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Luke's F20 M135 rebuild- kleiner deutscher wagen

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    Luke's F20 M135 rebuild- kleiner deutscher wagen

    This isn’t going to be the most amazing build thread but someone might use this info in the future so thought I’d write about it. My affection for BMWs is growing as some mates and I race our E46 330. The race car is a 330ci with stock motor (apart from durability work like new water pump, thermostat, hoses, oil pump nut welded, some gaskets etc), ZF 6 speed manual upgrade using an SSG box, custom flywheel and clutch, stripped, cage by Brown Davis, locked diff etc. 5 of us own and race it and we bloody love every event we can run in.

    So when I needed a new daily my love for the bavarian inline 6 motors came out in my subconscious and I was looking at BMW options. I’m a tight arse and like a challenge so I was looking at 10yo stuff. Then an F20 M135 popped up on faceballs cheap with a banana shaped conrod. One can only assume some tofty wanker was in a hurry to get to their moderately inner-north townhouse to feed their designer breed dog and thought their BMW had a 600mm wading depth.

    The M135 has an N55B30 which is a 3.0 aluminium inline 6 with DOHC, Direct injection, Vanos, Valvetronic, and a single twin-scroll turbro. They appear to have 235-240kW stock. It has a ZF8HP45 which is a bangin gearbox as most people know, and an open diff I think. Brakes are decent- 4 & 2 piece brembos with an aluminium hat and 340/345mm rotors.

    Last edited by lukevl; 14-08-21, 11:25 PM.

    So I went and bought it and confirmed bent rod and some other scuffs but mostly ok. After looking into the cost of rebuilding the N55B30 it was clear it wasn’t a cheap rebuild but there were 2 reasons why I was keen: 1. I’m a sucker for punishment; and 2. At the 100k mark a modern BMW needs a lot of maintenance anyway (Read: Time bomb).

    I could pay a little more and have an M135 with similar kms and not have to rebuild it, but then I’d have to do all sorts of shit with the motor in the car and be annoyed like:
    • Remove intake and walnut blast the ports and back of valves
    • New coolant pump, thermostat, all coolant hoses
    • New Coils and plugs
    • ZF8 Oil pan/filter and oil change
    • Valve cover gasket
    • Sump Gasket
    • Oil filter housing gasket (which usually results in a busted bottom end because for some reason they hate getting oil pressure again)
    • Timing Chain and oil/vac pump chain
    And then I still have a motor which by all accounts will have piston rings jammed in the grooves and probably does SFA sealing. Yes I have seen inside 3 or 4 of these now and the carbon build up is pretty nasty.
    So I decided on buying this and building as a complete OEM rebuild. I have access to the factory manuals and all part numbers and the site FCP Euro sells everything by the part number. Its actually amazing and I’ve never played with cars that have that much aftermarket support.

    The way it works is you go to and type in your VIN and it gives you EVERY part number fitted to your car:

    Then I read through the factory manuals and see what they say must be replaced and make a list (spreadsheet of course) of what I need. Then that’s my shopping list. Go to and order the parts- its a US site so you can't just list your car in their website- you really want to go by part number:

    I budgeted for a $5k order from FCP euro (ok $6k by the time I pay the useless cunts in Canberra duties and GST and shit). That’s pretty much every gasket, component, nut and bolt that is recommended to be replaced when removed. And in BMW land that’s a fuckload of nuts, bolts and o-rings. Not gonna lie, I’m a bit of a geek and have never rebuilt something with just a huge pile of new OEM (or tier 1) parts. I was very much looking forward to that.


      Can't argue with the aftermarket support for BMW. I've got a near 20 year old VW, and slightly newer Citroen, here and I'm finding it abit of a challenge getting bits for the VW. Doesn't help it's actually rarer than the R32. Don't even ask about the Citroen, it's easier getting bits via the dealer, thankfully I have access to the PSA parts and service system but it's still a PITA


        Originally posted by irsa76 View Post
        Can't argue with the aftermarket support for BMW. I've got a near 20 year old VW, and slightly newer Citroen, here and I'm finding it abit of a challenge getting bits for the VW. Doesn't help it's actually rarer than the R32. Don't even ask about the Citroen, it's easier getting bits via the dealer, thankfully I have access to the PSA parts and service system but it's still a PITA
        Yeah I gotta admit the resources out there make it very enjoyable compared to other cars I've owned.


          ^^ pick the guy that hates himself ^^^^

          .... because every driver experiences the destructive potential of the effortless surge of power available through the smallest of body movements.

          Dr Hoon

          DrNick is king!!!! No, Mark Webber is now! Long live the king!... hold on a minute mate, Ricci is in charge now


            So first step is to set up the shed and start stripping it. Plenty of photos along the way to make sure it goes back together exactly as it was- just over 700 to be exact. Motor/Box/Subframe out the bottom was the easiest path for best access.

