Boxer engine knock Subaru


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virgilmobile
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Boxer engine knock Subaru

Post by virgilmobile »



Sorry about the confusion.I can't resolve this problem through regular channels.

Yes it's a subaru and is very similar to the GL1100 in design.
Yes I've owned both but this is a undiagnosed problem I'm struggling with.

I had to get rid of my truck and purchase the subaru.My better half couldn't get in the truck(disabled).
Now it's up to me to make this car right.

Severe knock when I got it.Solved all the major service work..eg.timing belt and idlers,worn rockers,etc,etc.




90% of the noise is gone...Except this annoying cold start knock and taking 15 miles of driving to quiet it away only to return the next start up.

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The frequency of the knock seems to follow one cylinder.Is it possible that the camshaft "bearings" were hammered during the time the timing belt tentioner was knocking?
I do still hear rocker noise(as expected) but the side in question is about twice as loud(stethoscope).
Also..pulling the injector power on one cylinder at a time does not change the knocking at all(Not a rod knock or piston slap)?
Still need to pull the spark plugs for inspection.Doesnt smoke or smell bad,starts easy and plenty of power.
Any ideas?



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Re: Boxer engine knock Subaru

Post by eklimek »

V

Video suggests its more on the passenger side. I had an exhaust leak from a cracked stud that closed up warm and “knocked” cold.

Ed

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virgilmobile
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Re: Boxer engine knock Subaru

Post by virgilmobile »

Hmmm.Ill run it up on the ramps and check that.Thanks.
Should be able to locate a exhaust leak with soapy water and a cold engine when first starting.
Thanks for the tip.

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Re: Boxer engine knock Subaru

Post by WingAdmin »

Does it have hydraulic lifters? I've had three Subarus over the years, and all three of them had issues pumping up the lifters in cold weather, causing horrendous knock until they warmed up. Maybe a dose of Seafoam to clear out lifter ports?

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Re: Boxer engine knock Subaru

Post by virgilmobile »

No.There roller rocker overhead cam.
My older Subaru had the hydraulic ones too.
This has the normal "tappet" noise but in the background is that low pitch knock.
It's design is very much like the 1100.

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Re: Boxer engine knock Subaru

Post by WingAdmin »

My next guess was going to be rod knock or piston slap, but then I read that you had already pulled injector harnesses to try to isolate.

Hm, this is reaching, but it disappears when warm, appears to happen under load at lower RPM...detonation maybe? Doesn't really sound like it, but...what if you ran a tank of premium in it?

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Re: Boxer engine knock Subaru

Post by virgilmobile »

Leaning away from a premium gas fix.It has a knock sensor it move the ignition timing for that.Im also at sea level.
I think pulling the plugs may help see what it looks like inside.

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Re: Boxer engine knock Subaru

Post by tamathumper »

I'd still run some Seafoam through it :lol:
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Re: Boxer engine knock Subaru

Post by virgilmobile »

I did that when I first picked it up.Full dose in the crankcase before the oil changed and through 300 miles of fuel.Fresh oil change with the good stuff including a half dose of MMO in both.
The knock is completely gone (as far as I can hear) after a 10 Mile drive to the store and back..about a hours time.It always returns after it cools off for a day.
I'll try to check for exhaust leak on Thursday evening.

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Re: Boxer engine knock Subaru

Post by ct1500 »

I hear the cold start knock that goes away in a few seconds and that would usually be piston slap from a collapsed skirt. I would start it cold with injector or spark disabled for each cylinder on successive morning starts to try and narrow it down to a particular jug. How many miles on the engine?
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Re: Boxer engine knock Subaru

Post by virgilmobile »

The car is new to me with 172K miles.Looks very well maintained and was a trade in at a new car dealership.Local shop repairs.Collage student from out of state.Had a new cat converter and CV axle within the last year or so.
Disconnecting each injector does not change the knocking.

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Re: Boxer engine knock Subaru

Post by pocketchange »

Starting with MMO and your other opening efforts were very positive.
The noise reduction after a few miles, points me toward something amiss with a piston.
Bearings having issues, never go away (cold or hot.)
Rather than drive yourself nuts, I'd suggest, start looking for another engine, in lieu of the miles on this one.
I'll guess the PO beat on the engine when it was cold and something (most likely a piston) cracked.
I'd drive it until it won't go anymore.. then locate another engine.
Rent/buy/borrow.. a leak tester and see what it has to report. pc

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Re: Boxer engine knock Subaru

Post by virgilmobile »

Assume nothing...How could I have overlooked this. :oops:


Not 100% confirmed but I think I found the source of the knocking.
I believe these are original plugs.


Noticed that the plug easily came loose but threaded very hard out of the head.
The threads appear carbon/heat damaged and may have been loose in the head.Also the seals are blown.The gap measured just over .060.. supposed to be around .038-.040.
The tip also has a red tint on the enamel.


This is close to the same for the cylinder next to it.
The opposite side plugs looked better on the tip but still have blown seals and one has a crack...leading to carbon tracking.
So I'll pick up a new set and report back.
Any idea the cause of the red tint?
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Re: Boxer engine knock Subaru

Post by eklimek »

Good to see it was not an internal problem, and an easy fix.

I do not know how the plugs became reddish.

Ed

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Re: Boxer engine knock Subaru

Post by virgilmobile »



Red tint.
I'm guessing here.
We know that the enamel tip is thermally cooled by heat transfer through the threads into the head.
Plugs loose..tip overheats...

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Re: Boxer engine knock Subaru

Post by eklimek »

Interesting that all plugs were affected albeit only 2 were red.

Are the plugs on top or under the head of the flat 4? moisture on head leaking past seal? Is the red iron oxide from corrosion?

Ed

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Re: Boxer engine knock Subaru

Post by virgilmobile »

Both red ones were on the same side(the noisy side).The plugs angle at about 80°.
There's no evidence of any corrosion anywhere around the plugs,just the red tint on one side.
Keep in mind,I have run Seafoam and MMO through it.

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Re: Boxer engine knock Subaru

Post by wing rider 2012 »

Typically the tinting of the electrode insulator is due to gas additives, but this should show up on all the plugs.
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virgilmobile
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Re: Boxer engine knock Subaru

Post by virgilmobile »

Maybe because these 2 plugs were loose and overheating compared to the other set the "tint"showed up first.?

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Re: Boxer engine knock Subaru

Post by tamathumper »

:shock: :o :shock:
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Re: Boxer engine knock Subaru

Post by virgilmobile »

I guess I'm done.Replacing the plugs stopped the loud cold startup knock and has left me with...piston slap..Not much else to do but run it.

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Re: Boxer engine knock Subaru

Post by eklimek »

As good as it is going to get.

Ed

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Re: Boxer engine knock Subaru

Post by virgilmobile »

I think so.If I run to Walmart and back the knock is completely gone.I can only speculate that it's piston slap.With a 172k miles,it's just normal wear.I suppose I could yank the motor and short block it but it is just a $3000 car.Already dropped $500 in it.Dont think I'll rebuild the block.Probably be down for a month and another $1000 in parts.
Sheesh..my 96 Subaru ran flawlessly for over 250k miles.Different motor.

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Re: Boxer engine knock Subaru

Post by AZgl1800 »

I would buy some of the Old Engine Long Life oil for it and just go on.
that will help to take up some of the slack in the cylinders
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virgilmobile
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Re: Boxer engine knock Subaru

Post by virgilmobile »

It's annoying but as far as I can diagnose..not a engine killer.Might move to the delco 400 15-40 for the next oil change.



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