Stegosaurus909

I would greatly appreciate any advice you all have on my current predicament.

So over the summer, I bought an 88 944 Turbo (non S) with the hopes of reviving it and making it a daily driver within a year. I knew the engine was toast and the #4 cylinder was completely seized and full of jello coolant. So I bought another 87 turbo long block with 90k miles to swap in and was told that it ran fine over the summer and ran when pulled. Upon disassembly (preventative maintenance while it was out) to do the head gasket and other seals, I found a large gouge in the #2 cylinder. The gouge catches a fingernail and the smaller one to the left can be felt as well. The nub at the top was removed with a ridge reamer and the other light scores can't be felt. All the other cylinders are perfect and don't have even the slightest scoring. Even the #2 piston and rings are very clean on the sides and don't seem to be damaged at all from whatever got in it (still planning on getting new rings though). From what I've found after scouring forums is that I should try and find another block as it is the least wallet-breaking option but would like to hear from y'all. I also want to attempt the 07k 20 valve swap in 3-4 years so I don't really want to drop a ton of money on an overbore and new pistons at the moment. I also just want to drive this on the street and don't plan on taking it to any track days.

Just wondering if anyone has any advice and if this engine could even be run without a lot of case pressure or oil burning. If I could run this engine and have to top off the oil every now and then, I'd be totally fine with that as it only needs to last a few years of street driving. But from my understanding, I might blow out the pan seal or dipstick but please correct me if I'm wrong. I am also up for the option to hone it myself with the felt pads and Alusil honing compound if that would help it at all but I'm not very optimistic about that option.

Also if anyone has a late NA or turbo block for sale (tolerance group 1) with the compatible balance shaft oil port, I would be very interested in purchasing it if it turns out that I should get another one.

GPA951s

Tough Call, only you can make the decision, You could go through all that work and hope for the best.. One thing for sure, left alone its only going to get worse.. At Min you sould go though the bore with the honing paste. Dont use anything but the honing paste. The good news is that you are REALLY close to RPR Tuning in MD (My sister and Brother in law live in Hollywood MD) I know John at RPR has a 100.5 mm Block that I just did for him that he might sell.. Or take your shortblock to him and ask his opinion. Looks loike something got Sucked into it and that piece dug in all the way up the bore..

Gage

Next step would be to remove and inspect that piston and get some measurements of the bore to see if there is any room to open it. Also be on the lookout for a tolerance 2 piston.

dr951

I've seen a similar fragment explosion damage (witness the several dozens pin hole hits on the cylinder wall - from metal shrapnel) to a 951 cylinder and head caused by a disintegrating multi-electrode spark plug in a highly boosted engine.The disintegrating electrode issue is much more evident if there is a head gasket leak and coolant enters the combustion chamber. Imaging the plug electrode temperature - one instant it is extremely hot, the next it is quenched with coolant mist, then repeat 50 times per second. Even the best plugs age and disintegrate quickly in this environment. With circular or multi-electrode plugs, the engine can still run fine after even 50% or more of the electrode burns up, so unless a big chunk breaks off and turns into a mobile glow plug, the driver may not feel or hear any signs of imminent serious engine damage. However I experienced a totally random combustion chamber explosion event a high RPM on a highly boosted 951 that I am almost certain was due to loose chunks of red hot spark plug electrode bouncing around in the combustion chamber. Actually it happened twice on the same drive, about 30 minutes apart. My car was gradually loosing coolant that day, I added about 1 full quart of water in 3 hours of highly spirited driving. When the event occurred, I was at full throttle, full boost, about 6500 RPM in 2nd gear and at the very instant I left off the gas to prepare to catch 3rd gear, I heard and felt an extremely loud metallic BLAM! The sound was like a 16 pound sledge hammer hitting an anvil - as the entire car shook, but the sound seemed to come from underneath the car - from the rear end of the car maybe. I though that maybe the transmission was damaged. An examination of the car at the side of the road found noting amiss, other than the coolant was low. The car started perfectly and ran perfectly and then after 30 minutes of very fine performance, again BLAM! I gently drove back home 30 miles with no issues. Leak-Down test nailed it - #4 head gasket was blown. The air pressure being fed into #4 cylinder via the spark plug hole was causing the coolant to back up and bubble into the expansion tank. Oops. Days later with the head off, l saw the shrapnel explosion damage on #4, and matched it up with the plug for #4 - it had lost 60% of its once stout circular electrode, the other plugs looked worn but they still worked great. Luckily the explosion shrapnel damage was more like pre-ignition since it was confined to the very top of the cylinder wall, above the ring path, but the cylinder head was severely pitted and gouged. I was lucky that there were only 2 faint scratches that were about 2 inches long on the cylinder wall.

Stegosaurus909

Yeah that's a good point, thanks GPA951, I should probably get the honing paste anyways so I might try going through it with the paste and see if it makes a difference. And awesome thanks, yeah I will definitely give RPR a call and see if they could look at it, only about 45 minutes from me. Thanks for the advice!

And Gage are you saying I would be able to use just one tolerance 2 piston and the rest tolerance 1? Would the change in weight not make much of a difference for the balancing then? If so then that sounds like a great idea because it would likely cost less than another block if I bore just that one out.

Oh dang gotcha dr951, I haven't checked the plugs that it came with but I'll definitely go check them now. Never thought about the ceramic on them breaking off. Also were you able to repair yours with a hone?

dr951

I judged that the cylinders did not need to be honed, the vertical scratches were so slight. I did work a very long time on the dented, dinged and pocked aluminum head. #4 looked like a moonscape. I used 5 different shaped files, 3 different burr and sanders on my Dremel and lots of 3M automotive polishing pads. I also used a new Wide Fire Ring gasket and ARP ultra high strength head studs torqued to 100 lb-ft. Also new Rennlist exhaust studs made the LR headers slip right on.Thankfully, the reassembled engine is fine - nearly zero 5W-40 oil usage, no exhaust smoke, killer torque and power, great gas mileage at cruise and no coolant loss. The metal electrode, the part of the plug that projects into the combustion chamber, is what disintegrated on my plugs, the white ceramic insulator(s) were fine.

Gage

And Gage are you saying I would be able to use just one tolerance 2 piston and the rest tolerance 1? Would the change in weight not make much of a difference for the balancing then? If so then that sounds like a great idea because it would likely cost less than another block if I bore just that one out.

That's correct. No difference to balance. Don't think of it as boring. The dimensional difference between tolerance groups is so small, it requires only a few strokes of a hone. In a "used" bore, it is likely that material will only be removed toward the bottom of the bore but it can be an opportunity to "clean up" the surface and move toward a cylindrical geometry.