Hey guys, I need help finding out why my 98 Civic LX 120.000 miles on it has a very loud knock in the engine when I start it up everytime. After it warms up, it is gone. I read on the web about bad Fram filters, I just changed my oil and filter to a Purolator PureONE and it did not stop. I am using Castrol GTX High Milage SAE 10W-30 motor oil and I tried putting in Hy-per lube to try if it stops but nothing helped. What could be the problem???

 

if it is only during cold start ups then most likely its a rod knock. Try some engine treatment like Seafoam, if it continues then you will most likely need new bearings.

This is just going off of the little bit of information you gave us, without actually hearing the knock its hard to say exactly what it might be.

 

It is very loud at first start. It lasts until the engine warms up. I also heard it today while waiting on the traffic lights. When I had it in neutral and stepped on gas couple times, I heard it but not as loud as when I start it. It sounds like an older diesel engine before it warms up.

 

yea i want to lean towards rod knock

 

That doesn't sound too good. Is there anything that can be done to fix this? Is it expensive?

 

if its to the point of no return, then the engine needs to be pulled out and the pistons and rods removed to have new bearings installed.

 

You could try adjusting the valves just to rule that out. If they're way loose, it can almost sound like a diesel. Valve noise will be from the top of the engine. If it's of a lower pitch and from the bottom part of the engine, that is rod knock.

 

pistons dont have to come out, pull the oil pan, pull the rod and main caps, take the crank out check it for damage if there is get it machined, get over sized bearings and put it all backtogether....no top end stuff has to come apart...maybe the timing belt off the cam gear(s) but nothing else on the top of the motor.

I sometimes add a shot of atf to quiet lifters but i'm not sure it would help a rod knock.

It could also be pistion slap from worn rings combined with the pistons and block expanding at different rates. but any type of engine knock is not good. and by the sounds of things its not gonna be cheep either.

hope it helps, 93

 

With 2 '94 Civics and 2 '95 Civics, and two out of the four having the condition known as "COLD ENGINE KNOCK"; yesterday I found it-- I found the answer to this long-standing dilemma while resetting a timing belt on one of my 94's.

Last week I had a mechanic install a new timing belt in this car (total mileage 188,000, last belt at 100,000) and afterward heard a terrible knock that would not quit after the motor got warm... I complained and was told to bring it in, the belt would have to be repositioned and it would be the same three hours and same labor charge... I looked at my Haynes repair, decided to try it myself, got half way through the job, discovered all that's really needed is take off the top belt cover, slip the belt off, make a mark on belt, make mark on cam sprocket tooth that you want the belt mark to line up with (one tooth to the left) then turn the crankshaft two inches, slip the belt on again making sure the two marks line up-- total time required 20 minutes.

But my situation wasn't that simple... I first moved the belt in the wrong direction, then had to move it two teeth the other way; this should have solved it, but no way-- turned out it needed to be moved yet another tooth! How did the mechanic get it so wrong.

And here's where it gets really interesting and why the answer to the mystery was finally revealed...

1) By the third time I removed the belt after running the motor sufficiently to warm it up to see if the knock would go away, I found the belt was much more difficult to remove and reset.

2) The thought occurred that the belt had shrunk due to the temperature increase-- garbage thought-- no, what happened was the motor expanded due to the temp increase, and therefore the distance from the cam sprocket to the crank pulley increased, causing the belt to tighten.

3) OK, the rest is obvious-- the motor warms, the belt tightens, it moves the cam shaft timing just enough to overcome the knock-- which is an IGNITION KNOCK, NOT A MECHANICAL PISTON SLAP, BEARING NOISE OR ANYTHING ELSE MECHANICAL (which would invariably get louder as the engine gets warmer).

4) If you suspect the truth of this analysis, all you have to do is loosen the distributor and rotate it counterclockwise 1/16 inch and see how much louder it makes the knocking sound when the engine is cold-- this will prove to all but the most stubborn that what you are hearing IS an ignition knock.

5) Finally-- (and now I'm in uncharted water needing more investigation); it might be better to let the "cold engine knock" live, since retarding the distributor could cause a slight loss of power, I'm just not sure about this part of it.

6) If you go through the usual procedure of timing with a timing light, and if the cold knock persists, I say leave well enough alone since you're probably getting the proper power level.

7) The real reason older high-mileage motors develop the knock might be some microscopic wear in the cam line that is happily overcome by the expansion when the motor warms up.

8) Do we care about the real reason-- I say it's enough to know it's ignition knock, not mechanical; and if you don't want to hear it you can turn the distributor clockwise 1/16" and put up with a possible slight loss of power (counterclockwise makes the noise louder and serves to identify it as ignition knock).


Case closed!

Have a great day, Richard