18 replies to this topic

[tom1]

I seemed to have failed to fix my wife's head gasket. Just rebuilt the engine after the head went on the way back from Whitby (goth weekend). So we have a standard 1986,998cc mini. I took the engine and gearbox out of the car, as the oil and dirt was quite amazing for all the wrong reasons. Had the head skimmed at a local, engine machine shop. Dint have the block skimmed and haven't fitted new head bolts(please don't shout at me),I would never do this with one of my own engines.

 

When I tried to get it going, I saw some bubbles coming out between the head and the block and it was running like a bi+ch. Not a a good sign. I picked up my brake cleaner gun a give it a quick squirt and there was some more bubbles.

 

My question is this how far back in the rebuild do you think I have to go to put this right ?

[tiger99]

Well, you will need to have the head off for a start. Hopefully that will be all. Get a new set of studs s they only withstand a certain number of fatigue cycles, and I have had them break on a recon engine. Check for visible damage to head and block faces, and absolute cleanliness. Obtain a new, genuine gasket.

 

At this point I am going to add something that has come to my attention just recently as a possible cause of head gasket problems. They are tedious and repetitive on this forum (we don't mind people asking about their problems, I mean more that it is unfortunately happening to too many people). That tells me that something is wrong. Every time the brand of gasket, the torquing up process, head skimming, etc are discussed, correctly. So it occurred to me that something is being missed. Have a look at the washers on the head studs. Do they look soft and somewhat chewed up? I have seen that so often, and never really understood the possible significance. I recommend Googling for "through hardened washer" or try here: http://shop.aseriess...rs-self-colour/

and procure a set of 9 or 11, depending on engine. It is 9 on yours, you may have to buy 10. They are 3/8" bore, Also, the coil bracket wants to go on top of the head nut, with a second half nut, as was done at one time. I would be inclined to get new nuts too.

 

Also, as a precautionary measure, while the studs are out use a countersink gently to remove any raised rim of metal or dirt around the stud holes in the block, and the same on the gasket face of the head. Make sure that the mating surfaces are perfectly clean and dry. Yes I know you most likely did all of that last time, just trying to be sure to cover everything.

 

You will want a Payen gasket (unless someone recommends a better brand), and torque up 10 ft lb at a time in the correct order, on clean, dry threads. By that I mean, do them all up to 10, then start at the beginning again, loosen the first nut very slightly, then nip it up to 20, same for the second, etc, always loosening the nut you are doing slightly before taking it to its next increment of torque. Finish at the correct torque for your engine. I have not got the manual to hand right now, but from memory it is probably 40 lb ft.

 

When that is done, the coolant replaced and valves adjusted, you can start it up, and run it up to full temperature. A short trip on the road is ideal. Then, with it still hot, back off the nuts slightly, one at a time again, and nip up to the full torque. check the valve clearances and adjust as necessary. Repeat after 500 miles.

 

If that does not provide a permanent cure you are going to need to have the block skimmed and possibly the block and head crack tested, but it is not common for Mini blocks to distort.

[carbon]

+1 for above.

 

Also when head is off you need to check block deck for flatness. They will distort if cooked (ie run without enough coolant).

 

Use a dead straight metal edge, such as a 12 inch steel ruler, place on top of cleaned block and look for daylight between the block and metal ruler. This may be easier with a torch or similar light behind the ruler. If you see daylight try to measure distortion using feeler gauges, anything over 4 thou and you may need to get the block deck skimmed.

 

PS. Wouldn't bother replacing the head studs, the original A+ ones are very good quality (should be stamped with 'Y' on end of the studs). Just make sure all of the threads are nice and clean, ditto with nuts.

[Dusky]

À hot retorque ?
Anyone else done this? Me and my dad have never heard of it.

[tiger99]

Dusky, well, that is what I have done maybe 12 times and never had a gasket fail afterwards. But I am interested in various opinions on the matter. I had never really thought about it.

carbon, yes the studs are supposed to be good quality, but I had 5 or 6 break at first careful retorque of a recon engine, and that was in the days when engine parts were properly made. They broke well before 40 lb ft! The problem is that you can't know whether some past moron has taken them beyond the fatigue threshold, or how many times he has done it.

Of course in many modern engines you MUST throw away the studs and in many more you have to check the length and throw them away if they have stretched beyond a specified limit. But the Mini has none if that because the studs are not taken to the elastic limit, unless you go to 50 lb ft and use an efficient lubricant.

Edited by tiger99, 29 May 2017 - 08:39 PM.

[Magneto]

I also have not heard of retorquing the head hot, I always cool it down completely, then retorque and recheck the valve clearances.....been doing this for 45 or more years now.

Edited by Magneto, 29 May 2017 - 09:09 PM.

[tom1]

Going to take my torque wrench into work tomorrow and see how close 40 lbs it is. We have a calibrated one in the bonding room.

[Magneto]

I torque mine to 45, just for what it's worth - it's a high strength 3/8 stud, the official torqe rating for a bolt that size is 49. And it's definitely a good idea to check your torque wrench for accuracy - I use an electronic version for critical things like this.

Edited by Magneto, 29 May 2017 - 11:46 PM.

[tiger99]

Thinking about it, the coefficient of expansion of steel is similar to that of cast iron, so if everything is hot, or everything is cold, the stud tension should be the same, albeit the thin copper in between might make a slight difference. SO that is why my method, which I never really thought about till now, gave satisfactory results.

