Rebuilding my original motor -- Nikasil?

[Tom]

I'm seriously thinking about rebuilding the original 2.5 motor from my car. I pulled it out in favor of a 3 liter motor in 2008, which has been great fun, but am thinking it would be nice to have a near stock motor with AFM, cat, the works. I'm thinking maybe a cheater k26/8 with chips to max out the stock engine management. Looking for a tinker-free motor that passes smog without blinking, etc. Still mulling how to go about it, but am leaning toward having the bores done in Nikasil by Millennium, primarily to open up piston options. It appears US Chrome doesn't do auto engines anymore other than maybe for commercial customers? Anyone here have experience with Millennium?

[michaelmount123]

I've had good experiences with Millennium. Further, I like the Nikasil bores for the 951, and suggest a Goetze 964 ring set for same. I presume you'll use new pistons, and what I don't know is whether the 951 rings are dimensionally identical to 964 rings, so they may not fit a Porsche 951 piston. I always used custom JE pistons and had the ring grooves cut to my spec. I could also adjust C/R with the dish volume and add other tweaks that I like. Millennium offers a service (at no additional charge) where they will keep tolerances to +/- .0002" which I always took advantage of and they accomplished. Of course they can also enlarge the bore if that floats your boat. The 964 rings seated quickly and effectively and held up nicely with moderate boost. I have piston specs for JE if you are interested.

I did find that the oil passages in the block came back full of some sort of grey substance that required careful cleaning.

[996C438]

Powerseal and Millennium are two major players in the US . The company I worked for 5 years used both with excellent results . When applied correctly it is an excellent coating and very durable .

Sumebore is another option but mostly used in Europe . Not sure if anyone in the US is using this yet . Just as tough as nickasil but much easier on the environment .

[Tom]

Powerseal and Millennium are two major players in the US . The company I worked for 5 years used both with excellent results . When applied correctly it is an excellent coating and very durable .

Sumebore is another option but mostly used in Europe . Not sure if anyone in the US is using this yet . Just as tough as nickasil but much easier on the environment .

Is my memory bad -- back in the day, I remember US Chrome being very into this. When I went to their website recently, they don't even list regular car motors, just boats, ATVs, etc. And they have a big notice saying they don't take orders from anyone but dealers...

[Tom]

I've had good experiences with Millennium. Further, I like the Nikasil bores for the 951, and suggest a Goetze 964 ring set for same. I presume you'll use new pistons, and what I don't know is whether the 951 rings are dimensionally identical to 964 rings, so they may not fit a Porsche 951 piston. I always used custom JE pistons and had the ring grooves cut to my spec. I could also adjust C/R with the dish volume and add other tweaks that I like. Millennium offers a service (at no additional charge) where they will keep tolerances to +/- .0002" which I always took advantage of and they accomplished. Of course they can also enlarge the bore if that floats your boat. The 964 rings seated quickly and effectively and held up nicely with moderate boost. I have piston specs for JE if you are interested.

I did find that the oil passages in the block came back full of some sort of grey substance that required careful cleaning.

Thanks for this. That's the kind of endorsement I was hoping for. Yes on new pistons. That's one of the reasons I am looking at Nikasil -- so I can use 'regular' pistons. I was thinking of opening the cylinders as little as possible to clean them up -- hopefully 100.5. I could be convinced otherwise, but I'd be worried about reducing the head-sealing surface for marginal gains. Seems like I could max out the AFM/air filter box all too easily without increasing the bore. If you are willing to share your spec for JE pistons with those rings, that would be awesome. I love doing R&D on just about everything on these cars, but for rebuilding the stock motor, I'd love to use a set up that's tried, true, and known to work! If you are willing to point me in that direction, I'm in!

[michaelmount123]

OK, Tom. Happy to share pistons specs.
Are you going to freshen the head? I could help with that if you like. I'll need bore size, combustion chamber volume and C/R desired. With this info I can give you accurate specs for new JE pistons.
MM

[996C438]

I am no expert but I think US Chrome changed their business model to commercial accounts only . So the average DIYer can't do business with them . At least that's my understanding .

[Tom]

OK, Tom. Happy to share pistons specs.
Are you going to freshen the head? I could help with that if you like. I'll need bore size, combustion chamber volume and C/R desired. With this info I can give you accurate specs for new JE pistons.
MM

I'm just formulating my plan now. Happy to have you freshen the head if you are up for that. I did have it skimmed twice if memory serves before doing the 3 liter -- so that might complicates things? The ceramic liners looked good though, last I checked anyway. In the past, I've sourced pistons first, then gave them to the machine shop to guide their cylinder work. Not sure if Millennium works that way? I am a bit hesitant to spec pistons until they look at these bores and let me know how much they need to remove to get clean bores. I understand they can add back some thickness via plating, but not sure how much thickness they can add back that way?

[michaelmount123]

Yes, the final bore size needs to be established before pistons are ordered. As you've done in the past, best case is to finalize bores once pistons are in hand. This is the typical approach, but ONLY when bores are finalized in the shop, and not outside like at Millennium. With close tolerances, the pistons can be ordered for a specific bore size, and both Millennium and JE can accomplish this. Keep in mind, if 964 rings are used (recommended), hopefully you can have the bores finished back to 100mm. We should talk about filling out the work order that goes to Millennium with your block.

I still do a few cylinder heads and am happy to do yours. The skims on the deck surface only affects combustion chamber volume and is not an issue otherwise. I will measure amount removed so there's no issue with cam belt tension. Head gasket thickness can make up for it if required. A bit of intake porting and a NA cam will enhance breathing and boost power. Were the chambers opened up for the 3L bore? Are the valves sizes still stock size? 2.7L intake valves are a nice mod, but here we go getting away from a 'stock' 951.

[Tom]

I removed the factory 951 motor from the car when I built/installed the 3 liter motor in 2008. That original 951 motor is the one I'd be rebuilding, and it still has the twice-skimmed head on it. That's the head I'd like to use if possible. The crank and rods should be good, though I'd probably get the crank polished for good order's sake. As for bigger valves and cams -- maybe, but not sure it's worth it given my goals, especially since factory smoothness and tinker-free CA smog legality are at the top of my list.

The motor is still on a stand and all assembled, just like the day I yanked it out, so I can't take pics of the cylinders right now. Below is a picture of the worst cylinder from like 2007 (from an even older camera) when I last had that head off. That's a factory 100mm bore with scoring. Assuming it's no worse now, think Millennium can bring these back to a true 100mm bore?

cylinder.jpg (343.56 KiB) Viewed 903 times

And yes on getting your help with the Millennium order, pistons, head, rings, etc!!! Thank you!!