Howdy... Where do I start? So I took my car to a local performance shop, which mainly work on classics and vettes to fix the oil pan & pickup tube oil leak. At the same time, tune the carb and timing adjustment. Picked up car two weeks ago and drove it home. No issues, no oil leak, car was running strong and idling beautifully. All looked great. Last Tuesday, I decided to take the car out for a spin. It is a 67 GS400, bored 30 over, so 406. Did my basic cruising around my town, had dinner and headed up. On my way home as I reached a red light, the car started to hesitate and next thing I heard was a bang and crushing of metal. I was able to keep the car running till I pulled to the side of the road. Tried once to turn it on but did not turn. I had to have it towed. The next morning, I tried to turn the car on and engine would not turn. I attempted to turn the crankshaft manually and nothing. I figured the engine was locked up. Finally yesterday I was able to take it back to the shop that did the original repairs. Today I headed over as they had the oil pan off. Piston #6 was crushed and in pieces. To the point that it looked like shredded meat. The owner of the shop had no idea what would cause this. He said he normally sees this in cars that have nitrous or forced induction, mind you this car has never had neither. I then asked him about the engine running lean and causing this. He showed me the piston head and told me if that was the case, the head would have carbon build up. Again I am no mechanic so not sure if that is true. With all this said, what would cause a piston to become crushed like this? It does have .030 over TA pistons and it was rebuilt around 6 years ago, not by me, but previous owner. The shop owner said he is going to look at both heads and see if other pistons are showing such issues and what would be the next steps to take, if to just do one side or both, which at such point I am looking at rebuilding the engine. To think that I was just looking to spend money on getting the oil leak fixed and now I am talking about rebuilding the engine. So there is my story, now let me have it... I can say September has been a hell of a month for me. First the expense of this car, my dog racking in around $2500 in vet bills, my ex wife losing her job and now another high end expense to come to fix the car again.
Piston crushed and in pieces? The one thing that can cause that is detonation. Detonation can come from improper timing, lean mixture, inadequate octane, or excessive coolant temperatures in combination with the other things mentioned. It is audible to anyone who knows what it sounds like, like marbles in a can when getting on the engine. If you operate an engine under conditions that cause detonation, you will hurt the engine, simple as that. hypereutectic pistons can shatter from detonation. You probably have no idea what kind of pistons you have there, TA pistons doesn't tell me anything.
Meaning the top of the piston. He said it would have carbon buildup on the top of the piston if it was running too lean.
The Hypereutectic pistons can shatter even without detonation, just too much power/rpm can cause them to crack and shatter. Usually around the pin. As far as I know TA doesn't sell them for that very reason. The earliest versions were the most trouble prone. I totally shattered a stock cast piston in a 401 but that was for a different reason and too long a story. What kind of beatings has the engine endured over the years? Racing or just for street cruising. It took a lot of racing for my Hyper to break. Pictures are definitely needed of the piston. Hopefully your cylinder walls are ok or a sleeve may be in order.
Not really sure which pistons original owner put in there. From the paper work all he said was .030 over TA pistons purchased around 2012. I will dig through the box of documentation to see if there is anything that specifies which TA pistons.
Carbon buildup would more likely be the result of rich running and/or oil burning. Detonation can erode the top of the piston giving it a sand blasted appearance. BTW, you can't just stuff another piston in there, there is likely cylinder wall damage.
In the last 2 years that I have owned it, mainly cruising and never any racing. The previous owner the same as me. Original owner, not sure, but he sold it back in 2014.
If it was that catastrophically lean the other cylinders would show damage as well- melted piston tops. My first thought with that kind of failure would be a foreign object got in the cylinder or a valve dropped. What kind of pistons were they?
Just got off the phone with the owner and he said just as 436'd Skylark said, if it was detonation it would be across all piston tops. They are going to remove heads and call me to show me what is seen. He believes it was not detonation. Now foreign object? Well they did have the oil pan out attempting to fix the oil leak. Foreign object via such means? The exact piston I am not sure, all i know they were/are TA pistons .030 over. Not sure of material.
Foreign object as a screw or other metal piece (wingnut) ingested through the carburetor. Or as Joe said, a valve or seat that drops/breaks and gets slapped around inside the cylinder. That would be apparent once the head comes off on that side.
Apparent to expert eye. How would I determine exactly what caused it? I’m trying to figure out if it was engine faulty or something they screwed up. Shop owner says he will work with me but still... He told me detonation would be caused by high revving or high speeds, neither which I was doing. I did probably 15 total miles after picking it up, the one specific night was 10 miles round trip.He asked if I heard anything leading up to this or if the car was pinging. I said no. Car was working just fine and all came crashing down fairly fast as I stopped at red light.
If it was a dropped valve, the valve head would still be in the cylinder. The same for a dropped seat, and you would see missing pieces in the head you removed, so no expert eye. Detonation is improper combustion, and it would occur when you put the engine under high load, not necessarily at high RPM, or road speed. We need pictures.
At this point the parts would likely be in the pan. There is no seat from the factory but it is possible seats were installed during the rebuild. It'll be obvious if that is the case. It's not unheard of for a valve head to break off. Especially if the valvetrain is sloppy and the valve is bouncing closed. It'll be hard to diagnose what happened at this point but some information can be gathered. It is quite an accomplishment on his part to tell you none of the cylinders are carboned up with out having the heads off yet...
You should be there when they pull the head. Take pictures. I'm not saying its their fault or you should not trust them, but at least you will know what they find. I would have a buick expert rebuild the engine, btw.
I agree. Hopefully I can reach the shop before they remove the head, if they have not already done so. Also I haven't been able to find a local buick expert in SFLA.
So shop owner called me around an hour ago. He told me he got the drivers side head out which is the side of the destroyed piston. He told me it was piston 8 and not 6. He told me the valve broke off causing the piston to shatter and informed me that two pistons forward the exhaust valve is ready to crack. he said he was planning on taking the other head out to compare. He told me the engine is 60 over and not 30 over as I was informed. Per documentation that I have on the car, when original owner rebuilt it in 2012, he put in .030 pistons and within all documentation that he kept, he mentions 406 and nothing higher. I didn't think these engines could be 60 over as they would overheat, something I have never experienced. So tomorrow I will be headed to the shop alongside a buddy of mine that knows a bit more then I when it comes to mechanics. Will provide feedback and pictures after I leave the shop.
First things first. Get the engine completely assessed including the heads. If it ran hot, or lean and the impact of the valve, you may have cracks in the head(s). It does not sound as if you had run it long enough with broken parts to end up with any metal in the oil, but if it were detonating, you may have rod/crank problems. Once you know the issues your are facing, then decide what your goal is if you can repair this engine. If you can, have the block sonic tested and if core shift is not a problem, you may be able to take it to 430 standard bore dimension. But knowing where baseline is and the variables, will dictate where X will be. Then you can start solving for X. And as already mentioned. Pictures. Get those if you can.
Assuming its a 400, yes .060" over is fine, same block as a 430 and 455 and not near either one. If a .030 pisto was installed in a .060 overbore problems will arise. Were they 2 piece valves, more prone to coming apart. Hopefully cylinder walls aren't too damaged and can be overbored a little, if not go to 430 as mentioned above. FYI if its driver side the cylinder numbers are 1,3,5 and 7.
