hearing a knock when engine is revved upto 2500 rpms

kfcmgr
0

Asked by kfcmgr Feb 20, 2013 at 02:37 PM about the 1994 Subaru Legacy 4 Dr L Wagon

Question type: Maintenance & Repair

10 Answers

tenspeed
51,825

That's never good. Rod knock? Does the knock go away above 2.5K?

1 out of 1 people think this is helpful.
Derek Dilts
95

Knocking isn't a good thing. How fast is the knock, and does it get faster as RPMs increase? If the knock is more of a "tick" that's really fast, it's likely in the valve train. If it's slower and more "low pitched", it's probably rod knock.

1 out of 1 people think this is helpful.
Jeff Smith
1,085

It could also be piston slap on cold starts. Does it go away once the car warms up?

2 out of 2 people think this is helpful.
John Sturman
1,205

youve also forgot about the shells on the bottom end as theese wear if the car has been thrashed hard on a regular basis

Jeff Smith
1,085

John, what 'shells' are you talking about?

John Sturman
1,205

on the crank shaft there is a series of shell bearings normally made of phosfer bronze if theese wear you will hear a knocking sound when under load as the crank will vibrate and start causing damage to the crank itself to get access to theese you will need to drop the sump/oil pan and then undo the crankshaft this will give you access to the shells. if you can read a micromiter then mic up the shells to work out how much wear there is and replace them accordingly with new shells to correct tolerances and dont forget to replace the oil seals at the same time you will have a rebuilt bottom end which will last quite sometime you can also drop out the pistons from the bottom end if you wish and replace the rings with a set of cords piston rings which hone out the bore and clean it up but you would have to run in the engine for at least a thousand miles drop the engine oil and replace with a good quality oil after this and it would be as if it was a new engine

1 out of 1 people think this is helpful.
Jeff Smith
1,085

What you are recommending then is a full rebuild. The block must be split to replace those rod bearings.

John Sturman
1,205

a rebuild is the best option as a second hand motor would cost more with fitting than you rebuilding the bottom end

1 out of 1 people think this is helpful.
tenspeed
51,825

Rod knock is a result of the "shells" or rod bearings being worn out. The noise is only heard when the gas pedal is pressed. --- Sometimes engines will make noise from pistons with short skirts. They will rattle a bit until the engine warms up and the piston expands to fill the bore. Pontiac 3100 and 3400 engines do that.

Jeff Smith
1,085

In the Subaru world, this is referred to as piston slap. It's very common on the higher mileage EJ engines.

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