need opinions please - are my cylinders shot?

[gssereik]

I need some help, please, to assess the condition of the head sealing surface of the original KS alusil cylinders from my 83 SC engine...

The engine of my SC targa is currently on an engine stand in my garage. I have just installed new steel Head Studs to replace all of the dilaver studs, eight of which were snapped. This is the first time the heads were ever removed from this engine. Before I tackle the re-assembly, the only concern I have is whether or not the cylinder to head sealing surface will be adequate. Unfortunately, the broken head studs caused the heads to beat against the lower edge of some of the cylinders. I have reached out to CGARR on this forum for his help to assess the condition of my heads. But I am not sure what I should do with my cylinders. Three or four of the cylinders have obvious damage to the head sealing surface. See below picture of the worst of them (this happens to be cylinder #5). My SC engine, of course, uses sealing rings. Most of the original sealing rings were banged up and broken at their lower edge but the area of each cylinder BENEATH the sealing ring seems to be in good shape. Also, the metal circle INSIDE of the sealing ring does not seem to be damaged in any of these cylinders. All of the damage seems to be focused on the metal circle that is OUTSIDE of the sealing ring. Essentially, the inner 2/3rds of the cylinder sealing surface appears (to me) to be OK. But the outer 1/3rd of the sealing surface is damaged.

Bottom line... Based on what you see in the below picture and what I have described, might i be able to re-use these cylinders? They are in good shape otherwise.

thank you,
George

[gled49]

Polish up your bank card and go shopping for new P&C’s, sorry for your loss.

[Henry Schmidt]

Originally Posted by gssereik

Bottom line... Based on what you see in the below picture and what I have described, might i be able to re-use these cylinders? They are in good shape otherwise.

thank you,
George

Based on that single cylinder, you will need at least one. If you can source one, to make a good set, you can have those cylinder Nilasil coated to produce a nice "new" set. At that point you will need to source a new set of pistons compatible with Nikasil.
You can buy new set of various specs.
Or you might consider this option:

https://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/1030224-remanufactured-911sc-3-1l-pistons-cylinders.html

[faapgar]

The head gaskets for SC have a spring wire that gets compressed with torque.When studs break and the head becomes loose the head gasket disintegrates and the spring wire is forced out and makes those marks on the cylinder.Ciao Fred

[Richey]

Maybe Ollies can remachine the cylinder grooves and provide thicker base gaskets . If not , new P's & C's . This is why you should have stopped driving the car when you heard an unusual banging sound under acceleration .

[Walt Fricke]

A good machine shop can do almost anything, but at a price. My guess is that the cost of milling the sealing surface down past the damaged area, then recutting the groove for the metal gasket, and then milling the top of the fins (at a guess all of the boss around the stud hole would have to be removed), and then using a quite thick base gasket would be more than sourcing a good used cylinder. And keeping dimensions stock is valuable long run.

You say this (and by inference the other five) cylinder is otherwise in good shape. Did you use a bore gauge on it? It has been around rather a long time if original to the car. Worn bores can be brought back to size (at a cost usually less than getting new ones), but if yours are Alusil, it is the Nikasil Henry mentions which means you can't reuse your designed for Alusil pistons, as we are told you can't mix the two.

[Trackrash]

IF your 3 good cylinders ARE IN SPEC, and you can find 3 IN SPEC matching good condition cylinders then you are good to go and VERY LUCKY.

[Henry Schmidt]

I see a lot of optimistic posts but what you have a Alusil cylinders.
If you get lucky enough to find matching piston and cylinder combos your chance of success is only slightly improved. Re-ringing Alusil is a gamble at best.
Find yourself another set of Ps&Cs that fit your budget and forgo the thoughts of saving seriously damaged cylinders.

[burgermeister]

I am always trying to learn, so pardon my insolence ... I grew up in Germany, and the Sesame Street theme song's refrain is, coarsely translated, 'why, why, why - who doesn't ask stays stupid'

There are a lot of "they are junk" comments. *Why* are they junk? What function can the cylinders no longer perform?
I get the pitfalls of reusing old Alusils, having done so - though they did work just fine, excepting the 1 quart / 1500 mile oil consumption. But why would those cylinders no longer seal?

[gssereik]

Jumping off of burgermeister’s post... I am close to making the decision to bite the bullet to replace these p&c’s but I want to give reusing these alisil’s serious consideration. 127k gently driven miles. I would Not re-ring them as has been generally advised for allusils. I will expect 1 quart per 1500 mile oil consumption, or possibly more. I’ve measured th barrels which are still round and within spec. Inside barrel surfaces are smooth and not damaged. And 2/3rds of the head sealing surface appears to me to be in good shape (using new central sealing rings as required for these cylinders and new head studs holding them tight. Would it be folly to think these cylinders might seal ok? I am doing the work myself and would be just my time (and shame) to pull the engine again and swap out these p&c’s if they leak.
I really appreciate everyone’s input. Thank you for your advice, for or against

George

[dannobee]

Another option is to use 3.2L cylinders and source a set of pistons. 3.2L engines seal with a taper and don't use the springy "head gasket."

