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.

Thanks! PM sent...

Ahh...Thanks. No clyclone breather, just the hose from the breather to air filter inlet and a flexible fan shroud, ex-MoD engine, so I'm going to guess mid-to-late 80's? If I go by chassis numbers, it's an early 1973 engine (the lump is in my 109 ).

Any way of determining the date of manufacture for a 2.5 NA Diesel? Nothing too obvious on the block or the head...

Just getting ready to install new rings on my pistons (2.5 NA diesel with only 7000 miles on the Allmakes pistons). I sized all the ring gaps to their respective cylinders, then went to install the rings on the pistons and found the rings were too thick (tall) to fit the grooves on the pistons. The correct rings should be about .080" thick and these are about .095". Did the supplier of the rings send me rings for the oddball Hepworth-type pistons despite my specifically instructing them not to? I don't know the difference between the Hepworth pistons and the later non-Hepworth type, so I'd like to figure out if the Hepworth rings were thicker before I confront my supplier. Thanks!

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.

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!

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.

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.

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.

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. 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. 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. 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:

My theory is that the head gasket was installed for about 2 weeks after the rebuild before the engine was started, giving the composite head gasket some extra time to form a bond to the block and head. This lasted 7000 miles. On the most recent attempt, I torqued the head down and 15 minutes later I was running the engine. To my knowledge, the composite head gaskets form a bond to the mating surfaces using pressure plus high temperatures. Head bolts were always torqued in the order found in the workshop manual and in 3 increments, the last increment being the final torque. Looseness after the engine run was determined by putting a torque wrench on the exposed head bolts and turning them until either 1) the correct final torque was reached without the bolt turning or 2) the bolt began to turn prior to reaching the correct final torque. The torque reading when some bolts began to turn was about 25-30 pounds short of the correct final torque. Ahh...Thanks, Les. I was hoping they'd be an off-the-shelf item (at least in the UK). That's the point I'm at here. I've already drawn out the 2.5NA headgasket using a CAD program that will be read-able by a water jet machine. I just need to get a sheet of copper the apporpriate thickness (whatever that is) and find a machine shop to blast one out for me.

I saw that site during my search for 'Head Saver", though I missed the PDF booklet. The booklet lists a Land Rover 6 cylinder (presumably Freelander engine) and the 4.0l V-8. I'll give them a call after Easter and see is they have any listing for the 2.5D Thanks! --Mark

Thanks everyone... To clarify--Each cylinder had a sleeve in it to bring it back to standard bore size, presumably done by whomever refurbishes engines for the MoD. When I rebuilt this engine, I had to have these existing sleeves bored about 0.020" oversize to match the oversize pistons I was fitting, bringing the piston-to-cylinder clearance back within factory specifications. There's no evidence of piston-to-head/valve contact and the pistons are just about flush with the deck of the engine block at TDC, but not protruding any, IIRC (it's still in pieces in my garage). There were no interference issues between the thermostat housing and the timing case IIRC, but I'll pay specific attention to this area on the next build-up of this engine to make sure. I've never heard of a Head Saver, but having since researched it, it sounds like EXACTLY what I need! Nothing I could find online suggests there is one available for the 2.5NA diesel though. Does anyone have a source for Head Saver shims for a 2.5 diesel? I'm certainly not going to have any luck with that here in America. I may send another e-mail to Turner asking how to determine how much material was removed from a head and block over the years. I just hate to ask for free advise/info but not order parts from them due to the weak dollar and insane trans-Atlantic shipping costs.

Ahh...you reminded me--I also have .020" oversize pistons contributing to my issue, so I'm taking a bigger gulp or air and squeezing it into a smaller space, if I'm thinking about it correctly.

That's what I was thinking. I could always have the volume of a combustion chamber measured along with the volume of a cylinder (piston-up and piston down) to determine the compression ratio then mathematicaly figure out what head gasket thickness will give me 21:1 I suppose. Awful lot of work for a 2.5, but I can't keep blowing head gaskets every week...

