That's good to hear.
I finally am 99% finished my restoration after a year everything is finally back in place and running really good. HPDC is this weekend at Summitt Point. Once that is behind me I'll have some time to take a sample of mine.

Before I rebuilt the engine I did have interesting compression numbers. They were in the high 180 - 190's except the one set that had the broken ring. I assume this indicates higher CR.
The P&C's are alusil. This is on a 930-16 engine but it has been rebuilt before. Has anyone seen a set from the 930-10 engine with the 9.8:1 CR? I'm just wondering how the pistons compaire.
I didn't bother with CC-ing them because it is what it is.
Someone in the past mentioned that valve timing might have something to do with it, but I'm not sure.
Any thoughts?
Can anyone with the 9.8:1 set post their compression results?

Your numbers, 180 to 190 plus are consistant with 10:1 (approx) and a typical Porsche cam. Broken rings will result in lower compression, not higher. A leak down test is next. The test will determine if valves, rings or whatever is bad.

Thanks! That may help explain quite a bit.
I guess I wasn't clear. This happened in the past.

After the compression test indicated a problem with #4 I did a leakdown which was bad and the air comming out of the oil breather indicating that air was getting past the rings. Upon teardown, I found the broken ring and the marks the intake valve left on top of the piston. There was some carbon on all the piston tops and some others had slight valve depressions in the carbon, but not metal to metal contact.
My guess is this is a set of the 9.8:1 euro pistons and the extra carbon upped the CR a bit. They look like the stock type CIS pistons I've seen in books.

I did a full rebuild (Except P&C's) and found that the valve seats had been replaced and not cut very deep if at all. The valves projected into the cylinder a bit. I did replace the valve springs and rockers for insurance and had the mechine shop recut the valve seats and install new guides. Upon re-assembly, I found the intake valve clearance was still tighter than recommended. By retarding the valve timing to the Euro Specs. The clearance increased to "acceptable" levels as shown in Waynes book. (Although I have not found any documentation, I think the valve clearance issue may have been the real reason Porsche retatded the valve timing on Euro cars. Can anyone confirm?)
The cam has stock numbers on it for an 81-83 and no other marks indicating that it has been reground. (They could use cleaning up and next time it's apart I'll look into other grinds.)
I'd still like to see a benchmark compression test numbers for the Euro 9.8:1 pistons. Like I mentioned above I'll post my results in a few weeks!

BTW, What are the differences in the pistons that make the higher CR?
Are the wrist pin lower? Are the crowns taller?
Thanks!

Do you really mean retard the cam timing? Usually this will result in the exhaust valve coming much closer to the piston. Advancing the cam timing will usually result in more valve clearence, better low end performance.

If you put a piece of clay on top of the piston and rotate the engine two times and measure the vavle impression in the clay you should have something like 0.100" or more piston clearence for any street engine. Mininum would be something like 0.040" for a race engine, and this would be very conterversial to say the least.

Thanks Jack
Yup, cam timing retarded. (Intake valve clearance was tight.)
I think in theory that retarding the valve timing gives a little higher hp in the upper rpms at the expense of low end torque. It was also written that the 84 carerra the split the difference between the two settings.


Intake was too close with the US cam timing spec. Some where I came up with the idea to retard it to the Euro specs and that solved the clearance issue.
It's been a while and I don't have my books with me, but isn't one turn on the valve adjustment screw .1mm. I didn't do the clay test because everything was stock parts, but when buttoned up and timed to the US spec. I used the other test in Waynes book. I believe The test is to tighten the valve adjustment screw one turn after it contacts the valve.
Then carefully turn the engine. If no contact then clearance has been proven. I had slight contact which led me to resetting the cam timing.
The next test there was no contact (even at slightly more than one turn or whatever the test was supposed to be.) Exhaust clearance was supposed to be larger. I think. I'll have to get the book and look it off.
Sorry all for the OT discussion.

Yes, I believe your test method is correct.

Thanks!

Is there a reason not to use a ring like TOTAL SEAL in a cleaned not honed alusis cylinder?

Total seal rings have a problem. ITs related to the second ring and blowby or lack of it. The ring becoms unseated because of lack of blowby.

My plan is to clean inside of cylinders with green scrubbie pads on a hone tool and drill, rering with geotz is there anyone that has had bad results yet?

Why not spend the $30 on AN-30?

My cylinders are dull light grey with what appears to be a cross hatch the only reason I am reringing is a piston slipped out and I broke an oil ring. if I use the an-30 how would I apply it? piece of felt over a hone with the paste(an-30) on that? send them out to have it done? they have about 80k on them

Rondinone:

Did you receive the package I sent?

Car hit it's 260,000 mile mark.
8,000 on rebuild with Gotes rings. (No, not original engine)
P&C's measured in spec. Cleaned barrels with green scotch brite covering 3 stone hone. Procedures noted somewhere in this thread.
Took a while to rack up the miles because the restoration took about a year. Back on the road in April and driving almost daily.

I had a miss which is why I did the leakdown test. Miss was on #2. Leakdowns showed 95% +- 1% except for #2. BAD (My heart stopped) Air leaking out of exhaust. I found the exhaust valve clearance way tight. Readjusted and leakdown showed 95% across the board.

I believe the error was because I adjusted the valves in April after the engine sat so long. Valve must have had something keeping it slightly open when I adjusted it.

All is very good now!!!
Best it's ever run (6 cyl makes a difference!)

So Bottom line 8,000 test at 95% +-1% on all 6.
Racking up the miles now. Will keep everyone posted!

Any progress here....

I've taken the baseline measurements. I'll send it back tomorrow. Things have been busy...

Okay. I'll have it cleaned up and returned, thanks.

Here I go brining this thread back to life. Here are some pics of an alusil cylinder that had a flex hone taken to it.

Jack, can you confirm this is the pattern to look for?

http://forums.pelicanparts.com/uploa...1120960072.jpg



http://forums.pelicanparts.com/uploa...1120960328.jpg

jeff

IMHO, that looks way to aggressive. The rings will be shot in no time.

My feelings exactly. These are out of spec so in the interest of science I got them flex honed. They are pretty rough inside.

Jeff