Weird rhythmic knocking M20B23 in 1990 320i

[LemonHunter 583]

So basically since I've owned this car it's had a weird almost rhythmic knocking.

It sounds to me like a count of 6 knocks then a lull then 6 more.

Obviously, it's a 6 cylinder car so it could be seriously bad news like a bearing, but this engine was allegedly a pretty recent rebuild when I bought it, and for all the dramas I was warned of by others that viewed the car, no one seemed worried about this noise from the engine bay.

So I'm hoping it's either just totally normal for this engine, or it's a one of the pulley driven doodads on the front of the motor, because that does seem to be where it's loudest.

[jonoe30 53]

It doesn't sound normal... It does sound like it's something running in time with the crank revolutions... maybe something running off one of the drive belts (does it sound louder on any particular side? Does it change when you turn AC on [engaging compressor clutch]?) I would start by removing accessory belts from PS pump and AC compressor and see if it goes away. You could also run engine from cold for a short time without alternator belt (which also runs waterpump and fan, so only for a few minutes tops) to help eliminate them.

Alternatively it if it doesn't go away with accessory belts could be timing belt related: tensioner, intermediary shaft bearings or belt rubbing on cover.

​(Disclaimer: I'm not a mechanic... just DIY who has solved similar problems on my own car)

[Ahmedsinc 414]

Long shot, but if the engines been rebuilt it could be an idea to check the crank pulley bolt. Is the main belt pulley / AC pulley a bolt on item? Check the bolts holding it on are the correct length too. Drain the oil and chop the filter open and have a good look for any trace of metal in the oil - if theres some there, your bearings are about to grenade themselves. Probably the first place I'd look tbh, noise does sound a little like rod knock but hard to say from the video

Edited November 18, 2015 by Ahmedsinc

[*Glenn* 854]

You have a bit of a wobble going on with the front crank pulley's. Check and see if all 6 bolts that hold them on to the crank flange are there, and tight. Also do what Jono just suggested and check for play and roughness in the water pump bearing

[LemonHunter 583]

The thing with the teeth, shiny on the front, looks like interference with waterpump pulley? And it does seem to wobble.

Could be a clue me thinks

It looks like all 6 accessory pully bolts are good. But is the crank bolt missing?!

Edited November 18, 2015 by Charlie F.

[LemonHunter 583]

Definite interference between waterpump pully and toothed thing. The pump pulley won't spin without scraping on the thing even with the belt fully slacked off.

Son of seven whores... I'm guessing this is a radiator out and few nights work kinda job.

[jonoe30 53]

I've got an M20B25 and the crankshaft bolt sticks out past accessory pulley, so I'm guessing yours is missing (judging by the hole) and the accessory pulley and it's six bolts are the only things holding your vibration damper on (the thing that is striking your water pump pulley). I don't know what the other ramifications of a missing crankshaft bolt would be... I'm sure Glenn would know.

Here's my crankshaft bolt (accessory pulley and vibration damper removed):

Edited November 18, 2015 by jonoe30

[jonoe30 53]

It might just be a case of making sure vibration damper is seated correctly, accessory pulley bolts are tight and refitting your crankshaft bolt... can probably done with just fan and shroud removed... but access would be much easier without radiator fitted.

[LemonHunter 583]

I think there might be more to this.

It's a 320 repowered with an M20B23, so the toothed pully and crank shaft sensor appear like they might are B20 parts and they don't quite fit the B23... the plot thickens.

[Allanw 1071]

2015-11-18 14.15.36.jpg

Is it just me, or does it look like someone siliconed that on???

It's wrong anyway - you need to get the bolt in, before it stuffs the crankshaft.

Radiator only takes about 10 mins to get out, but the bolt is tightened to some quite impressive torque : From memory: 2 really fat guys on a long breaker bar, or if you're built like I think you are, you and 4 mates

It's actually 410 NM: I used a 1" drive socket set and torque wrench (no!, nobody can borrow it, no it's not mine), WITH a nearly 2M pole on, and the crank pulley holding tool was pushing on the garage floor - it lifted the car a surprising height from the force involved.

[LemonHunter 583]

Given they seem to have used superglue to fix the dizzy rotor... not much surprises me about this car now.

I'm very close to giving this task to the professionals.

It may already be too late for the crank shaft as it's been like this for about 3000km that i know of, and God only knows how many of the km since rebuild as i only just fixed the odometer which had been busted for a few years

[e30ftw 410]

Fuuuck, missed all that about the crank bolt. That whole car seem like a botch job.

When we opened the passenger door the door handle surround was already broken barely handing on and it fell off and snapped. He got real angry about it and I offered to give him another, but he went and got superglue stuck it together and stuck it back in right away.

You might notice it, its probably glued itself stuck or to the cloth of the door card.

[*Glenn* 854]

The bolt appears to have been broken off inside the crank---------throw away motor

[LemonHunter 583]

Expletive.

[KwS 2425]

The bolt appears to have been broken off inside the crank---------throw away motor

oh sh*t.

[Ahmedsinc 414]

I was expecting the crank bolt to have been a little loose - the M50+ engines have a single use stretch bolt so I figured it wouldn't be impossible for the M20 to be the same - but thats just nuts! Wonder if there was a bit of crud in the bolthole when it was reassembled, bolt bottomed out and the head twisted when torqued. A sufficient number of revolutions later and the head spins itself off, and the only thing stopping the crank pulley from running away is the water pump housing.

At the very least you'll need a new crank - probably rebuild the bottom end too. Or make a 2.7 stroker with a B25 depending on how cancerous the body is - if this is how the PO 'rebuilds' engines, I'd be considering parting this out and getting another car!

[Allanw 1071]

[hybrid 1043]

sweet ..cup half full .... conversion time. m54b30

[LemonHunter 583]

I did find this,

http://ls1tech.com/forums/generation-iii-internal-engine/792751-broken-crank-bolt-removal.html

There goes my weekend.

[KwS 2425]

hell, its worth a crack eh

[LemonHunter 583]

I'm sure it's a lot quicker than an engine swap.

[Valvebounce 2]

Anything can be fixed.

if it were me, I'd drill the broken out part of the bolt out. Maybe start with a small hole, and try an easy out first. sometimes when a bolt loses it's head the tension goes, and they undo easy as. I used to run 12.9 tensile cap screws (loctited in) on the flywheel of my old supercharged Datsun engine. One time after a monster over rev at the drags they flywheel came loose. (Those motors are known to do that) Most of then had the heads broken off. I was sh!tting broken glass about drilling them out on account of how hard they are. But they undid easy as.

If an easy out doesn't work, then you'll need to drill it right out. Make sure you get the center punch mark in the centre of the bolt stub.

Start nice and small, and work your way up. Get a mate to help sight for you, so you know that you're drilling parallel to the crack axis. Keep going up in size until it's out.

I dunno how much room you'll have in your engine bay. (Might be an engine out job)

If the shout of the crankshaft has fretted, whack it back together with generous lashings of loc-tite bearing retaining compound.

"If at first it doesn't fit, fill it up with glue and sh!t".

[polley 916]

Looking at the dirt accumulated in there, it's been missing for a long time!

[eliongater 718]

I've got an m20b25 crank, rods and Pistons (and the block). If any of that could be useful to you send me a pm

[LemonHunter 583]

So I've decided to start a Lemon Log as opposed to a Project Log

http://bimmersport.co.nz/topic/54502-the-lemon-log-aka-my-e30-saga/