69T Rebuild

[D69S]

I have started rebuilding my '69T motor and have significant history on the car. According to the documentation the motor was rebuilt in 1977 in California, unfortunately there are no details of the shop that completed the rebuild, only an invoice with basic information. When I pulled the heads off it looked as if there were interference between the pistons and inlet valves. I am curious if higher compression pistons were installed with the last rebuild, and clearance were not checked? See photo's attached.
I would also like to know if the 103 stamping is the compression ratio?

[Emery G.]

my understanding is that type of interference is caused by the heads having been fly cut and the valves contacting the valve relief cut in the piston. seems to me the clearances were not checked properly. the pistons should have been cut back some in the valve relief area.

[porschetub]

Originally Posted by Emery G.

my understanding is that type of interference is caused by the heads having been fly cut and the valves contacting the valve relief cut in the piston. seems to me the clearances were not checked properly. the pistons should have been cut back some in the valve relief area.

Not sure about that ,looks like valve guide wear to me ,my 2 cents no expert here

[911pcars]

What makes you think there was valve-to-piston interference? Typically, if that happens, something has to give - usually a rocker arm breaks and/or the valve head(s) bends. In drastic cases, the piston will suffer structural damage. The images don't appear to indicate piston damage.

Those don't appear to be pistons from a T engine. Could be E pistons.

Suggest adding these reference manuals to your automotive library:
911 Performance Engines, Bruce Anderson
Rebuilding Porsche Engines, Wayne Dempsey

They contain numerous photos and specs to help you determine your engine build.

Sherwood

Oops. Missed the piston brow-meets-valve head.

[D69S]

The car has driven 90,000 miles since the motor was last opened, and could well be worn valve guides. The motor had a "misfire" at idle and was audible on the induction side, this disappeared at higher rpm and had more power than expected from a T. I suppose I am only curious to know what pistons were installed? I am planning to rebuild with new 80 mm JE 10:1 Cr pistons with ported heads, not sure about what cams I want to use. I use it as a street car, with occasional track use. Thus an E cam could work fine, although I owned a 2.0L S which I loved. Unfortunately a S cam begs to be driven on the limit and I am living in the wrong country for that!
I have Bruce Anderson's book, but cannot tell what pistons I have, all I know it is not T pistons.

[Flat6pac]

If you're going for more power,go up to 2.2 or 2.3. The heads are relatively inexpensive as are the cylinders. The valves are larger and will flow better.
Bruce

[911pcars]

Originally Posted by Flat6pac

If you're going for more power,go up to 2.2 or 2.3. The heads are relatively inexpensive as are the cylinders. The valves are larger and will flow better.
Bruce

Yes. Later, compatible heads provide larger valves/ports and improved combustion chamber volume. The aftermarket reportedly offers better "E" type cams for improved mid-range. Higher CR goes a long way for improvements in that rpm range as well and mitigate the effects of increased duration when used in smaller displacement engines.

Sherwood

[crummasel]

It looks like the P/C set is not '69T as normally it should have iron barrels.
And if this is a std. early 911 P/C set which probably has been exchanged in 1977 it could explain the contact since the '69T had larger valves than the early std. 911.

[Lapkritis]

Looks like valve contact to me. Perhaps a money shift and the valve survived with altered geometry. Misfire would appear at idle with imperfect seal of the valve.

[D69S]

Thanks Crummasel, I think you nailed the piston on the head! These pistons look like the older style pistons, and clearly was not meant to be used on the T heads.
I have seen recommendations for the mod E cam, think it will work well to give greater torque spread accross the rev range.

[crummasel]

You may well mic the pistons out and if they prove to be ok, why not reuse them with new rings and reworked valve pockets. The depth of the pockets should be OK for an E cam since this one is quite close to the orig. 911 cam (even slightly lower Lift and duration compared to the solex one if i recall well)