I have a 68 camaro with a 69 camaro engine installed 350-300HP The engine was completely rebuilt, but the guy who rebuilt it moved away. The car starts, but smokes bad. There are no knocking or scrapping noises and no leaks. There is oil on the plugs. I believe the pistons that were installed are too small. They are 30 over pistons and rings, but I believe the engine was bored 40 over. I am pretty sure I need to pull the engine and disassemble. Is there a way to know for sure this is the problem? I didn't do a compression test, but I assume that is where to start. Should I pull the head(s) first to inspect. The car is almost complete, but have to figure out this issue first.
Mike

 

yep start with a compression test. with oil on the plugs i think your gona find your right. is oil on all plugs? i am going move your thread to the 1st gen general section for you.

 

The only way to know if the piston size is matched to the bore diameter is to pull a head and mic the bore, the pistons will be stamped "030" or "040" etc.). Curious what makes you suspect the size mismatch, did the builder say that? And is the builder an actual engine builder, or a shadetree mechanic? Using 40 over pistons on a 40 over bore isn't a point that has to be stressed to a builder, or even to someone with an ounce of mechanical knowledge, it's common sense.

 

You have no idea what some people think. If some is good more is better and a little extra will be just fine. THEN, It couldn't be something I did BUT I have no idea how that happened?????????????????????????????

 

The guy that did the work told me he could handle it and rebuilt many engines. I wasn't there the whole time he did the work but checked on the progress every 2 or 3 days. I am just guessing that is what happened as I am getting blow by. All the plugs are that way, that's why I'm guessing the wrong piston/ring size. I will be taking the head off this weekend and measuring the bore to see what I'm up against. I will post back with my findings. I guess you have to learn by your mistakes...

 

Yes, experience is the best teacher.
As Super Mod suggests, removing the cylinder head, intake manifold can be removed first, but not needed, and look for the stamped oversize on the piston head and compare cylinder diameter to see if they match.

If a match is found, then rings may need seating as in find a low traveled road, shift to high gear, start at 25 MPH, mash pedal to the floor accelerating to 60 MPH, then coast back to 25 MPH.
Repeat above step 10-12 times. If good quality rings, should be seated.
If not, then a couple other items to check.
1. Valve stem seals may be installed incorrectly - remove a valve cover and check the location of seal. Square seal should be in the groove at the top of the valve stem and mate with the spring retainer and seal should not be twisted.
2. This event will require engine disassembly as rings may be installed upside down. Some rings have a punch mark denoting the top of the ring. If ring is upside down, then ring will twist wrong and let oil through to combustion chamber. Rings should have their gaps not aligned with each other. Bottom ring is a multiple place ring and the joint of the expanded ring should be inline with piston pin/wrist pin, and two top compression ring gaps should be 180° apart with one ring aligned with piton pin. I'm sure youtube has an instructional video.
3. Cross hatch on cylinder wall should be approximately at a 30° angle. If not, not much one can do for correction, but smoothness counts. If surface is too rough, it wears away the new ring. The pattern/cut should look like one using emery paper, not coarse grit stones/sandpaper.
4. On assembly - cleanliness next to Godliness - one cannot be too clean.
Oil cylinders and rings liberally upon reassembly.

As said, I'm sure youtube has videos as well as a Haynes manual from the local auto parts store. Follow instructions given in manual and learn.

Oh, welcome to the School Of Hard Knocks - once a student, you never graduate.
Good luck and keep us informed of your experience/journey with her.
Take notes and right them down, you will forget, ask any elderly person.

 

I decided to start the car and let it run this past weekend. It still smokes pretty bad. It is not coolant. After about 5 minutes the engine was still smoking but only out of the passenger side header. I am wondering if you are correct about the rings not being seated. The car is not street legal yet, so I can't take it down the road as you suggest. I plan on doing a compression test on all cylinders this weekend. The car sounds really good as most with open headers. Revs good with no popping. Again, I have no noises coming form the engine scrapeing, tapping, knocking ect. The amount of smoke was incredible, Im lucky the fire department wasn't called. I am wondering how long the car needs to run before the engine lube burns off? -the concrete shakes under your feet when its running. Hope the neighbors don't hate me.

 

You can buy header mufflers and at least cut down on some noise.
Depending on the assembly lube used will determine the burn-off time plus idling doesn't help as much as if were street driven.

 

ok, I will mess with it some more this weekend and post back. Thanks !!

 

I have seen this before. This takes a combination of mistakes. Not all engine builder check piston clearance if a machine bore the motor .03 and they buy .03 over and the piston seem to fit cold, done. (I am not saying that is correct just common) But ring gap should always be checked. Even the ring manufacture wants you to double check them. A wrong size ring should be painfully obvious at that point.

The engine I was repairing had the wrong rings in it and the owner had kept all the boxes, labels and receipts. The manufacture just put the wrong rings in the pack.Even with the wrong rings and low compression the car did not smoke much. His complaint was no power. He though he had something set in the carb or timing wrong. With a compression at right around 100 PSI the fresh 383 was barely firing.

If your piston were .010 under you would have a knock at idle that would fade away as the car warmed up. I know because GM has install pistons that where too small many times on new cars. You can start to hear them once they hit about .006" undersize from what they should be.

With a -.01 ring install you should have very low compression also a cylinder leak down test would show the rings as an issue very quickly. Are you sure he remembers intake valve seals? Fresh motors tend to generate a lot of vacuum and a lot of oil in the valve cover. If the intake seal is not there or installed wrong you can get a nice cloud going pretty quickly.