RX8 Project – Part 22, Engine Rebuild

To preface this I am not an engine builder, this is just the approximate process I followed more to give you all some handy reference photos and some info that might be helpful to someone. Please don’t take any of this as gospel! I still don’t even know if the engine will actually work!

Anyone reading this blog may have noticed that the mechanical work on the car seemed to stop a very long time ago. While there has been a bit of a gap due to other aspects of life getting in the way there was more progress than it may have appeared. Back in 2018, some 3 years ago as I type this, I took my recently stripped engine parts (ostensibly the block and crank) along with the custom flywheel and spacer to be checked and relevant parts balanced with a view to rebuilding the engine.

With little surprise I got a call back shortly after to tell me the pistons were not serviceable and would need replacing. Following my earlier research (mentioned in a previous post) into the Noble M12 and later cars I decided that for the power point I was aiming for (300 bhp approximately) the stock cast type pistons should be up to the job with Noble moving over to forged parts with the M400 model and target power above 400 bhp. Online I’ve seen many people reporting the cast pistons hitting their limits up around 500bhp but what their life expectancy is at that point who knows. With some luck I manged to find a set of +0.5mm oversize stock replacement pistons online ( part H663CP ) so sent these up to be checked for balance with the engine. The thing Noble did upgrade was to upgrade the factory rods with forged ones so I had already sourced some suitable rods although even that was a bit of a challenge. The ones I bought were from XPOWER Engines in Essex and are still listed on Ebay as I type this as ST220 3.0 H-section EN24 steel rods and come with ARP 2000 bolts. I’d not come across this company until this point but some research showed they are quite well known so I felt pretty confident they’d be ok.

So now I’ve got these parts all shipped up to MJA Automotive in Bromsgrove who would rebore and hone the block to match the new oversize pistons as well as giving everything a proper clean, checked and completely balanced. They’re a small firm but attention to detail was great, they even sand blasted and repainted the original crank pully because it was a bit rusty.

So now I had a pile of goodies to put together :

S-type engine parts for rebuild

This picture is another good indication of how small this engine block actually is for the potential power output. You can see all the goodies here and basically everything that should be replaced was so new pistons, rings, rods, clutch, upgraded engine bearings (more on this later) and then obviously the custom flywheel and cleaned crank. This means only one thing, I had to build up the engine. Now when most people rebuild their own engine for the first time they start with something like a lawnmower engine but not me…In retrospect I probably should’ve just paid MJA to build it but I like a challenge!

First things first I decided to assemble all the pistons on the rods to have a quick win. This is as simple as taking the ring clip and pin out of the piston, putting the rod in place, sliding the pin back through and putting the ring clip back in. Add a dab of lubricant inside the small bearing before you put it together. The pin should be a slip fit on this because its a fully floating arrangement and so the rod bushing may need reaming to fit correctly if this isn’t the case. It’s also with noting these rods are not handed because in this engine they all have individual locations on the crank and do not touch each other whereas some engines have paired locations leading to the rod big end bearing having a flat side and a curved/chamfered side on the outer faces. If you see this the flat faces of the rods should be oriented to touch each other in the pair.

Comparison of used stock piston and rod and new piston and forged rod

Here you can see the state of the old pistons and the massive difference in the size of the rods. The keen eyed amongst you may notice this piston has the rings installed, what I actually did was installed all the oil rings at the bottom of the pistons but left the compression rings of so they could be correctly trimmed and fitted to the engine later. The ones show I’d slotted on for my own curiosity about how it all went together and removed shortly afterwards.

Box of assembled pistons and forged rods for S-type v6

That all looks rather shiny, I’m not used to car parts being this clean!

This was around the time I tried to find a manual for how to actually rebuild this engine with all the tolerances allowed for all the various parts and after a brief search found the S-type workshop manual located on jagrepair.com . This manual is massive at some 3300 pages and covers basically every aspect of the car but obviously since I don’t have the rest of the car I concentrated on the engine section which for this engine starts on page 635. I can’t add much on the instruction in it – it really is step by step so that’s the place to go for the detail!

