83 sc bad cylinder
 

i thought my 911sc had a broken head stud as i could hear cylinder leakage under load. studs are fine but what caused this http://forums.pelicanparts.com/uploa...1316834959.jpg

http://forums.pelicanparts.com/uploa...1316834999.jpg

Wow, and this car wasn't smoking? Honestly, it doesn't even look like the cylinder has been firing for some time.

Time for some diag for sure. Get the heads cleaned and inspected. Don't be surprised to find worn guides. I'd pull that motor down to the case and inspect the P&C's as well. Actually I'd be rebuilding the entire thing if that was at my shop :) Just speaking as if I was a non-shop, DIY person.

hi there
definitely i would rebuild this engine.Your problem was that you had a loose heads for a long time.
If you do your engine the best would be to replace all case studs..
Like boxxersix said valve job as well....

proporsche

The heads are loose, replace the bottom studs, do a valve job which might consist of the need to flycut all the heads to square up the bad one, disassemble to clean and put together.
Bruce

what about pistons and cylinders
 

i have read that pistons should not be removed from alusil cylinders. the engine had less than 100k miles, should i remove the pistons and cylinders intact, clean the domes and reuse them with new lower studs and a valve job.

hi rgm
as we can see on the picture this middle cylinder was using oil.So i recommend take it a part clean all the metal and alu part .Mark the cylinders with pistons so they go back together.Get new piston rings(if you see any damage on this oil cylinder,100 000 miles is very low milage.Really replace ALL case studs.Don`t do any metal shaving to the heads or any other parts.Do not hone the cylinders they look very nice but i cannot see the one which was using oil.
Take a picture of it....


proporsche

RG - it isn't pulling Alusils apart which is controversial. It is re-ringing them. So if the rings on the crudded up hole are OK, you won't have to deal with that. Just keep things together for reassembly.

Interesting that there still seems to be a clean line around the full diameter of the head other than the spot at 6 oclock so at least no serious damage has been done though certainly well advised to deck the heads to ensure no more problems. And Walt is right about re-ringing Alusil.
By all means dont run a ball hone or anything through that-and it would be nice to check the bore in that jug for diameter and roundness. I have re-ringed those without problems but I think good breakin procedures are important.

^ Agreed. I think the amount of oil present at the sealing surface somehow kept this from cooking, although that still doesn't explain how that motor was NOT smoking while running. Unless that cylinder was dead, either no spark or such low compression that there was no combustion. I mean that cylinder is soaked.

Definitely best to rebuild. At this point it's not going to hurt anything to go further into it and work your way back out.

leak down test was not bad
 

i had a leak down test done about 3000 miles before i quit using this engine range was 2% to 6% cylinder #2 was 5% i think it only leaked under load at that time, but obviously deteriorated over that last 3000 miles. no smoke until i got on it at higher rpm. oil everywhere made tear down easy, all exhaust nuts came off easy.

Best check on the valve guides too

The lower stud threads are still caked with oil - doesn't look like they had nuts on them?

studs
 

that carbon was moved up the stud as I pulled the head off which was difficult . the sealing ring between the head and cylinder was compromised. i'll post a pic later. I do not know the history of this engine but i question some of the assembly issues i observed. rtv on the oil cooler seals, compression ring gaps not staggered on two cylinders, dilvar studs came out pretty easily with one exception #4 cyl front stud. i did not notice that any of the head bolts required less force to break loose but none were difficult.

Bruce (flat6pac) just did a loose head engine like this, look for his thread.

Frankly Bruce and Walt have told you everything you need, in a handful of brief sentences. The rest of us are just making noise. :)

Bad assembly job?
 

the case through bolts had blue rtv sealant on them so i am pretty sure that the case was split prior to me getting the car. odometer reads less than 100k and i have had the car for almost 20 years and it has been in storage for the last ten years. ran ok when i got it but smoked a little on hard acceleration and deteriorated some over the years i drove it until i parked it. perhaps cylinder #2 was not installed tight enough. the sealing ring was shot on the lower part of the cylinder
http://forums.pelicanparts.com/uploa...1317246259.jpg
http://forums.pelicanparts.com/uploa...1317246625.jpg

carbon had built up under the seal.

http://forums.pelicanparts.com/uploa...1317246691.jpg

Is that a piston ring being used for a sealing ring?

Not a piston ring

Sure looks like a spring on the inside....such as the oil seal piston ring used at ring land 3 (bottom ring).

Could just be my eyes are failing me. LOL:D

That's how those sealing rings are designed. Not a solid copper or steel ring.

tear down complete
 

i suspect the case had been split before i got the car in 1992. case through bolts had blue rtv on both ends so i want to see what was repaired but can't find anything out of the ordinary so far, rod and main bearings look good
http://forums.pelicanparts.com/uploa...1318545885.jpg

http://forums.pelicanparts.com/uploa...1318545937.jpg
five of the rods have a casting number 54C one has 51A i dont know if that means anything

main bearings have a part number 930 132 02 and a date 1-83 rod bearings have part number 930 148 00 and a date of 12-82


http://forums.pelicanparts.com/uploa...1318546153.jpg

http://forums.pelicanparts.com/uploa...1318546323.jpg

what little wear i can see on the main bearing is on the bottom i guess to be expected as when the car sits for a while there is not much oil there when it starts. I have tore down a lot of small block chevys for post race inspections and would reuse bearings that showed this kind of wear, slight shine and stain, and pitting that cannot be felt with a finger nail. when do you all recommend a change of bearings