Head Gaskets

[Ronminch1]

Help, whats thought to be the best head gasket solution hear in the uk? I believe the engine was rebuilt by QED to 1700 big valve spec, 140bhp, some twenty plus years ago, no real proof of this, head is still fitted.

[ncm]

I think you might have to supply a little more information about the engine..Has it got a twincam block or a 1600 crossflow block? 1700cc using twincam block and crank will have a much larger bore than one built on a 1600 block/crank. Look for the block casting number below the water drain bung.
QED did sell complete engines based on the 1600 block.
Headgaskets here :- https://qedmotorsport.co.uk/product/hea ... ous-types/

Brian.

[Ronminch1]

Thanks for the reply Brian will have a look in the morning, head now off the engine, blow between cylinder 4 and water jacket. Tried add picture.

[nmauduit]

I would go for the composite (you may want to check the corrosion of the head before reassembly, in case water or poor coolant has sit for years eroding away the passageways)

[ncm]

That looks like a standard copper gasket. If the engine is a 1700 then it is not surprising that it has blown. QED list that as "The standard copper gasket is suitable up to +0.020″ bore size". Now the head is off, check the piston crowns for oversize markings. 1700 on a 1600 crossflow block is +.0.040".

[jono]

I always had great success with an oversize Ajusa gasket, in fact it was the only one that would work on my +40 engine.

[Ronminch1]

Morning all, had a better look this morning block is marked 681F 6015 DA, are +040 8L. The failed gasket is AF880 marked 56 in one corner. Some sort on silacon sealant has been use on both sides. See photo attached head has some corrosion, not happy.

[2cams70]

What is the cylinder block bore diameter?
What is the diameter of the cylinder hole size of the gasket you removed?

This information is critical.

[nmauduit]

Morning all, had a better look this morning block is marked 681F 6015 DA, are +040 8L. The failed gasket is AF880 marked 56 in one corner. Some sort on silacon sealant has been use on both sides. See photo attached head has some corrosion, not happy.

looks like it'll be fine (I've seen much worse that would seal for a long time, and it is not likely that overheating distortion would have compromised the head flatness as far as I understand) , you may want to clean it up to make sure and start with a nice surface for the new (composite) gasket.

if you want to be absolutely sure and you have a reliable machine shop, he would confirm that and/or offer a skim pass (couple thou) to clean up the face. This is not expensive (less than 100) but requires the head to be fully bare (make sure each valve will get numbered to go back where it was, etc.).
What I would do first is just rub it lightly on 320/400 grit quality paper attached on a surface plate (or possibly thick slab of glass onto a flat piece of particle wood if on the cheap side), the motion has to be so as to maintain flatness in applying pressure and rotating the head. From what you'll see once cleaned up you'll know if you need a skim pass or not.
As for cleaning the block top face (I suppose still in the car), again if not taking the whole thing apart (safest route) you'll need to protect the bore the best you can, taping plastic so that no grit or dirt would get into the oil, then clean with 3M 400 paper on a flat block, to assess the amount of corrosion.

Then you may also use Wellseal rather than installing the head gasket dry, which would help sealing micro porosity (if they don't go in deep) - this is more of a temporary fix, like on the tarmac of the track, but would help waiting for a more complete winter overhaul for instance... Along that approach deeper dips (yet not very deep... use your best judgment at your own risks) may be resealed with a dab of high temperature metal epoxy, which would stay if it is under compression afterwards.

good luck.

[ncm]

"Morning all, had a better look this morning block is marked 681F 6015 DA, are +040 8L. The failed gasket is AF880 marked 56 in one corner. Some sort on silacon sealant has been use on both sides. See photo attached head has some corrosion, not happy."

681f block is early 1600cc , so the good news is that you do have a 1700cc motor, however I doubt that the bottom end will have been supplied by QED as I recall the engines they were selling were all based on the later, 711M, block. The gasket fitted will have blown because the fire ring would have been overhanging the bores. In my experience, the best gasket will be the Ajusa composite gasket as sold by QED & Burtons (and probably many others ) with an 84mm bore.

Brian.

[nmauduit]

" The gasket fitted will have blown because the fire ring would have been overhanging the bores. In my experience, the best gasket will be the Ajusa composite gasket as sold by QED & Burtons (and probably many others ) with an 84mm bore.

The corrosion of the head gasket coming from the coolant/water passageway would have played a role imho, eroding away the gasket to the point the fire ring was not supported and hollowed out (while at the same time opening up a way for the coolant to seep towards the rear of the head).

At this point the question is what amount of work should be undertaken for having the repair last the desired amount of time (e.g. if the bottom is tip-top or average, the amount of effort on the head would not be the same so as to restore an homogeneous health till the next complete overhaul).

[Ronminch1]

2cams70, in answer to your earlier qurstion the bore is 83.3, and the gasket was the sameish, I would have thought the gasket bore should be slightly larger, is this the case?

[rgh0]

I like the gasket bore to be around 1mm larger than the cylinder bore. This ensures the fire ring does not overlap the bore allowing for the tolerances on the bore versus the head bolts versus the gasket holes and after it is compressed. You can get away with less depending on the components but 1 mm larger generally works in most cases for normal road engine rebuilds.

I use 85mm bore gaskets in my race engines which have a 83.5 mm cylinder bore to allow for extra bore shift due to the offset boring that I normally do to maximise cylinder bore wall thickness.

cheers
Rohan

[Ronminch1]

Hi Rohan, Thanks for the advice, Would anyone have a prefered supplier in the UK for 85mm composite gaskets?
Ron.

[2cams70]

2cams70, in answer to your earlier qurstion the bore is 83.3, and the gasket was the sameish, I would have thought the gasket bore should be slightly larger, is this the case?

The reason for my original question regarding block bore size versus cylinder head gasket bore size is that from the picture you posted of the block surface it looks like a gasket has been used that has a bore size significantly larger than that that of the block.

Look at the impression mark on the block surface from contact with the gasket fire ring. It's a long way outboard from the cylinder bore. It looks like an 87.5mm gasket has been used with a bore size close to standard. Either that or the gasket has been fitted grossly off centre. Is the surface of the block near the other 3 cylinders similarly marked?

If your bore size is 83.5mm you can use an 84mm Ajusa composite gasket no problem. You don't need an 85mm gasket and you certainly would not want to use an 87.5mm one. You won't be able to find an 85mm composite gasket in any case unless you have one custom made specially.