            Motor on the stand but first need to undo the front crank bolt. More on this later but it came off ok with this fixture. Going back on was a different story..

            Yep that could be an issue. Its so tight inside this motor that it won’t rotate far with any bend in the rod.

            Ok so now its stripped, what did we find- one bent rod. That’s to be expected. Piston on that rod is junk. So is No 5 since the rings won’t come out for love or money. Ok so two pistons and all the rings are fucked- mostly to plan..

            Oh hang on, the block has corroded a bit while sitting with water in it. At this point I was stressing that it was an Alusil/Nikasil aluminium bore but upon closer inspection it has cast in iron liners. Win. I’ll spare you the pain of my research but in the end I decided to go +0.5mm and run CPs as this was more cost effective than BMW pistons (not including finding a new std bore block) and the liners look like they have plenty of meat in them. So off to PLR in Brendale for a bore, hone and deck.

            While it was there I got them to skim the head, hot tank, new valve stem seals (BMW ones from FCP of course), valve seat grind* and exhaust guides (which were rooted apparently). The head has dual cam timing adjustment (VANOS) and variable rocker ratio on the inlet (Valvetronic). I’m not sure the valvetronic does much apart from drivability but its certainly cool stuff. I remember reading about it 15 years ago thinking how awesome it was. I stripped all that jizz off and dropped it off with the block

            Last edited by lukevl; 02-08-21, 09:55 AM.


              Now I think this is a pretty cool motor. Its very nicely engineered and aside from the crank bolt, head bolts, every TTY aluminium bolt, it’s a dream to work on. Here is some interesting stuff I found while stripping the motor:

              Camshafts are hydroformed. Absolute dedication to lightness and performance using high pressure oil to form the shaft shape in a die and run thin rings for the lobes

              Exhaust cam runs in its own little 2 piece bucket system. Maybe for windage and BMW efficiency and powers? Fuck knows but its cute (and as I find out later needs a special tool to locate it wtf

              The inlet side has the Valvetronic system which alters rocker ratio. It has an eccentric shaft that rotates through around 150 deg or so using a stepper motor and a worm gear which moves pivot points. It looks like at the absolute minimum it has maybe 1mm of valve lift. It also uses hairpin style springs which by all accounts are superior to coils apart from packaging. These springs hold the intermediate rockers in place.

              Oil squirters (again needs a special tool to orient them

              Aluminium bolts. Ok single use sucks, they feel horrid to torque up etc but still pretty cool. My understanding is they started running aluminium fasteners in the N54B30 which was a high magnesium alloy and would suffer from galvanic corrosion with steel fasteners. They carried quite a few across to the N55 but areas like the bellhousing are steel fasteners now thank fuck and the odd steel fastener here and there.


                I guess its time to talk about the build. The plan was just to make this stock. Clean, new motor, stock with all stock parts so I can just beat on it and enjoy it. They are plenty fast at 235-240kw or so. Then I found the turbo looked like this:

                Had weird soapyness to it. Anyway wasn't part of the plan but oh well..
                And we all know that when you’re buying a new turbo, only a weirdo spends good money on a completely stock one. So I ordered a high flow (yeah they call it a stage 1) from Pure turbos in the US. High flow compressor wheel and machined cover basically. That is still en route..

                Obviously once this decision was made it was a very short, slippery slope to a VRSF 6.5” stepped intercooler and catted down pipe. And a tune- probably MHD. I’ve never played with these euro style plug and play tunes and stuff but it looks interesting what they can do.

                Also as a side note its strange how pro de-cat the BMW community is. Its mental.
                Last edited by lukevl; 01-08-21, 10:33 PM.


                  interesting (re)build ...

                  so orig owner got water in intake and hydro'd a cylinder?

                  ..needs more snorkel....


                    Originally posted by 9triton View Post
                    interesting (re)build ...

                    so orig owner got water in intake and hydro'd a cylinder?

                    ..needs more snorkel....
                    Yeah hydraulic lock driving through some storm water. Car is dry and has no evidence of sitting in water anywhere apart from the intake.

                    will investigate 5” stainless snorkel options


                      Fark. Lot of work! Enjoying the thread.
                      "If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower." - Mark Donahue Penske Porsche 917

                      "In Japan we no give fark for Subaru" - Trust Japan Technical Director
                      (TM - AVENGE)

                      "You can never have enough power. I remember when we had Group B cars... THEN we had enough power!"
                      Juha Kankkunen - Rally of Argentina '02


                        bukkake in the turbo inlet, thats a first!


                          "The plan was just to make this stock."

                          Good read so far! Cool cars these


                            Very cool, good read so far.
                            Interesting Intercooler, why the step?


                              Looks like such a fun project. Here's to getting exactly the sounds you hope for when you start it up.