It would be very bad to do it if the temperature was changing rapidly and was non-uniform. The worst thing would be to start from cold, give it a blast of revs for maybe a minute, switch off and apply the torque wrench. Combustion chambers hot, cylinder walls lukewarm, studs cold....

[sonikk4]

Do a head re torque after one heat cycle. However it's more likely to be the brand of head gasket.

Was it a Copper one by chance?? Been there had that issue. Fitted a different brand and no more leaking.

Checking the torque wrench to see if it's in calibration is always a good thing. Been bitten once by my own stupidity there. Now I always take mine to work ( I have a few) and check them for tolerance.

[Spider]

Alloy Heads are normally re-torqued hot and iron heads, cold.

 

The factory Torque for the latest heads studs / nuts was 50 ft / lb. These are the studs that have a very pronounced taper on the UNF end and the flanged nuts (in fact, they were changed to this spec in 1968). If these studs and nuts are what is fitted and they are in good order, I'd suggest not replacing them as so many of the new studs are pretty poor quality these days. If you do replace them with those currently available, only torque them to 45 ft / lb.

 

Oil the threads (as per factory advice) and torque up in at least 2 stages.

 

If it is bubbling, then likely it's too late and as sonic has suggested, a new gasket will be needed.

 

I'd say something was seriously adrift here if it started bubbling so quickly, however, has it really failed / leaking or is it just some trapped air still coming out?

[sonikk4]

Alloy Heads are normally re-torqued hot and iron heads, cold.

 

The factory Torque for the latest heads studs / nuts was 50 ft / lb. These are the studs that have a very pronounced taper on the UNF end and the flanged nuts (in fact, they were changed to this spec in 1968). If these studs and nuts are what is fitted and they are in good order, I'd suggest not replacing them as so many of the new studs are pretty poor quality these days. If you do replace them with those currently available, only torque them to 45 ft / lb.

 

Oil the threads (as per factory advice) and torque up in at least 2 stages.

 

If it is bubbling, then likely it's too late and as sonic has suggested, a new gasket will be needed.

 

I'd say something was seriously adrift here if it started bubbling so quickly, however, has it really failed / leaking or is it just some trapped air still coming out?

 

To add to this mine did straight away even after a retorque. It ran fine and even did the kent IMM however once home it came off. I contacted Simon@minispares to complain about it and he sent me a Payen type. Instant cure. 

[carbon]

Alloy Heads are normally re-torqued hot and iron heads, cold.

 

The factory Torque for the latest heads studs / nuts was 50 ft / lb. These are the studs that have a very pronounced taper on the UNF end and the flanged nuts (in fact, they were changed to this spec in 1968). If these studs and nuts are what is fitted and they are in good order, I'd suggest not replacing them as so many of the new studs are pretty poor quality these days. If you do replace them with those currently available, only torque them to 45 ft / lb.

 

Oil the threads (as per factory advice) and torque up in at least 2 stages.

 

If it is bubbling, then likely it's too late and as sonic has suggested, a new gasket will be needed.

 

I'd say something was seriously adrift here if it started bubbling so quickly, however, has it really failed / leaking or is it just some trapped air still coming out?

Just to throw another spanner in the works...

 

Metro repair manual AKM4694 (6th Edition), 1986, gives torque for cylinder head nuts as 55 ftlb.

 

And for the MG Metro Turbo is also 55 ftlb but includes comments:

- thread lightly oiled

- correct tightening procedure must be followed

 

Here is the cylinder head nut tightening procedure as stated in the AKM4694 (6th Edition), 1986:

- tighten the cylinder head nuts initially to half the torque figure given in Data

- then to full torque figure

- adjust valve clearances

- run engine for at least 15 minutes or drive at least 5 miles

- allow to cool

- then working in the order shown in Fig 13 slacken and tighten each cylinder head nut in turn; slackening half a turn and tightening to the torque figure given in Data

[RooBoonix]

I have used the copper GEG300 gasket from Minispares twice successfully, torqued up with dry threads in 2 stages. Including a retorque after a heat cycle.. no issues to date.

Both head and block have been skimmed however, and I have read that copper gaskets can be a bit fussier than composite gaskets in regards to the head and block finishes.

[Spider]

Carbon - I have found those numbers too, but after checking the Part Nos. and all other manuals, I concluded that it's likely a typo.

 

In regards to wet or dry torquing any fasteners, torquing them dry gives very very inconsistent stretch of the studs.When we torque up fasteners, what is (trying) to be achieved is a certain predetermined stretch of the studs / bolts.It does not matter one iota if it needs 1 ft / lb to achieve this or 100 ft / lb, it's the total stretch that matters.

 

For example, on the bigger diesel engines, rarely is a toque wrench used. For the cylinder head studs, these are all fitted up, then stretched hydraulically and the stretch measured with a dial gauge. The nuts are then wound to the head by hand and the hydraulic pressure released, while also checking for any settling. What's the fastener toque?  I doubt anyone knows or cares.

 

Using the best torque wrench in the best possible way will still produce stretch errors of up to 30%, however, in respect of the head gaskets most of us use, the gasket alone will introduce errors outside of that.

 

Find the ARP Catalogue and have a read of that, while not complete, it's one of the best guides I've found on the net.