My BMW V8 engine build thread

[CoreyZ]

From what I understand there are special honing stones and a special rubbing compound you can use to rehone alusil bores.

[The Dark Side of Will]

Although cool, I couldn't see sinking more money into another bottom end that would probably have twice the mileage on it for what might amount to a trivial bump in HP for the work and expense involved. I've yet to see one of these hybrids dynoed, so I may be wrong. But it all depends on my leak down test, I still may be in the B44 hunt after all. ;)

While I don't see a bump in horsepower of at least 10% as trivial, I agree that spending money on something outside your scope because it's potentially cool isn't the greatest idea.

Obviously, once you hone+rering, it's a zero mile engine ;)

Need facts...

[iamsam]

Not to derail Jean's post anymore, I didn't go with a B44 block due to the fact my B40 has only 60k (verified) on the Alusil replacement block. Although cool, I couldn't see sinking more money into another bottom end that would probably have twice the mileage on it for what might amount to a trivial bump in HP for the work and expense involved. I've yet to see one of these hybrids dynoed, so I may be wrong. But it all depends on my leak down test, I still may be in the B44 hunt after all. ;)

Logic makes sense.

I too want to see a dang dyno sheet already for a hybrid motor.

[senorcarey]

Not to derail Jean's post anymore, I didn't go with a B44 block due to the fact my B40 has only 60k (verified) on the Alusil replacement block. Although cool, I couldn't see sinking more money into another bottom end that would probably have twice the mileage on it for what might amount to a trivial bump in HP for the work and expense involved. I've yet to see one of these hybrids dynoed, so I may be wrong. But it all depends on my leak down test, I still may be in the B44 hunt after all. ;)

[iamsam]

^^^ very good info here. If I can easily hone an alusil block (and therefore re-ring the pistons), I will definitely be going the full teardown/hot tank/rebuild with all new bearings, rings, seals, etc.

All your talk of hypereutectic alloys brings me back to my college days, with arduous lectures in Materials Science... ;)

(I speak as if I am an old bloke, but I only graduated this past may...)

[The Dark Side of Will]

Alusil is basically a hypereutectic aluminum-silicon alloy used to cast the block.

Hypereutectic pistons have been used in production iron blocks for a while.

"Hypereutectic" means that there's more silicon than can dissolve in the aluminum. As the mixture cools, the silicon forms microscopic grains in the aluminum matrix. Once the bore has been honed, acid etching eats the aluminum away from the silicon grains. The silicon grains form the wear surface on which the pistons and rings ride, while the etched locations where aluminum used to be hold oil.

I know that honing an alusil block involves the additional step of the acid wash. I don't know how the initial specs for the surface roughness of the bore finish prior to the acid wash are different than for an iron/steel bore.

Also, I've heard that an iron skirt coating is required on the pistons for an alusil bore. I'm not sure if the usual moly-disulfide coating is appropriate/compatible or not.

Googling "Honing alusil" may provide some insight.

[iamsam]

As I understand it, only the Nikasil is a coating. The Alusil bore surface *IS* the native material of the block. However, the hone process for alusil is different than iron/steel, in that it involves an acid wash to etch the aluminum away from the silicon.

interesting. Do you have a link leading to more info on this?

[iamsam]

There's quite a lot of discussion about reringing alusil in the Porsche community. I think some 928 guys have successfully done it. It's tricky, though.

What makes the task itself tricky?

[The Dark Side of Will]

No on the rings was based on the reasoning that the rings on these wear with the cyl. walls but the walls having the special coating on them. So, if you put new rings, the concern is how that will wear with the already "worn in" cyl walls?

As I understand it, only the Nikasil is a coating. The Alusil bore surface *IS* the native material of the block. However, the hone process for alusil is different than iron/steel, in that it involves an acid wash to etch the aluminum away from the silicon.

[Jean]

Yeah I've seen that....don't want to attempt that. That's one main reason I went with 4.4 for the bottom end to not deal with 4.0 issues...

[CoreyZ]

No on the rings was based on the reasoning that the rings on these wear with the cyl. walls but the walls having the special coating on them. So, if you put new rings, the concern is how that will wear with the already "worn in" cyl walls?

There's quite a lot of discussion about reringing alusil in the Porsche community. I think some 928 guys have successfully done it. It's tricky, though.

[CoreyZ]

It's pretty easy to get sucked into the rabbit hole of M6x parts. I wasnt going to touch mine and now it's sitting in my garage completely stripped except for rotating assembly and heads. I cleaned the hell out of it, though.

I popped the cams out and will be doing a leak down test before resealing it. This is only to insure that I'm not wasting money on gaskets, etc. I still need 4 knock sensors (all cracked), a MAF, and miscellany.

I realize that I'm not building a B44 hybrid, but swore that if I broke it down this far I would. Looks like it will remain @ 4.0 liters.

You should buy my B44 block :D

[Jean]

No on the rings was based on the reasoning that the rings on these wear with the cyl. walls but the walls having the special coating on them. So, if you put new rings, the concern is how that will wear with the already "worn in" cyl walls?

[iamsam]

Yeah, a couple bmw mechanics locally told me to not touch the bottom end/rings and leave it alone but to do the rod bearings so.... I will do my best at cleaning the bottom end by hand but still not 100% sure on the rings.

What are you plan on doing?

hmmm, until now, I was going to take it apart and hot tank it... what exact reasoning did your mechanics use? why is it bad to hot tank and put in new rings?

How do you get all the carbon flakes out from around the pistons (between piston and cyl walls above rings)? I don't trust the air nozzle to get all of it.

Also, there is a metric ton of gunk and grease all over everything and it would be a PITA to scrub it off by hand, if all it took to hot tank it was new rings and bearings...

It's pretty easy to get sucked into the rabbit hole of M6x parts. I wasnt going to touch mine and now it's sitting in my garage completely stripped except for rotating assembly and heads. I cleaned the hell out of it, though.

I popped the cams out and will be doing a leak down test before resealing it. This is only to insure that I'm not wasting money on gaskets, etc. I still need 4 knock sensors (all cracked), a MAF, and miscellany.

I realize that I'm not building a B44 hybrid, but swore that if I broke it down this far I would. Looks like it will remain @ 4.0 liters.

I have 8 knock sensors, 3 MAFs, and a crap load of miscellany due to stripping down four M6x cars in my garage.

Why no B44 hybrid?

[senorcarey]

It's pretty easy to get sucked into the rabbit hole of M6x parts. I wasnt going to touch mine and now it's sitting in my garage completely stripped except for rotating assembly and heads. I cleaned the hell out of it, though.

I popped the cams out and will be doing a leak down test before resealing it. This is only to insure that I'm not wasting money on gaskets, etc. I still need 4 knock sensors (all cracked), a MAF, and miscellany.

I realize that I'm not building a B44 hybrid, but swore that if I broke it down this far I would. Looks like it will remain @ 4.0 liters.