2.5NA Headgasket keeps blowing...

[crusader]

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

[zeerover]

Are you sure it's the gasket?

[crusader]

Are you sure it's the gasket?

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.

[Snagger]

I think you either have bolts made of toffee or have a block that needs skimming again - my 12J had raised mounds around each head bolt hole like very shallow volcanos, but the only weep I ever had was at the back right corner and was very small.

|Did you fully clean out the bolt holes before assembly? Any fluid trapped in the holes will cause the bolts to hydraulically lock before their ideal depth is reached, so their required torque will register with the bottom of the bolt in compression instead of the top of the bolt in tension - the bores need to be completely cleaned and the bolts just given a wipe of oil before fitting, not a dunking.

[crusader]

Did you fully clean out the bolt holes before assembly? the bores need to be completely cleaned and the bolts just given a wipe of oil before fitting, not a dunking.

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?

[Snagger]

Land Rover get occasional quality problems just like anyone else, so faulty bolts are not impossible. The head should be re-torqued after about 500 miles to allow for bolt stretch and gasket settling anyway, but the amount you seem to be getting does seem extreme.

[crusader]

Are you sure it's the gasket?

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...

[Phil Hancock]

The head bolts are 1/2"UNF.

[Range Rover Blues]

As I understand it the deciding factor for gasket thickness will be the piston projection above the deck or face of the block. With the bottom end assembled you measure with a DTI how far the piston peek out of the block, then choose a gasket that when compressed just keep thepistons off the face of the head. On the head you have to check the valve stand-dwon ie how far above the piston the valves are when seated, this can be affected by cutting the valve seats.

[crusader]

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.

[western]

As I understand it the deciding factor for gasket thickness will be the piston projection above the deck or face of the block. With the bottom end assembled you measure with a DTI how far the piston peek out of the block, then choose a gasket that when compressed just keep thepistons off the face of the head. On the head you have to check the valve stand-dwon ie how far above the piston the valves are when seated, this can be affected by cutting the valve seats.

that's for the Tdi engines, not the older n/a TD diesel engines

[crusader]

that's for the Tdi engines, not the older n/a TD diesel engines

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...

[western]

2.5 n/a diesel is 21:1 compression ratio

piston area 257.1cm3

hth

[crusader]

piston area 257.1cm3

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.

[western]

I might be on the wrong track here but in your original question you mention 'previuosly sleeved bores' now .020" oversize.

are the bore sleeves still in place or have they been removed & the original bore machined .020 oversize ?

if the sleeves are still in place maybe these are moving & causing the gasket to blow

[Les Henson]

If the bores had previously been re-sleeved, then that would be back to standard, so perhaps you mean the have been rebored to +02mm oversize on the original liners?

If the deck has been skimmed as well, then something pretty drastic must have happened in the past ( or someone's a fussy bugger - these engines are incredibly tough.

You do have to measure the piston clearance at TDC if the deck has been skimmed. The pistons as standard do not protrude above the deck and burn happens above the piston crown, so there is a minimum squish band to allow for that. However, in the extreme, the piston would smack the head face (possibly), or maybe a valve. There would be signs of this though (rings on the piston crown where they contacted the valve), Bent conrods if the pistons have struck the head. On most engines - a deck skim requires a head saver - especially if the head has been skimmed as well,

Diesel engines are also known as compression engines - in that the diesel vapour/air mixture is compressed, and in that action - ignite explosively. Compression is everything therefore, so I would have a look at that forst - if only to get a general idea of what's going on inside the engine.

Head thickness reduction - due to unknown history - I would speak to Turner Engineering. What they don't know about Land Rover engines probably isn't worth knowing.

If too much has been taken off the head/deack, then it's not the end of the world nowadays - head savers of the required thickness can be bought and everything returned to as-original.

Les.

[pat_pending]

Just a thought, if the block and head have been skimmed, check the underside of the head where the thermostat sits isn't fouling the top of the front case above the water pump.

[crusader]

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.

[western]

head saver shims here on page 870 http://www.sbintl.com/downloads/sbi110-10.pdf

found it vis a google search, don't know if they can help.

S.B. INTERNATIONAL, INC.

2108 Utopia Avenue

Nashville, TN 37211

1-800-THE-SEAT (843-7328) ORDER DESK ONLY PLEASE

or

1-888-THE-SEAT (843-7328) ALL OTHER INQUIRIES

FAX # 615-248-6377

Website: www.sbintl.com

[crusader]

head saver shims here on page 870 http://www.sbintl.com/downloads/sbi110-10.pdf

found it vis a google search, don't know if they can help.

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

[pat_pending]

I'm curious about this, these engines do have a few problems but head gasket failure isn't one of them. So I reread your original post, and it seems the engine did 7000 miles from rebuild before the head gasket blew, then twice more in fairly quick succesion. That leads me to think that the cause of the problem happened at 7000 miles, not at the rebuild or any work done previously, otherwise how did the original gasket manage that mileage when a subsequent one only did a few hundred and the next one failed on warm up?

Can you post up pics of the failed gaskets, the head face and the block face?

You also said you thought the head bolts were 25-30lbft lower than they should have been when removeing the head on the last occasion, how did you estimate this and what torque/procedure did you use on assembly?

[Les Henson]

Head savers aren't generally an off-the-shelf item, as they are mostly a rarity. They are generally made to order from shim steel of the required thickness and are cut - using the head gasket as a pattern. If you get one - make sure you find out if it goes above or below the head gasket. There's a reason for this that I don't know.

Les.

[crusader]

...how did the original gasket manage [7000 miles] when a subsequent one only did a few hundred and the next one failed on warm up?...

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.

...You also said you thought the head bolts were 25-30lbft lower than they should have been...how did you estimate this and what torque/procedure did you use on assembly?

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.

Head savers aren't generally an off-the-shelf item, as they are mostly a rarity. They are geberally made to order from shim steel of the required thickness and are cut - using the head gasket as a pattern.

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.

[Les Henson]

Not copper - shim steel.

Les.

[Range Rover Blues]

Composite gaskets do react with heat and "bind" to the head/block provvided they are nto oily. AFAIK if the head uses stretch bolts they should not need further tightening once the engine had been run, that's part of why they came about.

The one time I found the head bolts were "loose" the head had warped.