240sx Build Nights, Thursdays 7:30pm

Automotive
#21

After overheating it would be good to ensure the head and top of block are flat, maybe clean up bore ridge, inspect for any cracks, these are all things we could attempt to do ourselves, but that goes to question of is it worth risking the money drivers put in to enter a race if something were to fail vs having a professional with experience do that work.

Will be at DMS Thursday after 7 to try and take oil pan off, it looks like the easiest approach will be suspending engine from strut tower brace and dropping the entire front crossmember. (There isnā€™t enough clearance without either removing crossmember or hoisting engine up a few inches). I think the front crossmember is the one part of the car we have yet to remove and reinstall.

#22

Iā€™m picturing this starter setupā€¦

#23

That very same arrangement, sans the clearly-futile pedal-pumping.

1 Like
#24

Will be at DMS today (thursday 7:30pm) to drop front cross member and oil pan to inspect the bottom end, anyone is welcome to come help or observe the potential carnage.

#25

Step 1, support engine

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Step 2, remove crossmember

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Step 3, poke at stuff

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Some rod bearings were worn, but none accounted for the rod knock. There was no perceptible up/down play on any of the rods, the front/back spacing was within limits (20 thousandth), no discoloration from overheating, no chunks of bearing material floating in the oil.

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After putting everything back together the noise is unchanged from the above video.

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'08 Mazda 3 2.3L apparent oil deprivation - "how f__ked is it?"
#26

Does it have a counter weight on the crank? Have you checked the timing chain tensioner? Doesnā€™t sound like chain slap, but just in case. Pull the spark plugs and see if youā€™ve got a chunk missing out of any of them. Stethoscope around to see exactly where the noise comes from, etc.

#27

Iā€™ll pitch in $100 if we can get enough people to pitch in to cover a new engine.

1 Like
#28

Something else occurred to me: piston wrist pin causing the noise. This would explain the absence of wear on the bearings. Should be a simple fix if you stethoscope to find the likely offender.

Http://www.onallcylinders.com/2014/01/24/sounds-like-trouble-quick-guide-diagnosing-common-engine-noises/

The short out test looks useful.

2 Likes
#29

Tried to stethoscope around some, but couldnā€™t isolate the noise at all, disconnecting one spark plug at a time to see if that changes noise is a good idea, will try that soon. Doing a compression check would also be good (most recent was before race).

Only pulled the rod end cap off cylinder #1 and #4, and in both of those there was no play in the wrist pin.

#30

The copper showing on that rod bearing is not good. Even of you could not
feel any slop in that bearing there has to be play equal to the thickness
of the babbitt that has worn away.

I would suggest getting a set of main and rod bearing shells, and some
Plastiguage. We can pull the pan, install the new shells and check the
clearances with the Plastigauge. PITA, but better than a new engine. I
have done this before, and would be willing to help.

4 Likes
#31

Is that photo the #4 or #1?
Either way, Chuckā€™s right; itā€™s hosed, eh.
Just that I would expect #4 to be worse than #1, so if thatā€™s #1ā€¦

#32

I was going to say the bearings were beginning to wipe but never hit the reply button. Lol I do tend to get side tracked at times.

Squirrel.

#33

Does it seem likely that the crankshaft is in good enough shape (not worn) that we can just get stock size replacement rod bearings and not have to send crank off for grinding? Couldnā€™t see any visible wear but also didnā€™t think to mic it previously.

#34

Obviously, mic would be best, and is easily performed on the rod journals; not so much on the mains. $15 in plastigage should tell most of the story, though, and 2 sticks in each size range (the blue is mostly useless in these engines) should be more than enough to do each journal twice (once to check before ordering bearings, once during assembly is overkill, but in a good way).

Are there any grooves in a journal? If so, the fingernail test and/or penny test works pretty well. If your fingernail grabs on it, it needs work. If your fingernail doesnā€™t grab, rub a penny across it. If it shows streaks it should be more carefully inspected, and likely polished at least.

For the record, Iā€™m having trouble placing that sound. Itā€™s too fast for crank noise, I think, but sounds too deep for valvetrain. Iā€™m liking the wrist pin idea, but I am undecided on whether I think thatā€™s it.Pulling a plug wire at a time (or a fuel injector, if thatā€™s easier, wonā€™t get you bit) to see if you can trace it to a cylinder might helpā€¦

1 Like
#35

That rod bearing with the copper showing is certainly worn out, but since it has not spun nor show signs of scoring, the crank should be Ok.

I have replaced con rod and main bearings in an engine without pulling the crank in the past. As long as the crank pins are not scored we can just install new, standard size bearings. A full set is ~$50-$60. We need a new pan gasket also.

1 Like
#36

Would replacing crankshaft bearings require pulling the transmission?

#37

Having never done it on a KA24DE specifically, in general, no.
Pull the cap, rotate the bearing out of the saddle, rotate the new one in, swap the bearing half on the cap, torque it back in.
From the photos, it looks like this should work.

#38

It depends on the style of main bearing.

My bet is yes, youā€™ll have to remove the Trans and the chain.

Many (not all) main bearings have one or more one piece bearing that slide over the end or snout at one end or the other.
Plus the front and rear crank seals are usually replaced at the same timeā€¦but again depends on the style of rear crank sealā€¦

#39

Do you have a time youā€™re going to do this? Iā€™m interested in watching this sort of heart surgery.

#40

I donā€™t think there was enough wear to justify replacing the main bearings - but that is just my view.

rod bearing - yes, no question, but they were not terrible.

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