Dear Weird Engine Noise Fairy

#21

What’s the right tool to do this? The plastigage will only measure clearances, not tell me which bearing size to order. I also didn’t realize there were two stock sizes. How to choose the right one?

#22

[quote=“RRhodes” post=65744]Nope, but good point. I think I may have lucked out and caught the failure early though. It may not have produced much metal yet. The thing I can’t quite figure out is that the noise seems to go away again under heavier throttle openings. It’s worst and loudest at the transition from 1/2 open to almost closed throttle.

Ranger, why not do the main bearings too while I’m under there?

Another stupid question, if the bearing(s) are worn enough to cause rod knock, why would a new stock bearing fit? Won’t I still have too much clearance? Wouldn’t this necessitate having the crank machined for an undersize bearing?[/quote]
In order to replace the main bearings you have to pull the engine so you can remove the crank.

A stock bearing should fit because it was the bearing that was worn, not (ideally) the crank, nor the rod.

There’s actually a number of different bearing sizes. I think that there’s 3 different cranks designated by some kind of “color” scheme that I never really understood, and then each bearing has a + size counterpart that is thicker than the normal bearing.

For example you might have a “Yellow” crank and that crank has a normal size rod bearing associated with it and a + size rod bearing. If you have have to machine a little off of the crank, then the diameter of it’s journal becomes smaller and you have to use the slight thicker + size bearing. It gets more interesting in that you can even mix and match normal and + sizes to get exactly the tolerance that you seek.

Ok, that all sounds complicated. But my perception is that the whole crank color thing isn’t all that meaningful because almost all cranks are the same designation and there’s very few of the other two. So most everyone assumes you’re talking about the same color crank and everyone seems to ignore the fact that two other colors of crank are supposed to exist. I don’t know this for a fact, but it’s my perception.

If your intent is just to replace rod bearings than I’d order a set of normal M20B25 rod bearings and be done with it. Except you might consider getting coated bearings because they are more robust. This assumes that you find no signs of damage to your crank shaft and therefore don’t need to remove any material from it’s journals. If you remove material from a crank journal then it’s time for a + size bearing.

#23

Got it. Any idea where to find the crank “color”?

#24

There’s a discussion of it in the Bentley. But just because this distinction seems to theoretically exist, I don’t know that I’d pay attention to it. Just find some coated rod bearings and be done with it. VAC carries them, among other places. And they don’t seem to talk about different crank color designations.

#25

There are two colors for rod bearings and three for main bearings for nominal and two re-grind diameters. You measure the journal diameter and use the table in the Bentley to pick the right color, which then results in the correct bearing clearance.

In most cases you can use a single color for rods and a single color for mains, but not always. Sometimes it is necessary to mix colors to get all of the bearings to have correct clearance.

#26

Tried the spark removal test and confirmed that it is highly likely that #6 rod bearing is shot. Fortunately there are no oil sparkles so I’m cautiously optimistic that I’ve caught it early. When you guys drop the subframe, do you disconnect the steering and move the whole subframe out of the way, or just lower it as far as it will go and work around it? Right now it’s resting on wheel dollies but I haven’t been able to pop the steering coupling yet. I also haven’t disconnected ABS sensors or brake calipers so it’s only going to move as far back as the tires will clear the wheel arches. Looks like almost enough room but will I regret not just going for it?

#27

When I do this I dismount the calipers & ABS sensors, disconnect the steering shaft, disconnect the CAB brackets, and get the subframe assembly out from under the car.

Know that you must remove the pinch bolt from the steering shaft coupler, not just loosen it.

#28

Thanks Jim. Found the coupler warning in Bentley. Left the ABS in but the answer became quickly self evident. The subframe is now safely tucked away under the tranny, there’s not much lateral maneuvering room in my garage.

Diagnosis confirmed, thanks all. Pics soon.

#29

[attachment=1841]E30BearingFailUpper.jpg[/attachment]

[attachment=1842]E30BearingFailure.jpg[/attachment]

#30

I’d say those bearings are shot!!! Any scoring on the crankshaft?

#31

Not that I could find. I’m going back in for another look this weekend. Hopefully my new coated Clevite bearings will have arrived for installation by then too.

#32

Got the new coated bearings in about 2 days from Streetside Auto in KC but, in spite of the fact that they appear to be packed correctly, appear to be unusable to the underinformed. The shells have obvious chips, pits, and scratches in the coating. Some of them are fairly deep. Guess I’m screwing with goobage and drinking beer this weekend instead of updating bearings.

[attachment=1847]NewRodBearing3.JPG[/attachment]

[attachment=1846]NewRodBearing4.JPG[/attachment]

#33

That sucks! I would not use those bearings, but do however have some extras at my place if you live in the KC area and want to come get them. I live in Lansing just outside Fort Leavenworth.

#34

Thanks for the offer. Unfortunately I’m in Indy. I’ve already contacted Streetside for an RMA. They were extremely responsive to my last e-mail so I’m cautiously optimistic. While waiting I started putting in the TC crankscraper. I guess I should have gone with the IJ. Although the TC didn’t need any grinding, it also has pretty big gaps and the mounting holes are off and need to be ovaled or enlarged.

#35

The TC Motorsports baffle is a lot better than their scraper. You going to put in some kind of baffle?

#36

Yup, that too. BTW thanks for the offer of a bottom end. The journals I’ve measured and the clearances I’ve checked all look very good w. clearances near the tight end and journals towards the large so I’m thinking the crank and rods are okay, even the one with the destroyed bearing. No significant wear on anything I’ve looked at so far. I’m marveling at how that can be in a quarter century old engine. I’m starting to believe the 138K mile claim by the owner and the paperwork. Also got the necessary excuse to get the HF engine support thingie. Perhaps the best $60 I ever spent. Wish I’d had it when I did the offspring’s Neon rear main seal.