Cylinder to head sealing surface damage

[sjf911]

This engine had a top end rebuild 5-6 years ago with JE/QCS 98mm P's and C's (from Supertec) with the addition of 3.2L heads and all steel head studs. After break in, the head nuts were fairly loose but torqued back and have held since. I have, however, had the impression that I was getting head lift since turbo'ing the car and recently noticed what appeared to be seepage from the head/cylinder interface on some of the cylinders, although leak down was only 1-2% across all cylinders with uniform compression. Since I was already considering swapping the pistons to reduce the CR and possibly flame ringing the heads I went ahead pulled the engine. Unfortunately, there is clear pitting of the surfaces most noticeable on cylinder #2 (I have only removed 1-3 so far) but no apparent burn through or obvious blow-by.

Seepage outside #6

#2 cylinder

#2 head


I assume the heads are salvageable but can/should the cylinders be similarly cut?

[NoEardGoat]

I believe both sides (cylinder and cylinder head) get a groove cut into them for the fire or flame ring.

What are fire rings

[Steve@Rennsport]

It looks like the heads have been fretting against the cylinders and thats a sign of heads lifting under boost.

This can be caused by excess boost pressure or detonation so one should do some detailed forensics to find out what is going on.
I'd find the root cause since flame rings will not help here.

[Raceboy]

If you didn't run the engine at 2+ bars of boost or more, it is caused by detonation.

[sjf911]

Thanks for the replies guys. My J&S has been suggesting low level detonation under boost since I installed it which is the real reason I wanted to lower compression. I have not measured the actual CR of the pistons but if I recall correctly they may be toward 10.5:1 so this is the likely explanation when run with 0.6 bar. The car is not burning oil and I have the crankcase vented outside so I don't think oil contamination is the issue. I have run nothing but 93 octane gas with meth injection and a conservative timing table but it does not appear to be enough. I'll cc the heads and piston domes and see what I come up with.
I was planning on dropping to a CR of 8.5:1 or even 8:1 with a new set of JE's but is this combination of cylinders and heads salvageable? Would flame ringing help reduce the amount of material cut from the head and cylinder surfaces as the damage looks to be in the area that the groove would be cut?

[lindy 911]

I've never seen anyone build forced induction on anything over 8.5:1 CR. I'm surprised your engine didn't eat itself at 10.5:1. If the damage can be cleaned up with a few thousandths cut to cylinder and head, it seems to me you would be OK. Remember that you move everything toward the crank when you cut heads and cylinders so corrected base gasket thickness is required. I would also make sure the is adequate clearance between head and piston after the cuts.

[sjf911]

They may only be 9.5:1 as I didn't get any documentation with them and I didn't bother to cc them when originally installed (normally aspirated at the time). It is a great failed experiment. It certainly confirms the J&S and makes me a big believer now. In any event, it is a great opportunity for me as my college age son was eager to get his hands dirty on a project over Christmas break. Now if I can only get everything together so we can spend his spring break putting everything back together. I did pull the 4-6 bank this morning and there is actually less damage there with less fretting and it is isolated to #5.

[aws]

Steve: I would definitely pull a rod bearing and check the bearing for crush in the big end of the rod. Detonation flattens the rod bearing out and removes the crush---opening the clearances up causing failure. I have had rod bearings halves that suffered bad detonation that would not stay in the rod----you install the bearing half in the rod---turn it upside down and the bearing half falls out--there is no "crush" to hold it in place. The off the shelf flat top JE 98's are 8.5 to one and reasonable. By the way the last time I had a detonation problem the Ni-resist rings kept the head from blowing off the cylinder----instead it blew a hole in the piston---and then thru the cylinder---I had absolutely no problem with the cylinder to head joint.....
aws

[sjf911]

Well, I got everything apart. The CR cc'd out right at 10.5:1. Interestingly there is no evidence of detonation on the pistons, spark plugs, etc.. I am going to go ahead and split the case and I will see what the rod bearings look like. I have a 3.2L crank and rod set so I'll bump up to a 3.4L with this build and drop the CR to 8.5:1, maybe the slight increase in displacement and stroke will offset the loss of off boost performance due to decreased CR a little.

[Henry Schmidt]

The answer to one of your earlier questions " can the cylinders be resurfaced ?" is yes.

The addition of Supertec head studs will greatly reduce the movements between heads and cylinders.
No solution is perfect but this type of instability between cylinder and head (resulting from constant fluctuations / inadequate clamping pressures) is exactly why we devoted so much time to developing an alternative to conventional head studs.

BTW: we no longer represent QSC as a distributor but if you need help replacing a cylinder or more, give me a call and I'll see what I can do.
Cheers

[sjf911]

Thanks Henry.

[Walt Fricke]

Steve

Cylinder base gaskets come on 0.25 and 0.5mm thicknesses from Porsche. EBS has some 1mm thick. Don't know if they have any other than these three sizes. I mention this so you can calculate what the combined amount you should take off, spread betwen the cylinders and the heads, so you can end up with a standard gasket to go with your more or less standard J&E pistons, and have your piston to head clearance within the normal range - not too little, but not too much.

