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Alan L's Avatar
 
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Quote:
Originally Posted by bpu699 View Post
How would you know you have broken rings? If the leakdown is normal, can you assume the rings are fine?
I guess if you just have a broken recent ring, it may not show up - basically you have just moved the ring gap to somewhere else on the piston. As the ring slowly grinds itself to bits, it would open the gap up. Add a few more rings and something would start looking suspicious. That would be my guess how it would play out with leak down.
So it would possibly take more than a single recent ring break to become suspicious.
I have been running mine at 1 bar on track for about 7 yrs. I have lost count of times engine torn down for mods etc (3-5). Never had a broken ring. The boost alone won't do it. Keep the AFR and timing in spec and you should be good.
Regards
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 08-07-2017, 12:16 PM
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Quote:
Originally Posted by Tippy View Post
From reading here, no, unfortunately.

Some have had ok numbers but the rings were broken.
Then how do you know? The threads I read mention leaving the piston in the cylinder with a rebuild, so you don't disturb anything. If you "look" now you committed to new rings, honing, maybe pistons, and heaven forbid its Alusil---new pistons and cylinders...

Whats the harm to running with broken piston rings if leak down is fine? Cylinder scoring?
Old 08-07-2017, 01:22 PM
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Originally Posted by 16Volt View Post
Before my motor grenaded -
12psi of boost
Stock head bolts
Reground SC profile-ish cams
3LDZ
B&B Headers/Exhaust/Intercooler

I dynoed the car before badness happened it and it put 337hp to the wheels, with 100F+ intake temps before the intercooler.

Initially I thought I had just puked a turbo but before I put in a K27/K29 did a leak down, bad news. When I opened the motor I had a bunch of broken rings, this was likely my fault though.

New build adds:
Twin plug heads
SC-ish
crank fired ignition
knock sensing
RPM switch/adjustable WUR
EBC
K27/K29

I hope to run a bar safely but I am super paranoid I wont be able to fuel it. But I feel allot safer with a .5 WG spring, EBC and knock sensing regardless.
Why the damage? Sounds like you had low boost?

How does one add knock sensors? Can't find anyone selling this for a 930?
Old 08-07-2017, 01:23 PM
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Quote:
Originally Posted by Alan L View Post
I guess if you just have a broken recent ring, it may not show up - basically you have just moved the ring gap to somewhere else on the piston. As the ring slowly grinds itself to bits, it would open the gap up. Add a few more rings and something would start looking suspicious. That would be my guess how it would play out with leak down.
So it would possibly take more than a single recent ring break to become suspicious.
I have been running mine at 1 bar on track for about 7 yrs. I have lost count of times engine torn down for mods etc (3-5). Never had a broken ring. The boost alone won't do it. Keep the AFR and timing in spec and you should be good.
Regards
Alan
Alan, did you simply reuse the rings after each rebuild? Can you peak at the rings, and if fine, put it all back together???

I am starting to understand this slippery slope thing...

I see rings for sale for $200 for a set, and $1000+ for a set...

If you put the best of everything on a motor, you an easily spent $15-20k on just parts!!!
Old 08-07-2017, 01:26 PM
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You can re insert your pistons if you pull them out, with the old rings. The rings move around a lot. I once pulled the engine down after about 2 short runs from a rebuild (ie about 30mins running). The rings had moved all over the place from where they had been set. I posted a pic somewhere on this forum - of before/after.
The issue with running with known broken (or unknown) rings is they eventually damage the piston and the bore. If you search enough threads you will find pics.
If you don't have reason to suspect any ring damage, you can extract the cylinders and pistons intact - ie leave them as a unit.
Regards
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 08-07-2017, 01:48 PM
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Alternatively - if the ring land gap is in spec and the current ring wear warrants it (ring gap) you can re ring the piston (since you have it apart). I just used the scotch brite hone method (you will find plenty of threads in the 911 engine forum). Never had an issue with them seating OK. Word of caution - many of the new ring sets seem to end up with a ring gap already at the high end of wear spec. Don't ask me why. But if they are nicely within spec, maybe best left.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 08-07-2017, 01:53 PM
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Quote:
Originally Posted by bpu699 View Post
Why the damage? Sounds like you had low boost?

How does one add knock sensors? Can't find anyone selling this for a 930?
The 3LDZ gave up the ghost initially, but before proceeding a leakdown showed a pretty bad cyl (there is a thread here somewhere I started).

I believe that the car was running more than 1.2bar in most street situations. I think this for a couple reasons -

1. The car usually would bang off overboost switch. When it was on the dyno the IATs were so high I think that that's why it was only seeing 12psi.
2. The TiAL the PO was running had two red springs, while that should equate to 1bar it does not account for the headers. TiAL wants you to run .2 or so lower than your target boost level if running running headers/free flowing exhaust.

