EJ207 Cold knock or piston slap?

[Cobrakai]

Originally Posted by D-Rodman

My v7 ej207 piston slaps at cold start but quiets down fairly quick, under a minute. Keep in mind when buying a used motor you are trusting the vendor is representing the mileage accurately. A higher miles motor will have more wear and looser tolerances.

Same, sometimes a bit longer in colder ambient temps.

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[Roland3]

my 05 wrx has knocked on cold start for 200K miles, when its really cold out it is even worse. but pretty much goes away when warmed up.

[Titter]

sounds like rod knock.

yes a slight rod knock can go away once oil is up to temp.

thats definitely NOT piston slap. piston slap is very rhythmic and goes away when throttle is applied and oil pressure builds.

i hope its a tensioner but really sounds like rod knock. perhaps one of your new ones was faulty or improperly installed.

[2slofouru]

Originally Posted by AspirinWhite

Is the bad tensioner noise temperature dependant though? The noise I'm hearing disappears once it's warm and appears only when lower rpm from cold start.

The tensioner noise sounds like it's constant

There is a similar issue with the honda V6 motors, as the tensioner ages it loses pressure and gets softer. When they are about done, they will rattle so hard you think it's a rod bearing. They first become obvious on really cold mornings and the noise goes away as it warms up because the heat of the engine raises the tensioner's internal pressure and helps it stop rattling. As it gets worse, the rattle stays longer every drive, until eventually it doesn't matter if the engine is warmed up.

I haven't watched your vids yet, because I'm too much of a wimp to check anything other than youtube hosted videos

[Samurai Jack]

Originally Posted by 2slofouru

There is a similar issue with the honda V6 motors, as the tensioner ages it loses pressure and gets softer. When they are about done, they will rattle so hard you think it's a rod bearing. They first become obvious on really cold mornings and the noise goes away as it warms up because the heat of the engine raises the tensioner's internal pressure and helps it stop rattling. As it gets worse, the rattle stays longer every drive, until eventually it doesn't matter if the engine is warmed up.

This has shown to be the case multiple times with Subarus. There are posts here discussing that as well as YouTube hosted videos of the noises with thread followups confirming that the tensioner was bad.

[tayl0rr]

I just rebuilt an ej251 in an 03 outback and it has a similar noise. Noise doesn't seem to go away after it warms up though. Worse on the number 2,4 cylinder side. Hasn't gotten any worse after 100 miles on the engine but I would like to figure out what it is since I did the rebuild. Any ideas?

This one is cold

Subaru knock after rebuild - YouTube

Subaru knock after rebuild - YouTube

This one is after it has warmed up. Started running rough toward the end because the battery died. Doesn't like to run without the alternator when the battery hits around 10 volts.

Subaru knock after rebuild. Warmed up. 2.5 SOHC 03 Outback - YouTube

Subaru knock after rebuild. Warmed up. 2.5 SOHC 03 Outback - YouTube

Everything went to the machine shop. Machinist said the crank was still spec. Bored 20 over. Put a topline kit in it with pistons and oil pump. Plastigauged the rods and they were near the upper limits but not out of spec. Couldn't plastiguage the mains. I adjusted the valves again at 100 miles on the 2,4 side. They were out so I snugged them up. The valve noise went away but I'm still left with that other noise. I thought maybe it was what people are calling piston slap but the pistons and rings are new and the noise doesn't get any better after warm. I think its loudest around the number 4 and very loud if I listen on the EGR tube with a stethoscope. Could this be something to do with the EGR system? Wrist pin? Rod knock? I'm pretty sure its not a main because I can't hear it with the stethoscope on the passenger side. I had the timing cover off to check it and saw that my Gates timing kit had a bearing that threw grease everywhere so I replaced it with all factory timing parts, but this wasn't part of the noise issue.

[AspirinWhite]

6 month update:

I've replaced timing belt, tensioner, all the idlers and the sound is still there. I also took another step further by replacing the possibily rusted exhaust manifold and the uppipe with a near new factory system and still did not fix the problem.

Then car went through about 7k miles including a track session in a hot day as well as some spirited canyon run... the engine is still running strong.

I also took a sample of a 5k mile old oil to Blackstones Lab and oil analysis came up good.

I'll continue to update this thread if anything comes up but looks like the engine is good for now.

[AspirinWhite]

Its been awhile but doing another update since the swap. The car has seen more track days and also many long road trips from California to Oklahoma and also to North Carolina and back. The noise is still definitely there, and its more audible in colder mornings in the winter. However
it still goes away when warm and the car has been running like a champ still.

I will be swapping my 20yr old VF30 for VF48 soon and planning on doing another tune afterwards. I do realize the engine is over 20 years old as well so there's always a rainy day fund in case.

[subaru_gc8]

Originally Posted by AspirinWhite

Its been awhile but doing another update since the swap. The car has seen more track days and also many long road trips from California to Oklahoma and also to North Carolina and back. The noise is still definitely there, and its more audible in colder mornings in the winter. However
it still goes away when warm and the car has been running like a champ still.

