Endless head gasket failure

Post by **matt993fod** » Tue Apr 21, 2009 8:04 pm

So my engine has munched four head gaskets in five months.

The engine suffered a spate of pinking, caused by the installation of a new electronic ignition system that allowed too much ignition advance. This was deemed to be the cause of the first gasket failure. Since the failure coincided with this pinking. We reduced the advance to stop the pinking and installed a new gasket.

The second time the gasket failed, we found that the torque wrench we used to install the head the first time was poorly calibrated, and had only tightened the head to 30 ft lb. A new gasket was installed, along with the later type of head studs that allow the head to be torqued to 50 ft lbs. The head was reinstalled to this torque, using a fresh wrench.

The third time the head gasket blew we were quite exasperated. After scratching our heads we guessed that because the compression was around 12:1, and since the engine was running quite hot, the strain on the gasket was such that it was prone to breakage. Removing the head, however, revealed that the head had been skimmed so far that the fire ring on number four cylinder was only sealing with 1mm of its width. A new, skimmed cylinder head was installed, with larger chambers and less material removed. We reasoned this would not only provide a larger area for the fire rings, but would also reduce the CR a bit to reduce the stress on the gasket.

But it has eaten this gasket as well. This is very irritating, as I hate changing head gaskets.

Anyone got any other suggestions? How much would you guys expect to pay for a block to be decked?

Post by **d_harris** » Tue Apr 21, 2009 8:17 pm

I'd get a straight edge and check if the block is true....

Post by **Alec** » Tue Apr 21, 2009 9:35 pm

Hello Matt,

what engine is it and how modified is it (the 12:1 gives a suggestion it is far from standard)
You mention the timing but because you have eliminated the pinking does not mean that it is timed correctly, too much advance at high revs is inaudible but can seriously damage the engine. That siad it usually destroys pistons etc.

Obviously a check on flatness is required, but is it the same spot or does it vary? Are you sure, if it is the same spot, that there is not a crack in the block? (Seeing as you changed heads). Use some emery to polish the area and a crack will be more visible.

Alec

Post by **bmcecosse** » Tue Apr 21, 2009 9:59 pm

12 :1 is ridiculous CR unless a full race engine - even then it's unlikely to run well on standard pump fuel without lots of octane boosting additive . It would be ok on LPG !
Does the gasket always blow in the same place ? If yes - then the block is likely scoured and will need stripping and skimming. Is the head always torqued down again after the engine has been put through a heat cycle ?

Post by **Kevin** » Tue Apr 21, 2009 10:42 pm

Hi Matt that is some compression ratio I would have thought you would have needed one of the special headgaskets designed for such a compression ratio similar to this one I expect.
http://www.minispares.com/Product.aspx? ... ITH%20AF46...
The other thing that Alec touched on regards timing I assume the engine has had a recent rebuild if so and you changed the cam did you check the timing when you installed the cam as the can be quite a bit out if fitted with the standard woodruff key, to give you an idea last week on my engine I am putting together with a SW5 cam which is quite mild has shown to need an offset key of between 5 & 7 degrees, so can you tell us what spec the engine is.

Post by **leyther8008** » Thu Apr 23, 2009 8:33 am

With that compression ratio you need a Metro Turbo head gasket known as a 'Black gasket' to have any chance of keeping the gas in.

Post by **bmcecosse** » Thu Apr 23, 2009 10:32 am

Not so - I have run A series in the past with 12:1 (probably nearer 13:1 !) race engine on standard 1275 gasket (it was S head on 998 block) without any problems. If the surfaces are FLAT and the head is well bolted down, it will be fine.

Post by **leyther8008** » Thu Apr 23, 2009 11:09 am

makes me wonder why MG fitted them then?

Post by **bmcecosse** » Thu Apr 23, 2009 11:43 am

Because they had to make sure the factory assembled engine lasted through warranty! Yes - they are a better gasket - but at a high price. Carefully assembled engine will be fine with a normal good quality gasket.

Post by **matt993fod** » Thu Apr 23, 2009 12:37 pm

With the new head the compression ratio is more sensible- 9.5-10:1

We only used the previous head because at the time it was all we had!

The engine is a 1098 midget engine (10CC engine number). It is quite mild. The current head casting is a 12G295, which has been skimmed for 25cc combustion chambers. With this skim, the pistons (which are 2cc dish) and the .20 rebore it had, this gives a compression of around 9.5-10:1. The previous head had much smaller combustion chambers, hence the ridiculous compression with the spec we were running.

Post by **bmcecosse** » Thu Apr 23, 2009 1:36 pm

Sounds good! Just make sure both block AND head are completely FLAT. Use studs with either the little 'dimple' or 'Y' on the top - and put washers under the head nuts unless you can get the later type which had a flat landing built in. With these studs you can safely torque to 44 ft lbf - in stages of course - although I have used 50 ft lbf, you should be ok at 44.

Post by **Matt** » Thu Apr 23, 2009 7:05 pm

The other question is what gaskets were you using?

If everything is flat source a good quality copper gasket and put that on, and forget the silver/composite ones

Post by **bmcecosse** » Thu Apr 23, 2009 7:29 pm

I'll certainly second that!

Post by **Longdog** » Thu Apr 23, 2009 7:43 pm

I know a lot of people think payen gaskets are over rated but they work fine for me after numerous failures in the past.If it was a 1275 I'd say use bk450 but obviously this is no good on a 1098.I run at 12:1 btw.There may be a 1098 equivalent.

Post by **katiekat** » Sat Apr 25, 2009 5:04 pm

I don't suppose this will be any help to you but I used k-seal in a modern car with head gasket failure and it stopped the water leak that it had. Just thought I would mention it!