[Ethanissan]

Just thought I’d make this thread in case anyone is interested, received my cheap eBay gasket kit today and thought I’d compare my genuine gaskets to the eBay ones.
This is specifically for the SD33-series of engines (SD33 and SD33T), but the same principles apply for any engine.

This is just a warning so that people know the differences between quality oem gaskets, and cheap aftermarket ones.

Firstly the head gasket. Genuine Nissan top, eBay bottom.

First things first. The material. The top gasket is a proper MLS (multi layer steel) gasket, meaning it will seal well and take a lot of abuse.
The cheap gasket is (from my research) a fibre/asbestos gasket, similar to what was used on the early Scout SD’s, but undoubtedly with far worse quality control. These are known for blowing easily in the scouts even when using genuine pieces, an aftermarket piece will not hold up.
From what I’ve seen on eBay, you can buy aftermarket MLS gaskets, and if you absolutely cannot get a genuine one for whatever reason, try to get your hands on one that looks like the top one, do not use one that looks like the lower option.

Now, onto the actual design of the gasket itself. Look at the top photo firstly, and pay close attention to where the oil and water sealing rings are on the genuine gasket, vs the cheap gasket. Genuine gasket they’re around the oil galleries, pushrod holes and water galleries. Cheap gasket they’re around the pushrod holes and oil return holes, and bottom head bolt holes? NOT the oil feed galleries and coolant galleries. Goes to show how much research they did on these motors before slapping a gasket together 🙄. The sealing rings on the genuine gasket are also a seperate material designed to compress less than the MLS, creating a seal when torqued down. The “sealing rings” on the cheap gasket are painted on, and only on one side.


Now onto the manifold gasket.

The cheap gasket is on top here, and the genuine one is on the bottom.
I’ll start with the cheap one this time. It’s a basic aluminium laminated gasket, which in a crossflow head or one with seperate gaskets for intake/exhaust, would be fine, but since the SD33 uses one gasket for both the intake and exhaust, it needs to be made to seal even with the different expansion rates of the intake and exhaust manifold materials. This one would likely start leaking quite quickly.
The genuine gasket looks to have a similar laminated base, but has extra materials added over the ports to seal them properly. The exhaust ports have raised sealing rings around the holes so that when the gasket is compressed it seals tight against the ports, and the intake ports have what looks to be a sealant already coated on that probably works with either heat or just pressure.
From what I’ve seen, all of the aftermarket manifold gaskets are the simple laminated type. If you cannot get a genuine gasket, you can use a laminated gasket with high temperature RTV, designed for manifolds, but the longevity may be decreased.

The front main seal in the kit may be able to be used, but doesn’t look like a proper rubber seal like the genuine one. The rear main came as one piece, so I’d have to cut it in half if I decided to use it.
Preferably get these genuine, especially the rear main which is prone to leaking if it’s aftermarket.

None of the above gaskets I’ll be using for the SD33T rebuild, I got the genuine ones so I could do it right first time. The only reason I bought the eBay kit was for the rest of the simpler gaskets/seals: timing cover, sump, rocker cover, oil cooler etc. the eBay kit will work perfectly fine for these.

One day I would definitely like to get my hands on an aftermarket MLS head gasket to see how the quality compares to the genuine one, but that’s for in the future.

 

[Ethanissan]

Keep in mind too, comparing these gaskets is comparing the two major ends of the spectrum;
Genuine Nissan, which is about as good as you can get,
and cheapest eBay kit I could find (whole kit including head gasket was $140 AUD).

There is stuff that sits in the middle most of the time, that's why I said at the end I want to get my hands on an aftermarket MLS gasket at some point, the main brand I can find on eBay is "Victor Reinz", and looks in images identical to the OEM gasket, but only costs $116 (head gasket only) as opposed to the genuine one which was $235 from Nissan.

Curious to see how this would differ, the company seems legitimate, they have a website and catalogue that includes the SD gasket, looks pretty good. This is the kind of one that I'd like to test, with the OEM as a spare, to see if there's a viable aftermarket solution since Nissan doesn't seem too keen on supporting their older vehicles anymore (Garry did good work getting me the gaskets as fast as he did, Nissan didn't seem to think they were worth stocking until ordered).

 

[Ethanissan]

An interesting perspective, I’ve actually found the the gaskets with a fibre layer are better at sealing on older engines that are pitted or slightly out of shape.

Let’s not automatically assume eBay stuff is rubbish, I’ve just pulled a ZD30 apart that the genuine head gasket had gone after less than 50k

A lot of people rag on eBay stuff, often with cause but also often with far too much generalisation.

To be honest the stock design of many motors leaves a lot to be desired and aftermarket parts can be far superior to genuine ones.

That’s true, a lot of the time you can find good stuff on eBay, and that’s why I made the clarification a couple comments up that this is comparing the best you can get, to the worst.
To address your last point, yes, most engines have performance upgrades available, parts better than stock, to handle more power or last longer etc. but this isn’t really the case with the SD-series of engines (hence my second-sentence comment in the original post). For these engines especially, no one seems to have made a good aftermarket gasket, and they’re at that point in life where no one probably will. MLS ones like the Reinz one I mentioned earlier can be found, but I’ll need to see one for myself and compare it to OEM before I’ve got a definitive answer on that one.

I wasn’t aware of the fiber-based gaskets sealing pitted surfaces better (although it makes sense), what I am aware of though is that the pre-patrol SD’s from the US used them, and blew head gaskets more often, so lots of people switched to the Patrol steel gaskets. I believe it’s just because the fiber gasket can’t handle the immense pressures generated by a high-compression turbo diesel, especially once giving it some more air and fuel, so even if they do generally mould to the surface better they just won’t hold up in this application.
Then you look at the fact that this is a cheaply made one, not the kind of quality you want at all (I mean c’mon, sealant around the head bolts 🤦‍♂️), and it’s easy to see why it shouldn’t be used.

And yes, I do sometimes come out with interesting perspectives, I think most of the time it’s just me being young and having no idea what’s going on lol.

I’ve just changed the title of the thread to better reflect what I’m trying to show 😉

 

[Ethanissan]

I also wouldn't be surprised if the early NA SD's run a composite gasket which was superceded later on with the turbo one.
I remember when i twisted spanners on UD's the PF6TA/B/C engine had the head gasket superceded many times.

That could definitely be right, like I mentioned the International Scout SD's (turbo and non-turbo, put in Scouts from 1976-1980) ran fibre gaskets (same as composite?), and the MQ SD33's are essentially the exact same engine, no differences as far as I'm aware. It does sound like the MLS was introduced with the updated SD's, or late in the life of the pre-update engines. So one day if I ever decide to pull apart the spare N/A engine that's currently in the car I'll be able to confirm that. Hasn't been rebuilt as far as I'm aware, certainly doesn't look it, so should be all original on the inside.