imminent head gasket failure...

[nigelrbfurness]

Been noticing lately that I'm losing a little water on a hard run over about 20 miles - not much - and I can't find any leaks. Taking the radiator cap off after about ten minutes cooling time, I hear a slight hiss. Sniffing the rad reveals a smell of oil. I suspect therefore that exhaust gas is leaking into the coolant, slightly pressurising the system and blowing a little water out through the recuperator.

There is no obvious loss of performance from the engine, so the I'm seeking opinions as to whether there is any mileage in tightening down the head bolts slightly - even torque all round of course. The head gasket was replaced not that long ago - less than 3000 miles I would say. I had the head checked and it appeared to be straight so the engineer didn't skim it. The gasket was replaced with a 87mm one as the correct 85mm I normally use on this engine wasn't available. Should I mess with it or just wait for it to fail completely and blow all the coolant out?

Or am I being unduly pessimistic and there's some other possibility. That would be nice.

Nigel F.

[RichC]

would help if u could indicate to forum torque value you placed on head bolts last time & were they new bolts or old?
& presume you retightened after 500miles ?
well worth a go cracking off head bolts and retightening but I don't have any experience with TC head to give you a ' 'real world' value ... i seem to remember there is wisdom beyond that written in workshop manual .

fingers crossed for you

[RichC]

p.s got any piccies of your '66 Bristol bus?

[nigelrbfurness]

Hi Rich

Thanks for your comments. Pic of bus sent by PM.

Head bolts were new, 65lbs/sq in torque - the same figure I have always used in the past.

Yes re torqued after around 500miles

Sounds like it might be worth giving them another tighten. I generally don't loosen them off, I just put on another 2-3lbs,,, should I undo them and re-tighten to the standard torque? If I do that, I'll have to drain the cooling system again. Maybe I've been doing it wrong all these years!

Nigel F.

[RogerFrench]

Well, I wouldn't say you've been d o ing it wrong, but I'm curious to know how you measure torque in lbs/sq. In........

If it were me, I'd get a pressure and a leakdown test done, and if they revealed a problem, I'd have the head off PDQ. If indeed you have exhaust gas leaking to the water jacket, it can carve nasty tracks in your head.

[nigelrbfurness]

Richard, I have a very special torque wrench. My radiator cap is calibrated in foot/lbs to make up the set
40 years an engineer this year. And we complain about the younger generation.

I think a re-torque (in foot/lbs) and then a compression test after a good run looks like the agenda.

Thanks to all who have replied. I'll let you know the outcome in brief!

Nigel F.

[rgh0]

i would Retorque like you plan to a few ft-lbs higher. If it moves a fraction that is good. If it does not move back it off a fraction and then retorque to the new setting.

regards
Rohan

[AHM]

No wonder us younger generation engineers have a problem, when our elders confuse ft.lb with ft/lb.

I also agree with your plan - Don't forget that tightening torque is a range. So try the top end when you check. It is pretty inaccurate as a method in any case.

[RogerFrench]

Richard, I have a very special torque wrench. My radiator cap is calibrated in foot/lbs to make up the set
40 years an engineer this year. And we complain about the younger generation.

I think a re-torque (in foot/lbs) and then a compression test after a good run looks like the agenda.

Thanks to all who have replied. I'll let you know the outcome in brief!

Nigel F.

Who's Richard?

[Elan45]

1st thing to do is a leak-down pressure test. If you get bubbles in the radiator, then you have a leakbetween combustion chamber and water jacket. Id try a re-torque at that point, then check again w/ leakdown. If bubbles in rad still happen, time to pull head. If no bubbles, then run the engine. Check for bubbles in rad w/ engine running and if they appear, time to pull head. W/ price for Weber head these days, take no chance.

Roger

[denicholls2]

As Rohan's recommendation suggests, you want to creep up on the proper torque. When you hit it, the torque setting should rise more quickly (because the setting is pretty much about the bolts getting as tight as they're designed to get.) When they've been sitting in place, it takes extra torque to move them -- prove this easily to yourself by checking the torque it takes to back off the bolts. If it happens to be easy, remember how hard it was when the head had been in place for a few years and a bunch of miles. I bet they didn't come off at the factory setting at any rate.

Ideally, you want to start well below the ending torque and move up to the ending torque. This assures that it's the torque on the bolt shaft and not other factors that are giving you the reading.

Good luck!

[2cams70]

What type of head gasket is it? Is it an MLS type? - if so surface finish is critical.

Also 87mm gasket hole size is very large - will be a large amount of "dead space" between the gasket and cylinder (assume the bore is around 84mm if you were using 85mm gasket previously) which is not ideal for combustion efficiency.

Since the gasket fire ring is now a larger diameter it is possible that it now overlays a small surface imperfection caused by waterway corrosion, for example, in either the head or block face that was not a problem previously.

I'd lift the head to check rather than risk a complete failure that could burn the face of the block and/or head.

[nigelrbfurness]

Just an update - bore is 85mm, gasket standard type from Burtons and looks exactly like the 82.5mm gasket from Payen. I re-torqued the head bolts following the advice given, but also fitted a 15lbs radiator cap in place of the 13lbs I'd been running previously. Several good lengthy runs reveals no further water loss, so either torqueing up the head did it or perhaps I was just being paranoid. In 45 years and thousands of miles of running Elans I've only had one head gasket failure before, so I would guess the loading is generally good and its not a weak point on these engines. But I will do a compression test within the next few weeks, just to be sure. I don't have the facilities here for a leak-down test.

Thanks to everyone who gave their opinions.

Nigel F.

[JJDraper]

I agree on the gasket size being too big. I have experience of fitting one a couple of mil too wide & the symptoms were exactly as you describe. No oil/water mix as the leak was bore to waterway & just enough to pressurise the system to blow out the coolant. If you kept a light foot on the pedal, coolant loss was lower than 'enthusiastic' driving. Suggests the chamber pressure was just enough to blow by a marginal head gasket. Fitting a gasket that matched the bore has stopped the leak in its tracks (+60 bore, 84mm Ajusa gasket). Recommend doing the work sooner rather than later to prevent any erosion of the head face.

Jeremy