Matt H

Block is trashed, send it my way

Hard to tell from the pics but those scores do not look that bad to me.
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hacker-pschorr

Good point, I was not clear (and didn't use 100% correct terminology) in my post. I know some people have honed out these blocks only to then cover the motor in Nakasil. Last person I know who did this could have bought a used short block for less money.

See Glen's post, I'm not sure what you have in mind, I do not want to miss lead you.

I'm sure there are many posts on this in the 944T forum since making larger bores is more common to the turbo circle.

Jfrahm

Those scratches are not ideal, but they don't look to bad to me. I say run it.

Look at all the people who have had wristpins walk, piston galling, rings seizing upon reassembly, not to mention all the issues with sleeving and learn to love your bores the way they are.

-Joel.

Jfrahm

Easier? Maybe. Hellishly expensive? Oh my yes. You could buy a nice 944 for what it'd cost, soup to nuts, to overbore a 2.5l, replace the pistons, etc. And why would you bother? For the 3HP you might find with a bit more bore and compression? If you mean to go with a 2.7l all bore motor, add another $5k to the bill, raising the price to that of a decent 951 or S2 (which would leave your 8v NA for dead.) And I'm not even factoring in a nickel for all your months of hard work.

Boring plating sleeving (ick, I hate sleeving) that sort of thing makes sense when you are building a 450HP 951 (and have 10-20 grand to throw at it) but not for an NA. For an NA (or a 300HP 951 for that matter) find a decent used short block and beat it like it owes you money.

-Joel.

420WHP944

Interesting views regarding boring/honing our blocks.

My block was bored out to 1st oversize (100.5) by one of only two shops in the UK who can do the Alusil bore/hone system using the sunnen honing machine, it use's a special paste to hone the cylinder walls after it has been bored to leave the walls with it's original factory spec Alusil silicon coating. It is the exact process that Porsche recommends and performs if you were to get it done by them.. cheers

Granite 944

Just for clarification.....one more time. IT IS NOT A COATING.

The block was casted with aluminum and silicon crystal compounds in it. When machine bored, than using a special honning prosses, AND using special tools to do so (WHICH CANNOT BE DONE BY THE HOME MECHANIC), then the silcon crystals are exposed on the surface of the cylinder walls in a microscopic pattern properly, giving it that "special" surface that will work so incredible well. IT IS NOT A COATING OF ANY KIND, SHAPE OR FORM. If you get in there, and start trying to hone it yourself, you WILL coverup, and ruin the exposed silicon cylinder bore, which is what makes it SO durable. Then, it will turn to crap within no time. Just don't do it. Take it to a machine shop that IS familiar with these Alusil blocks, and has the sunnen tools required, have them mic out the bores, and give you their complete report on the condition of this block, and what it will take to get ya back into shape for YOUR requirements.
If, your trying to get away "cheaply"..........wipe it out with solvent, maybe re-ring, and go for it. I'd still reccomend getting a good machine shop's opinion.

I have a complete, brand new set of 1st oversized Mahle piston sets, waiting for me to get one of my blocks into the machine shop. I got em cheap, about 2 years ago at about $450.00. You will NOT be able to find these anywhere (most likely) for under a minimum of $850.00 now. Good luck.

Mike C.

I too had my NA block properly rebored for oversize pistons about 14 years ago. The pistons (Porsche OEM) were not cheap even then iirc $800 for the set. I'm not sure that Porsche even offers these anymore. I also had the valves gone over at the same time I had everything apart. At that time (1988), finding a cheap used motor was not so easy. This post is the first time I've seen anything about preparing the bores for Nikasil coating. If this can be done without the need for oversize pistons, it might be a good way to go if $125/bore is real. Even if it allows you other choices for aftermarket pistons it might be worth it. I'd like to hear more details on this if annyone has them. By the way, my rebuilt motor now has 150K miles and is still going strong.

Granite 944

Then you may have some interest in this. http://www.928motorsports.com/services/uschrome.html

As far as Alusil, I could not find the article that I had on that subject right off hand here, explaining the process in depth, but this article might be of some interest. Mahle and Kolbenschmidt , are the OEM piston suppliers also, at least on our cars. I know someone out there has a good article to share regarding the alusil process, and the machining there of. If/when I run accross it, I'll post it here.

http://www.autofieldguide.com/articles/110307.html

Matt H

What I find amusing is the notion that Porsche is the only one to ever use alusil blocks. It is not that uncommon and LOTS of machine shops are able to hone the cylinder bores.
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Laust Pedersen

Granite 944, Thanks for the very informative and useful references. Maybe this reference is what you were looking for.

Somebody has got to ask the obvious questions, so:
StoogeMoe, why do your cylinders have scratches like that? And what have you done (or will do) to prevent it from happening on the next block?
However tempting it may be, cleaning the installed piston tops is not a good idea, due to the risk of something getting down in the groove between the piston and cylinder. The engine has “natural” balance of carbon depositing/flaking off, which it will revert to after a few hundred miles of driving anyway.

Laust

Jfrahm

I had not heard that Alusil was Porsche-only. I know some BMW and maybe MB engines are Alusil, it's not real common though. From what I read there are not a lot of shops that have the relevant hone and are experienced in using it.

IMO the dealbreakers for boring/honing is the cost of pistons, the procedure, and related machine work particularly when a used stock bottom end can last you the realistic life of your car for only a few hundred dollars. That and the many pontential screw-up points when a rebuilt bottom end is put together.

-Joel.

Granite 944

Laust, that link wasn't the one I really had in my mind at the time, but BOY! I likey this one!

It must be info from Kolbenshmidt. Their Logo is on every page. They are the ones that produce these engine types. Thanks! Great resource!

So, it goes to show, if ya got the money, you can even re-liner one of these engines back to stock spec, using alusil liners. It may not really be worth the cost in most cases, but it can be done.

StoogeMoe

Thanks for the great links. It's nice to know you can restore these blocks but the price makes it impractical for the 944. You can hunt down a complete running engine for less than that.

Laust, I don't know what caused it exactly. I got this engine from a car that was not well cared for as would be obvious if you saw the car. I can tell you that the engine suffered a belt breakage at one point in its life from obvious dings on the top of the piston. So maybe pieces of the valves got moved around. However, the original engine that this is replacing, suffered from overheating, which has similar vertical grooves, although much deeper. So I suspect this engine was slightly overheated. It came from FL, so that adds to my suspicion.

Matt H

BMW and MB both used alusil (BMW after having serious Nikasil problems). Maybe lots is an overstatement but there are well more than a handful of places that can do the work. The place that Scott mentioned is a good shop (and if Don I uses them that should be all the endorsement you need).
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M758

That cylinder looks fine to me.

I just see normal wear lines that I have seen on all my blocks. They have all run fine even with original rings.