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Old 03-07-2009, 09:16 AM   #1
pwmc86
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Question Engine problems after rebulid.

i recently had my engine rebulit 2002 sti wrx engine. I had the block bored and honed to 93mm, I replaced all bearings and gaskets. I replaced the pistons with Arais forged pistons! When I first started it the engine. It sounded like a diesel. Even when warm so i pulled the engine down and sent the crank and rods to be mesured. they were fine. I decided to replace the bearings once again with super high preformance bearings. When i put it back together again I started it and same problem. I have taken the car to sevral mechanics and they said it sounded like piston slap. So i took it back to the engine bulider he said it dident sound like the pistons, and not to worry unless it gets worse (the sound was much worse when could but was still very obvious when the engine was hot, but not as bad). Well it got worse so. I have removed the heads and inspected the bore. I relized in every bore there are very light scratches that are only on the top and bottom of the bore and start about 2-3cm down the bore and some go most of the way down the bore, I am not sure if this is a sign of piston slap. when i run my finger across the scratches i can not feel them! but i can see them under a bright light!. Any help would be greatly apreciated. Cheers Paul
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Old 03-07-2009, 11:19 AM   #2
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Did you assemble the engine, or did the machine shop? If you did, did you check every measurement, especially the bore size and the piston size? Blueprinting the engine to make sure the tolerances are correct is VITAL. You can also use a feeler gauge, by sliding it between the piston and the cylinder wall, to check on piston-to-wall clearances. Verify these measurements with your Subaru mechanics manual. Sounds to me like the tolerances aren't tight enough. Just take the measurements and it should answer your question.

Dave
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Old 03-07-2009, 11:20 AM   #3
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That sound is characteristic of piston slap, me thinks the engine builder used pistons that are the incorrect diameter for the over bore, and the fact that he told you its nothing to worry about sounds sketchy, any warranty on the work? Forged pistons also tend to make more noise than stock ones. I'm not an expert by any means, but this is just my 2 cents
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Old 03-07-2009, 12:06 PM   #4
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did you take any pics of the bore scratches? just from the post it sounds like a loose bore.. post the pics if you have any, that would help a lot.
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Old 03-07-2009, 12:45 PM   #5
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wrong something

rings or pistons or ???
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Old 03-07-2009, 12:48 PM   #6
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I don't think I've actually heard a quiet built engine. they do seem to have a characteristic tic.

Did you use the correct valve pucks? maybe your lifters are noisy.
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Old 03-08-2009, 12:28 AM   #7
pwmc86
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Question pics of the cyl 2 and 4

PIC OF CYL2




PICS OF THE CYL 4



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Old 03-08-2009, 03:20 AM   #8
pwmc86
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Question Correction

It seem as if the piston is just draging on the bottom of the cyl's.

The tolerances are real tight on the bottom side of the piston yet real loose on the top side, infact soo lose i can see the compression ring (see Photo's). why do pistons drag up and down one side, is it gravity? how do i correct the problem. and yes i rebulit the engine. i did check the clearences and quired them with the engine bulider (which i am now thinking is a engine reconditionare). He said they are the right pistons and the block has been bored to suite those pistons! I purched the pistons form the engine bulider before he bored the block to suite! Where to from hear? thank you guys so much for your help . Cheers Paul











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Old 03-08-2009, 04:15 AM   #9
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I am no expert, but the third pic from the bottom, those gaps look like your have the wrong size pistons. I'm sure that if you flip the motor over, the pistons would fall to the other side of the cylinder.

You don't need a feeler gauge, cause you can see the gaps clear as day. Plus, the largest size feeler guage will easily fit between the piston and wall.

Can you wiggle all the pistons around in the cylinder(from top to bottom), and do any of the gaps look differnt?

Those "mechanics marks" are not looking good either... you need a clean surface or else you may have headgasket issues.

Curious to see how this turns out.

Last edited by paintbing; 03-08-2009 at 04:30 AM.
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Old 03-08-2009, 04:23 AM   #10
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did your machinist use a decking plate when he bored out the block? Subaru engines are notorious for going out of round when boring or honing without the proper deck plate as it will tend to distort or go out of round. That could have been the cause of the various measurments of the block from top to bottom.
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Old 03-08-2009, 04:24 AM   #11
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sorry its called a decking plate or a torque plate. To simulate the head being torqued to factory specs or to ARP specs if your using them when boring the block
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Old 03-08-2009, 08:18 AM   #12
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Exclamation Is this normal?

