Jerry,

How did a plugged vent end up in detonation?

-michael

I finally got to take the cyls off and found what was left of piston #3... no real damage to the cyl walls though that I could detect with the naked eye.

I'm curious, if the cause was detonation wouldn't the top ring be shattered? As you can see below, its only broken in one place and was still on the piston as opposed to the other rings that basically disintegrated... Comments?

The parts that were left:

http://forums.pelicanparts.com/uploa...1131083118.jpg

Closeup of the damage:
http://forums.pelicanparts.com/uploa...1131083152.jpg

I'll have to mike everything and see if any other parts will need to be replaced. At least I have Nikie cyls so I can reuse them. Should the cyl and piston both be replaced even if the cyl check out ok?

Anyone got an '82 3.0 Euro piston they dont need?

-Michael

IMHO, this is definately detonation. The broken pistons explain my earlier question on how the pieces gfet to the sump. In my experiences with detonation, I cought it before the pistons broke thus the pieces were captive in the piston groove.

As far as your question to me about how a plugged vent could end up in detonation, I'll provide my theory. If the tank is full of fuel and you have no vent at all, the removal of fuel from the tank causes a vacuum over the fuel. The fuel pressure regulator on the motronic engines (and probably on the earlier engines, delivers the correct pressure of fuel based on the surrounding atmospheric pressure. I believe the fuel pressure is around 45 psi. Consider a 10 psi vacuum in the tank as your fuel level gets low in the tank. You are then really getting 35 psi delivered to your injectors (assumption). This obviously leans the engine out considerably. In my case, I had a Euro (10.3:1 CR). The result was detonation. Since I had the pleasre of detonating the engine two times, before I solved the problem, I'm pretty sure of my statements. One other clue that helped me solve the problem was the colapse of the fuel tank (hidden under the nice trunk felt).

You are seening exactly what I predicted.

One more thing. I twin plugged my 3.2 after the secong failure, to help prevent detonation. In my area we use MBTE and I am not confident that the fuel did not contribute to the whole mess. BY the way, Steve Weiner did the head work etc and I was very pleased with the results.

Thanks for pinpointing the destruction guys!

I know if it happened in one then it must have happened in others. Though, no other rings or pistons were broken. What should I check on the pistons to make sure I only need to replace the one that blew? Clearance of the ring in the groove from landing to ceiling seems logical?

What about the cyl? I cannot see any damage visually. I'll run my finger nails over the surface and see if I find anything, but it looks like I may only need a piston which would be amazing! Obviously I'll check roundness, taper, and anything else in The book, but is there something else I might look at?

Again, thanks for the help and advice!

-michael

You should check the width of the top two ring grooves. I would also look very closely for cracks in the root of the groove, posibly have them non-destructive tested. You sure don't want them to break after thew rebuild. My cylinders held up well, they were Nikasil.

How's this coming along?

HI i have S/H pistons if you req' a set, PM me

regards mike

Not to overstep my bounds here, Henry any photos my engine that you bought from me in it's teardown? Is this what happened to my old engine?

Update:

Reassembly started. With a little luck and patience it will start by August ;)

http://forums.pelicanparts.com/uploa...1181785521.jpg

Case sealing is up next :)

-Michael

Hey Michael! Glad to see that you hung in there! Good for you.
Can you sum up what you found and how you plan to rebuild (what specs) your motor?

Best of luck here! By the way, did #2 or #1 sellers help you out with the $$ you paid for the motor?? I sure hope so if they are TRUE Porsche gentlemen.

Bob

Motor will be stock. Trying to save the car for F Stock in the next 2 years. I have a plan, but weather or not the finances meet plan seems to be the down fall of all aspiring racers ;)

In summary, the ring landings and rings of #3 were blown off or failed in some way. Reasons range from bad gas, detonation, jumped timing. There was no single event to point to like missed gear or such.

#3 Piston was toast, but the cylinder walls were good. After inspection of the rest of the motor, one broken head stud found on #4. 2 Cylinders were shot because the head sealing surface was scarred beyond use. I was able to garner some free ones that needed a little machine clean up at the bottoms from a Pelicanite. Thanks!

