85' Carrera ~ over revved engine

[rgdtoo]

Not a pretty sight.
I am guessing based on prior input this is due to rod bolts and/or rods stretching due to my over rev.

cylinder 4-6



Cylinders 1-3




head




Depression sets in.

[YTNUKLR]

[efhughes3]

Valve float is probably the main culprit on that. I'm really sorry to see the damage. I'm sure some of the pros here have seen similar or worse, but out of the dozen or so I've been exposed to in the mis-shift category, that is the worst.

[BURN-BROS]

Tough break,


The motor looks like it was run for a good deal longer than when the failure occured. You're lucky that the damage is not as worse.

[david dolan]

Was cylinder #4 also experiencing an exhaust leak as shown from all the carbon around the cylinder edges on your picture?

[rgdtoo]

I am wondering what caused the marks on the five pistons that are still somewhat ok.

This might be a dumb question but is there any possibility I can salvage the these pistons. You will notice a crescent moon shape from hitting the valves in all of them.

[efhughes3]

Your exhaust valves all kissed the pistons-hence the marks.

[efhughes3]

Maybe we're talking different marks. Mine had similar impacts and bent all of my exhaust valves. The pistons were all fine. There is hope for you.

[rgdtoo]

Aaron, yes as I mentioned earlier I didn't want to shut the track down so I limped in. I know now that was not smart.

David, looks like 4 must have endured some damage causing an exhaust leak. There were no signs of a leak prior to the over rev. None that I was aware of anyway.

[rgdtoo]

Originally Posted by efhughes3

Maybe we're talking different marks. Mine had similar impacts and bent all of my exhaust valves. The pistons were all fine. There is hope for you.

So you think even though the pistons are scarred they might be savable? Hope is good.

[Walt Fricke]

RGD

When you remove those pistons, check the width of the top ring land. You can just use your rings and a feeler gauge set. You aren't looking for an absolute width, just an unwanted narrowing. If the ring groove was not compressed near where the marks are, I'd say you are OK. Or as OK as your engine was before this disaster.

Dress any sharp edges of the marks (ridges in combustion chambers = bad) and call it OK. That is, as long as you can find a spare piston of the right weight group (or a heavier one you can slim down) and a replacement cylinder of the same height group. Otherwise you may find purchasing a new set of Ps and Cs has advantages that outweigh the cost.

Where did the head of the #1 exhaust go? I had a trophy head which had it crammed sideways into the seat. Did it fall out on disassembly? Or did it get through that hole in the piston? If not, is the rod still attached to the piston? The crack in the cylinder suggests maybe not, but your pictures don't show any case damage.

Maybe the rod got loose late in your drive back to the pits and the cylinder was able to contain it? You didn't do more damage to the other cylinders/pistons/heads by that drive, at least not directly, though. Those "valve reliefs" in the pistons were caused by the initial overrev. Unless you also broke all of your exhaust inner and outer springs as well, no way low RPM running would cause a repeat of valve to piston contact. Either of those two springs is good for 5-6K RPM by itself.

As do others, I don't think rod bolts had anything to do with this. You need to replace them anyway, as the stock ones are a one time use item. You may find issues with the bearing at #1, but I'd suspect that would be due to the terrific pounding it took before the valve head made a hole large enough to accomodate it. If your #1 rod was still attached to the cylinder, you ought to have it carefully measured even if it looks like the other five, just to be sure the big end and wrist pin bores are in spec.

No lack of strength in your #1 head studs, though, despite the pounding the head took.

If your case is undamaged, count your blessings. Every time I have had either end of a rod get loose, it has taken the case out as well. You may have lucked out as far as dropping a valve is concerned.

Dollars to donuts all 5 of the remaining exhaust valves are bent. Won't take a shop but a minute to confirm that once the valves are out. Hard to say if that brief running distorted the guides - that would have to be measured.

But intakes all ought to be good - no marks in the carbon, nothing to bend them.

Consider having the sealing surfaces of your heads resurfaced as part of the valve work. At the same time the replacement head can be made the same depth. You can shim out the cylinders to bring things back to spec after the resurfacing. That ought to take care of the issue with #4.

And you have quite a cleaning job ahead of you everywhere oil circulates, as this created lots of particles small enough to get through the sump pickup oil screen. They got mashed smaller in the oil pump, and distributed everywhere by the pump, at least before the oil filter. I'd cut the filter apart to see for curiosity at least, but I bet some got through that and into the engine. If you got some aluminumy looking oil when you drained the oil tank, it got through (the sump oil, of course, would be full of the stuff). Your bearings may show that when you dig that deeply - aluminum junk embeded in the soft bearing material.

Walt (been there three times, three cases, which is three too many)

[rgdtoo]

Walt: Great input, thank you very much.

Per your suggestion, I will be checking the top ring gaps of each piston tomorrow.

I'm not sure where the head on #1 exhaust went. Unfortunately it didn't fall out during dis assembly.



At least the rod held onto the piston.

As far as I can tell there doesn't seen to be any serious damage to the case, time will tell. I am waiting on delivery of a 12mm 12pt star socket so I can split the case; it's due on Monday.

I spoke to a local machine shop yesterday and this is the work list we came up with so far:

1. valve job
2. remove replace valve guides, hone to size
3. surface cylinder heads
4. clean polish, check crankshaft
5. recondition con rod, both ends, bore bushings for identical center to center

Of course that's all sight unseen but it's a place to start.