I will be swapping my 20yr old VF30 for VF48 soon and planning on doing another tune afterwards. I do realize the engine is over 20 years old as well so there's always a rainy day fund in case.

why not go with a 18g or so? yeah rainy day funds... mine has grown to 5000ish lol

[AspirinWhite]

Originally Posted by subaru_gc8

why not go with a 18g or so? yeah rainy day funds... mine has grown to 5000ish lol

I guess I'm pretty happy with the car being in the 300hp range. Even at tracks I go to, power was never really my concern. Also I was able to grab this vf48 at a good price so..

[paulmahoney634]

Originally Posted by AspirinWhite

I recently completed my version 7 EJ207 swap into my 03 WRX and it fired up with a noise that was similar to a engine knocking noise. However when the engine was warmed to temperature, the noise disappeared.

I've been looking up through a lot of threads and most of the answers leaned toward piston slap while a handful claimed it was rod knock.

I'm quite stumped about this problem and really paranoid if the engine I've purchased was bad from the start. I tuned the engine immediately via open source to eliminate the possibility of pinging/detonation due to crappy California 91 gas. The engine runs very strong but the cold knock doesn't seem to go away.

Any help would be great.

Mine knocks for about 15 minutes then goes away slowly until it runs normal

[Rabbitrex44]

I put a junkyard short block in my 03 wrx and had a piston slap noise from the get go. Would go away when warm. Has run good for about 9k miles.

Recently has gotten worse and does not go away when warm now. Still runs ok but I have to commute about 30 miles per day and I'm getting ready to order a jdm replacement motor very soon.

Btw I think my problems with fuel tank not venting have caused lean problems and that's why motor has gotten hurt recently

[undyjr]

Originally Posted by Rabbitrex44

I put a junkyard short block in my 03 wrx and had a piston slap noise from the get go. Would go away when warm. Has run good for about 9k miles.

Recently has gotten worse and does not go away when warm now. Still runs ok but I have to commute about 30 miles per day and I'm getting ready to order a jdm replacement motor very soon.

Btw I think my problems with fuel tank not venting have caused lean problems and that's why motor has gotten hurt recently

The evap purge solenoid only opens when the manifold is in a vacuum (off boost) where a slightly lean condition would have little effect. We are talking about just gas vapor here.

If you're concerned about your motor perhaps a oil analysis, leak down, and compression test are in order.

[undyjr]

Originally Posted by Rabbitrex44

I put a junkyard short block in my 03 wrx and had a piston slap noise from the get go. Would go away when warm. Has run good for about 9k miles.

Recently has gotten worse and does not go away when warm now. Still runs ok but I have to commute about 30 miles per day and I'm getting ready to order a jdm replacement motor very soon.

Btw I think my problems with fuel tank not venting have caused lean problems and that's why motor has gotten hurt recently

The evap purge solenoid only opens when the manifold is in a vacuum (off boost) where a slightly lean condition would have little effect. We are talking about just gas vapor here.

If you're concerned about your motor perhaps a oil analysis, leak down, and compression test are in order. How's your oil consumption?

[Rabbitrex44]

Seems like it would have to let air in somehow. It's pretty hard to pump out of a sealed container. Evap might only open under no boost conditions but maybe some other vent? Maybe the return line deals with the negative pressure.

As far as the motor.. I decided to do one last oil change and nothing abnormal in oil no grey no metallics etc. Had about 3k on synthetic which is twice what I normally put on its oil.I thought this weird for something that sounds like it may kaboom.

Pulled out my cheap stethoscope and checked all cylinders and both heads from the bottom and it sounded ok. Put stethoscope on timing cover and oh boy its loud.

I have a thread going in conversion section to anyone interested.

But I still would like to know if clogged evap or venting would cause lean condition. I've already ordered charcoal canister after blowing out all the lines in the back and still have problems putting gas in her. And ordered a new tensioner.

Oil consumption has always been pretty bad. I think pcv system may not be hooked up properly and seems maybe I'm pooling oil somewhere and if I jump on it then it will puff some smoke. I'm using .5 to 1 qt per 1k miles

[Rabbitrex44]

Mine was tensioner. Replaced it today and sounds okay again.

[benflynn]

Originally Posted by Rabbitrex44

Mine was tensioner. Replaced it today and sounds okay again.

Nice, I have had a bad tensioner, knocks like hel but it is a beat than a rod. You can diagnose it by taking side cover off and sticking a long screwdriver in to the tensioner, clear as day. I also have a 253 that had piston slap forever, I rebuilt with new everything and damn thing still slaps, hot, cold, still slaps. I pulled the heads to verify and sure enough, sloppy pistons. One day lil pieces of skirt will tell u when it has slapped enough, smoke first I guess. Only seen an xr400 eat a skirt from lots of slap

[LostPringles]

I know I'm a little late to the party here, but I'm trying to track down a noise in my subie and I was wondering what you guys thought. Its a JDM ej205. Noise happens on cold starts and goes away after it comes up to temperature. Sounds an awful lot like knock to me, I listened using a stethoscope and it sounds slightly louder on the passenger side.



https://www.youtube.com/shorts/EUHQ4Zl-T3I

[D-Rodman]

Piston slap, the fact that the engine quiets down at optimal operating temperature is a clear indicator you don’t have an engine problem.


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