Rod knock.

[zellamay]

Just figured it out yesterday. No good reason for it that I know. I use good oil, drive light until it warms up, don't rev it high. I've only put about 9k on the car, so it must be due to abuse before I got it. ... So now, what to do? I've been reading on how to fix it myself, maybe to big a job for me. I've rebuilt engines, but have no good place to do it. A guy has one for sale with 95k on it for $2k, but of course that's a risk. (I know the condition of my engine regarding oil usage, no water leaks, performance, etc.) Also, I think if I pull the engine myself, I could just replace the rod bearings and save that money. Now, I wonder whether there is a reliable mechanic in Phoenix who could do that work.

[bluptgm3]

Just figured it out yesterday. No good reason for it that I know. I use good oil, drive light until it warms up, don't rev it high. I've only put about 9k on the car, so it must be due to abuse before I got it. ... So now, what to do? I've been reading on how to fix it myself, maybe to big a job for me. I've rebuilt engines, but have no good place to do it. A guy has one for sale with 95k on it for $2k, but of course that's a risk. (I know the condition of my engine regarding oil usage, no water leaks, performance, etc.) Also, I think if I pull the engine myself, I could just replace the rod bearings and save that money. Now, I wonder whether there is a reliable mechanic in Phoenix who could do that work.

I think you could hang the engine on an engine bay beam and drop the sub frame, then drop the pan to replace the rod bearings.

Your local BMW CCA Chapter is supported by this list of businesses who generally offer a discount on parts and service -
https://www.roadrunnerbmw.org/member-benefits/


Sent from my iPhone using Tapatalk

[Randy Forbes]

Rod bearings can most assuredly be done with the engine in the car__I must have hundreds of pictures in my gallery showing just that (99% S-54 engines, but I did do a couple of S-52s that way too.

Unfortunately, if you've really knackered a rod bearing, there is the possibility that the crankpin is scored (maybe not, but keep reading...) and I would absolutely recommend that the connecting rod(s) be checked for roundness at their big end.

That salvage engine will only cost 1/5 of a decent rebuild, and that's my recommended way to go, all day/any day. If you later find yourself in a position to rebuild your existing engine (single VANOS is really easy) you can do so at a leisurely pace/budget.

[BimmerBreaker]

I can repair rod bearings if thats whats really wrong, I think you have my number, text me and I can come by and look at it sometime, I've started doing mobile mechanic work in the Phoenix area, already getting very busy. Doing rod bearings on my X5 4.6is right now, done them on an M5 before, an S52 is very simple in comparison. If you caught the problem early the crank should be ok, if its not, you have options at that point

I charge less than a new engine to fix rod bearings... a full rebuild should not be required if rest of engine is OK - just buy the shells and the gaskets that will be removed to get at the bearings.

[328 Power 04]

And new conrod bolts too!
Not a hard job. I changed mine out while doing oil pan and oil pump nut.
Having a trusted hand doing it is win/win.

Very unusual to have rod knock. I wonder if you lost lubrication.

[zellamay]

I can repair rod bearings if thats whats really wrong, I think you have my number, text me and I can come by and look at it sometime, I've started doing mobile mechanic work in the Phoenix area, already getting very busy. Doing rod bearings on my X5 4.6is right now, done them on an M5 before, an S52 is very simple in comparison. If you caught the problem early the crank should be ok, if its not, you have options at that point

I charge less than a new engine to fix rod bearings... a full rebuild should not be required if rest of engine is OK - just buy the shells and the gaskets that will be removed to get at the bearings.

I
I lost your number, sent you mine via PM.

[BimmerBreaker]

I PM'd you back. For the record, if you want to do it, it's pretty simple: split the steering linkage to let the whole front suspension drop out, suspend the engine from above, remove calipers and attach to chassis, drop the front subframe with suspension/struts, etc. Makes it less annoying to re-align too, since all the bushings will retain their pre-load and torque settings. Once the subframe is out of the way, drop the oil pan, replace the rod bearings. Follow very closely the TIS procedure for re-torqueing. If you want to do it yourself I have the torque angle tool I can loan you, or go ARP and then it's just a simple torque spec. Clean the con rod threads well too, any oil in them will change the torque specs of the bolts going in. Inspect the con rods too, if the bearings are spun badly, they may be scored. I have S52 connecting rods here if yours are that bad.

And new conrod bolts too!
Not a hard job. I changed mine out while doing oil pan and oil pump nut.
Having a trusted hand doing it is win/win.

