cracked piston WDIDW

[gorskined]

anyone have a useable 3.0l turbo piston for sale
Recap
Long time, old school 356 and 911 guy. over the years i have rebuilt a 1/2 dozen 356 and 911 non turbo motors .. This is my first turbo and haven't had a 911 apart in 25 years,. i followed How to Rebuild and Modify Porsche 911 Engines
by Wayne R. Dempsey as a guide, found it very helpful learned a few new tricks ...
it appears piston #1 is cracked . hard to believe as there is so much clearance in the 76 turbo motor 6.5 to1 flat top piston .....when going back together everything checked out, i triple checked everything so.
im thinking 1 of 3 things possibly

#1 an issue with my connecting rods when I had my connecting rods end balanced a rod came back with quite a bit of material taken off the small end . I questioned it they assured me it was correct and would not effect the operation . ill post a picture below. now that i found the picture i can see it was cylinder #4 that had the replacement connecting rod that had to be shaved down to balance.

#2 all my old 911 builds were pre Carrera oil feed tensioners. the motor came with a unused Carrera tensioner up grade kit still in the package . so i used them.... looking back probably not a smart thing, as they were 20+ years old ... i should have purchased new tensioners seeing as the car was put a way 20 years ago due to broken stud issues . i bleed the tensioners prior to install and everything held tight. could the tensioner be bleeding down at rest and when first starting possibly be sloppy ??? intermittently throwing my cam timing off?

#3 possibly a over boost issue or to lean, The motor ran less than 5 minutes total mostly at idle with a few quick blurbs to check the distributor advance . tattle tale says 4200rpms and 12psi max. it did sound great though when it was running.

none the less according to the borescope the piston looks to be cracked across the center not along the edges . ill know more once i get the motor apart. would love to hear your thoughts.. like the old saying knowledge is power .. so what did i do wrong?? my money is on a partial tensioner failure .

Regards Ned

[gorskined]

[gorskined]

[gorskined]

[img]http://forums.pelicanparts.com/uploads26/Photo_202111081655411636467474.jpg[/img

[infraredcalvin]

What prompted you to check? You said everything sounded great…. Noises, loss of compression? This looks and sounds strange to me. Looks like a lot of carbon buildup for 5 min of operation, could just be the lighting.

I’m no expert, but I’ve seen enough old pistons that have “crack like” features on/in the carbon layer, not the actual piston…thats what this looks like…

[Restore_84]

Not sure if these will work for you but I have a used set of 3.3 pistons in good shape I’ll sell you real cheap to help you out.

[pkabush]

Originally Posted by infraredcalvin

What prompted you to check? You said everything sounded great…. Noises, loss of compression? This looks and sounds strange to me. Looks like a lot of carbon buildup for 5 min of operation, could just be the lighting.

I’m no expert, but I’ve seen enough old pistons that have “crack like” features on/in the carbon layer, not the actual piston…thats what this looks like…

My thoughts as well.
Also wondering what prompted you to look into it. Keep us posted.

[gorskined]

The motor sounded and ran great for the 5 minutes i had it running while setting the timing then started running rough, so i shut it down and called it quits for the night. The next night i went to start it heard a clunking. The same clunk i thought i may have heard days earlier when i was first trying to start the motor but the first time it only lasted one or two engine cycles then was gone i wasn't even sure it was a clunk. i pulled all the plugs to check compression as i wasn't sure why it wouldn't start between 105 and 100 across all the cylinders cold. sounds low but normal for a cold un run engine not to mention the compression is only 6.5 to 1... FYI the motor did start because i was off a tooth once i corrected that it fired right up
after the second series of clunks9 previously mentioned while setting the timing that caused the engine to run awful . i removed all the plugs to take another compression test it sounded awful definitely a clunk, so i stopped and started turning over by hand that's when i felt a hard spot . at the top stroke on cylinder #1. like a valve is hitting the piston its there on the power stroke as well as the exhaust stroke . so most likely now a bent valve barely touching the piston .......
car is up, engine is out, motor is on the bench, removing the tins, the rear plumbing and the exhaust cross over. Hopefully tonight i should have it on the engine stand with timing and valve covers off. its amazing the amount of stuff crammed on a turbo motor compared to a non turbo motor. and the best part nothing is easily accessible.

Regards Ned

[gorskined]

Originally Posted by Restore_84

Not sure if these will work for you but I have a used set of 3.3 pistons in good shape I’ll sell you real cheap to help you out.

thanks for the offer but those are a little to big 97mm i need a 95mm . i may have to buy a new set of p&c

Regards Ned

[JJK78-951]

I've got a good set - PM sent~
John

[krasuskyp]

Great chatting w/ you yest Ned - keep us posted on your findings.

I'll reiterate tho with hopes of maybe others offering guidance that you rebuild the 3.0l for sale and fit a less stratosphereically valuable 3.3l instead .

Guidance from the peanut gallery on how to best rebuild then market a motor for sale but being John Q. Pubic and not a reputable build joint.

LMK when you want to grab a bev of your choice & talk shop - either here / there!

[Ollies930]

Unless I am mistaken, I believe all the Mahle 3.0 95mm pistons have the same shape underneath and only differ on top. Might be difficult to find a single 3.0 turbo piston, but any decent 95mm SC piston should work with a little bit of machining to the dome. Might want to call Henry @ Supertec, with his stock of used parts and a full machine shop, he would probably have no problem getting you sorted. For that matter, he may even have a turbo piston.