You can't use 3.2L pistons in a 3.0L because the piston pin is a different diameter and the compression height is different.

[Henry Schmidt]

The head gasket in early versions of the 911 cylinder is/was not designed to seal in compression gasses. It's purpose is to prevent oil seepage do to expansion differentials. If the metal surfaces surrounding the sealing ring a damaged, compression control will be compromised.

As for trying to reuse high mileage Alusil cylinders: When attempting to reinstall pistons in used cylinders, installing new rings is generally the rule. New rings should have a de-glazed surface with cross-hatched honing to promote proper break-in.
Honing Alusil properly is not an easy proposition but even if you can, you would need to source the proper rings for an Alusil cylinder. To my knowledge, that ring set is no long available.
Reuse Alusil: you roll the dice and take your chances.

[burgermeister]

Originally Posted by Henry Schmidt

The head gasket in early versions of the 911 cylinder is/was not designed to seal in compression gasses. It's purpose is to prevent oil seepage do to expansion differentials. If the metal surfaces surrounding the sealing ring a damaged, compression control will be compromised.

Thanks Henry! I did not understand that the sealing ring was not for combustion pressure. I am now a little bit smarter than when I woke up this morning!

[gssereik]

Ha! I am getting smarter too!! Thank you, Henry, for helping me understand the actual role of the seal ring. It seems to me that that the entire metal surface (both inside and outside of the seal ring) is important to hold in the combustion pressure. I am now back on the track of either trying to find used alusil cylinder replacements (looks like I need four of them, frankly) or swapping out my p&c’s entirely for something else. I appreciate everyone’s help and advice.

[ahh911]

Originally Posted by Henry Schmidt

The head gasket in early versions of the 911 cylinder is/was not designed to seal in compression gasses. It's purpose is to prevent oil seepage do to expansion differentials. If the metal surfaces surrounding the sealing ring a damaged, compression control will be compromised.

As for trying to reuse high mileage Alusil cylinders: When attempting to reinstall pistons in used cylinders, installing new rings is generally the rule. New rings should have a de-glazed surface with cross-hatched honing to promote proper break-in.
Honing Alusil properly is not an easy proposition but even if you can, you would need to source the proper rings for an Alusil cylinder. To my knowledge, that ring set is no long available.
Reuse Alusil: you roll the dice and take your chances.

Henry,
He hasn't removed the pistons yet from the cylinders, and even so, sure it's a gamble, but keeping them together or re-using the rings is not the worst gamble is it? I've read of many people re-using the alusil cylinder and rings without excess oil consumption.

Also, if the gasket ring doesn't prevent combustion sealing, that would infer that the outer portion of the cylinder that is damaged is not the critical sealing surface, but rather the inner mating surface is what's important? When I blued the sealing surfaces and mated the heads to the top of the cylinders by hand, the inner section was well mated, the outer section had gaps in the 1/2 thou range, these were all the cylinders mated to the heads that had been trimmed nicely, some a little worse than others and yes without tightening down, but it seemed the inner sealing portion was the more critical, don't you agree? I ended up using a dial indicator and shaving down the cylinder evenly and for all cylinders on a bank to the same heights, but thought it unnessecary. Of course the head may wobble on the cylinder looking at the op post, but would that be a judgement call, sure looks beaten though.


Phil

[Henry Schmidt]

Originally Posted by ahh911

Henry,
He hasn't removed the pistons yet from the cylinders, and even so, sure it's a gamble, but keeping them together or re-using the rings is not the worst gamble is it? I've read of many people re-using the alusil cylinder and rings without excess oil consumption.

Also, if the gasket ring doesn't prevent combustion sealing, that would infer that the outer portion of the cylinder that is damaged is not the critical sealing surface, but rather the inner mating surface is what's important? When I blued the sealing surfaces and mated the heads to the top of the cylinders by hand, the inner section was well mated, the outer section had gaps in the 1/2 thou range, these were all the cylinders mated to the heads that had been trimmed nicely, some a little worse than others and yes without tightening down, but it seemed the inner sealing portion was the more critical, don't you agree? I ended up using a dial indicator and shaving down the cylinder evenly and for all cylinders on a bank to the same heights, but thought it unnessecary. Of course the head may wobble on the cylinder looking at the op post, but would that be a judgement call, sure looks beaten though.


Phil

This entire post look like an attempt to justify your own personal decision. For you, perhaps it was...who knows?

My decision making process requires that I give the best possible solutions to the dilemma presented based on decades of experience.
Both inner and outer surfaces offer sealing and cylinder to head joint stability.
The thought of reusing a piston and cylinder package with high mileage without at least new rings is abhorrent to me. But hey, everyone seeks a different level of craftsmanship.

[ahh911]

Originally Posted by Henry Schmidt

This entire post look like an attempt to justify your own personal decision. For you, perhaps it was...who knows?

