GlenL

Note that in the instructions for machining an Alusil liner that the honing is a multiple step precess finishing with polishing.

My guess is that the Alusil liners are not processed completely. Also, as the liners are put in with an interference fit the walls may take a bit of wave after the liners warm and the block cools. The machining will help achieve a more truely round bore. Then they suggest the final step of new block machining to raise the silicon. (Lower the AL, actually)

Hone like an Fe block if you want, lightly if you can, but the silicon will be worn back even with the Al. This may lead to increased blow-by when the Al is worn back by the rings.

Vilhuer

Local shop does final felt lapping to used blocks but anything more requires oversize piston or sleeving. Lapping compound does fill up some minor imperfections but I'm not sure how permanent it is once engine is started.

Raw Alusil liners are inserted when they are cooled enough to make them fit. Once block and liner are at same temperature they will not come out. To make it absolutely sure they don't move Kolbenschmidt liners have few mm ledge at the top. Once inserted, liners need same roughing, finishing, polishing and felt lapping as normal oversize boring.

m21sniper

The part that makes no sense to me is that if Porsche used cyl. liners anyway, why not just use a high grade steel?

Then you don't run into any of these problems.

Vilhuer

Stock block do not use liners. Pistons run against Alusil wall which is directly part of the block casting. To be able to do that, skirts need to be coated with iron oxide so that they do not wear during run in. If cylinder wall material is changed to steel it will wear out this coating making piston useless in Alusil block. Most important reason for using Alusil is that it allows much tighter clearancees and virtually wear free cylinder design as long as piston rings are ok.

m21sniper

OK, gotcha.

mark kibort

All thinks ive heard. thanks. well it sounds like the shop used some very light, drill mounted honing. ill have to find out how coarse it was, but it sounded like the surface was still very smooth, but didnt have that shinny gray perfect look like we all know in 928 land to be what we need! the picture still showed the stains at the top of the cylinders from the previous life of the engine. (you know the area just above where the rings touch , usually stained with carbon) is that a good sign? also, i wonder if it is just "scrached up" with the honing,if the rings now ride on more aluminum and maybe life is lowered, or you get that friction thing against the pistons that destroy the engine due to the tight clearances.
Mk

atb

Mark wrote:
>>>>>>> the picture still showed the stains at the top of the cylinders from the previous life of the engine. (you know the area just above where the rings touch , usually stained with carbon) is that a good sign?


That's called "the ridge". Discoloration is normal, but in my opinion it would be abnormal to actually feel a lip (ridge) between the discolored section and the gray section of cylinder wall on a 928 block. This phenomenom is the wonder of alusil bores. I've run my finger across the ridge of iron block V8's with less than 60K miles on them and there was a considerable lip. I've taken apart a 150K mile iron block V8 that the ridge was so extreme that some of the cylinder ridges had to be reemed before the pistons would come out of the hole.

All of the 928 blocks that I've seen only have the discoloration, but no discernable ridge by feel. That's pretty cool and shows the method to the madness of using alusil bores.

GlenL

Yes! I was really, and pleasantly, surprised that there was no ridge at all on my 150k engine. No need to use a ridge reamer or abuse the hone to remove it.

mark kibort

I also have seen this brown area on all motors ive taken apart now and it is cool that there has been NO wear to speak of (in the form of any ridge or lip) in the ring area. However, my point was that if the shop "honed" the bore, then maybe it was done so slightly if it didnt take this stain away. I wonder if they did a hone job on the bores if it was more subtle and didnt effect the wear advantages of a non honed or scuffed up surface.
It did happen, and it was on a 944 turbo.

Mk

mark kibort

Ok folks, i can let the cat out of the bag. the story is true about this shop and the 944 turbo with the light "honing" job. However, the main reason for my asking, is the shop helping Scot has been allowing us to prep the old replacement 82 euro motor 4.7L, has wanted to assemble the pistons in the block after we have taken it all apart, cleaned it and assembled the crank in the two case halves.

as i mentioned originally, the block cylinder walls were PERFECT, better than my 928 intl 5 liter block, which was as good as it gets i think for a used motor! anyway, the shop took it upon themselves, being very careful along the way of piston, ring and piston assembly process, to HONE the cylinders!!! AHHHHHHH. I couldnt believe it!!!! i specifically told them about the 3-4 stage silicon paste process of the 928 block. I think they did this thinking the rings would seat better as they dont want the engine to grenade again like our first one. (the badly gauled pistons on initial start up, and it didnt even start, just siezed). one of the mechanics helping us is now gone on vacation and i asked the other that works with him, what was up with the "honing" of our block! he told me of the 944 turbo engine he did, and said that ours was done like this. to me, it looked a little too shinney in there, as we all know what a proper surface cylinder wall looks like!

Ill go tomorrow AM and take a few pics and ask what in the heck they were thinking in suffing up our block. now, its almost together, and im wondering if we should just pull the pan before we move forward with the head installation, and take the pistons out and get this thing done right!

any thoughts here. Let me see what it looks like and get some tollerances of the pistons and cylinders.

MK

Fastest928

Hey Mark,
Sounds like quite an effort of time and money to get it up and running. Is this the same block that blew out the head gasket immediately after purchase and that I diagnosed with the rotting cylinder tops ?

mark kibort

Hi Marc,

No, this is another block (euro 82) that we stumbled upon and the bores looked really really good. no question of scratches being a problem like the first block.
all stock internals, and we just cleaned and re-ringed, (we thought) until they did a quicky honing job for whatever reason. Now we are hosed i think!

the old block with the cracked tops, we had machined and looked really good upon assembly. there must have been some problem when it siezed, but we have no idea why. Elsworth did the paste job after the rim bore (just up top where the welding was) but we used the used rings. it siezed and two of the bores are destroyed . probably a good candidate for a 5 liter bore job now. (newer crank, good rods, etc)

what are your thoughts?

Ill take few shots of it this am and post them tonight.

thanks,

MK

Herr-Kuhn

Bore it

Nikasil Plate it

Install what you want

Abuse it

I've build (2) 4.5 liter motors this way without issues (except the abuse part ...about to build a 3rd. I can have the block plated and diamond honed for just a bit more than what it costs to resurface alusil bores. It is a very good option...no option has zero risk, but for performance 928 motors I think the Nikasil is really hard (no pun intended) to beat. My first 4.5 has like 13,000 since rebuild I think. I have to admit it is a garage queen.

mark kibort

here is the entire engine, and shots of the block cylinderwalls after the monkeys honed it with the stone only 4 passes and real slow, but here is the results. they say they have done this before but most say, the block is done.
the 3rd picuture is a little fuzzy, but shows the little nick that they took down, but then they decided to hone to blend their repair in. Devek says, they probably just should have taken it down and left 99.9% of the rest of the block alone!

Now, i think we have a time bomb if we move forward. is the honing done here what you guys have seen on iron block v8s? he did only a light few passes?? no chance of using it????

thanks.

MK

THE last picture is scots old block that siezed but here is one of the 6 cylinder walls in good shape and after the silicon paste technique to freshen it up. it kind of looked like that before too, except for a couple of holes that had some minor scratches. this is how a cylinder should look

enjoy

MK

mark kibort

a few more