Kandlhoft

I have multiple issues going on and I have another thread asking about the MAF and rough idle conditions. I am spinning the screeching sound issue off into this thread for posterity of anyone else who may have my issue.

For those just joining in- I have a MY 1985 928 US 32V. I bought the car as a non-runner. It was last registered in 1998 and I believe it spent the past 25 years parked outside- exposed to the gentle California Bay Area climate. Anyways, I have cleaned the engine and did a complete refresh and she does fire up! However, there is an extremely loud screeching sound, almost deafening like a freight train stopping.

To recap relevant posts from the other thread:

@Mrmerlin Suggested- "a roller that might have gotten coolant in it when you drained the block."
@leperboy Suggested- "Get a mechanic's stethoscope and place it near each pulley and rotating part at the front of the block to see if you can isolate/rule out the source of the squeal."

The noise is from the front half of the 928. I checked around with a stethoscope and could not localize the noise to the front or sides of the engine. I ordered a front and top end engine refresh from 928sRus. I removed the timing belt and checked around and

everything that is supposed to move with ease and freely did so

. No metal shavings to be found.

@jbrob007 Suggested- "Off the top of my head that screeching MAY be coming from the Air Pump and/or Air Pump Pulley. If the car sat for 25 years, then this is highly suspect as the bearings may be frozen and it's a common issue."

All accessory belts had been disconnected. So it is not the air pump.

@leperboy Suggested "It sounds like a bearing to me, but it's hard to tell. The sound seems constant, not rhythmic like if something were rubbing once per cycle. I might have missed this above, but does the sound increase/decrease with RPM?"

The sound did change when I increased the RPM

@Mrmerlin Suggested- "is this car an automatic? if so did you perform a flex plate check?"

depami

Time to do the last thing on the above list & check crank end play and hope like heck it isn't TBF (Thrust Bearing Failure).

Kandlhoft

@Mrmerlin The 928 is an automatic. I followed this flex plate check from 928intl. I understand a dial gauge is preferred, I ordered one and its currently in the mail. I had a digital micrometer on hand, so that's what I used.


A) View down the Torque Tube


B) I did notice a small smooth metal patch of metal above the starter


C) View of the flexplate with PB blaster sprayed on the clamp bolt.


D) Another view of the flexplate pre-loosening the clamp.


E) Approximately 8.5mm of spline showing pre-loosening.


F) Approximately 6.5mm of spline showing after loosening the clamp.

depami

Next you need to pry the fly wheel fore and aft and see how far it moves and compare to spec. You should be able to measure that reasonably accurately with a caliper. You should hear/feel a thud when the crank hits each end.

Kandlhoft

G) When checking endplay, push forwarward I measured 40.5mm. I did find the accuracy of the caliper to be poor and difficult to manage.


H) When pushed rearward, I measured 39.9mm... again not the most accurate. but that is roughly a 0.6mm difference...

Kandlhoft

@depami I can not say I heard of felt any "thud".

I will get more details posted when I get the dial indicator in....

Thanks everyone!

depami

You can get a good view by removing the oil pan but that's a bit of work.

depami

Check it with belts removed and clamp loose so crank can move as freely as possible. Ideally with timing belt removed too but that's probably not feasible at this point.
I don't remember for sure, and I can't find the pictures, but I think I had the flex plat off when I checked mine. Timing belt was still on and I definitely had a thud.

Mrmerlin

NOTE you can leave the belts on for the amount that the crank moves they wont affect the result.
BUT as Denny said, the pinch bolt must be removed.

Clearly you should hear a thunk as the crank bottoms on each side of the thrust bearing.

a quick test is to pull the dipstick and drip the oil onto a black piece of cardboard then look at the oil in the sun,
if you see lots of metallic s then your making metal.

You need a dial indicator that caliper is not good enough for this measurement,
based on your report the thrust bearing is worn beyond spec/. SB 0.40 MM
convert to inches you should see nominal .008 in is what you should see.
your range is .008 in. to .016 in. max
most are from .008 to .012 in.