So back to the things I did differently and some gratuitous photos of shiny stuff. while We’re still on the subject of piston rods I actually found and ordered some Mahle motorsport “high performance” racing bearings but curiously I found out shortly afterwards that Mahle Motorsport don’t sell a kit for this engine. After a concerning period waiting to see what would turn up and if I’d just been conned what actually arrived was the following :

Racing rod bearing for S-type

Checking the Mahle racing bearings catalogue I’d already found told me this was actually a bearing for a 2.3L Duratec which is a 4 cylinder engine and I’d been shipped one complete 4 cyl bearing kit ( kit number VC1013) and half a second one to make up a complete set for the V6. Checking it all out sure enough they do seem to be the correct dimensions for this engine.

Rod bearing installation detail for S-type V6

They fit well but the only bit of strangeness is racing bearings don’t have the location notch usually found on rod bearings so a lot of care must be taken to make sure they’re correctly centred in the rod when it’s assembled. Apparently this is because the notch reduces the bearing area adjacent to the notch. More info about this can be found from Mahle themselves here . Contrary to common belief the notch isn’t there to prevent the bearing from spinning and is purely to centre it on assembly. Once the rod is assembled the the hoop stress in the bearing produces so much friction it will stay in place with no issues. Spun bearings are caused when the bearing seizes onto the crank, this is usually caused by insufficient lubrication and if this happens the bearing will spin whether or not you have the notch.

So back to the block, once it’s mounted upside down on the stand go ahead and drop the block side halves of the crank bearings in place. The parts I used here are King bearings kit number MB4056SI :

Crank bearing installation photo for S-type V6

Crank bearing photo at an angle, S-type v6

Also don’t forget to add the thrust bearing on the flywheel end. It’s a bit hard to see in the photo because I haven’t got a photo without assembly lubricant but it’s there.

Lubricated bearings, S-type V6 assembly

Apply assembly lubricant to all the bearing faces

Now drop in the crank, carefully! then go ahead and apply assembly lubricant to all the running surfaces. In the photo the middle two rod locations aren’t lubricated yet because they’re at the back and needs rotating for access.

S-type crank installed

Next take the lower block housing and install the other bearing halves into the appropriate locations. As above apply assembly lubricant on the bearing faces.

S-type v6 lower block

Check the bearings are holding on as the next step involves dropping this section downward onto the upper block so make sure they don’t fall out. If they wont stay put you can lift the crank back out, drop it on this section then use it to hold the bearing shells in place when you flip it over and put it on the upper block. Run a bead of RTV along the mating face of one the two block halves before you put it together. Read the instructions on the RTV – usually you need to let it partly cure before pushing the parts together. Remember the RTV goes to the inside of the bolt holes otherwise oil will weep past the bolts. This is also why the flange is wider on the inside.

S-type v6 lower block assembled

Hopefully you should have something that looks like this. Note the locations of the bolts with the M6 thread on the reverse side – these are the ones the the windage tray bolts onto so they have to be in the right positions. Torque all the bolts down following the workshop manual.

Now for the top side. We need to set the piston ring gaps which will involve working out what your gap should be (there are various online calculators now which make this easy). We need to be looking at larger gaps due to running a turbo and I wanted to make sure I had some headroom to run higher boost later without issues so worked on the side of going a touch larger. I ended up with a number of 0.57mm on the top ring and 0.72mm on the second ring but I think this is probably overly cautious. Who knows, maybe one day I’ll run nitrous. The rings are measured by inserting them into the bore, making sure they’re totally parallel to the block deck using some sort of depth tool, this can be done with a vernier caliper or a variety of other methods. You then measure the gap with feeler gauges when in this position and file back the ends of the ring as necessary to get the required gap. The filed ends need to be totally flat and parallel to each other. I put a flat file in a vice and carefully filed it down. Be careful, you can’t put it back if you go too far. Also piston rings are very brittle. Don’t mix up your top and second rings of install them wrong. I suggest buying a cheap piston ring installer plier to get them on easily.

It’s quite common to lubricate the cylinder walls prior to installing the pistons but some ring manufacturers actually specify not to do this now. Check the instructions on your rings. I used a light coat of some slightly thicker engine oil I had lying about and wiped it off with a rag. The general guidance here is assembly lubricant shouldn’t be used on cylinder walls as it prevents the rings bedding in correctly.

Next up you need a piston ring compressor to tighten up the rings to fit into the cylinder bore. Make sure you get this tight enough because why you try to tap the piston into place if the ring is sticking out relative to the bore it’s possible to break the ring. Traditionally people drive the piston in with the wooden handle of a hammer to avoid damaging the piston face. I came up with a different solution tapping a section of silicone hose to avoid damage. Be careful to line the piston up with the bore. If you can rotate you engine stand such that the piston you are trying to put in is vertical then do so, this way you are less likely to scratch the bore with the rod as you lower it in.

