Just my luck...

[Superdave]

So after my 13.08 @ 105.5 MPH run i noticed a slight knock from the 3500, nothing terrible but it was there..

I kept the RPM's low all the way home and started investigating that night, didn't find anything right away and it seemed to have stopped.. so i drove it to work, was fine in the morning but in the afternoon heat the engine really warmed up and the knock came back.

I pulled the pan tonight to check and found that #1 rod bearing was spun




the rod cap is scratched up a little but the crank looks fine, i'm going to check the crank with the micrometer this weekend. If it's ok and the rod end is still useable i might just toss another bearing in there (i have a set of spares) and hope it lasts.. lol


I have yet to pull the rest of the rod caps but i plan on it, this is on a bottom end with roughly 3K miles running Mobile 1 10W30.

[3400-95-Modified]

Which rod?

Nevermind I'm retarded... #1


So how much timing were you running?

[Superdave]

26 degrees on 91 octaine.

I found that the #1 piston is the only one that will come out the bottom, so i might just go ahead and swap it out with a spare. we'll see what happens this weekend...

[3400-95-Modified]

good luck compressing those rings

Hopefully no others look like that either, that would suck.

[Superdave]

that's what the ring compressor is for.. lol


we'll see

[3400-95-Modified]

Can you fit the ring compressor up in there tho? thats what my thought was that it would be too tight to get that in and out but then again its not that big of a tool.

[Joseph Upson]

What's with pulling the piston when you can change the bearings without removing the rod from the engine.

Dave you should look into the recommended bearing clearances for the high rpm you are running, I seem to recall that high rpm engines need to be a little looser than production engines. This is also another reason I installed an oil cooler, although there is an optimum operating temp for everything, all friction related engine problems seem to correlate with normal to high engine operating temps.

It makes sense, metals are softer and oil is thinner as temps increase. I'm already eyeing a larger radiator and planning to move my oil cooler to the front of my Fiero for retro engine temps around 170-180 deg tops. My dad is a big time motorhead and said that back in his day if your engine ran as high as 200 deg the heads were toast.

Sorry you keep having major unscheduled pit stops after so much hard work, I think I'll keep my rev limit at 6500.

[ForcedFirebird]

Joseph, I thing the concern is the rod now being oversized. Dave said he has replacements, but I had a spun bearing that looked very similar to his, and just put a new bearing in, but it spun again (detonation probably played a part in it, though).

[Joseph Upson]

Joseph, I thing the concern is the rod now being oversized. Dave said he has replacements, but I had a spun bearing that looked very similar to his, and just put a new bearing in, but it spun again (detonation probably played a part in it, though).

Bearings should be double tanged with notches on both sides of the cap and ends of the bearing to help make this a very difficult thing to do.

[Superdave]

here is the end cap..



and what was left in the oil pan..

[Joseph Upson]

Looks like left over from more than one bearing.

[Superdave]

after running a magnet through the pan i found lots of small pieces.. and one big one




at this point i'm considering pulling the engine and tossing it on the stand for a bottom end rebuild, i'd just have to pick up yet another top end gasket kit.

guess i'll have to sell a few more OBD1 3400 swap chips to finance it... lol

[IsaacHayes]

You could sell some of the UIM metal gaskets to help out... People can re-use those and port to them.

Wish you luck man. Do post what you find out. If it all fails, 3900 or ls4 time?

[Monzsta]

Lower your rpm a bit when it goes together next time. It looks like the bearing got pinched by the big end of the rod egging out. Clevite sells high rpm bearings that are thinner towards the parting line to avoid this, but I don't know if they're available for our engines. You'll need to either replace that rod or recondition it. What kind of oil are you running?

[gectek]

i ran up to 7k rpm on my shifts for well over 2 yrs and didnt have that prob, when i got my bolts put in they did a competition cut on the caps and rods and then honed them out to stock size...but they really didnt need to, the big ends were still in perfect shape...just a little colord from high rpms and not using good enough oil...wont make the oil mistake again...