1/2 UNF--Thanks! As for the piston protrusion--there isn't any--they come up just about flush with the block mating surface using my uncalibrated eyeball. I'm just trying to figure out a way to get back to the compressed air volume (and therefore compression ratio) originally specified by the factory as I suspect overpressurization is contributing to my woes.

Well...It's somewhat official in my mind now. Finally dragged the block down to the machine shop where it was magna-fluxed to check for cracks. None found. The coolant passages were pressure-checked and were OK. The upper surface was checked for flatness and found to be fine. A clean bill of health was declared by the machine shop, just like the head. The only point left where compression could leak into the crankcase and coolant into the oil is at the head gasket. Now my quest is to figure out: 1) The distance measurement between the rocker cover flat and the bottom of the head of an unmachined 2.5 NA head so I can calculate how much was shaved off mine over several rebuilds and 2) The thread pitch of the head bolts so I can properly chase the threads with a tap before re-assembly. Any help along those two lines would be greatly appreciated as I attempt to set a new record for the most expensive rebuild of a tractor engine...

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?

Not completely. I'm going to pull the block and have it inspected by the machine shop before reassembly. I feel confident that it'll check OK though--It hasn't been through anything traumatic in the 7000 miles since the rebuild; No freezing temps or overheating episodes. Break-in was by the book.

Rebuilt the 2.5NA diesel 7000 miles ago. Had the head and block resurfaced and the (previously sleeved) cylinders bored .020" oversized. Used Allmakes gasket kits. Recently it blew a head gaasket--Lots of blowby, and coolant in the oil. Replaced the headgasket (Using an OEM gasket) in accordance with the Workshop Manual. Head gasket again leaked a few hundred miles later. Removed the head and had it checked for cracks, flatness and integrity of the coolant passages. All was OK. Re-replaced the headgasket (Allmakes again) and used brand new head bolts this time. This time, it leaked almost immediately upon warming up. I Noted that the head bolt torques were 25-30 foot-pounds looser than when the head was reinstalled just a few hours earlier. I'm thinking that in a previous rebuild of this engine (remember, it already had its cylinders sleeved) the block and head were probably skimmed to flatten them. They were also skimmed during my rebuild. Perhaps there has been too much material removed and now overpressurization is blowing the head gaskets? Or maybe there has been enough material removed that the head bolts are bottoming out, causing insufficient force to be applied to the head? Either way, is there a way of measuring the thickness of the head and block to determine how much material has been removed? I'm probably going to have a custom copper head gasket made and I need to know the correct thickness to use. Thanks, --Mark

I hate to say this, but I've just done this very thing in trying to work out temp gauge issues. Only 3 and a half years after the original post! I believe that these results are +- 8 degrees farenheit--a huge margain, I know. I hooked up an ohmmeter to the sender and stuck it in a pot of water along with a thermometer on my kitchen stove and came up with these non-scientific results. Note that the Ohms scale on the bottom is not to scale--It goes from 10-ohm intervals to 5 ohm intervals past 120. --Mark

M10 x 1mm--Perfect, thanks! That's what the guy at my local auto parts store said too, but I wanted to get a 2nd opinion. (post 8^^^^^ seemed to question all the others)

I hate to drag an old thread back to life, but I'm trying to split the oil pressure port on my 2.5 NAD to run a mechanical pressure gauge while retaining the low pressure warning lamp. I've re-read the thread several times, but I can't figure out what the definitive thread pitch was on the PRC6387 sender. Is it 10x1 or 1/8 BSP or "other"? Just trying to order the right adapter here: http://www.holden.co.uk/displayproducts.asp?sg=2&pgCode=070&sgName=Hardware&pgName=Gauges&agCode=0611&agName=Smiths+Classic+Gauge+Fittings Thanks!

I now suspect that being off (very briefly) by 1 tooth on the cam wheel when I replaced the timing belt 5000 miles ago may have caused this. I can't find a chart showing 2.5 valve opening/cam curves to confirm this though. Is it possible that the cam lagging by 7.5 degrees for a couple of cranking revs caused this? The damages to the piston tops are only a few thousandths of an inch deep.