Using a section of hose to install pistons

The pistons should have an indication mark on it which shows which side should point to the front of the engine. In this case this is the drilled mark but on other pistons it can be an arrow on the piston face or other mark, make sure you get this right!

Once the piston is fully in the bore go underneath and carefully guide the rod onto the crank then bolt the end of the rod back on (with its bearing inside) and do up the bolts. At this point they only need to be tight enough to stop it all falling apart so even finger tight is probably enough or a little over.

S-type V6 with new pistons installed

Now that’s quite shiny!

One question that comes up all the time is the correct socket for ARP rod bolts. after a lot of searching I’ve found according to their catalogue they do them with two common sizes of head, either a 3/8″ AF or a 7/16″ AF, both of which are of 12 point type so standard 6 point sockets will not fit. I’ve seen numerous reports online where people are saying it’s a 10mm metric. It isn’t, a 12 point 10mm will fit over the 3/8″ head but it’s a very sloppy fit you’d be only contacting the bolt on the very top of the points making the risk of stripping the head quite high. The correct socket should be a very nice slip fit.

ARP2000 con rod bolt

I’m not sure exactly which kit the rod bolts are from (or even if they are from one) because they came assembled into the rods to keep them together. ARP themselves don’t seem to to a specific kit for this engine so I would assume much like the rod bearings (which I bought from the same company) they’re actually repurposed parts from the Duratec 2.3 kits or something similar. With the forged rods they could be almost be anything just selected to fit the rod so I suggest either buying them with the rods or you can buy ARP bolts by thread and length to suit whatever you have.

Once you’ve put all your pistons in and torqued all the bolts up we move on to new head gaskets. First of check where the location sleeves are – as you look at the mating faces of the block two of the holes are larger, these are intended to have steel sleeves in which locate the head relative to the block. I installed these in the block but if you do the next few steps the same as me you might find it easier to install these into the head to make the assembly easier. The head gaskets I used were genuine Ford originals parts (actually badged FoMoCo) but sold as Jaguar parts they are specific to this version of the engine because the Ford version of the engine has different water flow routes open/blocked to make the coolant flow differently. The parts I used are as follows :

RH Head Gasket 2.5 Jaguar – C2S44649
LH Head Gasket 2.5 Jaguar – XR857984
Head Bolts (Single) – XR85387

You might want to order an ARP head stud kit at this point rather than the standard head bolts. I didn’t as at the time it was an expensive add-on (around £300) for what was supposed to be a budget project but in retrospect it might have been a safer option. I don’t have the part number for the kit noted anywhere.

S-type v6 with gasket in place

Bolt on the water pipe pipe on the top front of the block at this point. It’s much easier than doing it later! Don’t forget to install the O-ring on it and for belt and braces it might be best to add some RTV round it because fixing it if it leaks is a big job involving removing at least one head.

S-type v6 front of block water fitting

Now the next bit is something people will probably hate me for but whatever, as I’ve said before this was supposed to be a budget build with the potential for later upgrade if it ever worked. What I did was get a decompression plate cut to space out each cylinder head a little because these engines are 10.3:1 as standard and I wanted to run a not insignificant amount of boost through it. Because my plan was to have the best response I could from the engine I still wanted to keep the CR as high as I could while having a safe enough margin after a discussion with Mike at Ferriday Engineering. While I write this in 2021 his website is giving me a security warning so I don’t know what’s going on there but his email is mike@ferriday.co.uk, I can only assume (and hope) he’s still operating because he’s a very nice and knowledgeable guy. He told me that standard 1.5mm plate would give a compression ratio of 9.1:1 which should be fine. We started under the assumption the mating face would be the same as the Mondeo V6 he already had on file but that turned out to not be the case and he ended up taking my old gaskets as a template and then during a couple revisions by email I highlighted some holes that didn’t exist in the head so could safely be taken out of the decompression plate.