My decision making process requires that I give the best possible solutions to the dilemma presented based on decades of experience.
Both inner and outer surfaces offer sealing and cylinder to head joint stability.
The thought of reusing a piston and cylinder package with high mileage without at least new rings is abhorrent to me. But hey, everyone seeks a different level of craftsmanship.

Thanks, I thought the outer edge would add stability.

Once you've taken apart your engine and have done all the other work, removing it and accessing the rings later in time is a three day job at home, re-installing is another 3 days, don't replace your rings unless you are going to sell the car, have smoke out that back, or don't ever want to open up again, then but with alusil does it get tricky? Remember, the exhaust nuts will all come free easily the next time if necessary, the head assembly with carrier can be removed easily, you have the techniques, it's well worth the risk unless you think your rings are damaged. For a 911 sc that you work on yourself, get a cylinder with matching height code or a set, whatever they suggest, if not whatever, it's run for years without a gasket and headstuds, so... let's not get dramatic, you could probably shove it back together and get another 50k miles with new headstuds, and what the heck, you can replace the cylinders and rings in another year if it's gone wrong, it's not difficult once you've spent the time once. Make sure not to shave off the inner lip to match the outer as the spec for the cylinder is in Bentley and you'd blow right past that, I think it's less than 1 thou. I've seen the crap people sell you, so replacing the cylinder might be more work than it's worth. I'd be less worried about replacing the rings then the cylinder profile if it's been wobbling about.
Phil

Besides, what happens a couple years down the line when you want to upgrade the engine for more performance? If it's your only 911, take it slow and easy and run a little risk, then in a few years after you may like the car so much and swap in some major mods including new cylinders with bore/stroke of your liking.

[Henry Schmidt]

Originally Posted by ahh911

Thanks, I thought the outer edge would add stability.

Once you've taken apart your engine and have done all the other work, removing it and accessing the rings later in time is a three day job at home, re-installing is another 3 days, don't replace your rings unless you are going to sell the car, have smoke out that back, or don't ever want to open up again, then but with alusil does it get tricky? Remember, the exhaust nuts will all come free easily the next time if necessary, the head assembly with carrier can be removed easily, you have the techniques, it's well worth the risk unless you think your rings are damaged. For a 911 sc that you work on yourself, get a cylinder with matching height code or a set, whatever they suggest, if not whatever, it's run for years without a gasket and headstuds, so... let's not get dramatic, you could probably shove it back together and get another 50k miles with new headstuds, and what the heck, you can replace the cylinders and rings in another year if it's gone wrong, it's not difficult once you've spent the time once. Make sure not to shave off the inner lip to match the outer as the spec for the cylinder is in Bentley and you'd blow right past that, I think it's less than 1 thou. I've seen the crap people sell you, so replacing the cylinder might be more work than it's worth. I'd be less worried about replacing the rings then the cylinder profile if it's been wobbling about.
Phil

Besides, what happens a couple years down the line when you want to upgrade the engine for more performance? If it's your only 911, take it slow and easy and run a little risk, then in a few years after you may like the car so much and swap in some major mods including new cylinders with bore/stroke of your liking.

So, these are the reasons to do a half-assed job.....really? Yikes, I guess I'm getting old. I always thought if you see an issue, deal with it.....
What you are saying is "not enough money to do it right but plenty of money to do it twice."

[ahh911]

Nah Henry you are correct, no debate. Are you suggesting all new cylinders and pistons in a move away from Alusil?

Henry, one question that bothers me. The outer contact surface is all beat up, the inner looks good. Once he measures the inner sealing surface, he's going to find a dip in the same area, isn't he?

I measured like this, flat granite surface, dial indicator on an arm this contact surface up and rotate the cylinder and you can measure the sealing surface imperfections to within 0.1 thous with typical dial indic. I'd be interested in hearing the results from the o/p on this test.

[Henry Schmidt]

Generally, measurements like that have little meaning. The only way to properly measure the cylinder is under compression with a torque plate.
Even new cylinders often measure out of round with deviations on the base and head sealing surfaces.
I once had a new 100mm Mahle for a 3.2 that measured .004" out of round. When I spoke to the tech at Mahle Motorsport, his response was "we don't measure them with a bore gauge, we test for "air-gap" ( basically, an air flow meter). If you don't have a torque plate, you have no idea what shape the cylinder will have when installed."

"Ok so what about my cylinder?" His response was "prang it". What? "Prang it....hit it with a mallet".
No, I'll pass. I'll be sending these back and you can send me a new set.

To answer your question about Alusil cylinders: If I had a new set on the self, they would be up for sale. If a customer brought me some to put in his engine, I would not comply. I would rather use a reconditioned set of Nikasil than a new set of Alusil. One main reason is the need for iron coated cast pistons...Not what I consider to be "performance oriented".
Now, we have been known to coat Alusil cylinders with Nikasil. That actually makes a nicer cylinder than a Mahle. Why you ask?....the Alusil cylinder has a higher silicon content which adds to stability during changes in heat.