Cylinder advice for 3.0 SC Case.

[TargaCoupe]

I'm preparing to rebuild an engine that was initially built in 2000 and was only run for maybe 30 hours before developing ignition issues and was put in storage for 15 years.

The build consisted of a 1978 3.0 case with Mahle 100mm cylinders and pistions with 105mm spigots. The case was machined to accept the larger cylinders. The cylinders all have pitting which I presume is from a lean running engine. The pitting is near the top of the cylinder, otherwise the walls look to be in decent shape.

The heads are ported and converted to a twin spark. It was built as a racing engine and came with an RSR MFI setup which I have sold and now plan on going with a more modern EFI system with ITB's to make it more streetable.

My decision now is whether to reuse the 100mm cylinders and pistons or purchase a set of new 98mm P&C's. I've contacted Millennium and they are not sure replating will address the pitting issues. I don't believe the 98mm pistons come with 105mm spigots though so am I stuck reusing the 100mm cylinders? Are there other options for cylinders?

I've attached a photo of the pitting.

Thanks
Dave

[GG Allin]

I have a similar engine set up. Mine is a 3.2 case with Mahle 100mm cylinders. My spigot bores are closer to 104mm though. You could look for another set of Mahles, they're relatively inexpensive, used.

[TargaCoupe]

After some more research, it looks like I'm stuck with the 100mm cylinders seeing the case has been machined to 105mm from the stock 103mm spigot bore.

[MBruns]

I would suggest getting a set from L&N Engineering, the set I built an engine from had around 12k miles on them and they were straight and round, very good quality, it’s tough for 100mm cyls to do that but they have it figured out
Mike Bruns

[safe]

I hope you have read the recent threads of plating experiences.
Short form: Get new cylinders.

[TargaCoupe]

Originally Posted by safe

I hope you have read the recent threads of plating experiences.
Short form: Get new cylinders.

I hadn't noticed the posts on the plating, Magnus. I had called a national plating company to ask about the pitting and they were happy to replate the cylinders but I was told that the pitting could not be addressed. Not sure what the point in replating them is if they can't fix the reason I wanted them replated?

I guess I'll look at new cylinder options. I'm assuming I'll need to go with the 100mm one's again since the case has been machined to fit the larger spigots.

Dave

[porschedude996]

I bet you could sleeve new cylinders spigots to 105mm. I was thinking the sleeves would steel (similar coefficient of expansion). Maybe press-fit on the outside of the cylinder spigots. Machine sleeves to a interference fit, chill cylinder and heat sleeve press it on. Then machine the sleeve on the cylinder. Could be expensive…

[PeteKz]

Ditto what Magnus said. Read those threads. Then buy new cylinders. "Porsche" and "inexpensive" can't be used in the same sentence.

[porschedude996]

Originally Posted by PeteKz

Ditto what Magnus said. Read those threads. Then buy new cylinders. "Porsche" and "inexpensive" can't be used in the same sentence.

Doesn’t he still have the 103/105mm spigot problem with the case? Or can he get 105’s from Porsche?

[PeteKz]

Buy from L&N. If they don't have in stock, I'm sure they can customize.

Shrink-fitting steel sleeves on the bottom of the cylinders to take up the excess room for the spigot hole will compress the bottom of the cylinder, probably enough to require re-honing, and maybe replating and rehoning. It ain't gonna be cheap either way.

[porschedude996]

Originally Posted by PeteKz

Buy from L&N. If they don't have in stock, I'm sure they can customize.

Shrink-fitting steel sleeves on the bottom of the cylinders to take up the excess room for the spigot hole will compress the bottom of the cylinder, probably enough to require re-honing, and maybe replating and rehoning. It ain't gonna be cheap either way.

I doubt that a 1mm hoop with an Interference fit is going to influence the cylinder’s internal diameter. Not to spout off, retired aerospace design engineer here. Just a bit of experience.

[PeteKz]

You may be right, but Murphy as a way of popping up when least expected. Not to spout off, retired (but still learning) mechanical engineer.

We could figure out a good approximation with some numbers. Aluminum has about 1/3 the Young's modulus as steel. How thick is the bottom skirt of the cylinder? How much interference fit should we assume, .002"/.05mm?

[porschedude996]

A battle of coefficients? I was thinking (0.0005”). Standard interference fit tables exist when i was working at Lockheed Martin, and most would be surprised how little interference is needed to hold. Also the RMS finish is not great (ruff). I thought both a steel band around the cylinder, and an insert in the case halves. If I was to estimate, the setup to machine the project would require more effort to setup the case halves. Where as setting up a cylinder in a lathe is simple. Maybe just make the rings, and press them on the cylinder spigots. No case setup and no cylinder on lathe. I’m sure the concentricity is good on the spigot and would not benefit by machining the ring while on the cylinder.


Could go either way. I’m still leaning as well.


No learning to me mean’s i’m brain dead.

[PeteKz]

Or don't even depend on an interference fit, just use JB Weld! Then no "battle of coefficients". We might still have to calculate the delta due to different coefficients of thermal expansion when in use. (joking)

The JB Weld seems to be working on the RSR front bushings I recently installed.

[porschedude996]

Originally Posted by PeteKz

Or don't even depend on an interference fit, just use JB Weld! Then no "battle of coefficients". We might still have to calculate the delta due to different coefficients of thermal expansion when in use. (joking)

The JB Weld seems to be working on the RSR front bushings I recently installed.

Haha , maybe too much over kill from two retired engineers…

My ferrari uses “Specialty Formulated” Epoxy for it’s ball joints and that works. “Specialty Formulated”, yah right. Probably just Hysol rebranded.

[PeteKz]

There are some bonded sections in my all-aluminum Ford GT. 80,000 miles so far and nothing has rattled loose. Yet... But I know that technology was well developed in the aircraft industry, so I think it will be okay.

[TargaCoupe]

Thanks for the interesting discussion! I'm leaning towards a new set of the LN Nickies, it's only money...

[porschedude996]

It was good food for thought.

[PeteKz]

And I really appreciate that engagement. Thanks, PK