pulled the head, had it inspected by the machine shop, who OK'ed it, and reassembled it with a new head gasket. Immediate same results--coolant in the oil. I pulled the engine, had the block inspected by the machine shop, who OK'ed it.

UPDATE:

I meticulously reassembled the engine (for the third time) in accordance with the factory Workshop Manual using brand new piston rings, paying special attention to head bolt installation.

Stuffed the engine back in the Rover, drove it for 10 miles, pulled the dipstick and found tan goop on the end of it--Cooling water STILL getting in the oil!!!

As the engine was officially toast, I didn't have any problem adding a half-quart of industrial-strength radiator/head gasket stop-leak to the radiator, something I would NEVER do otherwise.

That was several hundred miles ago and I haven't had even a hint of water in the oil or a depleted radiator water since.

I suspect an internal fault that a magna-flux inspection won't find and that somehow a pressure test didn't find.

The good news is that my parts supplier and machine shop guy will have no problem paying for their kid's college tuuition as a result of this engine.