Is this normal?
http://www.youtube.com/watch?v=RQX1evTbgkQ

i made this video!


i have no idea if he used a torque plate!

Thanks Again guys!
Paul
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Old 03-08-2009, 01:11 PM   #13
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damn it definately seems like either your builder overbored it too much, or that your pistons are the incorrect size. put a bore gauge in there and measure the bore then pull a piston and measure it again. i've never seen pistons so loose like that before in the cylinder
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Old 03-08-2009, 05:43 PM   #14
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take your block to another machine shop or engine specialist to get a second opinion.

Not too familiar with the area but have you tried Performance wholesale?

http://www.performancewholesale.com.au/index.asp good luck
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Old 03-08-2009, 07:22 PM   #15
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Default Hey Pal

Quote:
Originally Posted by pwmc86 View Post
Is this normal?
http://www.youtube.com/watch?v=RQX1evTbgkQ


i made this video!


i have no idea if he used a torque plate!

Thanks Again guys!
Paul
That motor has to come back out for sure, that is not normal for the piston to move around like that and make that noise! Your engine builder should be slapped for telling you that " slapping noise " is normal, take your motor to another builder and get another opinion, the piston is either wrong, but I think it was bored incorrectly! Good luck and keep us up-todate.
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Old 03-09-2009, 08:38 AM   #16
pwmc86
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Question update

Talked to the engine builder and he said high performance pistons fail regally. I have pulled a piston and measured it here are the picks and measurements. also I was looking at another post on nasioc where a
User "
SubyDuz
Scooby Specialist"
said "ARIAS pistons are horrible...I have had two motors assembled with Arias pistons and both times the motors failed. cause was the pistons, once they went egg shaped...I highly highly caution against arias pistons. This was just my experiance...so take it as it is

Motor now has CP pistons and hasn't had a hick up, nothing else changed by the way....nothing".

maybe this is what i am experxing!






















light scratvhes on the side of the piston.



the old piston and the new piston


[FONT='Verdana','sans-serif']Bore was finished to 3.662[/font]
[FONT='Verdana','sans-serif'] [/font]
[FONT='Verdana','sans-serif']so 3.662 - 3.655 =0.007 clearance! recommended is 0.005 and this is the highest point on the piston Picture 2[/font]
[FONT='Verdana','sans-serif'] [/font]
[FONT='Verdana','sans-serif']worse is 3.662 - 3.653 = 0.009 Clearance![/font]

Last edited by pwmc86; 03-09-2009 at 08:41 AM. Reason: spelling
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Old 03-09-2009, 10:30 AM   #17
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Once I switched to CP and/or JE pistons....never a problem....lasted 20,000 thousand miles....I wouldn't waste your time just get something else
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Old 03-09-2009, 04:17 PM   #18
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Hey Ivan, Were the Arias pistons the ones that grenaded when you were racing Jon's 'wedding rental'?
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Old 03-22-2009, 08:45 PM   #19
pwmc86
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News Update

The engine builder is sending the pistons back to arias.

In the meantime i have talked to another engine builder he said he has had a similar problem on a ej20. he said whehn they overheat (which mine has never done. well at least while i have owned it). the block will warp and when you take them apart and put them back together they don't seat properly generating excessive clearances in the main bearings! is this possible? Has anyone had this happen to them?

THANKS AGAIN

CHEERS PAUL
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Old 03-24-2009, 03:50 PM   #20
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you would be hard pressed to find main bearing clearances having a direct correlation to the piston being too small for the cylinder.
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Old 06-07-2009, 03:46 AM   #21
pwmc86
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Hi Everyone,
------Problem Solved-------- the engine builder measured the piston from the bottom of the skirt when he bored the block. In the specs sheet it says to measure 1.1inch below the oil ring witch is directly opposite the wrist pin. he has since provided me with a new block and bored honed and fitted new pistons. and no cost.

Thank you all for your contribution. i hope someone else can use this post to help solve any similar problems.

Cheers Paul
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