Questions about Case Machining for big bore

polizei · 12-31-2011, 06:22 AM

Guys,

I need to perform a top end rebuild on my 3.2 Carrera, and I'm kicking around which set of pistons/cylinders I should go with. I'm leaning towards a set of Nickies with JE's because of the terrific reputation Charles has. A few questions:

1. What are the benefits of the machine-in 100mm cylinders over the slip fits?

2. Does the crankcase need to be split for it to be machined to fit 100mm or 102mm machine-in cylinders?

3. Are stock rods suitable for these bigger cylinders if I'm driving mostly on the street? Or is it an important "while you're in there" item?

4. If I do machine the case for a set of machine-in cylinders, is there any reason I should not jump to 102mm cylinders?

Thanks!

jwasbury · 12-31-2011, 06:57 AM

I'm not sure how one would machine the case spigots without splitting the case. I suppose it is possible in theory, you would need to at least remove the rods, and then seal up the case bores to keep the chips out. I think the problem then is how to securely and squarely fix the bottom end in the machine tool. While it may be possible with the right machinery, I would bet that your machinist will say "no way"

I chose 100mm machine in Nickies for my build. My thinking is that the slip fits have less meat where they plug into the case, so opted for what I believe is a stronger cylinder. Charles would be able to tell you exactly, but I would think that the 102mm machine in cylinders end up with a similar thickness where they plug into the case as the 100mm slip fit.

porterdog · 12-31-2011, 07:07 AM

Quote:

Originally Posted by polizei

Does the crankcase need to be split for it to be machined to fit 100mm or 102mm machine-in cylinders?

Doing otherwise sounds like an invitation to a very expensive disaster.

polizei · 12-31-2011, 07:36 AM

That's what i needed to know. Slip fits for me!

What are the concerns about choosing between 98mm and 100mm slip fits? Will there be any difference between these sizes in terms of oil circulation, oil cooling or header/muffler breathing requirements?

Walt Fricke · 12-31-2011, 03:14 PM

Andy - you are going to replace your rod bolts with high strength aftermarket ones, like ARP or Raceware, aren't you? Essential, it seems to me, when you boost power with this crank.

Which means new rod bearings. Now you can change bearings without splitting the case, but I'd suggest you split the case anyway. That way you can use the stretch method of getting the proper preload on your new rod bolts.

If you decide that you are going to reuse your main bearings, after inspecting them, then the only cost of splitting the case is a set of through bolt O rings. You already have orange Loctite or a similar sealant for putting your heads back on, right? Or were you planning on removing the heads on the cam carriers as a unit?