AJP Head Gaskets

[Adambul]

I’m in the process of fitting new standard head gaskets to my 4.2 V8 and firstly I’m surprised by the quality of the gaskets in relation to the high cost! Secondly, I noticed that there is no steel compression ring around the oil way. The old gasket does have the steel ring similar to the piston seals. I read a thread from about 10 years ago where Longbow mentioned inserting an ‘O’ ring, it feels a good thing to do to avoid a gasket failure on the oil way supply to the heads. Its very close to the edge of the head, have others done this or is it ok to just rely on the gasket?

Also, it may be my naivety but what stops water from going up the cylinder head studs that go through the water jacket? I can only see the main washer and head bolt at the top on the cylinder head and fear water will find its way up and out without some sort of seal. Am I missing something?

Thanks all.

[Flatplane8]

Can’t help but good questions. Looking forward to the answers.

[plasticman]

all the gaskets that I have fitted come with an o ring for the oil feed . There is nothing to stop the water going up the studs . It would be very hard to do and the nuts and washers do complete the seal . It works quite well till the aluminium grows round the studs and prevents head removal .

[CER927]

Definitely use the O ring, it will leak if you don’t. I have bitter experience of this, when a junior parts man didn’t supply the O ring, and I did not know it was required. Mucho water in the oil :-((

[Adambul]

Thanks for the reply's. 'O' rings now purchased, also appreciate the clarification around the head studs, although that still worry's me. I'll make sure the head and washers are super clean which should help with the seal.

It does make sense with the corrosion around the head studs and as previously said not really an issue until you try and get the heads off!

[spitfire4v8]

After having seen coolant leaking through past the nuts/washers on an engine built by a knowledgable engine builder I always put a none setting compound between them just in case. Whilst the vast majority of them don't leak, it's certainly not unheard of to have them weep.

[Adambul]

spitfire4v8 said:

After having seen coolant leaking through past the nuts/washers on an engine built by a knowledgable engine builder I always put a none setting compound between them just in case. Whilst the vast majority of them don't leak, it's certainly not unheard of to have them weep.

Good advice thanks, I will definitely do that. I certainly don't want to trying to do it retrospectively if they do weep!

[Flatplane8]

Out of interest why did you take the heads off? I did a leak down test on my 4.2 engine yesterday and have quite a few valves not sealing……

[ukkid35]

Because the heads on my car have been skimmed so many times, I've fitted oversize headgaskets made by Cometic

This is what they offered a couple of years ago

Cometic said:

.043"
H2789SP1043F (RHS) are £119.16 + VAT each.
H2790SP1043F (LHS) are £119.16 + VAT each.

.059"
H2789SP1059F (RHS) are £119.16 + VAT each.
H2790SP1059F (LHS) are £119.16 + VAT each.

Shipping is £16 + VAT

However, they were missing the oil feed O rings which come with the Racing Green gaskets

The problem was making sure I found and used the correct O rings for the 0.059" thick gaskets, so I bought a selection and used the ones that I thought fitted best

[Adambul]

Flatplane8 said:

Out of interest why did you take the heads off? I did a leak down test on my 4.2 engine yesterday and have quite a few valves not sealing……

I've carried out a bottom end rebuild due to piston slap and low oil pressure. I didn't do a leak down test on mine before strip down, but I did find the valves, particularly the exhaust valves were very coked up and I wouldn't be surprised if they were leaking.

[Adambul]

ukkid35 said:

Because the heads on my car have been skimmed so many times, I've fitted oversize headgaskets made by Cometic

This is what they offered a couple of years ago

Cometic said:

.043"
H2789SP1043F (RHS) are £119.16 + VAT each.
H2790SP1043F (LHS) are £119.16 + VAT each.

.059"
H2789SP1059F (RHS) are £119.16 + VAT each.
H2790SP1059F (LHS) are £119.16 + VAT each.

Shipping is £16 + VAT

However, they were missing the oil feed O rings which come with the Racing Green gaskets

The problem was making sure I found and used the correct O rings for the 0.059" thick gaskets, so I bought a selection and used the ones that I thought fitted best

I purchased mine from Powers and was told they didn't need an 'O' ring but I'm definitely putting one in, the gasket is poor quality and the hole is so oversized its crying out for an 'O' ring. Especially as its so close to the water jacket!

