3.8 head gasket

[dxke38]

Hi all, I know head gaskets have been talked about forever but I have just started a 3.8 engine that was overhauled at great expense some years back and not commissioned and its leaking water from the head gasket. Took the head off and it looks like the gaskets been fitted with a smear of silicone, or it could be the coating off the gasket. Has anyone seen this before?

[abowie]

Some composite gasket do have a layer of clear material on the mating surfaces that is supposed to aid sealing but it is very thin. I think I have seen this on the MLS gaskets that Cometic do as well. I doubt it would look like silicone; in fact I doubt you would see it at all if you took the head off. Sometimes agents like Hylomar are used if the gasket doesn't have this sort of coating, but putting silicone on a head gasket would seem an odd choice to me.

Leaving an engine sitting for a protracted time is always a gamble, especially in terms of getting warranty work out of the builder. Did you check the head stud torque settings prior to removing the head? That might provide some information.

You don't say how much water is leaking or where it is coming from. Sometimes the leak can be from the inlet manifold water rail or even from the thermostat housing and it can look like it's coming from the head gasket itself. Water can also leak up past the studs as some of them, even in a 3.8, are in the water jacket although this is a lot more common in the long stud 4.2.

Firstly have a really careful look at the gasket and see if there is any obvious damage that might account for the leak.

Now the head is off, my approach would be to ensure the deck and head were flat and to check the water passages in the block and head for excessive corrosion.

I would ensure that the head had been crack tested prior to the original engine rebuild.

This head has had the water passages welded and recut:


This 3.8 block has had the water passages brazed and recut:


With those things rectified I would remove all the head studs. Check that the threads in the block are ok. Assuming the studs were replaced with new ones in the rebuild I would then put them back in.

I would fit a good quality brand name head gasket, torque it down properly and then try the engine again.

[dxke38]

Thankyou for the reply Kevin, you are spot on. The coating is definitely the lacquer that has broken down on the gasket. No other sealant had been applied. On checking I realised that cast lifting brackets had been fitted without fitting the four longer studs and this caused four head nuts to pull their threads. Also one of the new head studs had a poorly cut thread which caused another nut to pull its thread. If I had just tried to torque the head down I would have seen the problem. Hopefully new domed nuts and a new stud will rectify the problem. Just need to decide tin or composite. Thanks again.

[dxke38]

Sorry Andrew, don't know where Kevin came from.

[abowie]

Sorry Andrew, don't know where Kevin came from.

Very simple. Kevin is my dog. He's a tough little bastard. Nearly got killed a couple of years ago when he took on a greyhound about 5 times his size in an argument over a bone. He was not going to back down.

That's him on the left with his sister Sparkle on the right. Both 12 years old and going strong.

[dxke38]

I thought it was just me losing it, say hello to Kevin for me.
Do you have any advice re tin or composite gasket. I.ve always stuck with original type but I can see benefit of newer material.

[abowie]

If they didn't replace all of the studs during the rebuild you should do so.

Chase all the threads in the head nuts and bin anything you don't like. Make sure any washers you use are hardened steel. From what you've said I suspect you know to do all of his already so apologies if I'm telling you things you already know.

There is a recent thread on the badly manufactured dowel studs here:
http://forum.etypeuk.com/viewtopic.php?f=3&t=14541

I've used both the Cometic MLS gaskets and the brand name composites with equal success. The MLS gaskets are nice if you have an engine that has had a lot skimmed off the block and head and you're wanting a thicker gasket to bring the compression down to normal levels.You can get them off the shelf up to 80 thou and special order to 120. Otherwise the quality composites are fine and are about a quarter the price.

[dxke38]

Thanks again Andrew, ordered a composite gasket, new studs and nuts. I hope this cures the problem, I'll let you know the results.

[abowie]

Do check the head and block faces to make sure they're flat. You can do this approximately at home with a straight edge, but it's good insurance to get it done professionally. If the guys who rebuilt you engine did what they did with the studs, you might wonder if they did that properly too.

[abowie]

If the guys who rebuilt you engine did what they did with the studs, you might wonder if they did that properly too.

And this is where paranoia sets in.

Have a good read through the invoice they gave you.

It should tell you that they charged you for skimming the head and the block.

Check the bore diameters with a proper gauge. You could probably blag one off your machinist. Ensure that the bore to piston clearance is correct. It should be around 2.5 thou, depending on your pistons. Your pistons should still have legible markings on their crowns and these will let you know exactly who made them and from there you can find out the recommended clearance. I recently stripped the engine on one of my own cars, rebuilt "by an expert" before I bought it. All bores were 2 thou, except for one which was 5 thou. I rebuilt the engine.

Look to see if they have billed you for new rod bolts and nuts, an a new oil pump. If they haven't and the suspicion is that they have reused the old rod bolts, especially if they are the ones with split pins and castellated nuts, you might want to look further. Apart from the issue of reusing 50 year old rod bolts the split pins need to be special hardened ones not soft ones from the DIY shop. We have an oil pump that has lovely impressions of broken bits of split pins on its impeller. A new pump is a no brainer.

While the head is off I would check the valve clearances as it is a lot easier to rectify problems now, with the head off. Support the back of the head with a piece of 1" square wood a foot long. You can't turn the cams with both of them installed as you will bend valves. You will need to remove the exhaust cam, measure the inlet side, then replace the exhaust, remove the inlet and measure the exhaust shims. If they are not within one thou of correct fix them now. Reset both cams to TDC and make sure your engine is at TDC before you reinstall (I'm sure you know this).

Assuming that your invoice checks out properly and they have done the right thing though, I reckon that taking the head only to an good machinist and having it checked for flatness would be enough. If it's flat and the valve clearances are right, I'd just refit it. The bore clearance is easy to check and will give you peace of mind. If on the other hand they have not done things properly I will post Kevin over to you and he can sort them out.

[dxke38]

Hi Andrew, one more question. With the tin gaskets I've always used Welseal or Hylomar to seal the waterways and chain area. I've got a composite gasket ' Australian made' and wondered about any sealant.
Derek

[abowie]

Wow! I didn't know we even had a domestic car parts manufacturing industry, never mind making Jag parts.

The composites come with the sealant on them and AFAIK so do the MLS ones. We don't spray them with anything, just fit them. I can't see that a bit of Hylomar around the water holes could hurt though.