I assume you will have all heads cut the same amount, and ditto the cylinders, so you don't have to match things together?

I wouldn't mention this, as you seem an accomplished hot rodder, but for the fact that you plopped a turbo on there with that 10.5/1 CR, even if you did run fairly modest boost.

[sjf911]

Originally Posted by Walt Fricke

Steve

Cylinder base gaskets come on 0.25 and 0.5mm thicknesses from Porsche. EBS has some 1mm thick. Don't know if they have any other than these three sizes. I mention this so you can calculate what the combined amount you should take off, spread betwen the cylinders and the heads, so you can end up with a standard gasket to go with your more or less standard J&E pistons, and have your piston to head clearance within the normal range - not too little, but not too much.

I assume you will have all heads cut the same amount, and ditto the cylinders, so you don't have to match things together?

I wouldn't mention this, as you seem an accomplished hot rodder, but for the fact that you plopped a turbo on there with that 10.5/1 CR, even if you did run fairly modest boost.

LOL, criticism accepted. OTOH, accomplished hot rodder is not a title I have earned, it is more like delayed adolescent hot rodder, but I'm having fun and it's a great excuse to spend time with the oldest son that doesn't involve rock climbing (I just can't keep up anymore).

[sjf911]

Finished disassembling the engine and no suprises. No broken rings, the pistons look almost brand new, and the rod bearings appear fine without loss of crush. The case was nice and clean inside without any debris or sludge and all 6 piston squirters are confirmed operational. I see the expected wear on the intermediate shaft bearings and the thrust side of #1 main. The crank looks pristine and is off at the shop getting magnafluxed.





New bearings are already here thanks to the fast service of PP. The plan is to swap in the 3.2L crank I have sitting around, add a set of custom 8.5:1 JE pistons for the 3.2L heads, and a 930 oil pump so I'll sell off the crank, rods, and oil pump from this engine. Would the pistons be reusable if we think there was some detonation going on (only 5K miles on them)?
I'm also going to try to add the 993 knock bridges and go to a double knock sensor setup with my J&S if I can locate some, PP can't seem to locate any of the bridges in country right now. I am still debating how best to solve my turbo oil scavenging issue. If I can salvage my current cylinders, I will have enough funds to send my left hand cam back to Camgrinder to have a scavenge drive added to the front and then I will switch to the new Clewett scavenge pump with integrated cam sensor. Otherwise I will have to figure out where to remount my electric scavenge pump as I don't want to continue to run a passive drain to the sump. I have a 930 oil tank that I can swap in for a stock like scavenge return but I also like the idea of returning the oil to the case vent cover.
Has anyone used aluminum tubing for making your own oil scavenge hard lines?

[lindy 911]

OK, so with the 3.2 crank and 98mm slugs you're building a 3.4, so you'll be using a 3.2 rod with custom pistons to locate the pin. New rod bolts are a must. I would also strongly consider a cross-drill of the crank center main and grove the matching bearing. Also, the newer coatings work great (Poly-Dyne) on the bearings and piston skirts. Cheap insurance against galling.

I think I would stick with a 3.0 crank and rods and reduce the static CR to 7.5-8.0:1 and turn up the turbo. The 3.0 rods have a bigger bolt that I think would help your need for speed...

[sjf911]

At one point I was thinking of a 3.5L build with 100mm pistons so I already had the 3.2 crank and a set of Carrillo H-beam rods with ARP bolts. Also, my driving is almost exclusively street (at altitude) so I would rather have slightly more static compression at the cost of less boost so the slight increase in displacement may help offset some of the effect of the decrease in CR between builds. My goal really was to keep the stock rev limit so I didn't think the crank/bearing mods would that worthwhile but I am certainly willing to entertain it. Who does the bearing mods/coatings and how do you account for it as far as clearances? The pistons will include the complete package of coatings.

[sjf911]

I got one of the pistons cleaned up and I don't see any evidence of detonation. A little scuffing on the sides and that is about it. I'm glad I had my J&S suggesting knock because I would have been less likely to tear this down.

[Walt Fricke]

I think about every time I have disassembled one of my engines, the thrust bearing surfaces looked more or less like this, even though the main bearing surfaces looked acceptable, as these do..

Has anyone had an engine failure because the thrust bearings wore too much, even though the regular parts of the bearings were fine?

For a street motor, especially with the 930 pump, I'd not think center main crank oiling for the rods (crossdrilling) would be all that important. How high in the RPM range do you think you will twist it?

[sjf911]

Originally Posted by Walt Fricke

For a street motor, especially with the 930 pump, I'd not think center main crank oiling for the rods (crossdrilling) would be all that important. How high in the RPM range do you think you will twist it?

I have a stock valve train so I was planning on staying below 7K.

[lindy 911]

I've mentioned this before in another post but I have seen JE pistons that looked just like your pictures that came out of a 468 BBC that had been super-charged. It detonated so hard that it broke both of the cast iron heads and caused an incredible lifter valley explosion that blew the intake manifold completely off along with the blower. These engines have 5140 Eagle cranks with Eagle H-beam rods, +.250" and the JE 8.0:1 Pistons. I said earlier that the JEs are bullet-proof...