There are a few different options for adding knock sensing. Now this is my opinion, but if you want to be safe and run higher boost levels, go to stand-alone. Do not pass go.

Now you can also go the route I chose (which I am already regretting and the car hasnt even started for the first time) and thats an XDI-2 system to handle ignition.

JS also I believe also makes a add-on system which can be used on a 930.
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Old 08-07-2017, 03:22 PM
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Quote:
Originally Posted by Alan L View Post
Alternatively - if the ring land gap is in spec and the current ring wear warrants it (ring gap) you can re ring the piston (since you have it apart). I just used the scotch brite hone method (you will find plenty of threads in the 911 engine forum). Never had an issue with them seating OK. Word of caution - many of the new ring sets seem to end up with a ring gap already at the high end of wear spec. Don't ask me why. But if they are nicely within spec, maybe best left.
Alan
Plan to disassemble long block Friday...

Need to see if I have Alusil or nikasil from what I gather...

Appreciate all the advice...
Old 08-07-2017, 04:33 PM
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Originally Posted by 16Volt View Post
The 3LDZ gave up the ghost initially, but before proceeding a leakdown showed a pretty bad cyl (there is a thread here somewhere I started).

I believe that the car was running more than 1.2bar in most street situations. I think this for a couple reasons -

1. The car usually would bang off overboost switch. When it was on the dyno the IATs were so high I think that that's why it was only seeing 12psi.
2. The TiAL the PO was running had two red springs, while that should equate to 1bar it does not account for the headers. TiAL wants you to run .2 or so lower than your target boost level if running running headers/free flowing exhaust.

There are a few different options for adding knock sensing. Now this is my opinion, but if you want to be safe and run higher boost levels, go to stand-alone. Do not pass go.

Now you can also go the route I chose (which I am already regretting and the car hasnt even started for the first time) and thats an XDI-2 system to handle ignition.

JS also I believe also makes a add-on system which can be used on a 930.
Sorry to hear...

Will look into that...
Old 08-07-2017, 04:35 PM
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dont worry about it unless you have running problems or have run extremely hi boost, but even then i would not worry too much.
if compression and leak down are good just keep driving it.

sorry, did not mean to worry you. like i said, lots of guys have broken rings and dont know until they pull a piston.
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Old 08-08-2017, 05:32 AM
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Originally Posted by T77911S View Post
sorry, did not mean to worry you. like i said, lots of guys have broken rings and dont know until they pull a piston.
QFT

I think I may have done in a couple of the rings but I firmly believe that some of them had been busted for along time. My car passed a comp/leakdown in the PPI with no issues. The cylinder with the low comp/leakdown we found was the only one which had a compression ring busted.

Bench testing the wastegate showed it was opening around 26psi fwiw.

There were zero issues with my ring lands when I pull the pistons and likewise with the cylinders.
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Old 08-08-2017, 06:40 AM
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Originally Posted by bpu699 View Post
Plan to disassemble long block Friday...

Need to see if I have Alusil or nikasil from what I gather...

Appreciate all the advice...
You have nikasil. 930s only had nikasil cylinders, never alusil.

Of course the pistons may be removed from their cylinders for inspection. What is important when re-using parts is to keep each cylinder+piston+pin assembly together, i.e. do not put piston #2 into cylinder #4. Use new pin circlips when reassembling.
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Old 08-08-2017, 11:35 AM
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Bigger fuel lines would be a plus with your usual bolt ons and a 1bar
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Last edited by speednme1; 08-09-2017 at 08:08 PM..
Old 08-08-2017, 02:05 PM
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Originally Posted by TurboKraft View Post
You have nikasil. 930s only had nikasil cylinders, never alusil.

Of course the pistons may be removed from their cylinders for inspection. What is important when re-using parts is to keep each cylinder+piston+pin assembly together, i.e. do not put piston #2 into cylinder #4. Use new pin circlips when reassembling.
You guys are making my day... so far everything is going my way

Silly question, maybe...

Any point in lapping the valves? Hate to rebuild the heads as reportedly done by po. I have a couple cylinders I have to look at as there is buildup on the exhaust valves...

Would lapping the valves get the leak down better by 3-4 %? Would a 7% leak down get better? It looks like it's carbon buildup...

I assume lapping the valves doesn't damage anything...

Otherwise, can you just rebuild a couple heads, and leave the others?

Trying really hard not to end up with a complete rebuild...
Old 08-08-2017, 06:06 PM
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Any good automotive machine shop has a vacuum tool that measures leakage past the valves. When these are done right, it's 0-1%.
If numbers are higher, and it's got very low miles since last time the heads were off, maybe just lap the valves. Your machine shop would know for certain when the valves are out if they can get by with just lapping, or if cutting is also needed.
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Old 08-08-2017, 06:41 PM
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