[ukkid35]

This is before I put in the thicker head gaskets

Haven't done a compression test recently, may well do another soon, just to see what difference the Cometics have made

[Flatplane8]

Thanks for the reply, my valves don't look too bad but from what I can see the piston tops are pretty covered in carbon.

How are people who are working on their engines finding parts supply? Mine is a 1997 4.2, engine number 630 so I'm guessing a small journal crank, but probably the later variant not prone to snapping.

I won't know until I get into it, but pistons, rings and liners don't seem to be listed anywhere. Have you guys found alternatives?

[spitfire4v8]

Andy at APM will be your go-to for engine parts. I would only ever use Andy in the future for parts, having been bitten by another supplier in the past. What Andy doesn't know about ajps isn't worth knowing! Plus he's a genuinely likeable fella.

[Adambul]

Flatplane8 said:

Thanks for the reply, my valves don't look too bad but from what I can see the piston tops are pretty covered in carbon.

How are people who are working on their engines finding parts supply? Mine is a 1997 4.2, engine number 630 so I'm guessing a small journal crank, but probably the later variant not prone to snapping.

I won't know until I get into it, but pistons, rings and liners don't seem to be listed anywhere. Have you guys found alternatives?

Sounds like you have exactly the same engine as me, mine is a 97 4.2 and I think the engine number is around 550. It did turn out to have the more robust 2.3" small journal crank. The was in excellent condition, just needing a quick polish and then a re-shell with new bearings.

Regarding parts, I was lucky enough to buy some 0.010" over sized forged pistons from someone who had two sets commissioned a few years ago. They were supplied with new rings and all had to do was get the existing liners honed to accommodate the new pistons.

My old pistons were shot and I don't believe you can get new pistons for the 4.2 now, maybe give Dom at Powers a call and see if he can suggest anything. Depending on condition you may get away with just new rings which you could get from one of the piston ring suppliers.

[Flatplane8]

Thanks both. Andy at APM did the pre-purchase inspection on my car 21 years ago. I used him for servicing until I moved away from the area.

I think my plan will be to disassemble the engine and then see what I've got. I'll possibly get the crank magnafluxed and then it'll be a case of what state the bores and pistons are in. I'd rather keep it as a 4.2, but pistons could be a challenge by the sounds of it if I need new ones.

[Byker28i]

Adambul said:

Flatplane8 said:

Thanks for the reply, my valves don't look too bad but from what I can see the piston tops are pretty covered in carbon.

How are people who are working on their engines finding parts supply? Mine is a 1997 4.2, engine number 630 so I'm guessing a small journal crank, but probably the later variant not prone to snapping.

I won't know until I get into it, but pistons, rings and liners don't seem to be listed anywhere. Have you guys found alternatives?

Sounds like you have exactly the same engine as me, mine is a 97 4.2 and I think the engine number is around 550. It did turn out to have the more robust 2.3" small journal crank. The was in excellent condition, just needing a quick polish and then a re-shell with new bearings.

Regarding parts, I was lucky enough to buy some 0.010" over sized forged pistons from someone who had two sets commissioned a few years ago. They were supplied with new rings and all had to do was get the existing liners honed to accommodate the new pistons.

My old pistons were shot and I don't believe you can get new pistons for the 4.2 now, maybe give Dom at Powers a call and see if he can suggest anything. Depending on condition you may get away with just new rings which you could get from one of the piston ring suppliers.

You can get new pistons for the 4.2 but Dom has them having had them remade, so is I think the only source now.

Mines engine 474, 97 4.2. Bore was fine as were the pistons, my trouble were the early valve guides wore. I had the early small journal crank that I had converted to the later, because no-one would warranty the engine without it.

I'd suspect, depending on your mileage, you've probably find the same as me, that some of the valve stems were really lose allowing gasses to escape.

[Flatplane8]

Its done 176K miles, I brought it with 82k miles on it in May 2003. Although it starts and runs fine I would guess there are a few bits that could do with refreshing whilst the chassis is off.

As an aside, I've been amazed at how much information is around on the forum, even found posts that I made over 20 years ago. I've got a copy of the engine manual so will read through that, but I think we'll have a go at doing a lot of the work (apart from specialist machining) here.