Make sure to remove the rear pinch bolt at the transaxle connection,
NOTE how loose it is, ( they are usually loose.)
NOTE make sure the driveshaft is centered in the rear cutout before you reinstall it ,
use a drop of blue loctite on the bolt threads ,
torque to 66 FT lbs

FredR

Although far from perfect the measuring technique you are using should be able to resolve 0.1mm very easily providing the reference surfaces you mount the caliper blades on are consistent. If you use such technique you really need two pairs of hands to have a fighting chance of a half decent result - one to pry and hold the crank at each extremity and the other to manipulate the vernier caliper. You also need to take three or more measurements to check for consistency- if the readings are all over the place forget it until you get the dial gauge. Needless to say no need for such concerns with a hard mounted dial gauge. It will be interesting to see what reading you get with a dial gauge but at face value it does look a bit ominous given 0.4mm is the retiurement dimension and one should expect to see circa 0.2mm on a corrrectly functioning installation with 100k plus miles on it.

When the clamp is held rigid in the correct position as intended by design thrust bearing wear is almost non existant as the thrust load when operating correctly is minimal. When the clamp slips and places a false load on the the thrust bearing it then becomes a bit of a crap shoot as to what happens over time. Hard contact of the crank against the webbing does not seem to occur until end float reaches something in excess of 1.0mm but when that happens the engine is almost certain to be a right off. If your thrust bearing has exceeded retirement specification chances are it will not have done serious [i.e. terminal] damage to the engine

One can see from the photo that the clamp is sitting too far along the splines and a closer look suggests a polished look on the leading edge of the splines. 2mm of slippage does not usually cause a serious issue but my experience some 24 years ago suggests that 2mm to 3mm of slippage can be enough to induce a "strange vibration" at 3050 rpms- did you notice anything of this kind?

I have no recollection of anyone complaining about strange noises and the biggest problem with this syndrome invariably is that there are no obvious warning signs that something is amiss until it is too late.

Suggest you also check the position [depth] of the front bearing in relation to the torque tube mounting flange- it looks suspiciously deep to me- unfortunately I cannot remember off the top of my head what the insertion depth should be.

Kandlhoft

@Fredr, I can not speak for any strange vibration. I have probably run the vehicle for 2 minutes total.

@depami @Mrmerlin

I was able to remove the the rear pinch bolt at the transaxle connection. It was well torqued and took force to break loose. There appears to be no wear on either pinch bolt.


The 928 was almost all complete (the main reason I decided to purchase and dive into this project), however, I noticed on the transaxle, there were these two exposed studs (circled in red) and an exhaust hanger missing. Someone at some point had been in this area before.



I attempted to pry the flywheel fore and aft, but I did not sense any movement or "thud". I removed the timing belt to see if that may remedy the situation, but still no movement or "thud". I've decided to wait for suggestions on how to proceed properly.

- Jake

Mrmerlin

The flywheel will move about the thickness of a matchbook cover so it could be imperceptible That said you did not need to remove any belts to check the crank end play

Kandlhoft

@Mrmerlin Thank you for the info, and yes, I understand the timing belt did not need to be removed. I initially removed the belt to see if there was a seized roller. When I put the belt back on, I was a tooth off on one of the cams. I figured that was good enough to turn the engine over by hand so I could access the pinch bolts on the torque tube. If the thrust bearing is indeed bad, no need to get the timing right...

Anyways, I've tried prying fore and aft on the on the flex plate with some force and I am not getting any discernible play with the crank. Both front and rear pinch bolts are removed. Both were securely torqued before removal.

https://www.youtube.com/shorts/E1Yy757calQ

**Note - I realize with the video, it only shows me prying one way. I attempted both ways with same result.



Open to any suggestions on how to proceed. As always, Thanks for the help!


- Jake

FredR

The end float you are looking for in an engine that is in good shape is 0.2mm [5 thou]. The retirement end float is 0.4mm. To be able to detect such end float you really need a dial gauge fitted albeit you can feel such if and when it is present.

The movement of the gauge appears to suggest 5 thou of movement so what exactly are you concerned about?

depami

Is the dial showing movement or flex? If movement, shouldn't it stay at each extreme?
It's a lot of work, but, removing the oil pan would expose the thrust bearing.