KA24E...thrown rod...

[godzirra]

okay, here is the scoop, my older brother has a 1988 D21 (I know, not a Datsun, forgive me) with a stock KA24E, auto tranny, power steering, a/c, the works. Absolutely NOTHING aftermarket has been done to this truck.

It has a whopping 154,000mi on it and has began to produce a mysterious ticking/knocking noise upon acceleration. He took it to some mechanic in Milledgeville, Ga (for those who know where that is) and he diagnosed it as a thrown rod via a sparkplug removal test.

 

Now, this begs the question, is this a likely diagnosis? I thought these engines were supposed to hold up a little better (I don't have a lot of experience with KA series). Given the pilot in question IS rough on a vehicle, but to throw a rod in a 154,000 mi KA24E, wouldn't you have to do something absolutely stupid like run it with no oil?

 

Also, assuming the whole block/cylinder wall isn't boogered up, what would I expect to see as far as repairs? (I would attempt the repair myself, if I had a little more familiarity with the engine. I could still probably do it, but the guy needs the truck up and running sooner than it would take for me to get it done).

 

Thanks for reading/all the input.,

 

And I do apologize if there is a thread about this floating somewhere... I did a 10-15 min search, didn't find what I wanted so I asked...

 

thanks again

[datzenmike]

Spark plug removal test?????

 

It might be a bad rod bearing but it's a long way from 'thrown'. Excessive rod clearance usually sounds like a clunking sound, very dull and metallic on acceleration and usually quiet or much quieter on deceleration. Louder the harder you step on the gas.

 

In the very early stages the rod bearing is totaled for sure, the question is if the crank bearing surface is damaged. You may be able to just replace the bearing with a new one. The bearing shell can be pounded to the thinness of a razor blade and almost certainly will slip out of place. At this point the piston is not properly clearanced and will hit the underside of the head. The bearing runs dry, overheats and welds to the rod and the crank. If traveling fast enough the rod cannot let go of the moving crank and shears off, usually smacking a hole in the side of the block as it rotates.

 

I would say one bearing, maybe the crank, if worse possibly a new rod and as this can't be changed without removing the piston, so new rings and if they are worn the cylinder over bored and oversize piston and rings.

 

____________________________________

 

I will say two things about the KA24E motor...

 

1/ They are known for very poor timing chain guides that last about 80K. They are plastic covered and disintegrate. The chain is then not properly supported and make a lot of noise. 

 

2/ The KA has 'hydraulic lifters' Actually oil filled 'dampers' on the rocker arms. If old or dirt gets in them the valves will make a ticking noise. But it will be a constant ticking and not dependent on throttle position.

[datsunaholic]

An '88 D21 with a KA?  Wouldn't be stock.

 

They used the Z24i through '89.

 

A thrown rod would make a helluva racket. and almost always a thrown rod results in a "vented" block- where the rod got thrown through it.

 

Could have a rod KNOCK, as in the bearing is trashed, but pulling a spark plug won't do anything towards diagnosing that.

[datzenmike]

KA has 4 spark plugse, the Z24i has 8.

[godzirra]

to clarify:

 

last I recall it was a KA, I am trying to be argumentative, just what I remember about the truck. I know there are several models 8/89 that have KAs instead of Zseries. but this was a 2nd owner truck, and not my personal ride, so for all I know it could be a legit 89 in reality. But that's not the point of the thread. (I am going to pick up this truck Tues. via trailor, I will slap up some pictures then).

 

The whole "spark plug removal" test sounded VERY shady to me, personally I had never heard of it before (I believe this "test" came from a friend of his who likes to think he's a big time engine mechanic because he managed to spray painted his 351W baby-poop green once.)

 

 As far as my mechanical comprehension of the basic combustion engine, when ever the cylinders fire, the piston moves up or down respectively turning the crank which all other pistons are connected to, SO if one of the rods IS thrown (causing the knocking noise) the knocking should STILL continue when the crank turns regardless of if there is combustion in the cylinder with the "thrown" rod.

 

SO this leads me to believe that if lack of combustion causes the knock to cease entirely, then it HAS to be a valve/lifter related problem, just my first hypothesis.

 

If it is a clearence issue, shouldn't the noise continue even if there is no combustion in the cylinder in question?

 

When I got the call from my brother the dialoge was as follows: "hey, there is this hammering sound when ever I accelerate, but it goes away when I take my foot off the gas." That was all he had to give me for information, not a bad thing, some people just are not mechanically inclined.

[datsunrides]

^{The "spark plug test"  will help diagnose a piston problem, like a bad wrist pin or perhaps a broken skirt etc. There is a possibility killing the spark to that cylinder would quiet a rod knock, but it would be unusual.}

 

^Mark