Engine Rebuild Adventure - Advice Needed

J

jthops

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Joined
Mar 28, 2023
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American Fork, UT
I've been working on a 93 YJ project
for my daughter. After doing body/paint and mechanical upgrades, I decided I wanted to rebuild the tired 2.5 L engine, which had low compression in cylinder 1 and some piston slap. It has been a pretty good experience, except for the premium I paid the machinist. Yesterday, about 15 minutes into the engine break in, a loud knock (not tick) showed up. I shut it down, dropped the oil pan, and everything looked good (no metal). Given the oil pressure and temperature were good, I convinced myself that the knock was coming from somewhere else. Put in more breakin oil, and fired it up again today. It's definitely rod knock - loud, increases with load and acceleration, deep knock, coming from the bottom of the engine, ... Ugh. A brand new engine and all that work.

So, I guess I'll drop the oil pan again and see if I can detect any play in any of the rods and check the rod bearings. Any advice on something specific I should be looking for? Is it possible replace a bad bearing without pulling the engine, again. The machinist ordered my rebuild kit and told me they confirmed all the clearances. I'm not sure where I went wrong, or if it was their fault.

Live and learn ... the hard way. Thanks in advance for any feedback.

 
jthops said:
I've been working on a 93 YJ project
for my daughter. After doing body/paint and mechanical upgrades, I decided I wanted to rebuild the tired 2.5 L engine, which had low compression in cylinder 1 and some piston slap. It has been a pretty good experience, except for the premium I paid the machinist. Yesterday, about 15 minutes into the engine break in, a loud knock (not tick) showed up. I shut it down, dropped the oil pan, and everything looked good (no metal). Given the oil pressure and temperature were good, I convinced myself that the knock was coming from somewhere else. Put in more breakin oil, and fired it up again today. It's definitely rod knock - loud, increases with load and acceleration, deep knock, coming from the bottom of the engine, ... Ugh. A brand new engine and all that work.

So, I guess I'll drop the oil pan again and see if I can detect any play in any of the rods and check the rod bearings. Any advice on something specific I should be looking for? Is it possible replace a bad bearing without pulling the engine, again. The machinist ordered my rebuild kit and told me they confirmed all the clearances. I'm not sure where I went wrong, or if it was their fault.

Live and learn ... the hard way. Thanks in advance for any feedback.

View attachment 121618
Click to expand...
I personally would pull the engine and check all bearing clearances with Plastigauge. Always check the clearances yourself after the machine shop and receiving parts because it is not uncommon to have mistakes made by someone along the line. I worked in an auto parts store in the early 80’s and cannot count the number of times that mis packaged bearings were found by the engine assembler.
 
You can do rod bearings by dropping the pan. Hopefully the crank isnt damaged though. Sounds like my friends deal where he paid a bunch and a few miles later the bearings went south.
 
I would not run the engine again until you look at the rods and ends. Did you have the journals ground or polished during the rebuild? Be sure to check them while the caps are off.
Shame to have happen on a new engine. Any warrantee?
 
Flyer58 said:
I would not run the engine again until you look at the rods and ends. Did you have the journals ground or polished during the rebuild? Be sure to check them while the caps are off.
Shame to have happen on a new engine. Any warrantee?
Click to expand...
The machinist ground the crank and allegedly made sure the bearings/kit had appropriate clearance for the crankshaft. I even asked if I should plastigage, and he said I could if I want, but there was no reason. Since I did all the assembly, I assume there is no warranty on anything other than a failure of a part. I should have plastigaged everything myself. Hard lesson to learn.

Maybe by some miracle, I can save it. I'll drop the pan again tomorrow. I really don't want to pull the engine and start over. My daughter has been hoping to have it for the remainder of the summer.
 
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When I rebuilt my '92 2.5L I had a local machine shop order the master rebuild kit and do all the machine work and I too did the assembly. In my case the previous owner ran it out of oil so the bearing spun and made the same sound when running.

During the inspection the shop found two connecting rods were damaged and needed to be replaced. I don't know how critical this slight damage is to bearing life but they thought it was.

Use lots of assembly lube when putting it back together. Post pics if you find something.

Screenshot 2023-07-23 134501.jpg
 
Flyer58 said:
When I rebuilt my '92 2.5L I had a local machine shop order the master rebuild kit and do all the machine work and I too did the assembly. In my case the previous owner ran it out of oil so the bearing spun and made the same sound when running.

During the inspection the shop found two connecting rods were damaged and needed to be replaced. I don't know how critical this slight damage is to bearing life but they thought it was.

Use lots of assembly lube when putting it back together. Post pics if you find something.

View attachment 121619
Click to expand...
Thanks for the info. I have the oil pan off now and pulling the rod caps. So far everything looks really good - no noticeable up/down play in the rods. I'll update again once I have more info.
 
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Well, good and bad news. The rod bearings look great (Pic below) - no obvious scoring and smooth surface on the crank. The bad news is that I don't know what's causing the knock. Is it possible that the endplay is causing the knocking? My endplay was just barely in spec when I built the engine - 0.0060". I guess I'll pull the main caps next and look at the bottom of those bearings. I've also been looking at the cylinder walls - nothing stands out.

Any other suggestions? Thanks-

IMG_2774.jpeg
 
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Well, it looks like excessive wear (for a brand new bearing) on my main bearings. Can someone tell me how this wear and the knock are related? Is this from clearance issues or something else? Thanks again for any feedback.

IMG_2783.jpegIMG_2785.jpeg
 
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So, my clearances are all normal. I'm at a loss. Warped crankshaft? It was ground by the machinist. Bent rod? The rod bearing look good though. Hhmmm...
 
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