I am fortunate to have a good friend who owns a metal finishing shop. I called him to ask about bead blasting etc just to see what his shops capabilities are. For the last 20yrs his business has been deburring electronics parts for various OEM manufacturers. That is until he got started working on Porsche engines two years ago. So as luck would have it, I will have everything cleaned professionally at the discount price of FREE. Thanks Carlos!

Thanks for the reminder, I want to cut the oil filter to see whats inside.

I was also told I should pump kerosene thru the oil cooler for at least 24hrs in order to re-use it. Does that sound reasonable?

I will be the guy standing on the street corner with a sign, will work for Porsche parts! So much to do, so little $.

Thanks again, Bob

[efhughes3]

While you have the engine apart, take your cooler to a local shop that works on airplane engine coolers. Have it tested and cleaned by them. I thought mine was fine, but two pinhole leaks were found, and when it came back it looked brand new. I think it was only $125 or so for the service.

[rgdtoo]

Originally Posted by efhughes3

While you have the engine apart, take your cooler to a local shop that works on airplane engine coolers. Have it tested and cleaned by them. I thought mine was fine, but two pinhole leaks were found, and when it came back it looked brand new. I think it was only $125 or so for the service.

Thanks that is good input.

Bob

[Walt Fricke]

Looks like you need a new rod? Wrist pin end bent? Try to get one which is a bit heavier than what you have, so only a little needs to be taken off when balancing it. This gets complicated some by "big end" vs "little end" weight, though. And you can't get very much weight off of a Porsche rod. I once had a shop grind off a lot of the rib on the cap end. Ouch - that's there for strength, not for balancing as on some Chebby rods. One ruined set of rods. Worth having a discussion with the rod balancer, unless it is one of the well known Porshe machine shops, just in case.

If you have tools, like a die grinder, you could balance your replacement piston yourself. Pretty clear where you can take off some weight inside. Helps if this is only a little heavier than the ones you have. An inexpensive office supply digital postal scale will do fine, as this balance is not as complicated as the rod balance.

[911 tweaks]

you may also want to look into having your crankshaft re worked... i.e. add a couple more main bearing bores to #5 & #1 bearing?? which do not get the amt of oil as the other main bearings...I am not looking at a crank now... ask the experts here or do a search for the correct specifics...Armando at Competition Crank is the guy this board likes...maybe talk to Henry @ Supoertec... he knows the answers... my point is the crank is starved for oil in its std comfiguration...
then get it mag'd & polished as you said above...
Good luck here!!
Bob

[rgdtoo]

Originally Posted by 911 tweaks

you may also want to look into having your crankshaft re worked... i.e. add a couple more main bearing bores to #5 & #1 bearing?? which do not get the amt of oil as the other main bearings...I am not looking at a crank now... ask the experts here or do a search for the correct specifics...Armando at Competition Crank is the guy this board likes...maybe talk to Henry @ Supoertec... he knows the answers... my point is the crank is starved for oil in its std comfiguration...
then get it mag'd & polished as you said above...
Good luck here!!
Bob

Thanks I will look at that too.

[Walt Fricke]

I understand that your 3.2 is a stock motor, used for DE. And you were happy with that.

I'd not be inclined to fuss with improved rod bearing oiling, given those goals. First off, your engine explosion had nothing to do with inadequate rod bearing oiling. And the #1 rod has decent oil supply anyway, since it is close to the #8 bearing, from whence oil flows. Secondly, only highly hopped up high RPM race motors may benefit from improved rod oiling. I'm doing that on a motor I am building, but my 2.7 motor has done fine at 8,000 rpm for some years now without that refinement. You only hit high RPMs due to a money shift, and better oiling would not have saved your bacon.

The 911 crank is fed oil to every crank journal, but only the #1 and #8 bearings let oil flow into the crank itself. This means the #2 and 5 rods are farthest from their oil supply. There are at least two ways of getting more oil into the crank, and hence the rod bearings, in other places. Typical is to cross drill the center main of the crank, and then either groove that journal or the bearing so the oil from the main bearing can also pressurize the crank.

Here are pictures of both:




If this was my motor, I'd consider stronger aftermarket rod bolts. You have to replace those anyway, and they are a relative weak spot on these engines. Our host's book on 911 engine rebuilding recommends this - you do have that book, don't you? Best bang for the buck you could ask for (this forum perhaps excepted) in this Oddesy.

Otherwise, the bills are going to add up quickly enough: machine work, replace a rod, piston, cylinder, head, gasket set. But good savings in labor, looks like.

You can justify having all your rod big ends checked for roundness, in case the overrev stretched something. Be sure the machinist gets your old rod bolts and nuts for use in any measuring and machining before you toss them away. If the rods check out, I'd have a heart to heart with the machinist about the need to do more with them. These parts are all fine to start with, as far as I know. There is a spec for how much out of round is acceptable.

Easy to justify having your crank checked for straightness, though the cranks are strong and have a main on either side of each throw, making them much less likely to bend than, say, a Chevvy. Shouldn't be expensive. Maybe polishing is fairly inexpensive too, and indicated if the journals look like they would benefit from it.



Walt

[rgdtoo]

No damage in here; finally something to about.







For now I my goal is rebuilding a strong engine that will last. I am planning on replacing the cylinder head studs, rod bolts, camshaft housing oil line restrictors, and obviously all my broken parts.

I would have preferred to plan this ahead of time and done a rebuild to increase hp and not a repair.

I am also looking for any possible performance upgrades that don't cost an arm and a leg.

My list so far:
replace the stock flywheel with a lightweight one if it makes sense
headers

Any other suggestions???

Thanks everybody as always for your thoughts, advice etc..

Bob