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That Guy
 
Techno Duck's Avatar
 
Join Date: Mar 2003
Location: San Diego, CA
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Check out my scored pistons and cylinders

About 15k on this split case rebuild which was done by a shop up in Northern California for the previous owner. New rings were installed on original pistons and cylinders. These are Alusil, Kolbenschmidt p&c's.

I put about 5k miles on after buying it; oil consumption was super high.. 1qt/500-600 miles. I did find the air flow meter was way of of whack.. clock spring tension was adjusted very tight so the car was running extremely lean.

Anyhow every piston is scored, 3 being really bad. 2 of the cylinders are really bad. My builder whom tore the engine down said it looked liked the rings never even seated.

Any theories on the cause of this?

New rings on old cylinders?
Overheating from running super lean?









Ive decided to split the case again and redo the entire engine, don't trust anything this other shop did. Still debating 3.2L or 3.4L. Jae at Mirage is building this one for me so it's in great hands.

Edit - apologies for the huge pictures, posted from my phone.
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Jon
1988 Granite Green 911 3.4L
2005 Arctic Silver 996 GT3
Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1
Old 10-04-2016, 01:57 PM
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Wow! Those are really scored. We're these original P&C's, or new?
Old 10-04-2016, 06:47 PM
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Re ringed alucil
Great cylinders to make 3.4 nikisil
Bruce
Old 10-04-2016, 07:21 PM
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That Guy
 
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Original p&c's as far as i know; ~167k miles on them.

Frankly I am surprised how well the car ran! And despite the huge oil consumption it wasn't really smoking much at all other than a little puff when coasting down in gear.

Decided to go 3.4L but will be using new Mahle p&c's. I'll sell the cylinders as cores to recoup some cost. The pistons will go on my wall of shame along with the blown 951 headgaskets and sacrificed ball joints to the autocross gods.
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Jon
1988 Granite Green 911 3.4L
2005 Arctic Silver 996 GT3
Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1
Old 10-04-2016, 07:59 PM
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If original pistons and cylinders, do you have any documentation of piston condition at time of the rebuild?
Old 10-04-2016, 09:55 PM
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Well i am only going to quote Wayne here as i dont pretend to have any real knowledge. When i rebuilt my engine the comment in the book was if they are alusil they were supposed to be one use only . you can not re-ring them so carefully take them out as a set do not seperate the piston from cylinder and put them on the shelf.
That is exactly what i did .. took them off, put them on the shelf , resealed my engine had head work done replaced the studs and then carefully put everything back .

After wards people said i was an idiot and i should have re-ringed the alusils. Looks like as Wayne pointed out, you just cant re-ring alusils, or if you do im sure you have to be super carefull with the seating of the rings.

Sad pics but thanks for sharing.
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Old 10-05-2016, 07:04 AM
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makes me happy i sent my cyl to get nik plated! I was about 80% sure i could throw them back on after taking the pistons out too.
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Old 10-05-2016, 12:03 PM
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Wait. Why don't those Pistons look like the typical KS Alusil brand.

Jon...are there any markings on them. They don't look stock to me.

I could understand the rings scratching the cylinders but not the Pistons. Maybe after market Pistons were used and caused this. Possible wrong material piston not compatible with Alusil cylinders.




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Old 10-05-2016, 04:59 PM
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Nikasil pistons in alusil cylinders?
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Old 10-05-2016, 05:25 PM
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That Guy
 
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Quote:
Originally Posted by fanaudical View Post
If original pistons and cylinders, do you have any documentation of piston condition at time of the rebuild?
No documentation other than the invoice and a few pictures the previous owner sent me before the case was put back together; nothing directly on the pistons or cylinders. I do have an invoice that showed a leakdown / compression test was done not long after the rebuild (forgot mileage, but it was within 1k or so) that showed all was good.

Prior to buying this car; the rebuilt engine actually made me a bit nervous, but it already had ~8k miles on it so i figured anything wrong probably would have popped up already. I did a lot of reading on the shop that did this rebuild and did not find anything bad, nor anything really good.. so decided to just go for it and take a chance.

Other than the quart of oil every 600 miles it ran pretty well. Live and learn! This is why i chose a shop with an excellent reputation to do the rebuild for me.. peace of mind goes a long way.