Very unusual to have rod knock. I wonder if you lost lubrication.

True, OE con-rod bolts are TTY so those need to be replaced as well. I had my X5 job on my mind where I have ARP conrod bolts here so those werent on my mind

I have an S52 here that had suffered a major oil leak eventually leading to oil starvation. It scored the cylinder really badly, but the rod bearings were actually in fine shape. I'm very curious what happened to this S52 if it is indeed the rod bearings that have failed. May be worth inspecting the oil pump...

[zellamay]

I PM'd you back. For the record, if you want to do it, it's pretty simple: split the steering linkage to let the whole front suspension drop out, suspend the engine from above, remove calipers and attach to chassis, drop the front subframe with suspension/struts, etc. Makes it less annoying to re-align too, since all the bushings will retain their pre-load and torque settings. Once the subframe is out of the way, drop the oil pan, replace the rod bearings. Follow very closely the TIS procedure for re-torqueing. If you want to do it yourself I have the torque angle tool I can loan you, or go ARP and then it's just a simple torque spec. Clean the con rod threads well too, any oil in them will change the torque specs of the bolts going in. Inspect the con rods too, if the bearings are spun badly, they may be scored. I have S52 connecting rods here if yours are that bad.


True, OE con-rod bolts are TTY so those need to be replaced as well. I had my X5 job on my mind where I have ARP conrod bolts here so those werent on my mind

I have an S52 here that had suffered a major oil leak eventually leading to oil starvation. It scored the cylinder really badly, but the rod bearings were actually in fine shape. I'm very curious what happened to this S52 if it is indeed the rod bearings that have failed. May be worth inspecting the oil pump...

Don't these cars have an oil light, so if pressure is completely gone, you would know it? I would love to be wrong in my diagnosis.

[BimmerBreaker]

Don't these cars have an oil light, so if pressure is completely gone, you would know it? I would love to be wrong in my diagnosis.

Yes, was it on? Curious what the other symptoms are

[zellamay]

No oil light. No other symptoms. Car ran great. (I just now remembered, the engine seemed to have more vibration at idle than it used to. Barely noticeable, but there. I wondered about spark or injector) Started as a small, dull thud, but it was cyclic. At first I thought of things like an exhaust leak, or some accessory noise. I know lifter noise, which is more like a "tick tick". Then on Saturday it got louder and was happening all the time. It took me some time to decide it was a rod knock because of my only previous experience: I had one go out on my wife's 4 cyl Mazda a few years ago, and it went from zero to very loud in about 30 seconds, and sounded much (crisper, tinnier, banging ???) than this does. I quit driving it, but of course am afraid of the few days I drove it with the knock.

[rf900rkw]

Take the drive belts off and see if the noise goes away.

[zellamay]

Take the drive belts off and see if the noise goes away.

Gladly, that's easy, tomorrow.

[s8ilver]

Have you checked for loose spark plugs? I had a "thud" sound, which wasn't metallic sounding, but it almost sounded like a knock. All 6 spark plugs were loose. Worth a shot. NA or FI?

You said you wondered about spark, but did you check it?

[jrkoupe]

rf900, great point!

I was convinced at 225k miles I had rod knock...convinced.....but puzzled and bummed. Took car to 2 techs and both said internal engine noise.


One weekend I open hood and start her up...........I looked for like 20 mins under hood as I was talking to car.....lol................one of my belts was badly cracked and chewed up and it was making the sound!!!!!...and of course it was cyclic


changed belt.....and rod knock gone


similiar noise on an s50 track car......it was plugs!!!!!........

tru rod knock is kinda rare on s50/2 engines

[BimmerBreaker]

I was driving my friend's S54 M roadster once (esess on here) and was just about to take it on a pretty long trip when I'm coasting to a red light when I start to hear "thunk thunk thunk thunk thunk". It was really late at night and it sounded like the VANOS exploded or rod bearings failed catastrophically so I didn't want to keep driving it or even let it idle. It sounded bad. Ended up being a little piece of belt cracked and was flapping around slapping stuff as it rotated around.

Got it replaced in a few minutes (how many of you have replaced a belt without removing the fan clutch? I have ) a few days later

Belt and spark plugs are going to be the first thing I was going to look at, as well as the pulleys themselves. I'm supposed to look at it Tuesday so curious how it looks and sounds in person.

