N52B30 Engine rebuild and head porting

[4JawChuck]

Not much more progress to report, waiting on mains straps to be fabricated by my machinist and more machining to fit on my end. Also parts ordered from BMW like AC lines and Jesus bolts parts are pending.

I did paint the engine cover wrinkle red, base layer of plastic compatible Matt flat black before red wrinkle.

[WrathOTM]

I dig it.

[4JawChuck]

Some final pics of the mains straps and grade 12.9, 1” longer cap screws, the bolt spacers are press fit on the capscrews which adds rigidity as well as close tolerance strap holes and register fit along the ends of the strap completes the repair.

A small amount of Superior Metal epoxy was added at the 0.030” deep casting ledge just to fill the space below the strap and the magnesium casting, I’ve had good luck with this repair epoxy in the past and works well under compression.

Mains are torqued to 65 ft/pds, not TTY except for the last two original mains bolts which were TTY to BMW spec.

Received a complete single mass flywheel conversion along with what has to be the most expensive parts collection for one rebuild I’ve ever seen, everything from shifter to A/C lines and timing components left to install before I’m done.

Total so far $4000 CDN parts/tools invested.

[WrathOTM]

Well this is getting interesting

[4JawChuck]

Some pics of the associated mods required to fit the capscrews under the oil pump and clearance holes around the windage tray. Simple stuff but time consuming to shorten bolts and check clearances etc. The front oil pump was the hardest to make fit and the strap side had to be thinned until the AL casting web was pierced slightly, this pocket was filled with Superior Metal as well to reinforce.

Straps were bonded and bedded in the center relief with additional Superior Metal and in the corners to locate the straps side to side, capscrews were torqued to 60ft/pds which is higher than the torque angle factory ones on number seven main position.

Bed plate was sealed with Loctite NS 5109 and got good squeeze out from the injection holes with a simple 1/8” diameter bead along the sealant groove.

Everything was done with a series of step hole drills and a 1/8” dremel with abrasive drum sanding rolls.

[4JawChuck]

Last pics after replacement of all the fasteners and final torqued and heads painted, BMW says it’s supposed to be blue…I had yellow and orange paint pens…orange won.

Next is head and timing chain, leaving the pan open for now just for bottom sprocket access.

The last image of main cap 1 which shows some of the squeeze out and bedding of the strap with the bed plate, turned out very well and is solid. The longer 12.9 capscrews deeper in the block added a lot of rigidity to the assembly.

[4JawChuck]

Long block bolting completed, mocked up with covers and headers to see how it looks.

Next Jesus bolt and timing components.

[WrathOTM]

What's the Jesus bolt?

[4JawChuck]

Originally Posted by WrathOTM

What's the Jesus bolt?

Crank shaft hub retaining bolt, holds the oil pump and timing gears in alignment.

Like a helicopter if that bolt comes loose you’ve lost the ship.

[bimmerchic]

I know this is probably a ridiculous question but I'm going to just ask anyways. Lol. Does anyone think I'm capable of rebuilding my own N55 engine. I see rebuild kits for sale online and the I can't buy a new one. I mean how much more could I possibly mess it up at this point?


I was sold a mechanically damaged 2012 BMW 135I CONVERTIBLE and was told it was a perfect car with no mechanical issues. I paid $10,700 in cash and they then said the title would be mailed to me the following week. That was Christmas Eve 2022. I've fought for 5 months to get a title and the bond company is starting the process tomorrow. I've replaced the missing parts, the radiator, front air intake duct etc. I need a N55 engine or rebuild it somehow. One or more lifter issues. Maybe rods. I can't pay out more money on that car. I love that car with all of my being. Any advice? Words of wisdom? Etc lol... Thanks in advance ☺️

[4JawChuck]

I’ll be honest, I don’t recommend anyone without years of experience take on the task of rebuilding one of these engines. It is much easier to find another engine and swap in to fix your issues.

Too many special tools required as well as parts that are hard to find in stock plus costs for shipping are brutal.

So far I am $2500 CDN into this repair not including labor, a good used engine is about that price. I am also upgrading a number of ancillary components like clutch and shifter which increases costs but I have not replaced major components like pistons and rings which are over $1000usd to buy just the parts.

The $12500 that BMW wants for a new replacement engine starts to look like a bargain when you start adding it up.

This was a cost effective repair for a guy like me and likely only a small percentage of the population who have the knowledge to make this work.

For the average owner I recommend engine replacement rather than repair used or new. If used I would still do the mains and rod bearings as PM with better than stock components for the shell bearings, tin/aluminum factory bearings don’t hold up.

[AmuroRay]

car-part.com

[4JawChuck]

Final engine assembly is complete, transmission has new seals, stainless pivot pin, release bearing and oil. Ready to install the trans once the engine is hanging to go into the car.

Still A/C lines to replace on the car (compressor was refilled with 6oz of PAG46), going to install a 120VAC wiring to the trunk as well to allow a battery tender to be plugged inwith my pan heaters for winter. Lots of little things to repair like the front subframe coolant line attachment bolts are seized in the frame, flush the rack, orings for cooling system etc.

Getting close to first startup, some pic attached.

[WrathOTM]

what primer/paint did you use on the cover? thinking of doing this too.

Looks real slick let me say.

[4JawChuck]

I used tremclad plastic paint in flat black as a base and then normal wrinkle red enamel for the top coat.

[4JawChuck]

Rebuilt shifter with new components (delrin bushings and new pins/clips and associated parts). Painted everything removed that was corroded, installed the trans (filled with Redline MTL oil) after eyeballing the plate alignment (slid right on), ready to slide the engine back in next weekend.

Here’s what she looks like completed.

[WrathOTM]

How soon is it going back in the car?

[4JawChuck]

Next weekend after shifter is reinstalled and AC lines replaced with new.

[4JawChuck]

Extra long weekend worth of work to get the engine/trans in and everything connected minus the rad and cradle.

Shifter feels great with the mix of aftermarket and factory parts, the rear shifter bushing and front oval bushing are the main culprit in the rubbery feel of the stock components, very soft durometer rubber in those mounts.

Likely start it like this with the rad hanging on hoses from a couple of egg crates to support it, need the exhaust connected of course but maybe first start up will be open header.

[4JawChuck]

Overhaul complete, not a single leak and no codes after startup. Readiness monitors didn’t set on the first start but did on the second warmup run which was a relief.

Exhaust note is pleasantly muted and quite a bit deeper in tone. My son says the exhaust note has a richness like a Borla muffler even though it’s stock with just a header.

Power wise I would guesstimate approximately 20HP on top end but it’s obvious it needs a tune, has a much better rush after 4500 that the stock engine didn’t have.

Currently running defouler spacers on the rear O2 sensors which cured the low catalyst efficiency code but the tune is way out with the ported head and header combo.

Found the rad fan motor had died, got one on order to drive it daily, attached a couple of pics of it all together, moved some cables and conduits around in the engine compartment which you can see but makes working on the engine so much nicer.

[WrathOTM]

So are you going to do a 3 stage intake manifold swap too plus 330i tune or perhaps N54 intake with aftermarket tune?

[4JawChuck]

Not positive the area under the torque curve results from the 3 stage intake mod are worth the result, just my opinion from seeing dyno graphs.

Right now it’s missing pump shot at throttle tip in, the head porting significantly changed how it responds to valve opening during throttle changes.

Had some more time to drive it under pressure and I can say it may be more than 30hp gain especially above 5K. It loses traction at gear changes where it never used to before even with the tune lean on pump shot.