The decompression plate gets bonded to the face of the heads and effectively forms an extension of it, there are a few sealers used for this but the most widely regarded of them seems to be Stag Wellseal which is a form of high temperature non setting sealer resistant to fuels and oils. It is initially quite liquid but goes very sticky rather quickly and after that its quite challenging to remove. Get a suitable plastic spreader and move quickly! Despite various tales on the internet of people using the plate with two head gaskets (one each side) that’s not how these are supposed to be used generally. The idea is the face of the head is freshly refinished and so is totally smooth and flat and the decomp plate will be the same so the actual thickness of sealer will be negligible. Add to this the plate, head and block are all aluminium and so there shouldn’t be any differential thermal expansion issues. So yes it’s technically a bit of a bodge, but it’s done in the best way we can and by all accounts should hold up to my use without issue. Plus I always have the option to get custom forged pistons made later if I want to throw lots of money at it. At the end of the day this is still a cheap engine so if it does all go wrong I’ll do something else!

S-type v6 with decompression plate test fitted

Here you can see the decomp plate in position for a trial fit before being bonded onto the head. If you look carefully you’ll notice the cylinder bores in the plate aren’t round, this is because they’re not actually round in the head gasket to provide clearance for the valves.

Its probably worth highlighting here that on this engine the head bolts are under the cams so you have to assemble the head after bolting it in place. The head bolts are M10 with 6 point hex heads but with a reduced size hex. They are recessed in narrow deep bores, I used a standard 15mm deep impact socket but it was very close to not fitting so worth checking this though if yours doesn’t fit you probably found out when you took it apart!

tolerance on S-type V6 head bolts

The head bolt tightening sequence and procedure are detailed in the workshop manual but long story short I suggest getting an angle gauge for this as they’re specified as a torque + angle. These are torque to yield bolts and so you get one shot to get it right since they’re single use.

Once the head is bolted down install the cams. At this point is doesn’t matter where in their rotation they are as we will set that later but try to put all the cam retainer pack in the same positions they came out of. Make sure to coat all bearing/contact surfaces with assembly grease.

S-type v6 reassembled head

Next if you are re-using the S-Type water fitting on this engine (though I think this applies to others as well) you will want to install this now if you haven’t already, if you don’t you won’t be able to with both heads bolted on so this is your last chance!

Now just rinse and repeat for the other head…

S-type v6 head on decomp plate

Once you’ve done that slip the oil pump onto the crank and bolt it in place. Hopefully at this point you should have an engine that looks a bit like this:

S-type v6 front of engine (no cover) with both heads in place

If you’ve got to this point I suggest going and having a break. This assembly will be continued in my next post…

14 thoughts on “RX8 Project – Part 22, Engine Rebuild”

  1. Great write up,I’ve just rebuilt a AJ30 with the same rods as you but coupled to a set of Diamond Forged pistons to lower the CR.

    Hopefully you’ve fitted the oil separator onto the block before the heads?!?😁

    1. Hi, Thanks!

      Do you mind me asking what part number your pistons were and what the resulting CR you got? This is still something I might do in future!

      I assume by oil separator you mean the PCV valve box thing that fits in the large oval port in the valley of the block? Interestingly that seems to only be fitted to some versions of the engine. I know the ford ST220 has one there but the 2.5 Jag one I have just has a blanking plate there which I did remember to fit but as you highlight I’ve not noted that in the write up so I should probably make an edit! I have a feeling this generation of engine relied on the two vent ports on the cam covers which are connected via numerous channels back to the block, whether that is enough is another question if other versions needed it so. Maybe I’ll look at adding a port for one into that plate – I think it’s actually thin enough it’s possible to slide it out even with both heads on.


      1. Hi
        The pistons are custom made,so I had my bores checked,honed and advised Diamond of the sizes.
        They are ceramic coated on the top too,cost just under £1300.
        Strange about the breather, as on the AJ30 those small connections on the cam covers are actually inlets,not outlets in normal use.
        So you get airflow threw the engine when the PCV opens to stop the vaccum draw pulling oil out of the crank case.
        The separator definitely won’t fit in or out with the heads in place!

  2. Sorry CR is low 9’s,I didn’t want to go for low comp 8:5,1 as I’m not planning on running massive boost and I didn’t want to make it laggy as my car is only 700kg I don’t want lag then a massive amount of torque coming in!
    So far it’s working perfectly, virtually no lag using a Borg Warner EFR single turbo.
    Base map running 7psi of boost is producing 322bhp at the wheels .