[jrkoupe]

....I would love to do belts w/o dealing w/ fan clutch.

but I just cannot figure it out......siiiiiigh

[zellamay]

Loose spark plugs. That was it. Seriously, I'm still in awe. I found 3 loose: 2 just not torqued down and 1 about 1/2 turn loose. I'm a little surprised that it produced that much noise. Now I know the diff between a rod knock and loose plugs (a skill I hope to never use) .... So, what went wrong? 1) I didn't tighten them enough. 2) I didn't connect the noise with the slight irregular idle. (that was a bad mistake because they happened about the same time) 3) Didn't check plugs/belts before panicking. So now, a big THANKS for all the input and help. I've appreciated this site since I found it, but today, a lot. ..... I'm going to take the money I didn't just spend and go to Las Vegas for a week: cheap blondes, room service. ......... Wait, my wife just told me it's now for a new washer/dryer.

[ProductUser]

I like easy fixes

[s8ilver]

Well that settles it. The first step in checking rod knock in the S52 is to check the spark plugs.

I was terrified when I first heard that sound, but I was convinced it wasn't a metal on metal sound. Hard to describe; it almost sounds exactly like a knock.

[328 Power 04]

Well that settles it. The first step in checking rod knock in the S52 is to check the spark plugs.

I was terrified when I first heard that sound, but I was convinced it wasn't a metal on metal sound. Hard to describe; it almost sounds exactly like a knock.

Well you win this one.

[s8ilver]

Well you win this one.

Hahaha...yeah my online diagnosis without hearing it was spot on. Now if I could just sort out all the things wrong with my own cars, I'd be all set. Sigh.

I did take a shot at my torn regulator mount this weekend. I'll have to say, that JB Steel Stick is pretty cool. I haven't had the guts to try the window again yet though. I'm letting it cure double what the tube said.

[325bob]

Hahaha...yeah my online diagnosis without hearing it was spot on. Now if I could just sort out all the things wrong with my own cars, I'd be all set. Sigh.

I did take a shot at my torn regulator mount this weekend. I'll have to say, that JB Steel Stick is pretty cool. I haven't had the guts to try the window again yet though. I'm letting it cure double what the tube said.

I hope you've led me to a simple fix, been dealing with this tap for 3oo miles,changed oil, stethoscope,on running lifters, oil everywhere.If its a loose plug, I'll let you know.

[325bob]

I hope you've led me to a simple fix, been dealing with this tap for 3oo miles,changed oil, stethoscope,on running lifters, oil everywhere.If its a loose plug, I'll let you know.

You guys bailed me out, after 50 yrs.wrenching on everything from lawnmowers to outboards, I still learn something, was ready to replace lifters for a ticking that started after I did a Shark injection on the DME, raising the redline by 500 rpm, I figured the extra rpm somehow pumped a lifter dry, or my oil was too thick(20w50).NOPE, none of the above, #5plug was loose ,electrode gone!, compression seems ok at 130.I've been autocrossing these s50's for 10 yrs., and thought I'd seen it all!

[zellamay]

You guys bailed me out, after 50 yrs.wrenching on everything from lawnmowers to outboards, I still learn something, was ready to replace lifters for a ticking that started after I did a Shark injection on the DME, raising the redline by 500 rpm, I figured the extra rpm somehow pumped a lifter dry, or my oil was too thick(20w50).NOPE, none of the above, #5plug was loose ,electrode gone!, compression seems ok at 130.I've been autocrossing these s50's for 10 yrs., and thought I'd seen it all!

Thanks, now I don't feel quite so stupid.

[Randy Forbes]

You guys bailed me out, after 50 yrs.wrenching on everything from lawnmowers to outboards, I still learn something, was ready to replace lifters for a ticking that started after I did a Shark injection on the DME, raising the redline by 500 rpm, I figured the extra rpm somehow pumped a lifter dry, or my oil was too thick(20w50).NOPE, none of the above, #5plug was loose ,electrode gone!, compression seems ok at 130.I've been autocrossing these s50's for 10 yrs., and thought I'd seen it all!

I don't know why, but #5 is the problem child; loose plug, spitting connecting rods, or just worse wear on the big-end bearings.

If let go long enough, you'd have had to resort to this (yep, it's #5)...



Spot-facing the top of the plug hole to restore a flat sealing surface





Heli-Coil thread insert (required two__2__coils due to length of thread, second coil being trimmed)







After spot-facing, this cylinder will always require the use of a sparkplug indexing washer to reset the electrode depth