Everything went to the local shop, The 901 Shop, for inspection/clean. Now I'm down to cleaning my case for final assy. Heads were totally rebuilt by Extreme Cylinder Head in Palm City, FL.

Enjoy!

Michael

Hey Mike:

This seems like a stupid question, but did the rings in number 3 meet specifications?

Just wondering if "mechanic" who used RTV might have tried saving some cash by using the wrong rings.

Sometimes the fundamental things get lost in the forest of problems.

Very good information on this post by the way.

Good luck with this project.

Hunh... didn't really think about that. They did last for over 7 years of me beating the hell out it every summer ;)

Not sure how I would even measure them as ... well... they are in tiny pieces. I do have all the parts I pulled out so I could put a new ring on the old piston and measure the ring gap. I could also measure the old ring thickness vs. new. Would this tell me anything?? No idea if they were installed incorrectly as they were all off the piston pretty much...

I'll take a look and see what turns up.


Project update:
Just got the case back from the soda blaster. Wife and kids are off visiting inlaws for the next 10 days... I have to stay home and work... darn... what will I do with my self every night... hrmnnn.... I'll think of sumtin' ;)

Best regards,

Michael

Michael,
How is the project coming along?

I am doing a very similar rebuild with less broken piston pieces, but more broken head studs. Here is a link to my project -> http://forums.pelicanparts.com/porsche-911-technical-forum/309970-my-new-old-1981-911sc-project-car.html

I couldn't find any Euro pistons so I picked these US pistons up from a fellow pelianite. http://forums.pelicanparts.com/911-engine-rebuilding-forum/324293-used-p-c-s.html

I still need to take everything to the machine shop to have it cleaned, examined, and head work done.

Let me know what you think?

Michael,

Glad to see this is coming along well!!!

Just posting to say hi and to register to the thread!

Michael,

You say you're rebuilding stock. Do you mean Euro stock or did you replace all the pistons with U.S. pistons. It seemed to me that you were headed towards just replacing the one piston.

If you're keeping the motor Euro then what will you do to prevent this from happening again? Twin plug, race gas?

It will be a stock ROW. I found a single 9.8 to match from ... I think it was Vertex here in So. FL. IT was not cheap, but worth it to keep the HP and engine complete.

I am making no modifications to prevent detonation in the future outside of ensuring that everything is in tip top shape. I ran the car for 7 years on 93 pump gas with no issues at all so I think I can do that again at least. I may put a 1/2 tank of race gas in on track days though.

Update:
Well gents, sorry to say but not much progress has been made. 1st, Ive been a traveling fool for work and 2nd, Porsche has not be cooperative with me.

I need 3 new studs that go near the nose. They are 8 x 78 (as listed in PET). I got the p/n and ordered through the dealer along with other studs I needed to replace along the case perimeter. Everything came in about a week... but the 3 studs were too short. All the other studs were correct.

The bag had the right p/n and the total length measured 78mm. Well, as discussed in this thread (my needed studs are the green ones):

http://forums.pelicanparts.com/911-engine-rebuilding-forum/358675-interesting-note-case-studs.html?highlight=stud+din

total length is not the length in the description of the part. What they sent me was 8 x 64 according to the spec and confirmed by the other studs in the shipment that matched correctly. So back to the parts guy I went. He had to call Atlanta, which had to call Germany... and now its 4 weeks later and I still have no studs...

*sigh*

So, I scrounged around the local performance shops and found a dead 2.0 case that I might be able to harvest some good usable replacements from. We'll see.

I really wanted to get the engine together BEFORE the birth of my daughter... that ain't gonna happen... Perhaps I'll just take a few days off for paternity leave ;) Don't worry... both sets of grand parents will be on hand and my dear wife will be well pampered.

Best regards,

Michael

93 pump gas I see . We only get 91 here.

Keeping the carbon from building up, conservative timing and adequate cooling are all things that will help you achieve a safe margin. Race gas on track days is a good idea.