[356911930]

Ned,

Sorry to hear about your engine issues. Hopefully it is nothing more than one piston! I was thinking it could also be that a piston pin retaining clip has migrated and the pin has slipped out of one side of the piston. Looking forward to yuo fixing this and getting your Porsche back on the road soon.

Best of luck,

Rahl

[pkabush]

Originally Posted by gorskined

The motor sounded and ran great for the 5 minutes i had it running while setting the timing then started running rough, so i shut it down and called it quits for the night. The next night i went to start it heard a clunking. The same clunk i thought i may have heard days earlier when i was first trying to start the motor but the first time it only lasted one or two engine cycles then was gone i wasn't even sure it was a clunk. i pulled all the plugs to check compression as i wasn't sure why it wouldn't start between 105 and 100 across all the cylinders cold. sounds low but normal for a cold un run engine not to mention the compression is only 6.5 to 1... FYI the motor did start because i was off a tooth once i corrected that it fired right up
after the second series of clunks9 previously mentioned while setting the timing that caused the engine to run awful . i removed all the plugs to take another compression test it sounded awful definitely a clunk, so i stopped and started turning over by hand that's when i felt a hard spot . at the top stroke on cylinder #1. like a valve is hitting the piston its there on the power stroke as well as the exhaust stroke . so most likely now a bent valve barely touching the piston .......
car is up, engine is out, motor is on the bench, removing the tins, the rear plumbing and the exhaust cross over. Hopefully tonight i should have it on the engine stand with timing and valve covers off. its amazing the amount of stuff crammed on a turbo motor compared to a non turbo motor. and the best part nothing is easily accessible.

Regards Ned

That doesn’t sound good. Sorry to hear.

[mark houghton]

Originally Posted by gorskined

#3 possibly a over boost issue or to lean, The motor ran less than 5 minutes total mostly at idle with a few quick blurbs to check the distributor advance . tattle tale says 4200rpms and 12psi max. it did sound great though when it was running.

This part has me scratching my head. Doesn't sound as if you actually drove the car under load, just did the normal checks sitting in the shop. So, how were you able to get 12psi boost? (The problem with the written word is often the interpretation by the reader).

Anyway, with your other comments re: clunking noises....oh boy....that to me sounds like cam/valve timing resulting in valve(s) crashing into piston crowns. I've only a couple times torn down a 911 (my old '73 Targa) due to tensioner failure, causing said damage, so by no means am I an expert. It's been over 30 years since I've gone that deep into an engine.

Guess you'll be fining out soon once you pull things apart again. Good luck, hope for the best.

[gorskined]

Originally Posted by mark houghton

This part has me scratching my head. Doesn't sound as if you actually drove the car under load, just did the normal checks sitting in the shop. So, how were you able to get 12psi boost? (The problem with the written word is often the interpretation by the reader).

Anyway, with your other comments re: clunking noises....oh boy....that to me sounds like cam/valve timing resulting in valve(s) crashing into piston crowns. I've only a couple times torn down a 911 (my old '73 Targa) due to tensioner failure, causing said damage, so by no means am I an expert. It's been over 30 years since I've gone that deep into an engine.

Guess you'll be fining out soon once you pull things apart again. Good luck, hope for the best.

correct i should have been a little clearer i have not driven the car according to the portable digital gauge i put on my intercooler the pressure has never surpassed 12lbs at the intercooler, not throttle body pressure . so i would think the actual pressure after the throttle body would be very low. again first turbo I've worked on still a little fuzzy with the entire turbo thing and how it works. still don't understand where the vacuum comes from if the entire intake is under pressure.

[flightlead404]

Originally Posted by gorskined

correct i should have been a little clearer i have not driven the car according to the portable digital gauge i put on my intercooler the pressure has never surpassed 12lbs at the intercooler, not throttle body pressure . so i would think the actual pressure after the throttle body would be very low. again first turbo I've worked on still a little fuzzy with the entire turbo thing and how it works. still don't understand where the vacuum comes from if the entire intake is under pressure.

Sure that's not 12 psi absolute? vs 12 psi boost. ie that would be a vacuum of 2.7 psi.

[gorskined]

Originally Posted by flightlead404

Sure that's not 12 psi absolute? vs 12 psi boost. ie that would be a vacuum of 2.7 psi.

defiantly 12 psi boost, 100 percent sure as the intercooler has a extra 19mm take off with a cap that was loose.. needles to say it went shoothing across the garage. when i fist started the motor . reminded me of one of those old school cork guns .. im running a k27 with a raptor mod from evergreen turbo. it start to build boost around 2700 rpms.

[dos531]

Originally Posted by gorskined

defiantly 12 psi boost, 100 percent sure as the intercooler has a extra 19mm take off with a cap that was loose.. needles to say it went shoothing across the garage. when i fist started the motor . reminded me of one of those old school cork guns .. im running a k27 with a raptor mod from evergreen turbo. it start to build boost around 2700 rpms.

Its pretty difficult to hit 12psi with no load on the engine.

[pkabush]

Originally Posted by dos531

Its pretty difficult to hit 12psi with no load on the engine.

Agreed. I can’t see 12# without load.