Cam lobe wear

[LAA66]

 Good advice on this thread. Just wondering whether piston rings must go back to the original bore and alignment to seal right?

[Chryco Psycho]

ifeel no ring will reseal if removed even if it is in the same bore it came out of , no cylinder is perfectly round & each ring will seat to the bore using crosshatch to wear them in , re- crosshatch the bores & the rings stand a decent chance of resealing assuming the tension in the ring is still good

[Supercuda]

If it is still early in the service life of the rings, then a light hone of the bore will allow a resealing of the cylinder. Seal won't be as good as if a new set were used, but it is acceptable in a low-hours engine. The most important thing that must be remembered is this: don't use the rings again if you pull them off of the pistons. If you find it necessary to remove the rings from the pistons, it is time to install new ones.

[Belgium Cuda]

Very good advice about the pistonrings  Step 1 is done and now it's waiting for the verdict, I really hope I find something. 

[Belgium Cuda]

First pics of an engine with 500 miles on it, also has lowcompression pistons instead of the HP the engineshop sold the previous owner.
Please advice on what to do with the bore. 

[71chally416]

That's a bunch of carbon for just 500 miles. I would first check the seat seal and the guides and seals in the heads. Spray some WD-40 into each port and see if any leaks past the valves, then remove one Intake and one exhaust and see if either valve rocks excessively in the guides. If you can see movement of the valve head with the valves about 1/4" off the seats you need new valve guides.

And I think you said it had low compression in just one cylinder?? You'll want to remove that piston and check the rings to see if a compression ring is broke (they can easily be broke assembling the motor) or maybe installed upside down if there are no obvious valve leaking problems in that hole. And make sure the piston isn't cracked.   

[Chryco Psycho]

1 exhaust valve is not getting hot as it is all black spo there is 1 problem , the bores should nopt be vertically scored so it is either overheating or broken rings or fitted to tight . Did you choose low comp pistons or were you sold the engine thing high comp were in there ?  I would hone the bores swap to 10:1 pistons & install new rings check if the wet exhaust valve is seating or whet the real problem is in that bore

[Supercuda]

What Chryco said. You want a zero deck for your pistons, and a re-hone of the cylinders to establish a better seal. The low-compression pistons are murder on performance and almost every other aspect of the engine. With the compression ratio calculated at 7.8:1 in my friend's 440, we figured that it should run ok, but be no monster. Boy, were we wrong! This thing ran horribly, and no amount of tuning would bring it around. We finally swapped in a set of closed-chamber heads (small exhaust valve), raising the compression to a more reasonable 9.5:1. This smoothed out a lot of rough road. Due to cost considerations, we couldn't do the right thing and change the pistons, but we found a way to cope with the low-comp stockers.

[LAA66]

 I agree you need a proper hone to for the new rings, also check the valves and springs as suggested earlier. Whether you want to pop for pistons is up to you. I (barley) get away with the stock 10.5 on my 340 and the best fuel here is 91 octane. If you do pistons you may want to have it all balanced again though, and maybe check all the bearings, and,,, it just goes on and on with the precautionary measures.

[Belgium Cuda]

Thanks guys! Am currently abroad but will be home next week and pull the pistons and decide after that
what to do. Propably I will go for a total rebuild, the car beeing a conv -69 GTX in very good condition.

[Belgium Cuda]

Pulled the pistons and they are indeed new but low comp TRW 2266 0,040. Rings looks ok but rodbearings looked terrible.
Just like the block wasn't cleaned proparly. The bores lookes like they were not honed if I compare the lower part of the bore to the higher part.
Maybe that's why it sealed porly? Piston/rods were balanced and crank has been reworked everwhere, drillingholes and trace of grinding all over.
Pistons has a lot of scratches horisontally, why? Also a lot of signs of careless handling on them.
Would it be enough with a honing? I have a set of KB237 0,040 with matching Eaglerods I could use to get the comp up if I don't need a new bore.
For the heads I guess a disassembly has to be done to check for valvesealing.

[Chryco Psycho]

Marks like that in the cylinder walls could be loose or tight fit of the pistons so honing may or may not work but you are going to change the pistons anyway are you not ? you will have to carefully measure the block to see what size pistions you will need or if the KB pistons will fit properly , the fit HAs to be exact with Hyper pistons or the whole engine will be junk yet again only worse

[Belgium Cuda]

You were right Chryco  Almost zero clearence in the bore, same with ringgap. The KB pistons have moore although I have to let
the machineshop be the judge about that. The balancingwork on the crank stinks 

[Belgium Cuda]

Another one

[LAA66]

 Wow, that's a shame someone would put together a motor like that then sell it off as rebuilt. 

 How are the crank journals and cam bearings?