2.7 CIS engine questions

[mike95125]

Howdy,
I am refreshing my 2.7 and have found some interesting things that I am not sure what to think about them.

First are the pistons, they seem to be higher compression as the raised area is larger than any pic I have seen.

Second, I have discovered that the cylinders are Mahle and the piston skirts look like they are for the Nikasil type, but the inner lining of the cylinder has no magnetic properties Could these be one of the rarer Mahle Alusil sets?

Third, the last person that assembled the engine pinched the head gasket (I'll attatch pics as soon as I get a good set) and subsequently dented the cylinder sealing face. Is this fixable typically?

Fourth, there is material missing from two of the heads in the form of pits, can these be filled? the pits are about the size of BBs and there is one one one and two on the other.

If anyone knows what a ball park figure for some of these fixes are, or for replacements please let me know.

Thanks,
Mike

[mike95125]

Sorry, forgot the pics of the pistons:

[afterburn 549]

those are typical cis pistons and if you check with a magnet I hope you have a very sligh pull....you almst have to imagine it (in the cyl bore)
as for the heads anything is repairable Soooooo take the valves apart and see what you got ,mabe you want a diff set of used heads ?? or fix those

[Henry Schmidt]

Originally posted by mike95125
Howdy,
I am refreshing my 2.7 and have found some interesting things that I am not sure what to think about them.

First are the pistons, they seem to be higher compression as the raised area is larger than any pic I have seen.
These are stock CIS pistons

Second, I have discovered that the cylinders are Mahle and the piston skirts look like they are for the Nikasil type, but the inner lining of the cylinder has no magnetic properties Could these be one of the rarer Mahle Alusil sets?
I believe Mahle called this stuff Silimal (Alusil)

Third, the last person that assembled the engine pinched the head gasket (I'll attatch pics as soon as I get a good set) and subsequently dented the cylinder sealing face. Is this fixable typically?
2.7 heads are cheap, look for replacements

Fourth, there is material missing from two of the heads in the form of pits, can these be filled? the pits are about the size of BBs and there is one one one and two on the other.
Same as #3

If anyone knows what a ball park figure for some of these fixes are, or for replacements please let me know.
call, we'll talk

Thanks,
Mike

[mike95125]

Thanks guys. Henry, I'll be calling you tomarrow most likely. As per #2 it is the cylinder that is slightly buggered up...but I know you have replacements.

How do I tell if I have the 8.5:1 CR pistons? Those are what I am hoping to have....as well as SC grind cams.

[James Renfroe]

Mike,

Actually, this Mahle Alusil CIS sets are not really rare and the pistons are not plated, but rather a high silicon content aluminum cast piston. The raised portion of the piston in CIS pistons are designed to more efficiently burn the continuous type fuel delivery mixture associated with the CIS system. Waynes “Porsche 911 Engines” book explains this better than I could.

Secondly, in my experience, KS is the only OEM manufacturer that iron plates their pistons (at least in engines of your vintage). In all the Mahle CIS/Alusil pistons that I haves tested, have been non-magnetic. To my knowledge, none of the oem pistons manufacturers have ever thermally coded the crowns of their pistons in the earlier air-cooled engines (Nikasil or Alusil). I would be afraid to thermal (ceramic) coat air-cooled 911 pistons because I would think that this would elevate exhaust valve temperatures.

[mike95125]

Thanks for the info, James.