    1. That’s really interesting, as you’ll have read I guesstimated at low 9’s CR targeting 350bhp at low-ish boost so that sounds like it should be about right! Currently I’ve got a pair of tiny turbos for it, specifically they’re GT1549’s which were used on a whole range of 2.0 diesels but also the SAAB 9-5 3.0 V6 where they used one of them running on the exhaust of only half the cylinders apparently. Anyway the maps for them suggest I should get a similarly low lag situation to what you were after although admittedly being journal bearings they won’t be as good as your fancy ball bearing EFR! You are making me wonder about going to a single turbo now though….

  3. Great write up Jon, I know this will come in useful for reference for the parts if nothing else. I will be sourcing an AJ30 towards the end of this year for my current MK1 Escort project.

    1. Thanks! If it’s useful to someone for something then it’s done the job!

      I recommend grabbing the workshop manual I linked to, particularly if you go for a jag version as it’s very comprehensive. I stuck an old laptop and tv out in my workshop and had it on screen large enough to read across the room as I was working through the steps.

      Mk1 Escorts are lovely things, that sounds like a fantastic project!

  4. Hi! Did I missed the part where you are trying to fit the engine in the engine bay of rx8?
    It looks like forward part on the sump will be a problem…

    1. Hi,

      No, we did a trial fit before I rebuilt the engine and you’re absolutely right about the sump bulge. Currently my options are use the sump off the Jag X type which shares this engine but has it transverse mounted because it doesn’t have the lump on the front (it actually has a recess there which might be beneficial) though I’ve not actually tried it or failing that just custom build one.

      I never bothered to add a post about the trial fit because all in all I didn’t think it wasn’t terribly interesting but I can post some pictures if you’re interested? This year I’ve had major construction going on so I’ve not really had anywhere suitable for moving engines about on but hopefully in the not too distant future that should change!


      1. It is really interesting!
        I wonder how it will clear the subframe and cowl on top of the firewall. For most of the swaps in rx8 I saw that it has to be modified because rotary engine is very compact and placed quite far back.
        V6 is not as tall as most of inline engine, but still quite tall compared to original rotary one. Intake manifold also might be a problem…

  5. Hi Jon
    Word of warning the valve springs aren’t strong enough for a charged set up!
    I’ve just found out the hard way on a trackday,valve float let a cam shim come loose and fall out and get smashed to bits by the cam 😩
    So currently engine is out with both heads off whilst I try and sort out some springs for a reasonable cost.
    It was an exhaust valve that had the issue,so from some research and speaking to my mapper the pressure between the head and turbo has stopped the valve closing allowing the shim to be free to come out of the lifter 👎
    Uprated springs are very scarce 😔
    Piper Cams will sell you some,either single uprated or double springs with new spring caps but the downside is you then need to convert to the Piper shim under bucket system as the standard shim over bucket won’t work with the piper valve caps🙄
    So single uprated springs are circa £500,doubles are circa £600 and then the shim under bucket lifters are nearly £800🥺
    I’m in contact with a company to see if they can make me some custom uprated ones🤞

    1. Hi,

      Wow, sorry to hear you’re having problems but thanks for letting me know. That isn’t great news!

      That sounds like crazy money for what they are! To be honest you might be able to get a machine shop to accurately measure up the shim/bucket combination and swap them.

      Not sure if it’s any help but there’s a company I used years ago called springmasters who used to do custom springs (primarily for industrial applications) so that might be comparatively simple to sort out using an existing one as a reference and the stats off the Piper part listing . I’ve also just found a company called Mellings who say they will custom make valve springs but who knows the cost.

      If you get anywhere with a suitable alternative let me know as I’d be quite interested. That said right now I just want to get the engine in and running!


      1. Hi
        Yeah I have been in contact with Melling,but they are very busy so taking a age to sort, but they’ve got a minimum order of £1000🤦‍♂️
        I’ve got another engine I’ll be rebuilding to go in my Chevette soon so I need two sets.
        Would you be interested in a set at £150 delivered if I go ahead and buy enough springs to make up the minimum order amount?
        This will depend on what they offer once they’ve looked at a standard spring though and how much they can uprate the spring staying with the standard valve spring cap.

        Changing the subject how did you get on shimming the cams?
        Did you need to buy any new shims?
        I needed some new ones and the price was ridiculous, £7 each 🤬

      2. Hi
        I’ve heard off Melling the standard spring I sent in is 23.2 N/mm,the Piper single spring they offer is 42 N/mm so quite a lot stronger!
        Waiting now to see what Melling can offer in the standard diameter to let me use the standard spring cap and bucket etc.

Leave a Reply

Your email address will not be published. Required fields are marked *