Quote:
Originally Posted by arbita1 View Post
Wait. Why don't those Pistons look like the typical KS Alusil brand.

Jon...are there any markings on them. They don't look stock to me.

I could understand the rings scratching the cylinders but not the Pistons. Maybe after market Pistons were used and caused this. Possible wrong material piston not compatible with Alusil cylinders.
Matt, i didn't check markings on the pistons but anything is possible. However I don't recall the invoice saying the pistons were changed during the rebuild. I wont be able to check for a few weeks.

Does anyone know if these look anything like euro pistons? I had a number of issues with this engine including detonation and an extremely lean AFR. Infact, even after getting the AFR into check i was still getting some detonation with the 911Chip... i swapped the stock chip back in and the detonation went away. I forgot to ask my builder if they were euro pistons, any keen eyes able to determine based on the piston dome shape?

Looking forward to getting the car back on the road, my builder estimated 5-6 weeks to complete with most of the wait being on the machine work. Hopefully it will be back together by mid November. The plan with this engine is to keep it single spark, pass smog and run on 91oct...plan is to keep this a street car / canyon carver but will do a few DE's and autocrosses...so nothing crazy as far as output. Will be using new Mahle 3.4L P&C's, builder said he wants to aim for 9.5:1CR to keep it safe, 964 cams and keeping the Motronic.
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1988 Granite Green 911 3.4L
2005 Arctic Silver 996 GT3
Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1

Last edited by Techno Duck; 10-05-2016 at 05:54 PM..
Old 10-05-2016, 05:50 PM
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My bad. I'm used to 3.0 pistons. I just looked at a picture and those look like KS pistons for a 3.2. They could be 9.5:1. But I think you need to look at the model number to confirm. Hard to tell by the dome alone. Is the scratching on both sides of the skirt or just one?
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Old 10-05-2016, 06:56 PM
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Hey Jon:

First, I am no expert but have rebuilt a couple 3.0L engines before.

Those oil rings look like factory to me, so question is: Did rebuilder actually change the rings out?
Alusil uses chrome rings if I am not mistaken.

Second, the first picture looks like the first ring land has a hole at the top. Is that true?

Only other thing that comes to my mind here is that maybe the rebuilder used the wrong type of rings for this KS P/C set.

Like I said, I am no expert so…just trying to help with some observations. I still remember your kindness when I was new to the 1987 944 side of things.

How is the rest of the engine? Did you find a lot of metal chips in the oil sump?
Does the rods show wear?

I must agree with you, however, this puppy needs a complete tear-down and new build done.

Good luck.
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Last edited by TibetanT; 10-07-2016 at 01:38 PM..
Old 10-07-2016, 01:33 PM
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That Guy
 
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Hi Ed, the invoice showed new rings were purchased; entirely possible the wrong rings were used though. My builder said everything else looked okay; most of my parts were being sent out this week for all associated machine work, so hopefully no surprises! Cost of this rebuild is starting to scare me a bit lol.. need to order a new clutch kit (mine was nearly down to the rivets) and need to find yet another oil tank. My existing tank had a pretty gnarly dent in the side so i bought a perfect used one on here. Sent it out for cleaning and was informed today this one is now dented also .
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Jon
1988 Granite Green 911 3.4L
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Past worth mentioning - 1987 924S, 1987 944, 1988 944T with 5.7L LS1
Old 10-07-2016, 04:41 PM
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It sort of looks to me like a ring seized, and it's not the top ring. If you measure down from the top of the cylinders to where the scratches begin, you may be able to determine if it's the 2nd compression ring or the oil control ring. I once saw something similar on a newly overhauled aircraft engine that was assembling with insufficient ring gaps. I'm also wondering if the ferric coating on the piston might have been worn off and this is some sort of galling between the Alusil and the aluminum piston, but that's just a SWAG.
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Old 10-07-2016, 05:38 PM
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Skirt wear like that is due to lack of lubrication (check squirters in case) or improper piston to cylinder clearance when fitting, or loss of cylinder coating causing galling by rings microwelding....that balls up aluminum from the cylinder on the skirt I believe. I would be tempted to check the ring gap of materials removed.
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Old 10-17-2016, 05:13 PM
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